A Study of Relaying for the Primary Transmission System of the Municipal Light and Power Development, City of Pasadena Citation Evans, William Morris and Newmeyer, William Lawrence (1933) A Study of Relaying for the Primary Transmission System of the Municipal Light and Power Development, City of Pasadena. Master's thesis, California Institute of Technology. doi:10.7907/3rqc-dw75. https://resolver.caltech.edu/CaltechTHESIS:09262024-175529369 Abstract No abstract. Item Type: Thesis (Master's thesis) Subject Keywords: (Electrical Engineering) Degree Grantor: California Institute of Technology Division: Engineering and Applied Science Major Option: Electrical Engineering Thesis Availability: Public (worldwide access) Research Advisor(s): Unknown, Unknown Thesis Committee: Unknown, Unknown Defense Date: 1 January 1933 Record Number: CaltechTHESIS:09262024-175529369 Persistent URL: https://resolver.caltech.edu/CaltechTHESIS:09262024-175529369 DOI: 10.7907/3rqc-dw75 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 16760 Collection: CaltechTHESIS Deposited By: Benjamin Perez Deposited On: 26 Sep 2024 20:42 Last Modified: 26 Sep 2024 20:42 Thesis Files PDF (Thesis) - Final Version See Usage Policy. 28MB PDF (Proposed Relay Scheme for Completed Pasadena 16.5 K.V. Transmission System) - Supplemental Material See Usage Policy. 3MB Repository Staff Only: item control page

.A STUDY OF RELAYING FOR THE PRIMARY TRANSMISSION SYSTEM OF 1'HE MUNICIPAL LIGHT & PONER DEP.A.RTMI£NT CITY OF PAS.WEN.A. Thesis presented by w. M. ETens W. 1. Newmeyer In partial fulfillment of the requirements tor the degree of Master ot Science Oal1forn1a Institute of Technology Pasade?lf,,0alitorn1a 1933 AOUOWLEDGE.MENT We are very appreciative ot the courtesy and assistance extended to us by the Mtmioipal Light and Power Department of the City ot Pasadena. In ps.rtioular we wish to thank Mr. B. F. Det.anty, General Manager, for making available the tiles and records ot tha department. We also wish to thank Mr. E. L. Bettannier, Eleotrioal Engineer, and Messrs. M. W. Edwards a.nd K. R. Birge who greatly helped us in obtaining data on the system. We are also.very appreo1at1ve of the time and valuable suggestions given to ua by Mr. E. R. Btauffaoher of the southern California Edbon Company and 118n·rs. C. H. Hagey and P'. L. Eley, of the aame oompany, who made it possible for us to oheok so me ot our results on the oaloulating table. To Dr. w. A. Lewis, Engineer for the Westinghouae Eleetrio & Mfg. Co., we also wish to express our thanks for assisting us in making caloulations by the synmetrioal component method. TABLE OF CONTENTS Page Chapter I -- Pasadena Power System Present Power System Present Relaying Present and Future Developments System Diagram 1 2 Chapter II -- Types of Relaying Distanoe Type Relays Pilot Wire Relays Directional Overcurrent Relays Reoomnendations for Line and Ground Fault 9 11 proteot1on. Chapter III -- System Caloulations for Relay Determination and Setting. Equivalent System Impedanoe Operating Condition of the S~tem Symnetrioal Component Analysis Generator Resctanoes Zero Sequence Impedance of the Transmission System Sample Calculations Three Phase Faults Gr:>und Faul ts 5 6 8 12 13 19 20 20 23 25 28 34 37 37 42 Ohapter IV -- Relays, Desoript1~n--Connections-Bettings 45 Relay Settings 46 GrO'tlnd Rola.y Settings 48 Line Relay settings 57 Relaying at Cal-Teoh Substation 66 16.5 KV. Relaying for Power Station and Substation Relay Connections and Vector Relations for 67 Single Phase Relays 68 Relay Oonneot1ons and Vector Relations for Polyphase Relays Location of Relays w1 th Respect to Ciraui t Breakers 71 74 Recommendations and Conclusions 76 Bibliography 78 CHAPTER I THE PASADENA POWER SYSTEM The Mllnioipal Light &: Power Department of the 01 ty of Pasadena has been operating an independent eleotrio system tor twenty seven years and now supplies all of the city of Pasadena. It's growth is shown briefly as follows: 1906 1909 - 1914 1916 1920 - One 250 H.P. Generating Unit One 1000 H. P. Generating Unit One 1250 mv. '?ur~ine Generator One 3000 KW. Turbine Generator Purohase of Southern California Edison System in Pasadena 1924 1928 1932 - One 10.000 xw. Turbine Generator One 15,000 KW. Turbine Generator One 25,000 KW. Turbine Generator Inasmuch as Pasadena is essentially a residential city and the future growth will probably be quite slow. the estimated future consumption will not exoee4 eighty five_million kilowatt hours per year by 1940. Any planning will therefore be made on this basis and while certain ohangea and revisions of the existing system·are quite needed, they will be made only after due oonaideration from the economic point of view as well as the engineering point of view. This paper deals with the problem of revising and extending the present relay equipment for the 16.5 KV. transmission system. The present relaying oonsiste almost wholly of line inverse time element and definite time element overload relays applied at the power and sub-stations. An attempt has been made in this paper to consider the relaying problem as a whole and to make a more or less fundamental -1- study of the complete system, analyzing for short o1rouit currents and relay application by use of the symmetrical component method. However in so doing it has been necessary to limit the study to certain assumed conditions and also to assume that certain changes now planned will be oonsUlml!8.ted before the complete revision of the relaying. The study was limited to the primary 16.5 KV. transmission system since it is not contemplated that any radical change will be made in the present relay arrangement for the secondary 2400 volt distribution. Q,ui te complete supervisory oontrol may be installed at a later date but since this is a problem, quite separate, discussion of this will not be made in this paper. '.PR;~ SENT POWER SYSTEM. The present power system consists of: (A) One power station, in wh1oh are located the following main generating uni ts: Unit #8 - Allis Chalmers, 31,250 KVA •• 80% P.F., 16,600 volt, 50 cycle, 1500 R. P.M. Turbine Generator. Unit #7 - Allis Chalmers, 18,750 KVA., 80% P.F., 11,000 volt, 50 cycle, 1500 R.P.M. Turbine Generator. Unit #6 - Allis Chalmers, 12,500 KVA., 80~ P.F., 2400 volt, 50 oyole, 1500 R.P.M. Turbine Generator. units one to five consist of smaller older generators of up to 3000 XW. capacity, but for the purpose of this paper, they are not considered since they are small, more or less obsolete and not expected to be used except in a possible emergenoy. As now operating and as expected to operate, Unit #8 will ordinarily supply the load sinoe it -2- is the most efficient. Uni ts #6 and #7 will be standby and tor use e.t o:ttpeak times. From indioations now at hand, unit #8 alone will be able to handle even the peak load for some years to come, so the relay calculations inv:>lving detenninations of short oi rcui t currents are made assuming this machine on the line alone. Although the main power station is usually the only power supply, there is an arrangement with the louthern California Edison Company, whereby the load can be thr:,wn onto their system in case of emergency. · The tie-in feeder comes direotly t!l the Pasadena Power Station 16.5 KV. bus from the Garfield Substation of the Southern California Bdiaon Company. 1'his feeds power from a 15,000 KVA. bank: of tranafonners. the bank with its reactors (two in parallel) having an approximate reaotance of 12::'. This tie-in is tor emergency operation but is ocoasionally used when, on acoount of abundant water supply. the Southern Calitornia Edieon Company oan supply power at a rate which makes it advisable to shut down the steam station. The relaying tor this power feeder is done at the Ga.rtield Station so this is not considered in the present discussion. Because of the fact that this line 1a used only under abnormal conditions, and will practically never be operated in parallel with the power station, the caloulations are based only on the actual operating conditions of the power station. (B) Two main substations known as Raymond Substation and Lama.nda Park Substation. Each of these substations have two 3000 KVA •. banks ot transformers -3- steJ)Pc1%18 ~own trom l&,.500 voite ~o 240, . '°"alt,. "3-:e tJ.4H;londe.~ ~ •o.lt a1,tr1~t1 ,on •~tem ra~iat.e s from tbe,s , aul;>a1aUfui, -. welJ. _.,, ..from • 2400 v~l t aubstathli located at the pow,r plant • . , '. ,A' 1ta1mo~d ,µl 240-0 vol~ teedttr an _oontrolled b7. au,t omatio t"ebloa,ii,ig cireui,t breaJcera ( th'8e ~ime oloae! then l(>ckouJ} -.a thi• •~ba~at,iOJt 1a practloally unatten'1ed, an in•peotor v1,1ttng it ae-.,eral t111e a day. A;p.y trouble e>autt1ng • • tee~er to ~ema1J:l .open nqu1,es the vls1 t ot a trouble man. to oloee the breue,. Th• ,a.me h true it 8J'J'3 p.i-tmaey otrouit b.r eatter opens. lfot:1t1oat1on ' . ot, outs.ge~ on the 2400 vol.t teeaere h u~ually reodved by calls ~~om eu,tomere report111g outagee, . ,Lamanda Pa.11t Subtftatio~ is an old manually operated substation taken OTtr trom ~he Southe"1 Calitornia Edison OOmp&UJ' tn 1922. It 1a unattended .dul'ltig the da7 (except tor inepeotion periods) until 3;30 . p.m•.• at 1'h1eh time an 1napeotor oom,a to the aul>statiol';l and reme.iaa until attar the •antng peak. fht• 1ubstation 1• . qul te obaolete haY- lns b&en built many year• ago a-4 it 1• only a qulation of a Ten •hort time untt l • new atat1 on 'Will be ereqted on lan4 several ?;)look• away, thie . land already having been purchaae4. !he diagram on page 8. aho111 the achemaUc layout ot the ay,tem. :aa,mond and Lamt.nda Park Subatati ou" are f etl l)y a loop line trom the pGwer station. Also te,d fro~ both R&Jmond and Lamanda ParJt; 1a a 16.15 KV. line teecUng the water pump1,ng system, FlnaJ.ly there 18 a d!reot atub teede.r trom the power station to the California Institute of teoh- nology. A tie-in to the Laim.nda Park Feeder is also run to the In- stitute. On the diagram is also shown the proposed Maryland substa- tion and teeders to same, reference to which will be ma.de below. PRESENT REL.AYlNG. At the present time the relays (except for the differential protection of the generators) are all of the well known induction diso. time element overourrent type. Although some attempt has been made to obtain selective breaker tr1:p:p1ng, the method of operation today is to have all relays in the substations on the 16.5 KV. lines set for heavy overload and long time and the relays at the power station set to trip first. The reason for this is that the substations are usually unattended and it is considered better to trip at the power plant where an attendant oa.n immediately reolose, rather than attempt tn sectionlize at the substation, which would cause a line section to remain out until a man ~nt to the substation to reolose the breaker. The present method of operation has proven fairly satisfactory as there have been few outages and the system is comparatively sirrple. However there is no assurance that under the present operation, some fault may not completely shut down the system whereas wi tl1 proper relaying, sectionlizing would promptly take place, isolating the fault withing the smallest area possible and not putting out of service heal thy parts of the system. It is for this reason that a general revision of the relaying is being contemplated, particularly so as the critical demand for nearly perfect service is growing with the increase in use of synchronous apparatus, -5- electric clocks, etc. PRESE?n ..AND FUTURE DEVELOPMEW'l'S. The condition of load in the business seation has caused several feeders to have nearly reached their capacity and because this oentral load is somewhat distant from the substation :teeding it, propoaals have been made to build a new substation adjacent to this load. Thia substation it built, will be known as Maryland and will be · :ted from the power station by a new feeder. It would also be tied in to the system by a connection to the present Calitornia Institute ··of Tech- nology Line and to the Water Pump Line. The Pump Line ·could then receive power from any one, or mor, of the three substations, Raymond, Lama.nda Park, and Maryland • .Because it is quite possible that the Maryland Substation will be built within a few years, it was c~nsidered advisable to proceed with the problem an this basis. If other developments take place, the following analysis of the problem is still applicable though the actual calculations would have to be revised. Lama.nda Park, as already mentioned, is qu1te obsolete so a new substation to replace this is planned for the very near future. 