A ^, ^^2̂|1 cW . r . . be used merely for impedance matching,4 , U24,0 - K i ovar Series Capacitor in a purposes, to control the division of current

through parallel circuits. In such cases it

230-Kv Transmission Line may be possible to de-energize the circuitcontaining the series capacitor when a

fault occurs on that portion of the cir-

R. E. MARBURY F. D. JOHNSON cuit. In such applications a protectiveFELLOW AIEE MEMBER AIEE gap may be used to protect the capacitor

and this gap will recover its insulationduring the period while the line is de-

Synopsis: The necessity for long distance capacitor has been used in a high-voltage energized. However, tests have showntransmission of electric power has grown transmission line in the United States. that in the case of relatively large seriesrapidly during recent years. Line reactance The purpose of this paper is to describebecomes a problem of increasing importance this equipment and its method of operation. capactors the period of de-energizationwhen transmission distances continue to required for satisfactory de-ionization ofincrease. Long lines cannot be loaded gaps is longer than can be tolerated insufficiently for maximum over-all economy HE USE of series capacitors for line most cases. Also, if the gap restrikesbecause of limitations imposed by transient .Ustablit an kion iremen.The reactance compensation has been when the line is re-energized it becomesmost important alternative to reduction in recognized for many years as a means of necessary to extinguish the arc by theequivalent line impedance by further in- improving regulation and eliminating closing of a by-pass switch, thus removingcrease in transmission voltage, is the use of voltage dips caused by sudden changes in the series capacitor from service during aline reactance compensation. Such com- load. Such an installation on a 66-kv line period when it may be badly needed. Inpensation can best be obtained throughthe use of capacitors operating in series was described in a paper by Johnson, view of these facts there has been a needwith the line conductors. To permit the use Marbury and Arthur.' Many other and for a more satisfactory device, not onlyof series capacitors rated on the basis of smaller series capacitors have been in- for the application where stability is in-normal load conditions, it is necessary to stalled for this same purpose during the volved but even for those where it is pos-protect them effectively during line fault lat1yercotios.. T e mximu use ofa last 15 years. In these applications sta- sible to de-energize the line for a briefreactance compensation with capacitors it is bility was not a problem and it was not period following each fault.necessary to by-pass and protect them only necessary therefore to reinsert the series The protective device should not onlyduring line fault condition and reinsert capacitor instantly following the clearing protect the series capacitor while the linethem with minimum delay after the line of a line fault. Failure to do so merely current is excessive but should restore itfault is cleared. Lack of means for accom-plishing the latter has prevented the use of introduces a short period of operation to service at the instant the fault is re-capacitors for line reactance compensation where voltage dips and lamp flicker are moved. In the case where the line is de-where the primary objective is increasing present but can be tolerated. This fact energized, the protective device shouldpower transmission. While protective de- permitted the use of a by-pass switch to not function when the line is re-energized,vices have been developed which are ade-qucsatefueewit seriesoe whcapacors when transfer the current from the gap circuit even though the line is de-energized forused toimprove voltagerregulation, theyare to a switch circuit, such that the opening only a few cycles. Such a protectiveby far too slow in operation to meet the of the switch restores the series capacitor device permits the use of capacitor unitsrequirements when series capacitors are to service. In applications where the having a voltage rating based on theused to increase power transmission. A series capacitor is used to increase the maximum continuous load current, andprotective means has now been developed...wh.ic meetsthese r eents and a power that can be transmitted, the time also permits of a relatively close pro-24,000-kilovar series capacitor has been required for these operations is far too tection level. This close protectioninstalled by the Bonneville Power Adminis- great to permit of effective use because the level may be used since the operationtration in a 230-kv line at their Chehalis system usually becomes unstable unless of the protective device does not createsubstation, for the purpose of compensat- *119 * *iasusain fo th.upsfcmest the series capacitor is restored promptly risks as to system stability. Oper-ing line reactance and increasing the powerlimits of this line. This is the first installa- after the isolation of the fault on the line. ation of the protective device takes placetion of this type, and the first time a series In some cases the series capacitor may only during the actual periods of excessive

Paper 51-304, recommended by the AIEE Trans- XC:25.l X0-25.Imission and Distribution Committee and approved LINE I _ LINEby the AIEE Technical Program Committee for {F 1<presentation at the AIEE Pacific General Meeting,Portland, Oreg., August 20-23, 1951. Manuscriptsubmitted May i7, i951; made available for print-ing July 9, i95i. Figure 1. SimplikiedR. E. MARBURY and F. D. JOHNSON are with schemai GAgamWP GAPWestinghouse Electric Corporation, East Pitts- mai dagmburgh, Pa. of series capacitors R.I.251A R-1.25.fL.

