ABB Power T&D Company Inc.Relay DivisionCoral Springs, FL 33065

Instruction Leaflet

All possible contingencies which may arise during installation, operation or maintenance, and all details andvariations of this equipment do not purport to be covered by these instructions. If further information isdesired by purchaser regarding this particular installation, operation or maintenance of this equipment, thelocal ABB Power T&D Company Inc. representative should be contacted.

! CAUTION

Before putting protective relays into ser-vice, remove all blocking inserted for thepurpose of securing the parts duringshipment. Make sure that all moving partsoperate freely. Inspect the contacts to seethat they are clean and close properly,and operate the relay to check the set-tings and electrical connections.

Note: These instructions apply to 50 and 60Hertz relays.

1. APPLICATION

These relays have been specially designed andtested to establish their suitability for Class 1E appli-cations. Materials have been selected and tested toinsure that the relays will perform their intended func-tion for their design life when operated in a normalenvironment as defined by ANSI standard C37.90-1989, when exposed to radiation levels up to 104

rads, and when subjected to seismic events produc-ing a Shock Response Spectrum within the limits ofthe relay rating.

“Class 1E” is the safety classification of the electricequipment and systems in nuclear power generatingstations that are essential to emergency shutdown ofthe reactor, containment isolation, cooling of thereactor, or otherwise are essential to preventing sig-

nificant release of radioactive material to the environ-ment.

The type KAB relay is an instantaneous relay of thehigh impedance type used for bus differential protec-tion.

1.1. APPLICATION CONSIDERATIONS

The type KAB relay can be applied for bus protectionin most cases when bushing type ct’s are in use, andin metal-clad equipment when ct’s with toroidallywound cores, having their windings completely dis-tributed, are employed. Figure 7 shows the externalconnection.

The following points should be considered or shouldbe known on any proposed type KAB relay applica-tion:

1. All ct’s in the bus differential circuit should havethe same ratio, and should be operated on theirfull tap. If tap connection cannot be avoided, thewinding section between the taps being usedmust be fully distributed and the high voltagewhich may appear at the full tap terminal due tothe auto-transformer action should be checked.

2. The leakage impedance of the ct’s which are tobe used should be low.

3. The use of the auxiliary ct’s is not recommended.If this cannot be avoided the additional imped-ance from the auxiliary ct’s and the high voltagewhich transformed by the auxiliary ct should bechecked.

Type KAB High ImpedanceBUS Differential Relay(50 and 60 Hz for Class 1E Applications)

Effective: January 1996

Supersedes I.L. 41-337.41B, Dated July 1985

( | ) Denotes Changes since previous issue

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4. The best location for the junction points is electri-cally equidistant for all ct’s if all ct’s are identical.

5. The lead resistance from the junction points tothe relay terminals is not critical.

6. A lockout relay contact is recommended to shortcircuit the varistor following the relay operation inorder to prevent the varistor from overheating.

It is recommended that the 86B contact be wiredbetween terminals 9 and 6 to short out the varis-tor only. Following 86B operation the IT unit isinserted in the differential circuit as a straightovercurrent function allowing for the possibility ofusing the KAB to energize a breaker failure initi-ating relay, 62Z, as shown in Figure 7.

7. To insure a substantial margin of operation oninternal faults, the V-unit should not be set higherthan the knee voltage, VK, value of the poorestct which is connected to the relay.

To insure a substantial margin for preventing therelay from operation on external fault, the kneevoltage value of the best ct which is connectedto the relay should be used to determine thevalue of (RS + RL) IF/NVK in Figure 5. The kneevoltage is defined as the intersection of theextension of the two straight line portions of thesaturation curve. Ordinate and abscissa must beto the same scale for each decade.

8. A high voltage may be developed across therelay on internal faults. The magnitude of thevoltage that can be developed is a function of thetotal fault current and the characteristics of thect’s used in the differential circuit. The varistorwhich is built into the relay is used to limit thishigh voltage to a safe level. Curves in Figure 8should be used to investigate the applicationlimit.

If the fault current and knee point voltage (VK)

are such that the intersection of these two pointsplot below the curve, then the application will besafe with respect to the limits for 4 cycle clearingtime.