'l'he general scheme of connections on the 16.5 KV. side will be about as at present, though an emergency tie-in may be made with the Southern California ?idison System at this point to supplement the one now at the power station. The new substation will be made as fully auto- matio as possible and probably supervisJry control will be installed to pe.nnit oontrol from the power station. -6- At present nearly all 16. 5 KV. lines are overhead but muoh work has been done in installing conduit for placing underground both the primary 16.5 KV. lines and the secondary 2400 volt feeders. The lines from the power station to the Raymond, Lamanda Park and Maryland Subst.a tions and most of the Pump Line will be und.e rground oables. The cables used for these lines will be 500,000 c.m. and 350,000 c.m., three phase type H, 23,000 volt cables, eaoh conductor being separately wrapped by a metallic sleeve, the three conduotora being contained in a common lead sheath. Diagram, page 8 1s a single line diagram of the system as 1 t would be when the Maryland and new Lamanda Park Substations are built. '!'his diagram shows all 16.5 KV. lines with the distances and size of conductors used, location of apparatus, and the recormnended typee of relays. -7- CHAPTER II TYPES OF RELAYING At the present time induction type time element overcurrent .relays are used on all feeders. Howe,-er, the use of only this type in the future will cause difficulties. As an e:xample, oonsider the dia- · gram, figure 1, page 10. If the relays shown were timed in the usual consecutive manner, it would be necessary to give f l and #3 the longest time setting, say 1.5 seconds, f5 a.ud flO, 1.0 second, and #7 and #8 the shortest time, say 0.5 seconds. Under these conditions, with a short circuit on line #2, relays 17 and fS would operate before the others and clear the s.ystem. For a short ciroui t on line #1, however, since the same current flows through relays #7 and #8 as through #5, these relays would operate before #5, and hence as s·oon as relay fl operates (1.5 seconds), Raymond Substation would be isolated from the system, though the fault is only on one side. 61tnila.rly tor a short on line :fl:3, Lamanda Park b'Ubstation would be isolated. It, on the other hand, relay #5 ia set to operate in, say 0.5 seconds, and relay #7 in 1.0 seconds, relay #-5 would isolate a fault on line fl from Raymond substation before relay #7 operated but, ot course, the operation would then be improper it the short circuit occurred on line f2 or line #3. It is therefor, obvious that -9- the present relay~ng may cause unnecessary interruptions to service. The first step in this problem, then is to analyze the system conditions, determine what conditions must be met and pick out that method of relaying which will accomplish the desired result with the least complicatijns and cost. Ordinary time element non-directional overourrent relays are often supplemented by these other general methods of relaying for transmission line protection. These methods respeotively involve the following relays: Distance type relays Pilot wire relays Directional current relays alone or in combination with overcurrent relays The distance type relays work on the principle that the relay nearest the fault will operate first. This is accomplished by the use of a restraining coil operated from the potential of the line whioh aots in opposition to the overcurrent coil of the relay. As the voltage across the relay nearest the fault will be lowest, the restraining :potential coil :>n this relay will be least e:ffeotive and, therefore, this relay will operate before the others. The objections to this type of relay are, first, that it is considerably more expensive than the overourrent type; secondly, on comparatively short lines, it is sometimes difficult or impossible to get sufficient difference in petential to obtain the selectivity desired. It is also necessary to have potential for -11- all relays. This type of relay is used on long lines with a number of sectionalizing points, where the use of consecutively time overcurrent relays would make the maximum timing too long, or on complicated networks, where it is otherwise impossible to get proper selectivity. These relays are not intended to be used in plaoe of over- ourrent relays, but to suy,plement them where overcurrent relays cannot be made properly selective. The use of pilot wire relay protection system'3 has been considerably greater in England than in the United States because short cable lines have been used there to a comparatively greater extent than in the United 5tate.s . The earlier schemes developed were known as the Merz-Price system. Of late, modifications of the pilot wire syste~~ a re coming more prominently int3 use in the United States, some making ~se of commnication chamlela as the pilot wires. such systems however usually have a baak:Up relay protection in case of the failure ')f the pilot wires. The advantages of such s. system are~ 1. Nearly instantaneous operation. 2. Can be used on any number of lines independent ot the number of stations. 3. Will operate on small fault currents, thereby providing excellent protection against ground faults. 4. Potential connections not required. -12- The disadvantages are: 1. Cost of pilot wires and maintenance of same. 2. Necessaity of special, matched current transformers. 3 • .Possibility of undetected open circuit on pilot wires rendering scheme inoperable. 4. Dange of induced potentials on the pilots causing false ::,peration. Inasmuch as Pasadena is considering the use of supervisory control of the substations from the power station, a number of spare conductors c~ld be included in the supervisory control cable at small cost so the first disadvantage may not be objectionable. The other disadvantage, however, are quite serious, in fact, sufficiently so to make inadvisable such a soheme for this power system. DIRECTIONAL OVERCU'"'ARENT RELAYS The current directional relay has one pair jf c::>ntacts operated by a standard time element overourrent relay. tacts is directional: Another set of con- that is this contact will close only if power flow is in a certain directi::m and will atay open ii' in the opposite direction. The two sets of contacts are -e ither connected in series or are cascaded. That is, the overload contacts are prevented from operating if the directional cJntaots are open. This prevents the relay from operating on a surge beoau$e both sets of contacts would have to be closed for the time for which the relay was set. The directional element of the relay is so connected that it will operate only when power is flowing away from the substation; it will not operate when power flows into the station. -13- The current directional relay is suitable for use on loop systems having not more than tour stations {power and substationsl The reason for this is that good relay practice requires the _o pera ti on of a relay withing two sec1nds at most, after the occurrence of the fault. Intervals should not be shorter than 0.4 seconds and preferably o.5 to permit time £or the opening of a preceding breaker before the closure of the succeeding relay contacts. Therefore, a series of more than four relays is not advisable, it they have to be progressively timed. Figure 2 on page 10 illustrates an advantage sometimes attained by using directional relays. Relays #1~ f3, :/t-6 and #8 are non-di-. reotional overcurrent relays. Relays #2, #4, #5 and #7 are directional. The relays at the power station are set for the longest interval while #2 and f7 are set for the shortest. It a short oocurs on line A relays #1 and #2 will clear the fault without interrupting service to #1 substation. It is not necessary to make #3 relay directional because it has a longer time than either 12 or #5. If, however, a fault ooours on line B relays #3 and #4 will clear the fault. #4 will operate before #6 or #8 oan operate, while neither #7 nor f5 can operate since the power direction opposes their contacts closing. Likewise #3 will operate before #1, and #2 relay cannot operate with the power direction against it. Similar relay operation will take place for faults on lines C or D. In Pasadena, there are at present only two substations in the loop, while the proposed Maryland Substation can either tie in, in parallel _with either substation or be operated independently. The arrangement is shown on page a. -14- '!'he complete method of arriving at settings is given latter. Some of the advantages of this system are~ l. Simple to install, check, and maintain. 2. Least expensive of satisfactory schemes. 3. Operation independent ot line length. 4. Can be applied to grJund relaying and oan be made quite sensitive by using low energy direotional relays. Its disadvantages are: l. Not instantaneous in operation. 2. Line relays cannot be set to operate on fault currents equal to or less than full load. 3. Requires potential transformers for direotional elements. Once having decided on the use of directional overourrent relays on a system it is necessary to investigate the various types of directional protectiJn so that the best and most eaJnomical plan 11'.ay be submitted. The discussion will be divided into two parts; line fault protection, and ground fault protection. For the line protection three single phase overcurrent directional relays or one polyphase power diraotional relay and three single phase overourrent relays as shown on pages 69 and 72 respectively, may be used. For the eonneotions on page 69 with a fault in the right direction for tripping, the directional contact will close almost instantaneously, and be followed by the closing of the overcurrent element at a time determined by the magnitude of the short. The polyphase power directional relay of page 72 will close its contact regardless or which phase is faulted so long ·as the direction of power flow is correct. The operation of the current el- ement is the. same as for the case of single phase relays. '.!.'he choice between these two systems is largely a matter of opinion, some companj:ee pref'ering the use ot sil1gle phase relays and others the use of a polwha.se relay. Since the Pasadena system has already purchased several single pha.ee directional overcurrent relays this type has been recommended. For gr:)Und protection, page 69 shows the use of a. single phase low energy directional overourrent relay and page 72 shows the use of' a single phase low energy non-directional relay. The obvious ad- vantage for the conneotions shown on page 72 is the saving in aost. A first o:>st o:nnparison between the two installations using repre- sentative cost prices, which could be obtained by the City of Pasadena light and Power Department, is as follov:s.: Equipment Cost Polyphase power directional relay Directional overourrent standard relay Non-directional overcurrent standard relay Low energy directional ove.rourrent relay Low energy non-directional overourrent relay 2/1 ratio potential tranafDrmer 20/l ratio potential transformer (2400 v. Primary) 100/1 ratio potential transform.er (11,500 v .. Primary} -lo- $120_.oo 73.00 30.00 77.00 34.00 20.00 45.00 100.00 Initial