1951, VOLUME 70 MUarbury, Johnson-A 24,000-Kilovoar Series Capacitor 1621

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L"XaL _ | {LINE Figure 2. Schematic used. If this voltage is a multiple ofdiagram showing air standard ratings, the standard units may

AC.T.I C.Tblast gap arrange- also be used by means of series groups.CT_ CT xment For example each phase of a series capac-

RES. RES. itor may be made up of two groups of7,960-volt standard capacitor units. Unitswith standard kilovar ratings and specialvoltage ratings are sometimes required

ELECTRICALLY where the use of standard voltage unitsOPERATED AIR involves too much sacrifice due to the

LAST VALVESfact that the working voltage is too far

RESERVOIR below their rated voltage.

MAXIMUM MOMENTARY LINE CURRENT

currents. It is expected that since these the factors which influence a decision as This is the maximum expected linerequirements have now been met the to the amount of line reactance to be com- current associated with load fluctuationsseries capacitor will become a practical pensated by the series capacitor in a par- such as motor starting. This valuemeans of increasing the power capacity ticular case. should not exceed 150 per cent of theof existing transmission lines, and permit maximum continuous working current andthe use of longer lines. MAXIMUM CONTINUOUS LINE CURRENT no operation of the gaps should occur

The line current is determined by line under these conditions.Rating of Series Capacitors requirements and is the maximum con-

tinuous current expected to be present in MAXIMUM FAULT CURRENT AND

Five basic factors go to determine the the circuit in which the capacitor is in- DURATIONrating of a series capacitor as follows: stalled. The above line current when The expected fault current magnitude

multiplied by the reactance gives the and duration affect the design of the by-1. Reactance. rated voltage. The product of the current pass gap, and particularly the current2. Maximum continuous line current..3. Maximum momentary line current. squared and reactance gives rated kilovar limiting resistor which is used in con-4. Maximum fault current and duration. per phase. The number of capacitor junction with the by-pass gap.5. Line voltage. units required per phase may be deter-

mined by simply dividing this kilovar by First Transmission Line InstallationREACTANCE the rated kilovar of the standard capacitor

The reactance of each phase of a series units to be used. If the voltage obtained The first installation of a series capac-capacitor is determined by the line re- from the load current and capacitor ohms itor in a transmission line for the pur-actance and the degree of compensation is close to a standard shunt capacitor unit pose of increasing the transmission ofnecessary to meet the objectives. It is rating such as 4,160, 7,200 or 7,960, then power was energized February 23, 1951.not the purpose of this paper to discuss the standard shunt capacitor units may be This capacitor is located on the Bonne-

ville Power System at the Chehalis sub-Figure 3. Schematic diagram showing by-pass switch arrangement station, and is installed in a 230-kv line

LINE 4 LINE\ 1Figure 4. Schematic diagram showing means of detecting individual

fuse operation

REI RES.2,C,O 4= 3CPCTO NT_L_INE PRL11 EL

AIR AIRVALVEL T- FE- VALVE

BLASTRESERVOIR

POSITION (I)