9. The maximum number of circuits which can beconnected to the relay or the minimum internalfault current required to operate the relay can beestimated from the following equation

Imin. = (XIe + IR + IV) N

where Imin. = minimum internal fault current, RMS

Ie = ct secondary excitation current at avoltage equal to the setting value ofV-unit

IR = Current in V-unit at setting voltageVR (i.e. IR = VR/2600)

IV = Current in varistor circuit at a voltageequal to the setting value of V-unit

N = ct turn’s ratio

X = Number of circuits connected to thebus

2. CONSTRUCTION

The relay (see Figure 1) consists of a high speedovervoltage cylinder unit (V) a high speed overcur-rent unit (IT), a voltage limiting suppressor (varistor),and adjustable reactor and capacitors for completinga tuned circuit.

2.1. OVER VOLTAGE UNIT (V)

The voltage unit is a product type induction cylinderunit operating on the interaction between the polariz-ing circuit flux and the operating circuit flux.

Mechanically, the voltage unit is composed of fourbasic components: A die-cast aluminum frame, anelectromagnet, a moving element assembly, and amolded bridge.

The frame serves as the mounting structure for themagnetic core. The magnetic core which houses thelower pin bearing is secured to the frame by a lockingnut. The bearing can be replaced, if necessary, with-out having to remove the magnetic core from theframe.

The electromagnet has two series-connected polariz-ing coils mounted diametrically opposite oneanother; two magnetic adjusting plugs; upper andlower adjusting plug clips, and two locating pins. Thelocating pins are used to accurately position thelower pin bearing, which is threaded into the bridge.The electromagnet is secured to the frame by fourmounting screws.

The moving element assembly consists of a spiralspring, contact carrying member, and an aluminum

IFN----

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cylinder assembled to a molded hub which holds theshaft. The shaft has removable top and bottom jewelbearing. The shaft rides between the bottom pinbearing and the upper pin bearing with the cylinderrotating in an air gap formed by the electromagnetand the magnetic core.

The bridge is secured to the electromagnet andframe by two mounting screws. In addition to holdingthe upper pin bearing, the bridge is used for mount-ing the adjustable stationary contact housing. Thestationary contact housing is held in position by aspring type clamp. The spring adjuster is located onthe underside of the bridge and is attached to themoving contact arm by a spiral spring. The springadjuster is also held in place by a spring type clamp.

With the contacts closed, the electrical connection ismade through the stationary contact housing clamp,to the moving contact, through the spiral spring out tothe spring adjuster clamp.

2.2. OVERCURRENT UNIT (IT)

The instantaneous unit is a small ac operated clap-per type device. A magnetic armature, to which leaf-spring mounted contacts are attached, is attracted tothe magnetic core upon energization of the switch.When the switch closes, the moving contacts bridgetwo stationary contacts completing the trip circuit.

A core screw accessible from the top of the switchand taps on the coil provides the adjustable pickuprange.

The coil is tapped and the taps brought out to a tapblock. By means of the taps and the adjustable core,a pickup range of 16 to 1 may be obtained.

2.3. VARISTOR

The varistor is an non-linear voltage dependent resis-tor. It consists of one disc of electrical grade zincoxide material mounted between cooling fins. It isassembled in an integral mechanical assembly andshould not be taken apart.

2.4. REACTOR

The adjustable reactor is an air-gap type having twoiron screws which are used at the factory to tune the

circuit for maximum current at rated frequency. Thisfeature allows retuning of the circuit in the event otherparts of the circuit are replaced.

2.5. INDICATING CONTACTOR SWITCH UNIT(ICS)

The indicating contactor switch is a small dc oper-ated clapper type device. A magnetic armature, towhich leaf-spring mounted contacts are attached, isattracted to the magnetic core upon energization ofthe switch. When the switch closes, the moving con-tacts bridge two stationary contacts, completing thetrip circuit. Also during this operation two fingers onthe armature deflect a spring located on the front ofthe switch, which allows the operation indicator targetto drop. The target is reset from the outside of thecase by a push rod located at the bottom of thecover.

The front spring, in addition to holding the target, pro-vides restraint for the armature and thus controls thepickup value of the switch.

3. OPERATION

The relay is connected as shown in external connec-tion Figure 7. For normal operation the voltage at therelay terminals is approximately zero. In the case ofan external fault, the voltage at the relay terminalsstill remains approximately zero if both the sourcect’s and the faulted ct’s are not saturated.