CQst For Setup P~e 69 Relay Cost Per Line Directional overcurrent standard relays Low energy directional overcurrent relay 3 @ $ 73 l @ 77 For the six installations ot directional relays $219 77 $296 Total Cost----$1776 .Potential Transformer Cost( only one set of potential transfonners are needed at each substation) 2/1 Rati:> potential transformers 100/1 Ratio potential transformers 3@ $ 20 3 @ 100 $ 60 300 $360 For three substations, Total potential transformer c::>st------------$1080 Total relay and transformer cost--------$2856 InitiJ!:.l_Q_ost for Setup Page 72 Relay Cost Per Line Polyphase power directional relay Non-directional overcurrent relays Non-directional low energy relay l @ $120 3@ 30 1@ $120 90 34 34 $244 For six installations Total Cost----$1464 No additional potential transformers are necessary since the present met ering transformers rr.ay be used. If it is f:>und that the burden :>n the open delta p::>tential transformers is large enough to cause any voltage unbalance or an overload OJnditi :>n, it will be necessary to add a third trans- former t::> close the delta. -17- Hence add: 20/1 Ratio p::>tentia.l trG.r: sformer 3 @ $45 For the setup page 72 Resultant Saving by use of the method page 72 $135 Total Cost--$1599 Saving----$1257 From the above c::>mparison it is evident that there is a considerable saving in cost by using the second method. The polyphase relay as sbown on page 72 is and must be designed for operation as a line relay, due to the fact that its current coils must at all times carry the line current. P::>r this raas :m the polyphase relay will not operate :>n small ~round faults. The current coils of the single phase lov., energy directional overcurrent relays, ho,ivev 1"r. normally carry n::> current, hence their sensitivity can be made much P,reater. For this reason single phase directional relays are recommended. Since two new substations are pl~nned new potential transformers will be needed for one or both, hence it will be convenient to use the scheme of page 69 in which case the high tension potential transformers can be used fjr both metering and relaying purposes. The difference in cost bet•r een the 16.5 KV. transformers and the 2400 volt transformers, would be jnly the a dditional c:>st and this amount would be Sl'.11.a.ll enough to neglect when c :>nsiderlng the gain in sensi ti vi ty or relay protection. -18- RECillE'.&1J'. \,\TIONS FOR LtNE um GROUlID FAULT PROTJWTIOU For Line Protection: The use 0£ n,')n-directi:mal and directional ovsrourrent relays of the single phase type as shown or:. page 69. For Ground Fault Protection: The use of non-directional and directional low energy relays . ,:,f the single phase type as shown on page 69. -19- CHAPTER III SYSTEM CALCULATIONS FOR RELAY DETEIUtUNATION .AND SETTING With the preli~inary survey completed and the type of relays detenninea. the next step is to make the necessary calculations to determine what abnormal conditions may occur and the required action of the/relays under these conditions to: 1. 'Clear the fault as quickly as possible t:.> minimize disturbance on the system. 2. ls::ilate only the faulty seoti::m of' the line. This information provides a basis for decisi :>n as to wbich relays must be directional and vfuich may be non-directional. Also the p roper setting of the relays can be made both as to current tap and lever setting. Bef::>re making these calculations, the actual c::>ndi tions under which the system will operate must be known. That is the location, capacity and characteristics of the power supply, the line characteristics and the actual network arrangement. The ca lculations consist of finding the current which will flow in the different relays for sevs ral types ot faults, these faults being successively assumed to occur at different points in the system. With this data, the worst conditions for each part of the s ystem will be known and t he relays can then be set for :proper operation to oor~ rectly protect aga inst such faults. E9tUIV.ATE:t-.~ SYSTl_iJ?4 I M.PfilMlTC.r;~~ /issuming the fa.ult occuring at a certain p oint on the system it is nece s sary to find the eq1livalent impedance from the p:>wer source to -20- the fault in order to detennine the total current flowing over all paths to the fault. In the cas e of a bala.~ced three phase fault, the equivalent impedance to be found is the single phase impedance from neutral to the fault. To do this the i.mpedance of each part or section of the system must be found and all impedances combined aooording to the well known laws for electric circuits. In practice three different methods of combining line impedances are used. The first is to express the impedance of each line sec- tion as a complex quantity and combine them as complex quantities. This method is rigorously correct but becomes vary laborious if the system is at all oomplioated, particularly if there are many parallel circuits. The second method is to det ermine the impedance as a single scalar quantity, having only magnitude, the phase angle being neglected when combining them. This method is not altogether correct but in most practical solutions the a.mount of error is not serious for relay determinations, since at best these oan be only approximate when such undeterminable factors as fault impedance but enter int, the problem. Furthermare the more constant the ratio of resis- tance to reactsnce, the more correct the method will be, since the vector angle is dependant upon this ratio. The third method is to neglect the resistance entirely and consider only the reactanoe component. In this case the smount of er- ror depends upon the ratio of resista:nce t:> the reactance. If the resistance is equal to the reaotance, the assttned impedance of the circuit is 70.7% of the actual i~edance. -21- If the resistance be- oomes less. the error decreases quite rn.pidly. ?or this reason. if the resistance is leas t'han half the reactance, t Le a.m:mnt ::,f err;)r is not sufficient t:> warrant tte r1ddi t1:ma.l cJmr:,lioati r>n :>f the other meth::>ds. F:>r the study of the Pasadena. system. the third method (neglecting resistance l is used because the generat:>r reactn:.noe a11d the line reactor rea.ctance are a very cnnsi derable part ::>f the total krpadar.oe. 1'heref::>re the error introduced by using this method ls not serious . The f:>llowing nurnericn.1 example gives ar · 1dea of the variation obtained in results by the use of the three meth:>ds. Z =O. 911'1-t-j /.!176 , v Z::. o.S 2 6 +/o. 6q. l % ® ,,, Q) fa Error Current Sec. (2-3} Error 4.• s 3.6 763 700 730 4.3 Method Used Total current Err:>r Current Sec. (1) Complex Q,uantity Reaotance Impedance 3520 3570 3390 1.4 3.7 2757 2070 2660 fa a.2 r,.c. SiiORT CIRCiHT CALC f'LLTING TABLE By usi.ng the sec:md ::ir thi.rd rr:ethod ':Jf calculatl )n, helr,fnl d.c. short circuit calculating table can he used. the very lforncrms articles have up-pearod describinr, this eqn iprnent s:> sna.oe wi 11 n'.)t be taken here f:lr that purpose. t,uch a calculating table ~.1as used for checking s'Jme ::>f the results but all. va lues were actually Galculated in add1tl::in. -22- .QE~],ATING COlTD!TIONS OF THE . SYSt~ Under normal :>peratlng oonditi.:ms all power is supplied from the Pasadena Power St ation. Onit #8. the 31,250KVA. turbine generator, is the most efficient unit and will therefor be used practically continuously. This unit has ample capacity for the peak loads at present and t'or some time to come as nearly as can be determined. It is be- lieved logical therefor, to make all calculations relating to relay protection on the basis of this unit only. The short circuit current would of course be larger if several machines were operating in parallel on the bus or with the Edison line in parallel and such possibilities must be considered in determining circuit ~reaker duties. Such operation, however, must be classed as abnormal and it is neither desirable nor necessary to consider such in the relaying oalculati :ms. Ot the several different normal operating conditions possible tour rep resent a tive cases ha.ve been selected. Other setups, which might normally be used, will be found practically identical with one of these tour. The four oas es are: Case 1. All switches closed except switches 6, 9, and 11. {See pages 53 and 62) Case 2. All switches closed except numbers 9 and 12. (s ee pages 54 and 65) Case 3. All switches closed. except number 12. $See pages 55 and 64) Case 4~ All switehes closed. (See pages 56 and 65) -23- Case 1 is a typical setup for normal operation when the pump lines (see diagram, page 8 £or pump line designations) may be fed from a:ny one of the three substations but not from more than one. In this case. therefore, there is no interconnection of substations except the loop line from Raymond to Lamanda Park. Case 2 is the setup when the Y1aryland substation is fed by the 500,000 c.m. cable and Maryland and Raymond Substations are connected thr:,ugh the pump lines, thus feeding the pump lines from two sources. This case is typical of any one of the three cases possible, where the pump lines are fed from two substations. It may be more usual for l!a.ryland to be fed Jnly through the 500,000 c.m. cable (the 350,000 o.m. cable being held for emergency) beoause the 350,000 o.m. cable taps the feeder to the California Institute of Technology High Tension Laboratory Feeder. This feeder is subjoot ta severe surges so it is desirable to operate it independently. so preolude disturbance trom it to other parts of the system. Case 3 shows the system when the three substations all tedd into the pump lines. thus interconneot1ng all three substations. Only the 350,000 o.m. cable tJ 11aryland is open. Case 4 1s when all switches are olosed, and 1s the case when the highest total short oircuit currents may be experienced. No caae is considered with the loop tie between Raymond and Lamanda Park open. because this would be very abnormal, and not to be considered as an ordinary case of operation. Several other possible setups might be made but these also w~uld fall in the abnormal class and need not be considered. In studying these cases, faults are considered in turn at each of the substations. Two tl7Pes of f~ults are considered; 1. A balanced three phase fault. 2. A single phase to ground fault. The first type of fault was chosen because while not oommon 9 it is the severest fault that may be enoountered, so that a study of this type will show us the maximum currents with which it is necessary to deal. The ground fault was chosen because it 1s the most common tault to occur and the type requiring the most sensitive relays. Becauae the Pasadena system is grounded at one point (the generator) through a reaotance 9 the ground current will be limited but the appearance of any ground current (except a small charging current} is an indication of a fault. Therefore, particularly on a system where cables are 11sed, the quicker the fault is recognized and isolated the better and the oheaper. The single phase line to line ta.ult is not considered beoause it is not so likely to happen as a ground fault, it is almost always preoeeded by a ground fault, and it is not so severe as a three phase fault. The double ground fault is not considered because it is un- common and is almost oertain to be preceded by a single line to ground fault whioh would cause f'unctioning of relays. SY.MMETRIC.AL 00.MPONENT ANALYSIS The development of the symmetrical component method of solution of a.symnetrioal polypha.se net-works discovered by Dr. c. L. Fortesoue gives a ccnq,letely unique technique for the handling of relay problems on a three phase system. Use is made of this method for de- termining the currents flowing through the ground relays on occurrence of a ground fault. A series of articles published by Messrs. Wagner and Evans in the Electric Journal and sinoe reprinted by the Westinghouse Electric & Mfg. Co •• gives quite fully the development and application of this method. By this method the calculation ot system performance involtvea the setting up of three separate networks known as the positive sequence. negative sequence and zero sequence net•rorks. Each network has balanced phases and is represented by a single line diagram, which is made up of the various impedances of the different parts of the network under consideration. These impedances are the impedances of one phase of the network, the other phases are identical. The phase voltages and currents for each network are balanced. In the first network, known as the positive sequence network, the three phases 81_, b1 , and a1 are 120 wise direction. 