SWITCH

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Figure 5 (left).One phase ofChehalis seriescapacitor duringinstallation,showing the twohoused groups,insulated from

ground

Figure 6 (right).Chehalis seriescapacitor installa-tion showing cir-cuit connections

leading to the Longview Substation. The render the arc unstable so that it clears switch is a 15-kv indoor single-polerating of the initial installation was as at each current zero. Thus the gap re- switch, arranged to remain closed byfollows: strikes on each half cycle, and is extin- spring pressure, and to be opened by air

guished at each current zero so long as the pressure. The normal supply of air in the1. Reactance 51 ohms, line current exceeds 250 per cent of air blast reservoir keeps the switch nor-2. Continuous working currenit 312 ani- normal. As soon as the system short is mally in the open position. The switch isperes. removed (by high speed relays and circuit caused to close by shutting off the air3. Momentary working current 468 aui- breakers), and the line current is again from the switch operating cylinder andperes. near normal the gap will cease to break dumping the air from this cylinder. The4. Fault current 3,200 amperes; duration down and the resistor will no longer be previously mentioned operation of the15-cycle maximum. connected in parallel with the capacitor. inverse time relay performs this function.5. Line voltage 230 kv. The flow of air through the gap chamber Voltmeters are also provided to permit

The housings provide additional space is initiated by gap current. Termination reading the voltage across the seriesfor adding capacitor units to bring the of gap current de-energizes the solenoid capacitor. These are mounted so theyreactance to 31.84 ohms, for a working operated air valves and allows them to can be read from the ground. See Figurecurrent of 500 amperes and a 3-phase close. A time delay inherent in the design 3 for general arrangement of switches.kilovar rating of 23,800 kilovars. of these air valves allows the air to con-

tinue to flow and complete the deioniza- FUSE INDICATIONGeneral Requirements tion of the gap and fully restore the gap If several capacitor units are discon-

insulation value. The gap circuit con- nected from the group due to fuse opera-FAULT CURRENT PROTECTION nections are shown in Figure 2. tion the impedance of this group in-

The operation is the same whether sys-Since a tenfold increase in voltage oil tem relays and circuit breakers function or

the capacitor is expected corresponding if the fault is self clearing.to a line fault of 3,200 amperes, it wasnecessary to protect the capacitors from OVERLOAD PROTECTIONvoltages in excess of a predetermined Since the capacitor units must not beamount. This was accomplished by operated continuously above a predeter-shunting the capacitor with a gap and re- mined voltage for thermal reasons it wassistor. The gap shown in Figure 1 breaks considered necessary to provide overloaddown when the voltage across the capac- protection. The capacitors may beitor exceeds 21/2 times the capacitor con- operated continuously at the rated cur-tinuous rated voltage. The resistor in rent of 312 amperes plus 5 per cent cor-series with the gap is nominally 11/4 ohms responding to standard practice for shuntand is used to limit the capacitor dis- capacitors. They may be operated forcharge current when the gap breaks down. periods of 30 minutes at 135 per cent andThis permits repetitive discharges to oc- 5 minutes at 150 per cent voltage. Meanscur for duration of the line fault without were provided to prevent operation of theharm to the capacitors. series capacitor in excess of these estab-

After the fault current no longer exists lished limits. This was accomplished byand the current in the line is again normal, the use of an inverse time relay arrangedthe resistor must be permanently dis- to detect overvoltage across the series AIR INLETconnected. This is accomplished by the capacitor through a potential transformer.use of a special gap designed in a manner Completion of contact by the relay ini- lto permit the use of a constant blast of air tiates the closing of a by-pass switchduring the period current flows. The which then shorts out the series capacitor AIR EXHAUST

volume of air is made sufficiently large to until manually reset. This by-pass Figure 7. Detail construction of gap

1951, VOLUME 70 AMarbury, Johnson-A 24,000-Kilovar Series Capacitor 1623

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operator to determine if some fuses had reconnected for parallel operation, givingoperated before such a condition reached one-fourth the reactance and twice thea point where the operation of the capac- rated working current. When so operateditors was seriously affected with respect one gap is disconnected.

~;toworking votg.The 3-phase lesare plcdside bysideThis is accomplished by dividing the as shown in Figure 6, on 25 foot centers.

capacitor into two equal branches as The three phases of the series capacitorgr r 0 |shown in Figure 4 and providing relays to equipment are located within a fenced

compare the current in these branches. enclosure 100 feet wide and 135 feet long.Operation of these relays operates an air Another larger fence encloses associated

~ 8 g°Pvalve which in turn closes the by-pass equipment consisting of by-pass dis-~~~~ switch, connects and air supply equipment. This

r rgg L rE The closed position of the by-pass outside fence encloses an area 125 feetswitch is indicated at ground level by wide and approximately 260 feet long.means of a pneumatically operated relaylocated in the compressor station. The Compressed Air Gap