However, during severe external faults the faulted ctmay saturate and no voltage or current can be devel-oped from its secondary winding. The source ct’swould then have to force their currents through theirown windings and through the winding and leads ofthe faulted ct. In this case a voltage would appearacross the junction point equal to the total secondarycurrents of the source ct’s multiplied by the resis-tance of the faulted ct secondary winding plus itsleads to the junction point. The relay is usually set tooperate at some voltage higher than the anticipatedvoltage expected for this condition. This fault voltagewill be lower than the calculated voltage since the cton the faulted circuit will always produce some volt-age and also the other ct’s will tend to saturate. Thedc offset component of this voltage does not affectthe relay operation by reason of the series tuned cir-cuit as well as the insensitivity of the voltage unit to

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dc.

In the case of an internal fault, the feeder ct’s imped-ances, neglecting the load current, are equal to themagnetizing impedance which is high. Since therelay is high impedance, this makes a high imped-ance secondary burden to the source ct’s, a highvoltage will appear at the relay terminals and will bewell above the pickup setting.

During severe internal faults the source ct will satu-rate to limit the RMS value of secondary voltage.However, the peak voltages of the wave form couldbe quite high and overstress the insulation. A varistoris connected internally to reduce this voltage. Figure3 shows the electrical characteristics of this device.

The overvoltage unit is a high speed device and willoperate in 2 cycles at twice pickup using a sine wavetest voltage. Under fault condition, the crest voltageis rather high, the operating speed of the V-unit wouldbe faster. However, an overcurrent unit is providedwhich may be connected in series with the varistorand will operate in 1 cycle on current flow duringsevere internal faults when the varistor conducts cur-rent to limit the secondary voltage. The application ofovercurrent unit has no effect on the operating speedof the voltage unit.

3.1. IN-SERVICE CHECK

A high impedance bus differential relay will be sub-jected to high continuous voltage and will result indamage if any one ct is either open circuited orreversed polarity connection. The KAB relay with “inservice ct check” feature, shown in Figure 2, willsolve this problem. Before putting the relay into ser-vice, close all switch handles except terminals 4 and9. This shunts the high impedance elements, thevaristor and the voltage unit, and prevents over-volt-age. An ammeter can be inserted in the current testjack at terminal 9. A reading equal to one ct second-ary current indicates an open ct connection; a read-ing equal to twice the ct secondary current indicatesa reverse ct connection. The misconnected ct can beidentified by shorting and removing each ct in turnfrom the junction points.

4. CHARACTERISTICS(50 AND 60 HERTZ RELAYS)

4.1. OVERVOLTAGE UNIT (V)

The range of pickup of the overvoltage unit is adjust-able from 75 to 300 or 100 to 400 volts. The pickup isobtained by means of adjusting the spring windup.

Speed of operation is 2 cycles at twice pickup. (Sinewave test voltage)

4.2. OVERCURRENT UNIT (IT)

The usable range of the IT unit is 3 to 48 amperes.Taps are used to obtain the three following adjust-ment ranges; 3 to 9 amps, 9 to 20 amps, and 20 to 48amps.

4.3. INDICATING CONTACTOR SWITCH (ICS)

There are no settings to be made on the indicatingcontactor switch.

ICS units are available with 0.2, 1.0, or 2.0 amp fixedrated operating current values.

The seal-in contacts of the ICS will safely carry 30amperes at 250 volts dc long enough to trip a circuitbreaker.

4.4. TRIP CIRCUIT CONSTANTS

Indicating Contactor Switch Coil

5. SETTING CALCULATIONS

Use information shown for 1 disc KAB in Figures 3, 4,6 and 9 for making calculations where applicable.

1. SETTING VOLTAGE UNIT

The setting of the voltage can be expressed asfollows:

VR = K (RS + RL)

RATED PICKUP OHMS DC

0.2 amps1.0 amps2.0 amps

8.500.370.10

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where VR = Pick up setting of the V-unit,(RMS, volts)

RS = dc resistance of ct secondarywinding including internal leadsto bushing terminals.

RL = Resistor of lead from junctionpoints to the most distance ct.(One-way lead for phase fault,two way lead for phase toground fault)

IF = Maximum external fault current(RMS amp) contributed by thebus.