0 apart a.nd rotate in a counter clock- In the second network known as the negative se- quenoe netw?rk the corresponding throe phases a 2 , b , and o 2 also 2 rotate in a o:mnterclockwise direction but in the order a, o 2 , b. 2 • 2 In the third network known as the zero sequence network, the phases a , b0 , and c also rotate in a counter clockwise direction, but 0 0 they are all in phase. In detenn1n1ng the actual phase quantity such as current of the actual network, the positive. negative and zero phase components are added together. In a balanced three phase system. the zero and negative sequence components disappear, leaving only the positive sequence. The positive sequence network is in all respects similar to the usual networks considered: the resistances and reaotances are the values usually given to oa.loulate line regulation. For dete:nnination of relay ca.1- au.lation, the reactance of a generator is the transient reacts.nee. The reason tor this 1s discussed under generator reactanoea. The negative }Jhase sequence network is in general quite similar to the positive sequence network:. The negative sequence reactance of the generator, however, is taken as the subtransient reactance of the generator. In the case of single phase line to line faults, the positive and negative sequence networks only need be considered, since the zero phase component disappears. The zero phase sequence network impedance$ are radically different from those 0£ either the positive or negative sequence netw~rks. The line impeda.noes are those obtained by imagining the three conductors oonneoted in parallel, the ground forming the return oonductor. The generator zero sequence impedance is dependent upon such design characteristics as pitch faotor. It is generally much smaller than the positive or negative sequence impedanoes. For transformer, the im- pedance to zero sequence 1s infinite unless a path is provided to~ the flow of zero sequence current, that is a neutral or ground oonneotion. Since the power transformers on the Pasadena System are a.11 delta delta they have infinite impedance to ground and can be neglected in the zero sequence network. The following table gives approximate values of zero sequence reaotanoe of various part of a network in terms of positive sequence reacts.nee. Single Circuit Aerial Lines (no ground wires} Double Circuit Ditto Single Circuit Aerial Linea (non-magnetic ground wire) Double Cirouit Ditto Three Phase Cables· Single Phase Cables Neutral Impedance Ungrounded Trm'lsformers Grounded Delta Y 3.5 tirees positive sequence reactance. 5.5 times positive sequence reaotanoe. 2.0 times positive sequence reactanoe. 3.0 times positive sequence reactanoe. 3 to 5 times positive sequence reactance. 3.0 times positive sequence reactance. 3.0 times poai tive sequel1oe reaotanoe. Intinit6 Impedance. Equals positive sequence reactanoe to neutral on the Y side and open circuit on the delta side. GpERATOR REA.O'l'ANCE.S~ The generator reactance whioh limits the current at the instant of short circuit is a smaller value than after a short period. The current at the first instant may be regarded as having two components. (1) a direct component and (2) an alternating component. The direct component disappears quite rapidly, leaving the alternating component which is symmetrical about its axis. This component known as the transient component decreases more slowly until the steady state is reached, which is determined by the so called synchronous reactanoe of the generator. The reactanoe of the generator limiting the first rush of current is called the subtransient reactanoe, and the transient reactance is the : value of- react:mca twhioh gives the synmetrioal r.m.s. value of current for a three phase short oirouit at the terminals. -28- For relay operation, the value ot transient reacta.nce gives current valuea for whioh the calculated time very closely approaohes the actual tir.:ie of operation. However, to be strictly correct, the decay- ing current should be considered from the instant of short circuit until the operati~n of the relay and for this purpose decrement curves can be used. Decrement ourves vary for different machines but the standard decre~~nt curves now aooepted are sufficiently accurate for good approximation. To determine whether the use of the transient reaotan~e of the generator was sufficiently accurate to make it unnecessary to use the decrement curves, the following example was worked out. Relay 1 1n Case 2 was set to operate in 1.1 seconds on a our- rent of 1635 amperes. This is for the short circuit at Raymond sub- station and is the value obtained by using the transient reactanoe of. the generator. If however, the eubtransient reactanoe were used this value would ha.ve boon 2220 ampores, while the total current flowing at the instant of short oirouit would have been 5353 amperes. (see page 31) The percent system reaotanoe which is the full load current divided by the total short circuit current times 100, would be: 1090 5353 X 100 • ~ 20.310 Suppose, however the decrement curves, page 30, were used instead ot assuming a definite value of current flowing for the time of operation of the relay. Using the 20.3% reactanoe, the instantaneous (0.008 seconds) unsyrmnetrical short circuit current would reach a value of 8.6 -29- THREE PID E LHOR'P CI OUITS US! C 3?.. NSI '1! GE J ' TO RS CT CE -- OASE 2 X-- alues tor Short 01rcu1t .at Raymond Stlbatation. Y-Valuea tor Short Cirouit at Lamanda Park substation. ~-Vale f~r Short Oircuit at yland Substation. , - 117 25 z..... 50 5 C:) ~ x-- 6 X•-246.~ C) ~ ~ I.-- 539 N'wnb rs Indicate Relay z-1.120 Location. ~L-- - - - - - 1 - - - - - - ~x~-~-~~~~- - -- ~~ a x--10!8} 7 Z:::: 23~ :) (/) ~ ct L-----l~----------L----,--------- - 9 11 Q .c.--1170 1... - 5~ Y--3680 z..- 232 it-22 y... _ 48 $ z-- 938 4-gsoo l: J- SM ,J-3800 -------+-------- - ~u 14 15 l 2 PASADENA PoWER PLANT I .J J times full load current. Actually, however, fnr relay operation only the symmetrical values of the current {not to include the un- syrrmetrical or d.c. uomponent) is effective and this value for this reactance is 5.11 time full load current. (This value of 5.11 is given in the article by c. F. Wagner entitled Decrement Curves) This value continues for the whole interval of 0.12 seconds. The current in the line section to which tho rels,y is connected would for this interval have been: 2220 x 5 11 x 1090 5353 • =2320 amperes. This corresponds to 580% f-all load on the relay {with a current transformer ratio 0£ 400/5 and a relay tap setting of 5). For this value of current and a time lever setting of 5, the relay would close its contacts in l seo:>nd. actually o.6 0.12 x 5 However, the interval o:f' time is =0.158 seconds. The factor of 6.6/5 l'l!llst be introduced because the decrement curves are based on a time constant of 5 while the ma.chine in question has a time constant of 6.6. The actual distance the contact moves in this time is : .fh.15~ x 5 1.00 = 0.79 divisions. Taking the next interval of time from 0.12 to 0.15 seconds, the average value of currant for this interval is found to be 4.85 times the full load current. This will give: -32- 2~ x 4.85 x 1090 = 2200 a>nperes in the line section. 5353 Jr 550% full load ourrent in tho relay. For this value 0£ current it still ta.lees only one seoonu for the relay to closa its c~ntacts if starting from tho j5 time lever setting. be: The corrected time would (0.15 + 0.12) .2.!.& = o.04 seconds. 5 The movement of the contact would b6.: 0.0 4 x 5: 0.2 divisions. 1.00 By continuing this integration until the relay contacts close we get the following table. Time Interval o.oo to 0.1.2 0.12 to 0.1s 0.15 to 0.25 0.25 to 0.50 0.50 to o.83 Time Corrected ~r {'i "' ~. •••• Seoonds Time C.'urrent 0.12 ().03 0.158 580 0.040 O.l:.'i2 0.3:¾l 550 0.10 0. 25 o.~3 0.440 1.100 475 390 350 Di via ions Moved 0.79 0.20 0.63 0.46 l.87 4.95 It will thus he seen that the n.p:prox"hnate methoa of using the transient reactance value is sufficiently accurate f.c,r the relay settings in this oaso. The following tabla :,btained f'r:>m the paper presented by w. o. Hahn and C.1l'. Wsgnar :m Standard Decrement Curves in the A.1.~'. .;E. Transactions fro ,J'une 1932, gives the va:ri ous ma.chine unit raaotance values for typioa:i three phase 4 phle turblne generators s -33- ~:;ynchronous reactance o.95 to 1.45 Averar~e 1.10 Subtransient reactance 0.07 t!J 0.17 Average 0.12 Negative sequence reactance Same as Sub transient reactanca Zero sequence reactance 0.01 to 0.14 Average 0.0'75 Since the zero phase sequence reactance varies quite critically with the windine pitch, t1.n averaire value is not dependable. In the study for Pasadena a value of 0.06 was taken arbitrarily since the exact value was not 1{nown. 'l':his pll.rticular f actor is not sufficiently l a r ge to have a great effect upon the result so it is believed safe to assume such a value. The value of transient and subtransient reactance f:.ir generator #8 are given on page 8. The relati.::m between those reaot::mce values in pe rcent;::we is g iven as follows: Transien t reactance - (1.4 x Sub transi ent reactance + 2) 'l'he zero sequence impedance of a single three conductor cable can be de t~) rmined for either '.:>f the two cases as f:)11ows: 1. Return current through the sheath and gr::mnd in pa rallel. . 2. Return current thr: mp,h the sheath al::me. In this study, the fir ~, t condition is assumed because. althovgh the cable is to be laid in fiber or glazed tile duct, it is t3 be frequently gr:mnded at all unuergr:)Und vau lts. The impeda:nce of the caple per c:>nductor, :including the c r:mnd r e turn with zero fault impedance. per mile length as developed by -34- Wagner and Evans can be f :.m nd by solu tion of the following network. r of sl,~atl, CondivctoY r + ju.oolf6Slf/02 l'i+ +~ MR) 6 (cond) condvc..r,:,r '; [ where : r 4 is the radius to insi de of shea th. r 5 is the radius to outside of sheath. (r 4 +r5)/2 is the geometrio mean spacing , conductor to sheath. G. :,'l . R•.'Jf the conductors was calculat€d on the basis of round c onductors. De is the symbolic representa ti :m of the e qu ivalen t depth of the g r :mnd retu rn. This va lue was t aken as 2800 feet. 0.20 1,tean di ameter x thickness sheath in ohms per mile. is the resistance of the The va lue thus f1und is the value for the entire 3 conductor ca ble and a s the zern sequence current divides equally between the three conductors the i mpedance per phas e is t hree times this value. CABLE CHARACTlnU S'l'ICS USEJ2.__:[Ji TH!fi RE-PORT 500,000 0 . ±,1. Cable Pos itive or Neea ti ve Se quence Resistance Reaotanoe 0.0 249 ohms pe r 1000 feet. 0.0271 ohms pe r 1000 feet. Ze ro Sequence Resistar1oe 0. 228 Reactance 0 .114 0.255 I mpedance -35- ohms per 1000 f eet. per 1000 feet. ohms pe r 1000 fe e t. ohms 350,000 c. :::. Cable Positive :Jr Negative '.3e4.