General Construction The gap consists of an inverted cup

electrode of special graphite, a cylin-The capacitor units are single bushing, drical porcelain insulator, and a second

7,960-volt 15-kilovar outdoor units. One- graphite electrode located along the axishalf of the total quantity of capacitors of the porcelain tube. The central elec-are standard shunt capacitor units. The trode forms a gap in the cavity of this in-other half are of special design with ap- verted electrode, see Figure 7.

gpr . 1 iproximately 20 per cent added dielectric When a flow of current through theto gain field experience in the event mo- gap is initiated by the breakdown of thetality rate should prove to be high with gap, air is supplied to the bottom cham-

Figure S. Gap and air tank assembly standard units. Subsequent experience ber from which it flows into the porcelainhowever indicates that the protective tubular insulating body. The only out-equipment will adequately protect stand- let for this air is down through the hole in

creases, and the remaining capacitors in ard capacitor units. the center electrode, from which it maythe group operate at a higher voltage for Each unit is connected to the bus escape to the outside air.the same current flowing in the line. through a fuse especially designed to in- The two portions of each phase leg ofSince the series capacitor is insulated terrupt the stored energy in the large the series capacitor are each protected byfrom ground, it is not possible to inspect number of adjacent units. No fault cur- a gap as described above, with a resistorthe fuses conveniently as with a shunt rent interruption problem exists, but the connected in series with each gap. Onecapacitor, so it was felt desirable to pro- stored energy is quite large. tank supplies the air to these two gaps,vide some indicating means to enable the One hundred and sixty-six of the 15- Fi 8

kilovar units are assembled in an outdoor guresteel housing and arranged in two groupsof 83 units each as shown in Figure 4with a current transformer to compare thecurrent in each group of 83 units. Thesehousings have space for 288 capacitorunits to provide for later change in therating of the series capacitor to 23,000-kilovars and 520 amperes line current.

X Two of these housings are mountedon a platform 12'/2 feet wide and 80 feetlong, which is in turn supported on 24columns of insulators. On a platform be-tween the two housings is located a tankfor gap air supply, two gaps and two re-

sistors.Figure 5 shows the two metal enclosures

during installation, with the compressedair supply tank, two gaps and resistors inthe center between the housings. TheS aAAtwo housed groups shown are operated inseries to give the rating of 51 ohms for 312amperes, or the contemplated rating of31.84 ohms for 500 amperes, in which case

each group is protected by a gap and re-

sistor, with one compressed air supply forFigure 9. Air blast valve the two gaps. The two groups may he Figure 10. Cross section of blast valve

1624 Marbury, Johnson-A 24,000-Kilovar Series Capacitor AIEE TRANSACTIONS

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r - 5 ~-172 -

Figure I1 (left.) sulated air column, containing three airAir column lines: one to supply air to the gap res-

ervoirs, one to reset the by-pass switches,and one to operate a pneumatic relay toshow whether the by-pass switches were

Figure 12 (above.) in the open or closed position.Oscillogram of gap All three of these hose lines are as-

operation sembled in a porcelain stack as shown inFigure 11. This stack has ample wet anddry flashover to withstand the line to

Air Blast Valves large valve operated by a diaphragm. ground voltage. Three outlets are pro-The use of a diaphragm eliminates any vided at the bottom and top castings for