N = ct turn’s ratio

K = Margin factor

The margin factor is a modification number. It varieswith the reciprocal of the ct saturation factor i.e.

Figure 8 shows the margin factor curve, which isbased on the High Power Lab tests on the KAB relayand considers a safety factor of 2. The use of thiscurve is explained in the sample calculation.

2. SETTING CURRENT UNIT

The setting calculation for this unit is rather sim-

ple. First, calculate the value of ,

then from curves in Figure 6 find the value for thesetting. These curves have considered a safetyfactor of 2.

3. SAMPLE CALCULATION

Assume a 6 circuit bus, for which the maximumexternal 3-phase fault current is 60,000 amperesrms, symmetrical, maximum external phase toground fault current is 45,000 amperes, and theminimum internal fault current is 10,000amperes. Assume the ct’s ratios are 2000:5,class C400, VK = 375 volts, secondary winding

resistance RS = 0.93 Ω, and one way lead resis-

tance from the ct to the junction point RL =

1.07Ω.

From Figure 6 it can be found that the one-disc

type KAB relay would be satisfactory for thisapplication.

A. SETTING OF CURRENT UNIT

Since

for 3-phase fault.

for phase to ground fault.

From Figure 6 using the higher number of 345the current unit setting is determined to be 12amperes for one-disc KAB. Set the overcurrentunit at 15 amp.

B. SETTING OF VOLTAGE UNIT

a) for 3-phase condition

from Figure 5, K ≥ 0.82

b) for phase to ground fault condition

=

from Figure 5, K ≥ 0.77

choose the maximum of (a) and (b), to pre-vent the relay from false pickup on externalfaults, its minimum setting should be at leastthis maximum 266 volts. This adjustment ismade by varying the spring tension. See

RS RL+( )IFNVK

-------------------------------

RS RL+( )IFN----

RS RL+( )IFN---- 0.93 1.07+( ) 45000

400----------------× 300= =

RS RL+( )IFN---- 0.93 2 1.07×+( ) 45000

400----------------× 345= =

RS RL+( )IFN---- VK⁄ =

0.93 1.07+( ) 60000400

----------------× 375⁄ 0.8=

∴VR K RS RL+( )IFN----=

VR 0.82 0.93 1.07+( ) 60000400

----------------×≥ 246 volts=

RS RL+( )IFN---- VK⁄

0.93 2 1.07×+( ) 45000400

----------------× 375⁄ 0.92=

∴VR K RS RL+( )IFN----=

VR 0.77 0.93 2 1.07×+( ) 45000400

----------------×≥ 266 volts=

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“Routine Maintenance”.

c) To determine the minimum fault currentrequired to operate the relay at the setting of 266volts, assume that, from the ct saturation curve,Ie = 0.045 amp at 266 volts. from Figure 4, IV <

0.01 amp at 266 volts (RMS) and may beignored.

6. INSTALLATION

The relays should be mounted on switchboard pan-els or their equivalent in a location free from dirt,moisture, excessive vibration and heat. Mount therelay vertically by means of the four mounting holeson the flange for the semi-flush type FT case. Themounting screws may be utilized for grounding therelay. The electrical connections may be madedirectly to the terminals by means of screws for steelpanel mounting or to terminal studs furnished withthe relay for thick panel mounting. The terminal studsmay be easily removed or inserted by locking twonuts on the studs and then turning the proper nutwith a wrench.

For detailed FT case information, refer to I.L. 41-076.

External Connections are made per external connec-tion drawing (Figure 7).

Note the Varistor is brought out to a separate termi-

nal to provide flexibility in using the overcurrent unit.It must be connected in service. In addition, the con-tacts of an auxiliary 86 device should be wired acrossthe relay terminals to protect the Varistor against pro-longed overload.

Make in-service ct check as described on page 4,(last paragraph of OPERATION).

6.1. TRIP CIRCUIT

The overvoltage and overcurrent contacts will safelyclose 30 amperes at 250 volts dc and the seal-in con-tacts of the indicating contactor switch carry this cur-rent long enough to trip a circuit breaker.