-uence Resistance --- 0.031 o:ti..ms per 1000 feet. Reactance --- 0.0286 ohms per 1000 feet. Zero Sequence Resistance 0.263 ohms per 1000 feet. Reactance 0.129 ohms per 1000 feet. Impedance 0.284 ohms per 1000 feet. It will be noted from the above table that the zero sequence values thus calculated are much greater than the positive sequence values. For 500,000 c. :r. . cable the resistance is approximately 9.15 times as e reat and the reactance is approximately 4.2 times as great. Since in this case the resistance is such a large factor it cannot be neglected as was done in the positive sequence calculations, therefore the zero sequence impedances are considered as scalar quanti ties. The zero phase sequence impedance of the overhead lines is taken as 3.5 times the :positive sequence values. This value is an approx- imate value -obta ined by a number of calculat i :ms for typical overhead lines. Since the amount of overhead transmission lines at Pasadena will in the future be small this approxiw~te value was considered quite accura te enough fJr the purpose. The zero phase sequence impedance of the line reactors is taken as 3.5 times the positive phase sequence value while the zero phase sequenoe impedance ::,f the gr,mnd reactor nnist be taken a.s 3 times the positive phase sequence va lue. -36- §_/J,IT'LE Ci.J&L"l'.>..Vl: IOlIB As sta.ted ab .:ive there bave been chonen f:m:r cases Jf probable normal operu ti on for ·which the short circuit calculations must be made. nnoe caae 4 is the most complicated of these it has been ch::isen to exemplify the oalculati ons for both three phase short circuits and single line to eround faults. For both cases the fault is c :. msiderea to be at R;ci,ym::md Bubstution. In 1na.~ing any such calculati , ns on a system it is possible to use the values of reactance or impedance (as sta ted above only reactance values are used for three phase short circuits and i mpedance v:.ilues in the ze ro sequence network for ground f aults) either as a percentar,e value or as an actual ohmic value. For use in this re-port the actua.l ohmic values have been chosen and are sho1im on page 36 for the various line sections as well aa for the generator and reactor. CALCULATIONS F'OR A TFI.i.'ti~ E PHMiE . PAUL..L.Q.N THE BUS AT RAYIJOIW SUBST;~ TION The positive sequence net·.vork for the faulted phase• which is all that is necessary for three phase shJrt circuits calculations, is shown in fig. 3, page 39 9 in a convenient form for use. Each line section is numbered and in the following examples these numbers are used as subscripts to indicate the various line sections. The 16- cation of the short cirmlit is desi~nated by X. Once having the network: set up as in fig. 3 it is then necessary to reduce it to a single impedance as shown in fig.?; the total short circuit current may then be found and apportioned between tho respective lines in the inverse ratio of their impedanc es. -37- Charaoterietios ot No, 8 Generator and Auxilary Equipment x,_ X2 Xo Genera.tor Line Eea.etor 1.83 1.19 0.525 o.317 0.31? 1.11 Weutral Reactor 0.57 0.57 1.11 5 Ql ~ Cl) 7 B--0.108 x-... 0.100 R.--0 . 115 ~--0.107 z0 -1.07 n-0,520 65 .z 0 -6.l2 x.... o. -38- :a-0.:>2§ x ...... o,64'? z0-6.l0 T-' i f: & ,1- is Jbtained from fig. 3 by c 'Jmbining line sectiont; ( 9) and {10 ) into an e qu iva l ent va lue s ud add ing to it line ne~~tiort ( 8) t hus obtaining sec tion (8' ) . t, cctions ( 2), (~n. and (7l are similarl y C'.)mbined t:> form secti~n ( 2' l. By ins pecti :>n :>f fi g . 4 it can be s een that line sections (4,) ~ ( 6) , and (8') form a cl09ed delta s1 tha t the next step in the simplification of the circult is tJ c :mvert this delta into .:::.n e qu ivd e nt Y as s h ow n in fi g . 5. The forrrl'~ la us ed in ma~ing this c 'Jnversion may be written a s f:>llows: = 0.158 Similar expressions may 1)0 written for the other t wo branches 3, and C. Fig. 6 is next obtained fr3m fig. 5 by combining branches (C + 2') and (B -~ 5) to form line section (D). The va lue of total re.- ,ctance fig. ~; is next obt&ined by c1mbining section (A + D) and (11, this va lue then being added t:> the sum of the g enerat~r and reactor values. =2 0382 The total short circuit current h obtained bJr dividin g the line -40- t 'O neutral voltage by the total reactance. In order to detennine the current in the various line seotiJns it is now necessar.,r to work backWa.rd thr :mgh the network dividing the current at each line junction invers ely as the impedance of the remaining line. 'The first divisiJn wou ld be as sh:,wn in fig. 9 be- tween line seoti:ms (1) and · {D'). = (0.158 + 0.202) 4000 Oa55 + 0.158 + O. 202 - 1430 Fig. 10 is obta ined similarly by the division of the current (D' ) {o:.· Cid) int'.> secti:ms (C') tmd (B + :,). To obtain fi g . 11 from fi g. 10 it is also necassnry to consider f: s• 5 which c ovtains the equi vale11t Y. The sum of the voltage drops across sections {A) ~na (C) will give the voltage across one Hence the current in section (8') will be: _ 1?570) (0.158} + _{_2030) (0.0329J = 2290 0.207 The currents in sections (4) and (6) are detennined in a similar manner. Fig. 12 comes diroctiy from fi g . 11 by ma.king the necessary divisions for line sections (9), (10), and (2), (3). Calculatl :ms for other fault loca tions and system connectl ons are made in a similar manner the final results being shown on a form similar to that of fig. 12. ( ::;e e pages 62 t::, 65) -41- CALCUL ATIONS FOR A GROUND PAULT ON THE BUS AT ]iAYM:01'-."D 13UBSTI, TIOJ)! In the case of r rJund fault calcul at iJns it is neceso a ry to C'.lnsi dc r the three s equence net w:Jrks connec ted i n series thr:.mgh the g r1unded points. Sinc o in this s ys tern th ere is :mly :me p:Jint n?rma.ll y gr:mnded, the generat)r, the c:Jnnections betwe en the networks a re made fro m the p oint of fault t:; this g r)1maac1 point of the f)llowing netw::>rk. These c : >n.riecti ::ms are shown in fi g . 13 page 44 for the faulted p has e where the line values are indicated in the form of a general box network. These line values having been obtained by a s e ries of c::>mbinati::>ns as sho,., n for the three phase cal cu l a t i :ms fi p;::; . 3 to 12. The re a ctance values 0f the three se- quences are also indicated for the genera tor, line reactor, and neutra l reactor. Because p ositive '1equence voltages only a re genera ted in zynchr::mous ma.chines the 0nly vol t ago app earing will be that in the p osJ tive sequence netw::i rk.. Since those net...v::irks are now all in series the total equivalent reactance is the sum of the separ a te va lues. The current is then f::nmd by dividing the line to neutral volt aee by the total r eactance. = 9530 -- -- 890 amperes 10.723 From the connection of the netw~ rks it is evident that this same current of 890 amperes rrrust flo w through each network of the faulted phase. By the same procedure as f:>llowed for the three phas e cal- cula tions this current may then be apportioned between the various line secti ons in each network. It is well to note here that t he di vision -42- of current in the vari::>us netw::>rks will not nece s sarily be the same for the respective line sections due t::i the fact th1,.t impedance values for the corresponding secti :Jns a re :not the same in each network. If it is desired to obtain the current in the f aulted phase it is only necessa ry to add un the particul a r line secti :m current values from each of the sequence networks :for the faulted phase. It is also possible to obtain the sequence current in the other phases so tha t b y the addition of these other sequence currents the current in any phase may be obtained. For our case, however, we are int e rested .:>nly in the residual gr)und current, i.e., the current that will flow in the neutral lead of the current transformers. By definition the zero phase se quence currents in each phase are ln phase. hence all the zero phase se quence currents will combine and flow through the neutral lead, i.e., three times the current in any one phase. The positive sequence currents oonstituta a balanced three pmrne system. c)nsequently there can be no res~dual current flowinr, in the neutral lead. Bimila rly no negative sequence current can flow in the neutral lead. From the above it is evident that the residual ground current in the neutral lead would be t:hree times the value found in any line ,~ecti'.>n of the zero phase se- quence network:. Hence the total residual gr:>und current is 3 x 890 which equals 2670 a~peres. Page 56 shows the g~~und currents for the oase considered in this example and it is seen that for the ground at Raym:>nd Substation the total fault current is 2570 amperes while the current in the various line sections are as indicated. -43- ---7 Fault Pt:15- 5~~- Ne9 Se-i- zero Sett• /Vot:warfr Net-wotr1r Net:work ~~0.232 ~::0.232 I I I I I ,~ X = 0.3/7 I X =- 0,57 //1/ Retu>-n - - - -Ground - - -- -- I I _J CH.APTER I V ID~LAYS , DESOJU P TI ON--CONKECT IONS--SE'l'T INGS The :following desoripti::m while app lying specifically to ~Vestinghouse Type GO induct ion ov ercu.rrent and Type CR ove rcurrent directional relays, is a lso g enera lly acs crip tive of the Genera l Electric Relays IA-201, IK-104 and IB-1. The standa rd overourrent relay is the induction disc type having a current coil with a number of t aps. Each tap has a fUll load r ~ti:ng in amperes and these r a tings are from 4 t ~ 12 or 4 to 16 amperes depending up:m the particular style of relay used. The r a tings aro such that the r el a y will not st art until the current in the coil slightly exceeds the r l".ting . The tap se t tings of the r e lay permit the adjustment of the current flowing in the relay coil for a given value of current in the secondary of the current transformer. lever settine. .Another ad:tustr:ient is the time This simply consists of moving the contacts further apart or closer tor,ether so that it t~"ik:es a longer or shorter time for the rota ting c:>nta ct to close. As the relay i s designed to c;:ive ~s nea rly const an t, speed ::>f rot a tion as r; ossible for n given porcent lo a d, the time of closu re is directly proportional to the division setting of the relay . The directional current relay has an oveircurrent element :r;recisely the same as the above relay. In the s ame case is m'.luntea a wattmeter element having a potenti a l c:>il and a current coil. -45- The current coil is in series with the current winding of the overload element. The wa.ttmeter element is designed to closa its contacts practically insta ntaneously if the power flow is in the right direction. It will o:pernte on as low as one percent of normal voltage with a reas : m able excess current. Inasmuch as great sensitivity is desirable for the g r:n:u1J relay, that is aperati::m on a minirrn.1m am::mnt ~f cur.rent it is desi.rable to use l::>w current c::>ils on the ground relays. The line relays must have capacity to carry the fulJ nortrol lino current continuously but since there is n:, nor:1ml g rou....'1d current, a. relay thnt will operate on the nini r:ium current possible is desired. For this purpose the so called low energy relay with the low curront coil is applicable. ti to al nm1Je:res) Dy usinr: a low enarp,y relay. particularly. for the directional relays operation is obtained with great sensitivity even when the voltage a t tlie rela:r is very low. ;RELAY SET·rnrns Since the Pasadena System at present h.as t,ostly ~-;·estinghouse relays insta lled it is considered best to use the t ~'J) ical Westinghouse time current curves for r...aki!l{; the relay settings. The General .Electric 1·elay curves differ slightly from those of the Wet~tinglnuse so that if such relays a re purchased in the future it will be necessary to rnake the corresponding changes in relay settings. These curves are shown nn pages 60 nnd 49 for the Standard and Low Energy relays. For the curves of the standard relay page 50 it C3n oe seen that the higher the percenta?e of current a.b:)VC 100'.t the fas tar the -46- op er:,tion Jf the relay up to a ,n1lue of curren t a bout 410) to 900}& 0 (depending on the time l eve.r settin{d of rnting . the time of Jpc;ra tion is a definite minimum. Abwe ttds va lue The relay thus has an invorse ti me ch:1racteristic f::>r va lues of current fror.1 100;; to 400 1& or 900 1; of full load r a ting and n definite time ch.aracteris tic above this value. It is the c:mihinati on of this inverse and definite time characteristic which rr.akes possible the consecutive timing of a number of relays along any r iven line. The cur•,es for the low energy relay are similar to those fer the standard rela:r except that it truces a. l a rger })erceutage of ovarload before the relay becomes clefini te time. In order to make the necessary selective rsla~r setting s on 1c must; h~ve at hand cert:dn dat a. as follows~ 1. The ge neral t ;ype of relay to ba used rm;st be knovm. As stated above fer this system it has been decided to u3e non-directional and directional overcurrent relays. 