One of the most important detail problem of lubrication as would be the continuing these three air lines. Thepieces of equipment is the air blast valves. case with a piston. The solenoid lifts a bottom connections go to the compressorThese may be seen on either side of the magnetic member which has a slideable house, while the top connections go to theassembly shown in Figure 8. These relation to a needle valve stem. The im- air tank and proper air valves. Eachrather large air valves (W1/4-inch pipe pact of this magnetic member against the hose line consists of a 3/8 inside diametersize) must be operated from a current stop on this valve pin jerks the seat open X 3/4 outside diameter special high-pres-transformer. The current corresponding and admits air to the chamber above the sure synthetic rubber hose 57 feet long giv-to low load current in the line and even diaphragm. Air enters this chamber ing a stress of about 2,300 volts per foot.light load currents, if diverted through the faster than it can escape through the The hose is coiled on a core approximatelygap must pick up these air valves so as to calibrated vent to the discharge side of the 8-feet long, and compounded into thequench the arc if initiated by a surge. valve, consequently the pressure on the porcelain column. Activated AluminaIn addition, the valve solenoids must not diaphragm opens the main valve. dryers are provided at the compressorsuffer any damage on the fault current of When the current stops flowing in the location to eliminate moisture condensa-3,200 amperes through the gap. This solenoid the needle valve closes. The air tion in this hose line and maintain highwide range of requirements was met by pressure on the diaphragm then dies down level of insulation in the hose itself. Thethe use of a saturating current trans- at a rate governed by the escape path, complete assembly was given a 485-kv, l-former and surge damping resistor, with thus closing the main valve with a time minute 60-cycle test.the solenoid coil designed for very low delay. The time delay used is 7 to 10voltage. cycles. Compressor House

In addition to these requirements itwas necessary to use a valve which would Insulating Air Column Only one compressor is required for theopen in about 2 cycles after the solenoid complete series capacitor installation.is energized, and close with a delayed ac- In this series capacitor installation it This compressor supplies air to a reservoirtion to insure thorough removal of ionized was considered desirable to locate the located in the compressor house. Fromgases following termination of the arc in compressor at ground potential and this reservoir air flows through a filter,the gap. operate it from a local 230-volt power and pressure regulator and dryer. The

It was also felt necessary to provide a supply. Also it was considered desirable latter regulates the air supply to the gaptype of valve that would not foul up and to be able to reset the by-pass switches to air supply tanks. Three air pushbuttonsstick if it remains in one position for long the open position from the ground, and to are also located in the compressor house,periods of time. provide an indicating means to show for resetting the by-pass switches pre-The valve shown in Figure 9 is a modi- whether the by-pass switches, not visible viously mentioned. Interlocks are pro-

fied form of a standard air valve. The de- from the ground, were in the closed or vided to prevent resetting these by-passtail construction of this valve is shown in open position. switches unless the main by-pass dis-Figure 10, and may be seen to consist of a These requirements necessitated an in- connect is operated first to remove voltage

1951, VOLUME 70 Marbury, Johnson-A 24,000-Kilovar Series Capacitor 1625

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from the series capacitor. The three air voltage on the capacitor to approximately portant operations and relaying impor-operated signal relays are also located in 21/2 times its rated voltage. The low arc tant information to the ground. It alsothe compressor house. These indicate drop of the gap holds the capacitor volt- provides means of remotely controllingwhen operation of by-pass switches has age down thereafter until the compressed switches located at high potential tooccurred. air comes on. The energization of the air ground. Considering the over-all prob-

blast solenoid occurs when the gap breaks lem, the use of a compressed air system isOther Protective Features down as indicated by the trace second justified even for applications where it is

from the bottom. The effectiveness of not necessary to quickly reinsert theIn addition, provisions were made to the air is shown by the third trace from series capacitor following a fault.

automatically close the by-pass switch in the top where the discharge air from the Compressed air operated gaps may bethe event of loss of air in the reservoirs, or gap is made to operate a micro-switch. used without the necessity for supplyingprolonged arcing of the gaps due to inade- It will be noted that the air was dis- air from the ground, by the use of com-quate air supply or failure of air valve to charging 21/2 cycles after the coil was pressors operated directly from the seriesopen. Also to close the switch in the energized, and the gap started to restrike capacitor voltage drop. Such an arrange-event of flashover the auxiliary back-up at this time. About a cycle later the ment is practical where the line currentgaps. current through the series capacitor was remains within a range of 25 to 100 perA ground switch is provided for ground- reduced to the normal value of 1,150 am- cent of normal. This provides a simpler

ing the platforms of the series capacitor peres and the arc immediately went out. arrangement and when visible indicatorsand thus avoid the collection of static The termination of the arc is shown by the are used on the by-pass switches, thecharges on the large housings and plat- top trace and the de-energizing of the air transmission of switch position informa-forms. blast valve solenoid as shown on the tion to the ground is no longer necessary,

second trace from the bottom. The air unless the installation is remotely locatedOperation of Protective Gap actually shut off about 9 cycles later as from an attended substation.