6.2. BURDEN

The relay burden is approximately 2600 ohms in thetuned circuit. However, this burden is not seen by anyof the CTS during normal operation or during anexternal fault. During an internal fault the source CTsees a burden composed of the 2600 ohms in paral-lel with the Varistor resistance plus the parallelimpedance of the unloaded feeder CTS. The resis-tance of the Varistor can be calculated from the volt-ampere curve Figures 3 and 4.

6.3. ADJUSTMENTS AND MAINTENANCE

The proper adjustments to insure correct operation ofthis relay have been made at the factory. Uponreceipt of the relay, no customer adjustments, otherthan those covered under “SETTINGS” should berequired.

7. ACCEPTANCE CHECK

7.1. OVERVOLTAGE UNIT (V)

The overvoltage unit has been set at the factory for75 or 100 volts pickup. If a different pickup is desired,the relay should be energized from a variable voltagesource. Terminal 8 and 9 should be energized. TheVaristor should not be connected when makingadjustments for greater than 350 Vac (1 disc type).The voltage unit can withstand 250 volts ac, continu-ously and up to 300 volts ac (400 volts for the 100-400 range) for 15 seconds.

The pickup is increased by winding the spring CCW

RATINGS50 And 60 Hertz Relays

DEVICE CONTINUOUS RATING

Overvoltage (V) 75-300 V 100-400 Vrange range

250 Vac 250 Vac300 Vac 400 Vacfor 15 sec. For 15 sec.

Varistor 350 Vac 350 Vac

Overcurrent (IT)3-9 Amp Tap9-20 Amp Tap20-48 Amp Tap

3 Amps (100 for 1 sec.)7 Amps (140 for 1 sec.)10 Amps (230 for 1 sec.)

ICS

0.2 Amp Rating1.0 Amp Rating2.0 Amp Rating

0.6 Amps2.5 Amps5.0 Amps

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(top view) with a screwdriver and inserting it in one ofthe notches located on the periphery of the springadjuster. A tool style number 774B180G01 is avail-able and is used to vary the spring tension throughan opening in the front of the top surface of themolded bridge. By using this special tool, setting maybe changed without removing the relay from its case.

Contact Gap — The gap between the stationary andmoving contacts with the relay in the de-energizedposition should be approximately 0.030”.

7.2. OVERCURRENT UNIT (IT)

The pickup of the overcurrent unit should be within10% of its setting.

7.3. INDICATING CONTACT SWITCH (ICS)

Close the main relay contacts and pass sufficient dccurrent through the trip circuit to close the contacts ofthe ICS. This value of current should not be greaterthan the particular ICS nameplate rating. The indica-tor target should drop freely.

Close the main relay contacts and pass sufficient dccurrent through the trip circuit to close the contacts ofthe ICS. This value of current should not be greaterthan the particular ICS nameplate rating. The indica-tor target should drop freely.

Repeat above except pass 85% of ICS nameplaterating current. Contacts should not pickup and targetshould not drop.

The bridging moving contact should touch both sta-tionary contacts simultaneously.

After making the contacts should wipe for a distanceof 1/64 to 3/64”.

8. ROUTINE MAINTENANCE

All relays should be inspected periodically and theoperation should be checked at least once every yearor at such other time intervals as may be dictated byexperience to be suitable to the particular applica-tion.

All contacts should be periodically cleaned. A contactburnisher style number 182A836H01 is recom-

mended for this purpose. The use of abrasive mate-rial for cleaning contacts is not recommended,because of the danger of embedding small particlesin the face of the soft silver and thus impairing thecontact.

8.1. CALIBRATION

Use the following procedure for calibrating the relay ifthe relay has been taken apart for repairs or theadjustments have been disturbed. This procedureshould not be used unless it is apparent that the relayis not in proper working order. (See “ACCEPANCECHECK”).

8.2. TUNED CIRCUIT

If the capacitors, reactor, or overvoltage unit havebeen replaced, it may be necessary to retune the cir-cuit. This can be accomplished using a regulated acvoltage and good sine wave. Initially set the adjust-able reactor screws above 1/2 of their total travel.The screws may be adjusted without loosening thespring nuts.

Apply 75 volts (100V for the 100-400V range) ac toterminals 9 and 8 and adjust screw for maximum cur-rent as measured by a millimeter. This current shouldbe less than 30 mA (42 mA for the 100-400V range).The two screws should be positioned approximatelyequal for the final adjustment.