2. 'I"JPiCal time curre nt curves for the relays to be used. aro shov,n on par,es 49 rrnd 60. ':'hose Since the tj_mirlfl mechansim of the di- rectional und non-directional relays is the same, the curves apply equa lly well to both types. 3. A s~rmplified diag ram Jf the system on 1.<:h ich the relu;r locations mny be represented in some c:invcnieut manner. For this purpose, use has l>een made of pages ~1h:Jwinv the f au.l t current va lues; also each of these sheets ha s nu.mbers 1 to 15 at locations quite representPti ve of the necessary relay loca t:i :m. For insta nce~ #-5 is found on any of these sheets to be :m the Raymond Line at l?aymond SUbstation; hence -47- .relay f!,5 is loc a ted on the :Ea;:mor:d .Line ut llaym:md Substa tion. 4. The 3.llowe.ble time interval between .relay settings. this report the r:,inimum time -is t 2.ken as 0.4 sec :mds. For The minimum t i r:-i a interva l necessary depends u pon thfl rapidity of o:pera ti ::m of circuit bre/lkars a.no circuit breaker relays, beca:ase in less than this time interval the fault nr,rnt be cleal'od or the succeeding relay sets in orerati3:n the tripp ing of anJther breaker., which should not open. Thia ti!Tle intorval is long enough for the ordinary J11eru. tion of most b.realters, but if it is f::mnc} that the ci rcmi t breaker mechanisims are too slugg ish for this tt-~ ing, the tin~e int6l"V[,1s •will have to be increased accordingly. For Pasade113, it is believed tha t the a.p paratus is sufficiently s p (~edy, but this point sh'.Juld be checked by test. 5. 'i'he cu.r1·ent tra:r:sfJrmflr ratios at all points at which relays are to be l:>cated. l1he :3e (: an be f:rnnd :m the original system dia- gr:_,,rn pag e 8. 6. :s!inimum timo for \ J1ich a relay may be ~et. 0.2 sec::mds has been chneu as the minir.n.un trippinp tine since a shorter time might a.llo·;; the relay to close 1:n a 1:cavy surg e. The sett:i.ng Jf the gr~rnntJ rela;;rs bas beGn CJnsidered first as thay are somewhat simpler and s ho,. the advant age of using the in·•rnrse time part Jf the ti me current curves in ,ietting the line relays. As has been stated acveral times before it is denira ble tJ set the ground rela:,,·s so that they will :>p erate :m small values :>f grJund -48- current. hence the i\: ampere tap has been chosen for all such relays. From the tir."o cur.rent curves for the low energy relay it is f::mnd t}1at the relay will not trip f:Jr less than 200:; load or the equiva ... lent of 1 ampere in the relay. For ~11 loca tions having current trans form.er ratios of 400/5 t h is ·would mean a line current :,f 80 am- peres, f'ar 250/5 --- 5:J amperes; and for 170/5 ---- 34 amperes. In setting the r round rel ays advant age has b een taken of the f a ct that between <:w.ch time lever setting curve. rage 49 9 there is a11 interval of approxi ma tely 0.2 s ec:md3 for :J.11 va lues of load, honce i f the relays to have the lowest time were set on lever setting # 1; the next ::m lever setting -#3 etc. it i3 e,;-ident thc".t no matter what the fault current value in the rel ays there would always be discri minati 1n provided di:recti,:mal rE;l ays a re u.sed when needed. This is the general rJlan used for the r, round rela;'.! settin.r,i:1. Page 51 shows a table conta ining the settings as recnmmended. J:,s 3tci.ted abovo 0.2 sec:mds was sot as ~ minimum time alloYmble so that there w:)Uld be no chance for the rel a;y to go out on a surge but in the case )r the g r .:)1:md current a j t is not felt that the mini- rrr.im tirr;e necessarily need be held to this f::>r va lues of current of over about 100 &!T!f)eres so the minimum time setting has been e iven as 0.25 seconds at 500i~ current; for loads greater than 500,1, the relay will trip much faster. This results in a lever setting of J with a definite minimum trippi?l.f-:' timo of 0.1 sec'.:>nd. 8ince the relays at p oints 5, 10, 12, 13, have only to protect the lines c~::;inCT fro m the p 07'er stotion they have been chosen of the -50- GROUND RELAY SETTnms Re l ay C. ,,,.., . Ratio Tap %Load ~'i etting Time .Iinimu.m Tin1 e 1 400/5 -k· 500 4½ 1.60 o.9 2 400/5 ·:;,;· 500 st 2.25 1. 3 3 400/5 1( 500 4l 1.60 o. 9 4 400/5 ), 2 500 6-~ 2.25 1.3 5 400/5 .J . 500 ;J· 0. 25 0.1 6 170/5 _J_ 2 500 ~~ 0.95 0.5 7 250/5 .la 500 2;,.·1~ ~- 0.95 o.5 8 250/5 J._ 2 500 2'l- 0.95 0.5 9 170/5 i 500 2} 0.95 o.s 10 400/5 1i" .1 500 ·it 0.25 0.1 11 400/5 .L 500 4-~ 1.60 0.9 12 400/5 -2- 500 _1_ 0.25 0.1 13 400/5 1f ·'· 500 1f 1 0.25 0.1 14 170/5 -~- 500 ~1__ 0.25 0.1 15 170/5 . ;~ 500 ·i 0.25 0.1 Tir·:a Levar ., 2 2 2 1 -. ~ 2 2 - 51- 7 directional type and given the minimum ti me setting mentioned above. Relay 6 must be set tJ hold in over reluys 10. 12, and 13 and relay 9 over 5. 12 , ana 13, so the y r~re given a minimum setting of 0.5 tlec::mds with the time lever setting of 2} . 'r hese relays are made directiona l so that they do n:it have to be time d to hold in over 7 a nd 8. To secure correct selectivity relays 7 a nd 8 should be set to hol d in over 6 and 9 bu t due to the fact that this would increase the tripping ti rne ::m relays 1. 2. 3, and 4 n t the power sta tion, relays 7 and 8 have been set the same as 6 and 9. To find out just what trouble this will cause, c ::msider the case of a fault on the water department line .i ust autside of Raymond Substa tion, ca :; e 4. Relays 7 and 8 would have a primary current of 355 amperes or 1420~ loa d 't'l,i 'lich ·would cause the s e relnys to trip in approxi m9. tely 0.55 seconds. Relay 6 would have (355 -- 925) 1280 ampe res prirnary current :.>r 7500 7b current which would trip in t h · minimum time sec:>nds. :if 0.5 Hence with these settings t hc-; re would be caused the false opera tion of relays 7 and 8 but this would pe of no serious conse qu ence since it w::mld not is Jla.te any part :>f the sys tom from the p ower plant. It is felt of r:rea ter advanta1~e t :> a ll::>w such f a lse opera- tion in this c ase than to increase the time another 0.4 sec:>nds. Directional type relays have not been rec:.>mmended for 7 and 8 since they would p roduce n:> g re a ter discrimination; their :>n l y ndvanta fte would be that :>nly relay 8 w:mld go :mt, in such a c as e as cit rJd a bove, ins tead ~f 7 nnd 8. -52- GROUND FAULT CUilRRN'l'S - OJ.SE l x--Values for a Ground Fault at Raymond Substation. Y-•Values £or~ Ground Fault at Lamanda Park Substation. z--Valu.es for a Ground Fault at J.l aryland Substation. 5 (ll TOT AL GROUND CURRENTS !--2115, Y--2115 ~ V)~------t k=..®.QQ. ~ 6 Plg.nt 3us-:-3510 0 !q: c t l - - - - - - - + - - - - - - - " o X--619 : : ~ ~ - - - - - - - t co ::::> Y•-§16 7 8 (/) k: ct - Q 9 ~ __ ~ ~ _/. (Q :::> 11 ~ P.2 ~ 10 -J er,-------t Z-•1515 ~ ~ k,::....619 Y--1500 1 Cl: <"---------. ~ 13 (t) ~ V) - 14 &:----Wl. x--1500 ; l 2 PASADENA PoWER PLANT -53- -15 l:: (.) ~I ..J J x-Values tor a Ground 1'1.1,Ult at Ita,mond SUbstaUon. , Y--Val.ues tora Ground l!'ault at Laman:ia. Pan: SUbstat1on. i-.- Values tor a Ground Fault at Maryland substation. 5 roT.AL GROU?ID OlJRREm'S ~ ~ , ... -2580 Y-2175 0 z...i-22&0 x---1000 365 C) P!,ant Bo.• .351!) x-- - ~ z- 615 " CQ y __ A,.l:!n a : 1 - - - - - - - - - 1 - - - - - ~ ~ ~ - - - - - - ~ ::) I--15.9 8 z-- 200 (/) X: ct - 9 ~ Q :&:-1150 ·- - A.f'lt\ 'll ::> z.,._ 575 ~ b/------. Cr)---- <:t: tn: '(".,__ ____ ~ 13 x.,....1010 x--. 350 z;- ,425 l:: X-•J:l~O Y-. 400 z-. . 20§s ----------ll-~------ 14 X-- 420 I "-1425 z-- 200 l --- 15 3 PASADENA 4 POWER u ~ PLANT -54• .J ~ u x-Valuea tor a Ground Faul t at lia1JDOnd sa.batauon. Y-Valttea tor a Ground Paul t· a.t La.manda Pe.rlt SU'bstat1 on. z--Values for a. Ground Pault at Maryland substation. 0 x.... 110 ~- y_ ... (tl ~ V) C:) TOT.AL GROUND OtJR.BEMIS J-g,§80 I--ii92. X-...1~.41\ Y-- 35 0 ~ 3 45 ----Plant ,bt-:-3510 z ..... 2a20 z-- 500 y ... _ X-•1130 C) $2 ~- 455 ~<( er ., X-- SAO ,-- X-445 8 ~ .,-A.' 9 ·'•. ', 3--1090 ' Y- 890 Ill 11 ::::> Ct) Z-• 850 10 L/. ~~ 12 r.,._ ta: ~ ~ 510 '•-1 'l.20 , i!;... 395 13 co::) ·, V) =t: ' ,.;._ 280 I-!§Q g- i5~ , ..-10~ I ...... 8i0 i-1:970 l~ i - tilO x-1120 ?- 395 1 2 PASADENA 3 . 4 PoWEA PLANT ..55_ l&- l) ~I .J J GROUND F AU!..'l.' CTJRE J~!TS -- CADE 4 x--Values tor a Ground Fault at Raymond Substation. Y~-Values tor a Ground Fault e.t L ani.ands P&rk SUbs tation. z--vaiues tor a Ground Fault G Y-- ct} ~ _.§. 46 z-- :::, V) C:) at HarJland Substnti on. x-- 120 WTAL GRomID CURRElJTS x--2s10 Y-g535 z.. - -3000 l?l§At .B.t!J.-:--3510 6 0 ~'( (t 1---------f.------....:X.:...•_-...;;3:.:5.=.5_ _ _ _----1 y ...... 450 -·-.......~-- 30 7 8 QJ :::> (/) X: ct .___-1--_ _ _ _ _ _ _ _ _...___ _ _ _ _ _x_-_-_1_0_________ 1...;-J._0J._0_ z- 30 Q 9 ~ <:: ~ ~ ~ 11 ~ 12 C r ) - - - - -.... ~ z-- 535 10 x-- 665 Y- 540 .z--1276 t [t ...J X-• 425 Y--1065 ·z- 24s <"------....... ~ 13 (Q ~ V) k:.- 925 x-- ,395 ~-:- 29Q x;... -:, __65~ Y-... 535 z--1250 :t: --------+---------- - u 14 ~ I i5 .J J l 2 PASADENA 4, 3 POWER PLANT -56- Relay 11 l'!Rlst be set to hold in over relays 7 and 8 so that it is given a minimum tripping time of 0.9 seconds on lever setting 4½-. It is of the non-directional type since the relays on both sides of it are set f:>r shorter times. Relays land 3 at the power station must be set to hold in over 6. 7 9 a. and 9 so they are set with a minimum time of 0.9 seconds and a lever setting of 4½. Relays 2 and 4 must be set to hold in over 11 so they are given a setting of 1.3 seconds minimum time on lever*· Since there is only the one source of power on this system it. is obvious that only fi:Jn-directional relays should be used at the power station. Though the actual values of ground current as calculated have not been used directly in determining the relay settings it is of advantage to have the current for two reasons. 1. It can be used as a check on the operation of any doubtful relays such as was done in setting #7 and JS. 2. It is well to know the order of magnitude of the ground currents which might flow in the system. LINE fil.1:AY SETTINGS In determining the setting for the line relays the aotual values of current as calculated have been used as it is not considered necessary to isolate line faults until they have developed. By using the currents thus oalculated for the ~arious line seotiJns it is possible by setting the relays on the inverse part of the time ourves to obtain selectivity of operation without increasing the total time. -57- In making the settings care must be talcen so that no line will be tripped out on its full load value of current. These values a.re taken as 400 amperes for 500,000 c.m. cable and 300 amperes for 350,000 c.m. cable. A table showing the line relay setting is given on page 59. The time current curves are on page 60 and the short circuit current values are found on pages 62 to 65. Relay 5 has only to protect the line from Raymond to the power station so that the directional type is used with a minimum time setting. Since the full load on that line is 400 amperes tap 5 must be used as tap 4 would allow the relay to trip on lesi, than full load. The relay is set on division 1 as it has the allowable minimum time of 0.2 second. No actual current value need be considered in setting this relay. Rela1s 10, 12, and 13 are set in a similar manner as they mt1st meet the same requirements. Relay 6 is next set to hold in over 10. 