shown on the third trace from the top. The series capacitor described wasFigure 12 shows an oscillogram of a The model used for this test is consider- energized February 23, 1951, and was

laboratory test which illustrates the ably lower in reactance and has a much found to be quite free from noise oroperation of the compressed air protective higher continuous working current than visible corona. Tests were made to ob-device. In this test a 31/2 ohm series the series capacitor installation described, serve the operation of the protective de-capacitor was connected in a circuit making the gap working conditions con- vices by placing faults on the circuit orwhich would produce a large current siderably more severe. Actual tests on associated circuits and observing thethrough the capacitor, and a current the Chehalis installation are covered by operation of the gaps. The gap protectionwhich would develop a voltage across the an unpublished AIEE paper by C. C. Dia- operated in a manner quite similar to thecapacitor many times the breakdown mond, E. J. Harrington, and J. R. Curtin. laboratory test, Figure 12. The speedsetting of the gap, which was 2'/2 times with which air became effective at the gapthe continuous voltage rating of the series Conclusions was such as to insure fast re-insertion ofcapacitor. The bottom trace shows the the series capacitor even in the case offault current which was allowed to flow The use of compressed air makes pos- faults that are cleared in very shortfor 31/2 cycles, and then reduced to the sible a very effective type of self clearing periods such as 3 cycles.normal continuous current rating of this gap. With this type of gap the seriescapacitor which is 1,150 amperes. capacitor will be by-passed only during ReferenceThe voltage across the capacitor is the period of the fault, or when there is

shown on the trace second from the top. sufficient current to break down the gap 1 DRESIGN AND PRO 66KV TRANSOmi00N LINE,When the fault was applied to the capac- on each half cycle. Compressed air also A. A. Johnson, R. E. Marbury, J. M. Arthur.

AIEE Transactions, volume 67, part I, 1948, pagesitor the gap broke down and limited the provides a means of performing other im- 363-68.

Discussion from the circuit without interruption of load excessive accumulation of moisture in thein the 230-kv circuit. air line, but final analysis disclosed that theI would like to suggest that the authors trouble was entirely due to defective hose

describe their air column failure, its cause material. The hose material receivingE. J. Harrington (Bonneville Power Ad- and the measures they have taken to insure engineering approval contained only smallministration, Portland, Oreg.): Since its against similar failures in future equipment. traces of free carbon and measured well overinstallation this series capacitor has not been 50,000 megohms per foot, while the ma-subjected to line faults other than those terial actually used was found to contain upduring the staged tests. It has been and is R. E. Marbury and F. D. Johnson: Mr. to 50 per cent of free carbon and measuredstill being operated with the capacitor Harrington has mentioned a case of trouble 10 to 40 megohms per foot. The resultinggroups in parallel. with this series capacitor installation in- accumulation of heat resulted in excessiveWe hope to soon fill the housings to the full volving the air column used to maintain air heating of the hose and the failure in service.

24,000-kvar capacity and operate the groups pressure in the reservoirs mounted on the The rebuilt air columns were entirelyin series thereby obtaining approximately insulated platforms. The leakage current satisfactory on leakage and overvoltage24 ohms of capacitive reactance compensa- through one of the air columns became ex- tests, with or without the presence of con-tion. cessive and resulted in a failure in one air densate.

Operation so far has been trouble free line. The air line burned open at one point In view of the above there is no reason towith one exception. This was a failure of permitting a low current arc which ignited expect future trouble and the design isone of the air columns. This failure re- the compound in which the hose was em- entirely adequate when manufactured assultedl in a fire in the column which ulti- bedded. The escape of air at this point intended. Steps have been taken to rigidlymately caused the capacitor protective released pressure sufficient to rupture the control the manufacture in the future, andequipment to function. This resulted in by- porcelain casing. the physical and electrical properties of thepassing of the capacitors and their removal At first this condition was attributed to hose itself.

1626 Marbury, Johnson-A 24,OOO-Kilovatr Series Capacitor AJEE TRANSACIIONS

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