After the above adjustment has been made it may benecessary to re-adjust the overvoltage unit spring forthe desired operate voltage.

8.3. OVERVOLTAGE UNIT (V)

1. The upper bearing screw should be screweddown until there is approximately .025” clearancebetween it and the top of the shaft bearing. Theupper pin bearing should then be securely lockedin position with the lock nut.

2. The contact gap adjustment for the overcurrentunit is made with the moving contact in the resetposition, i.e., against the right side of the bridge.Move in the left-hand stationary contact until itjust touches the moving contact. Then back offthe stationary contact one turn for a gap ofapproximately.030”. The clamp holding the sta-tionary contact housing need not be loosened forthe adjustment since the clamp utilizes a spring-

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type action in holding the stationary contact inposition.

3. The sensitivity adjustment is made by varyingthe tension of the spiral spring attached to themoving element assembly. The spring isadjusted by placing a screwdriver or tool stylenumber 774B180G01 into one of the notcheslocated on the periphery of the spring adjusterand rotating it. The spring adjuster is located onthe underside of the bridge and is held in placeby a spring type clamp that does not have to beloosened prior to making the necessary adjust-ments.

4. Apply the desired pickup voltage and adjust thespring until the contacts just make. Voltageabove 250 volts ac RMS should not be appliedfor more than 15 seconds at a time. Continuousvoltage rating is 350 Vac for relays with the 1disc varistor.

8.4. OVERCURRENT UNIT (IT)

Initially adjust unit on the pedestal so that armaturefingers just clear the yoke in the reset position.(Viewed from top of switch between cover andframe). This can be done by loosening the mountingscrew in the molded pedestal and moving the IT inthe downward position.

a. Contact Wipe – Adjust the stationary con-tacts so that both stationary contacts makewith the moving contacts simultaneously andwipe 1/64” to 3/64” when the armature isagainst the core.

This can be accomplished by inserting a 0.0125thickness gauge between the armature and coreand adjusting the stationary contacts until theyjust touch the moving contacts.

b. Pickup – Place tap screw in the 3 to 9 tap andturn the core screw all the way in. Contactsshould pickup less than 3.0 amp. But not lowerthan 2.7 amperes. If pickup is above this range itmay be reduced by using a tweezer or similartool and squeezing each leaf spring approxi-mately equal by applying the tweezer betweenthe leaf spring and the front surface of the coverat the bottom of the lower window. If the pickup isbelow this range it may be increased by remov-ing the front cover and bending the leaf spring

outward equally. An approximate adjustmentwould be where the end of the leaf spring is inline with the edge of the molded cover.

The desired pickup is obtained by setting the tapscrew in the proper range and adjusting the corescrew.

8.5. INDICATING CONTACTOR SWITCH (ICS)

Initially adjust unit on the pedestal so that armaturefingers just clear the yoke in the reset position.(Viewed from top of switch between cover andframe). This can be done by loosening the mountingscrew in the molded pedestal and moving the ICS inthe downward position.

a. Contact Wipe – Adjust the stationary con-tact so that both stationary contacts makewith the moving contacts simultaneously andwipe 1/64” to 3/64” when the armature isagainst the core.

b. Target – Manually raise the moving contacts andcheck to see that the target drops at the sametime as the contacts make or 1/16” ahead. Thecover may be removed and the tab holding thetarget reformed slightly if necessary. However,care should be exercised so that the target willnot drop with a slight jar.

If pickup is low, the front cover must be removed andthe leaf spring bent outward equally.

8.6. VARISTOR

The varistor may be checked by passing 1 milliam-pere dc through it. Voltage across the varistor shouldmeasure 900 Vdc ±100 V.

If an ac test is preferred, pass 1 milliamp ac throughthe varistor. Voltage across the varistor should mea-sure 650 Vac ±75 V.

9. RENEWAL PARTS

Repair work can be done most satisfactorily at thefactory. However, interchangeable parts can be fur-nished to the customers who are equipped for doingrepair work. When ordering parts, always give thecomplete nameplate data.

ABB Power T&D Company Inc.4300 Coral Ridge DriveCoral Springs, Florida 33065

305-752-6700

FAX: 305-345-5329

ABB Network Partner

* Sub 43519A66

Figure 9: Outline and Drilling Plan for Type KAB Relay in Type FT21 Case

* Denotes change