12, and 13. Since it is advisable to have the relay operate on the inverse part of the curve it is desirable to find the maximum value of current on which this relay will be expected to trip (and still hold in over some other relay) and for this value set it Just on the beginning of the inverse part. This maximum value is found in case 2 to be 975 amperes for a short circuit adjacent to Maryland on the L'faryland Line. set to hold over 13 as shown :>n page 59. The relay is then Relay 9 is set in a similar Next relays 7 and 8 are set to hold in over 5, 6, 9, 10, 12, and 13. In oases 3 and 4 the current values are but slightly over the full load rating of the line ao that they can hardly be considered. -58- LINE REL AY SETTINGS .Approx. Leve:t." Setting Definite Tripping Min. !;Time Time• settip.g Primary C. T. Relay Current Ratio Secondary Current 1 1635 400/5 20.4 5 409 5 1.10 1.0 \' 2 3095 400/5 38.6 12 322 6 1.42 1.2 3 2870 400/5 35.9 10 359 5 1.15 1.0 4 2145 400/5 26.8 8 335 6 1.40 1.2 5 695 400/5 8.7 5 175 l 0.47 0.2 6 975 170/5 28.7 9 319 3 0.72 0.6 7 695 250/5 13.9 6 232 3 o.9o 0.6 8 695 250/5 13.9 6 232 3 o.9o 0.6 9 530 170/5 15.6 9 17·3 2 0.83 0.4 10 700 400/5 8.75 5 175 1 0.47 0.2 11 1400 400/5 17.5 10 175 4 1.65 o.e 12 2045 400/5 25.6 5 511 . 1 0.20 0.2 13 975 400/5 12.2 5 244 l 0.30 0.2 14 170/5 16.0 4 400 . 1 0.20 0.2 15 170/5 This setting will be governed by the opera tion of the Jv!illion Volt Laboratory. Tap %[..oad '\ *Tripping times are only for the primary current indicated. Since all these currents have not been chosen for one given fault condition the tripping times do not show selective operation of the relays. However, if any given fault condition is ohosen and the relay tripping times oheaked for the corresponding tap and lever setting, seleotive operation ~111 be indicated. Suoh a system of oheoki~ has been done for this system to assure against false operation. -59- Case 2 shows current values sufficiently large to trip the relays but the limiting case was found to be #l with the 03:idition of a short circuit on the Raymond Line at which time there would be a current of 695 amperes flO'i\,1ng in the primary clrcui t of relays 5, 7 and 8, .P age 59 shows the necessary setting so that relays 7 and e will hold in over #5. The setting was also checked to see that it would hold in over 6, 9, 10, 12, and 13. The settings of the remaining relays were obtained in a similar manner and can be followed through by the reader if desired. It is well to call attention to the fact that in making any such settings there are a good many more factors to consider than appear on the surface so that to really understand the why and wherefore of certain choice of' tap eta. it is neoessary to follow the wholo story through from beginning to end. These settings for the line relays ' as given will allow the oorreot operation of all relays; there will be no false operati :>n as in the case of the ground relays. By referring to the column of' mini- mum times it is also seen that the time is slightly less for the line relays than for the ground relays, hence the advantage of' setting on the inverse part of the curve is quite evident. The above settings have been made so that the relays will operate oorrectly £or any one of the normal operating conditi:>ns considered. If, however, a definite operating condition should be decided on the relays could be set for that condition only, in v:,hich case the settings might be somewhat simpler and the total time might be reduced. -61- THREE PH.A.SE SHORT CIRCUITS -- CASE I X--Values for a Short Circui t at Raymond SUbstation. Y--Val~es for a Short Circui tat Lamanda Park SU.bstation Z--Values for a Short Circui tat Maryland Substation. 5 en TOTAL SHORT CIRCUIT VALUES X--3560 Y--3570 Z--4190 Plant Bus--4430 ~ V) CJ ~ L/. 6 C ~ ~ ct x-- 695 7 Y-- 700 8 -·9 L/. o::i :::> 11 (/) ~ - X-- 695 Y--2870 Z--2145 ,12 'o:( ..j 10 >-(t ~ ~ 13 -14 X--2865 Y-- 700 Z--2045 X-- 695 Y--2870 1 2 PASADENA -15 4 3 PoWER PLANT -62- THREE PHASE SHORT CIRCUITS -- CASE 2 5 X--Values for a Short Circuit at Raymond Substation. Y--Values for a Short Circuit at Lamanda Park Substation. Z--VaJ.ues for a Short Circuit at l\JT..acyland SU.bs tat ion. x- 85 Y-Z-- Ill ~ 19 45 TOT.AL SHORT C mcUIT VALUES X--3937 Y--3600 Z--4070 Cl) ~ X--1895 Y-- 429 z-- 975 6 0 ~ Plant Bus--4430 X--1810 Y-- 410 Z-- 930 ! "( ~m ~1-------+------~x~-~-~4~0~7_ _ _ _ Y-- 800 :::> 7 a rV I"'\,/ z..;._ 190 X: Q:" L--'----------L-------------'-Q 9 X--1895 Z-- 975 -- L/-------12 X-- 407 t ct ~------~ 13 ·z-- 190 Y-- 429 § 11 10 Cr)~-----~ ' ~ Y--2800 tQ ~ V) X--1635 Y-- 371 z-- 765 X--1895 Y-- 429 Z--3095 1 2 PASADENA --------+------------ X-- 407 Y-2800 Z-- 190 PoWER -63- u 14 ~ 15 .J I 4 3 l:: PLANT ~ u THREE PHASE SHORT CIRCUITS - - CASE 3 X--Values for a Short Cirouit at Raymond Substation. Y--Values for a Short Circuit at Lamanda Park Substation. Z--Values for a Short Circuit at Maryland SUbs.ta t ion. 5 ~ ~ X- 100 Y-- 14 z- 32 X-3950 Y--3890 Z--4100 x--2090 Y-- 300 Z-- 720 6 C) TOTAL SHORT CIRCUIT VALUES X-1990 Y-- 286 Z-- 688 ! '( ct L - - - - - - - - - i - - - - - - ~x-_-~30:.:o;...__ _ _----1 C!l::) Y-- 360 Z-- 40 7 8 (/) X: ct X-- 365 L - - - l - - - - - - - - - - - L - - - - - r - - - - =y=-_-:_l:-:7~0-=o-------9-1 a: Z-- 530 X--1705 Y--1400 Z--1250 ~ 11 ~ L.../._____ er:>---- 12 ~ .:t: tn:: X-- 685 Y--1830 Z-- 570 <------- ~ X~-1560 Y-- 660 z-- 680 13 X--1705 Y--1400 z--2850 l:: ---------1---,-----.....1--...1 - 14 ~ X-- 685 Y--1830 z-- 570 l 2 PASADENA I 15 4 3 PoWER PLANT -64- l) ..J ~ u THREE PHASE SHORT OIRCUITS _,... C.AS.E 4 x--Valuea for a Short Oircu1 tat Raymond Substation. y...-val.ues for a Short C1rou1 t at La!!'.anda Park Subs t at ton. z--Values for a Short Circui t a t tla.ryland Substation. 5 ii-.Y-- Ql 90 7 20 Z-- ~ TOTAL SIIOllT CI RCUIT V.AL UES x....4000 V) Y- -3920 'lt- ... ,~Q() c:i ~ z...... 4 330 x--- 14.Q. 6 z-- ~5 C) ~ l?lant SUs--4430 ;K--2200 X.-:.-.J.J.3 ~--- 46Q, ~ Q:: X- co ?AO Y-- 390 Z-- 25 7 8 ·: :::> (/) X: ct Q X•- MO X::::,.1800 355 9 z-- - ~ ~ i--2030 ~- ~ Y......1 ~;,.n IQ :::, 11 Cr) (;l 12 ~ ~ 840 10 y_ .. 54Q. Y--1730 X-.-lQ!Q 1= 850 .J ).. g~. zaq z--17ao Cl: ~ ~ lZ x--1430 Y-- 530 z-- 4.§Q, A'":::. .9.9.Q Y- :-...fil:Q. z...- 1 nQ. .. X-- §!.Q_ Y- -1730 z-- 380 l 2 PASADENA 3 PLANT -65- 14 15 4 PoWER - ..J RELAYING AT C.AL-TECH SUBS TAT ION So far in the discussion no mention has been made of the necessary setting for the relays at the Cal-Tech Substation and the Million Volt Laboratory. The normal operation is to feed the Cal- Tech Substation from the 1amanda Park Line and the Tulillion Volt Laboratory from the combined Cal-Teoh and Water Department Line. The reason for this operation is, that the :Million Volt Laboratory during periods of experimental activity oauses large surges on the line which might cause disturbances at the local Cal-Tech SU.bstation if both were fed off the same feeder. For relay 14 on the line feeding the substation, since it 1s a stub feeder, it should be set as low as possible, hence tap 4 and lever setting l are used. For the condition of a short on the 16.5 KV. bus this relay might not operate to alear the fault before relay 10 opera.tea. liowever, the ohance or a short on the high tension bus is quite remote so that this operation is felt to bo quite satisfactory. For any fault on the low side of the transformer operation would be selective, because the current ia limited by the reactance of the transformer. Since the ground relays are set to operate on small values of current ground relay# 14 will start to operate mu.ch before ground relay :f/10 and hence it will be tripped out in plenty of time. Similarly groand relay #15 will operate before #12. The setting of line relay 115 depends on the operation of the Million Volt. Laboratory. However, it is recommended here that this -66- relay be . set to trip before the one at the power station #4. 16.5 KV. m,AYING FOR PO!ifElLS.TJ.TI0N MJD SUBSTATIONS The 16.5 KV. line relaying is not designed to relay for trouble inside the substations or ->n the 2400 volt distribution. Eaoh 2400 volt feeder has relay proteoti::m at the substation and the trouble will normally be very quickly cleared by the partieular 2400 volt breaker on that feeder. In case of trouble inside any bank of trans- formers, quick acting differential relays are reoorMtei¼ded. These operating, will trip the breakers on ei thor side of the transformer bank, isolating the faulty transformer but not interrupting the supply to the substation, if two banks are on. In the power station, differential protecti<>n is recommended ar:>und each ma.chine, arid also around the autotransformer for #-7 genera.tor. ~la proteotlon should overlap the differential protec- tion reoonmended and shown for the bus, so that no part of the circuit in the power sta.ti::>n is left unprotected. (See page 8} It is felt that the possibility of trouble on the busses in the substations is so remote, that differential protection here 1s hardly justified. Especially so as two complete and rather complicated differential connections would be needed (beoause of the double bus and bus seotionalizing), one for the low bus and one for the high. Furthermore if the highly improbable tr~ble did ocour, the line overload relays wcmld operate to clear the station from the system. The above analysis of the relay types and setting shows that the relay system recommended :fulfills the three requisites of good relay- -67- ing. These are: 1. Isolation of fault limited t::> the smallest area possible by taking out of service only that section ::>f the line on which the £aul t occurs. 2. As speedy operation as possible. consistent with proper selectivity. 3. Non operation of relays on legi ti.mate loads. (Relays operate only on overloads). RELAY CONNECTIONS AND vi,...;cTOR RELATIONS FOR SINGLE PHJSE RELAYS Referring to the vector diagram, page 69. for the line relays, it will be seen that for the relay on phase fl, the current in the relay will lag<·the voltage across the relay (voltage 1-3} by 150 degrees, when the power factor is unity and the power flow is in the directiJn to keep the relay contacts open. If the power flow is reversed in the direction for relay tripping, the ourrent reverses with respect to the voltage and then leads the voltage by 0 30, provided the power factor remains unity. Actually, however, it does·not, but becomes largely lagging on account of the reaotanae in the circuit. The ourrent therefor shifts to a lagging position but never more than 60° lagging. Even with this angle of lag the relay would close its directional contacts, as this element is very sensitive. If however, the angle of lag is going to be very large, a phase shifter box may be used to bring the current more nearly in phase with the voltage. -68- For the cases of single phase ground faults, the veotor relations of relay current and voltage are also shown. For this pur- pose three potential transformers (transformers X} are connected in Y across the 16,500 volt substation bus. The secondaries (also Y connected) feed the primaries of three auxiliary 200/100 potential transformers (transformers YI Y connected on the primary side and delta connected on the secondary side. The ground directional relay is connected into one corner of the delta. All star connected windings are solidly grounded at the neutral points, thus preventing shifting of these points. Now suppose phase l became grounded at or near the substation. There would then be no voltage across transformer 1 and lik , wise transformer a. The voltages of the other transformers would remain constant in magnitude and vector direction. On the delta side ot transformers a, b, and o, ainoe voltage has disappeared and voltage a band o !"lB.intain their magnitude and direction, a voltage appears across the relay c:>il which is shown by the dotted line in the vectors shown in the lower side of the diagram. It the power direction is normal (i.e. in the direction to keep the O(ntacts open) this voltage will be 180° out of phaae with the current in the ground lead, assuming the ground impedance is wholly resistance. If however, the power direction reverses, the relay current will reverse with respect to the relay voltage and will then be in phase, oaus ing closure of the directional contacts. Actually the current will be very considerably lagging on account of the reactance of the grounded cirouit. If this lag is too mu.ch a phase shifter box (combined resistance and reactance. external to relay) must be used which will bring the relay current more nearly in phase with the relay voltage. By a similar analysis, it ~~11 be found that no matter which phase is gr::mndad, the voltage appearing aoross the relays will have the same vector relati :>n to the relay current as shown above• 0£ course, the more distant the ground fault is from the potential transformers, the greater will be the variation from this relation. But fo:r the distance. of one line section, the variation will not exceed permissible limits in the case of the Pasadena system. It ~~ll be noted- that the generator neutral is ground through a reactor, not a resistance. This has the effect of causing any ground current to be more lagging than if it were a resistance. There- fore it is very likely that a phase shifter should be usad with the ground relays. T'his point should be carefully investigated before application of the relays is made. REL.A.Y CONNECTIONS Alm VECTOR RELATIONS F9R USE OF POLYPHASE RELAYS, The oonnoctions for use of one polyphase power directional relay in conjunction with three standard overcurrent relays for line protection and with one low energy overcurrent relay for ground protection is shown on page 72. Though this system of relay connection has not been recommended for Pasadena i t 1s considere<: worth while to give the corresponding vector relati.ons beoause so far as known such a method is not listed in any of the ilterature. -71- 'l'he vector relations shown in fig. a represent the oonditions on the line for normal direction of power flow in which oase the current in any given element of the power direotio:nal relay is 100° out of phase with the voltage across that element. henoe the relay will not operate. Now consider a three phase fault on the 16.5 KV. line outside the substation as shown on the diagram. Fig. b shows the vector relations at the relay under these oondi tions. Since it is a three phase fault the vectors oan be considered balanced even after the fault. The voltage .E 31 is shown dotted sinoe it is the voltage across the open side of the V connection. The ourrents in fig.bare reversed 1eo 0 with respect to their position in fig. a; this is due to the £act that the fault causes a reversal of current, it now flows away from the substation in the tripping direction. The above discussion has been for unity power faotor so that the ourrents as shown lead their respeotive voltages by 30°. Actually, of course, the current is largely lagging but in no case may it lage the voltage by more than 60°. Wow to consider a ground fault on phase 3. ln this case the line veotor relations are given in fig. c which shows the fact that since phase 3 is faulted the voltage E03 is equal to zero (at point of fault} so that the resultant line voltages are E12 , E02 , and E01 ; the currents are not altered except that I 3 is much greater in magnitude and is reversed. Fig. d shows the vector relations at the relay where the open V voltage is shown dotted as E31 • In this oase the current 13 leads the voltage by 60° at unity power factor so that -73- with the lagging ourrent ocouring in the fault, the relay will operate corraotly. i'he current 1 1 is still 150° out of phase with 0 is 180 out of phase with its voltage E ; 23 2 hence these elements would not act to close their oontaots; it is its voltage E12 , and r only necessar-.1 however, for one alement to act. A similar discussion rray be followed through for faults on either of the other phases as well au for a single phase line to line short. The fact that line 2 in the V connection is grounded oa.n make no difference in the actual vector relations; its purpose is to keep the metering equipment at ground potentials. LOCATION Of RELAY8, 'N ITH RESPECT TO CIRCUIT BRE.AKERS. On the system diagram page 8 all the directional relays have their current trans.f ormers located on the bus side of the circuit breaker. This practioe has been recommended so that if a fault should ooour in the oirouit brealcer the directional relay would operate to open the breaker and .olear the fault (depending on whioh part of the breaker was faulted} without :rnsking it necessary to isolate the substation from the system. As an example consider a fault on the line side of the breaker contacts of the breaker on the Raymond Line at Raymond Substation. In such a case if the ourrent transformer of the directional relay was on the line side of the breaker the power flow through the relay would be in the normal direction so that it would not operate. With the connections as recommended { with the current transformer on the bus side of the breaker) the power flow in the current transfomer and relay will be in the re- -74- verse direction and .henoe the relay will operate to clear the fault. If the relay did not .o perate it would be necessary to isolate Raymond Substation before the fault could be cleared from the system. The overourrent relays will trip rega.t'dless of which side of the breaker they are on. though for new ins ta.llati ons 1 t would be advisable to looa.te them en the bus side of the breaker baeause in suoh a location the~v would be subJect to the larger short circuit current and would henoe operate faster. Sinoe the Pasadena system has installed their current transformer on the line side of the breakers this change has not been recommended for the non-directional type of relay. -75- ,RJjSQlWJi}.1DATI ON S ANJ2 COHCL USI ON S 1 AI RECOW4]jNDATI ON.§, The present development and probable tutu.J:"e growth of this system b1dica.te that the relaying protection of the 15.5 KV• lines and equifment c~~ be most satisfactorily and economically accomplished by the combined use (Diagram, page e, shows a.11 :recommendations listed below) of: Time element, overourrent, non-directional and directional 1. relays for line fault protection. 2, (See pages 13 to 19 a.nd 66). Time element, low cu:rrent, low energ, non-directional and directional relays for ground «&ult protection, See pages 15 tp 19 and 66). 3, overlapping differential, quick acting relays for generatoes, transformers and busses at the power station. 4. (See pages 67-68), Differential protection tor the main transformers at the substations but no d1f'fere.ntia1 -,u:et )t,~t-.ett-tlo-n at the substations. s. Location of ourrent transformers tor all directional relays on the bus side of the circuit breakers. This same recommendation is made tor all new installations of non-directional relays. It 1s not recommended. however. that the changes be made on the old installations for this type of relay, B. {See pages 74-75), ULOT WJ RE IDLAYS The fundamental weakness of pilot wire relaying, unless backed up ' by other relays, makes this type of protection somewhat hazardous. - 76 - It should not be uaed. therefore, even if pilot wires oould be ob- tained, at little additional. cost, through the uae of spare wires in a supervisory cable if such were installed. (See pages 12 amt. 13) • CI PI STANCE TYPE RIL.AYS The s;yatem is simple enough to make it unnecessary to use a mofe costly or complioa.ted relqing method, such as distance type relays. DI ADVANTAGES OF RECO:t..'1M~ED JYl,.A.YINC. The advantages of the recommended relaying scheme are:- 1. Complete proteotion with go.cd etleot1v1ty. 2. Reasonably fast, 3• lt'aay to adjust and !l!aintaJ.n, 4. Moderate cost, 5, Su.tfioiently flexible to require no extensive al- terations as system expands, 6, Insures good protection tor an underground oable system as well as for overhead lines, without unnecessary 1nterru:ption to service. -77- BIBLI OORAPHY 1. - Synmetrical Components, Parts I to X. By R. D. Evans tmd C. F. Wagner Electric Journal, ~Tarah, April. June, July, 1928. September, December, 1929. April, May, Oct •• Nov., 1931. Als o :published e.s a reprint by the Westinghouse Elec. & Mfg., Co. 2. - '1.'he Short Circuit Calculating Table. By I. T. Monaeth and R. Decamp Electric Journal, June 1926~ 3. - Theory and Applications of Relay Systems. By I .. T. Monseth and P.H. Robinson Electric Journal, Monthly from July to Dec., 1930 " " Feb. to Dec., 1931 Feb .. , Mar •• 1932 4. - Standard Decrement Curves. By W. C. Hahn and C. F. Wagner Transactions of A. I . g . E •• June, 1932. 5. - Development of Short Circuit Curves By C. F. Wagnor Electric ~rournal,. .Maroh, 1933. 6. - Ground and Distance Relay Trend in Practice Eleotrio World, Page 398, Feb. 27, 1932. 7. - Decrement Curves By C. F. i.'.lagner Electric Journal, April,1933. 8. - D. C. Pil:>t Wire Loop Electrical World. !.furch 25, 1933 . 9. - Transmission System Protection ·By W. W. Edson Transactions A. I. t .: .E.• Oot., 1930. 10. - Directional Ground Relays By E. E. Ge:>rge and H. H. Burnett, Jr. Transactions, A.I. E.E., Oot., 1930. 11. - Impedance Relay Developments and Applications Transactions, A.I. E. E., July, 1928. 12. - Pilot Wire Relay Boheme Electrical World, June, 1928, Page 1390. 13. - Oaloulation of Single Phase Short Oirouits by the meth:>d of S:y?r'.metrioal components. G. E. Review, 1926, Pagos 218 und 468. 14. - Reactance of Transmission Lines with Ground Return. ·1.'mns aot ions of A.I. B. E •• s ept. 1931, .P age 901. 15 . - Trans a cti :ms, A. I. E. 3 • .March , 1929, Pages 1H3-185 Oct. 1930, Pages 1321-1334 July, 1931, Page 510 Dec. 1931 ~ }>age 942 16. - Calculating Tables G. E. Review, 1920, Pag e 669. 17. - ?Jeta l Clad Switchgear, .Aut oma tic Protecti ::m, and Rom:.>t e Oo:nt.rol. . By n . w. Clothier Briti s h Ins titute E. E . 1932, :Page 285. 18. - Recent Developments on 3 :Phase ])ransroissinn L ines and Feeders. By R:.>s3 and 3e 11 B.I.E.E., 1930, Page 861 . 19. - Faults and Their Clearances on Large Networks. By Ka.J?1} tmd Cai·rothers. B. !. E.E., 1932, Pag e 585. -7,9 ...  Cr Cae -©- 4 ist Fer. _ pile Sc ST-K TAK 2.4 KM Bus 250 Amp Regulators 1% XK 2-3000 KMA. 2400 VOLT FEEDERS Banks F%X% prey Lamanpa Park Sus STA. 2400 VOLT FEEDERS Cat TeEcH Sus STA. » To Pumps : ri x 2600 FT 3*4¥/o he \ XN x \ Zou 4 age oo aaa 29 LEGENO oat ime] he Epson Line Non-Dinectionar Overcurrent Aecay Re oom | Sir nae PIER: REESE RS Directionac Overcurrent RELAY <@ H ! oe # Oirrerentiac Recay rs s t wo Grouno Retrays are InoicaTeo ey THE \ > STEN =r Aoorrion of THE Grouno Symsor * Circurr Brearer 3 VoLtTAsE REGULATOR Disconnect og Pore Top Switcu SUBTRANSIENT FPREACTANCE TRANSIENT RREACTANCE ———__—., 6500 FE (WATER Deer Line —— + F0Q000 CM 3COR. CaBLe 350,000 CM. 3 COR. CABLE OverHean Lines | Evison Line y 3 2 4 Q ad 250 Amp Q = Regulators [eX Q k beer 22-3000 Kva. 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Bus 15,000 VA 2400 Vort Feeoers 250 Amp Regulators EK 2.4 KV Bus TX= BI Yo TH R= 405% Oy} ‘oe KVA Q 1200 amp. F Sanne «5%: wwe | 8 i 18,950 KVA ST-X=/3.7 %,| SI-X 27.570 12,500 KVA S.7=X=31 To PasaoeNna PowER PLANT anes T-K> 454% TRANSF'R: LAB. [ MUNICIPAL LIGHT AND POWER DEPT. CITY OF PASADENA Proposep RELAY SCHEME For CoMPLETED PASADENA 16.5 KY TRANSMISSION SYSTEM APPROVED iawn WA are IrRAceD WL. Sf tof32 Srerewen neces [MW EDwaRo: Lugs Meer Ener a IANGES LER Ed SCALE Dawe. No. FILE No. Malt 2 24 =4/-98 6-/- 98