Types KRD, KRP and KRC Directional Overcurrent Ground ... · The directional unit minimum pickup is approximately 1 volt and 2 amperes at its maximum torque angle for the 0.5 to 2,

41-137L KRD, KRP and KRC DirectionalOvercurrent Ground Relay

2

Figure 1: Type KRP and KRC Relay (without case)

Photo 9664A72 Photo 9664A71KRP KRC

KRD, KRP and KRC Directional 41-137LOvercurrent Ground Relay

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rotating in a air gap formed by the electromagnet andthe 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 (I)

The overcurrent unit is similar in construction to thedirectional unit. The time phase relationship of thetwo air gap fluxes necessary for the development oftorque is achieved by means of a capacitor con-nected in series with one pair of pole windings.

The normally-closed contact of the directional unit isconnected across one pair of pole windings of theovercurrent unit as shown in the internal schematics(figures 2, 3 and 4). This arrangement short-circuitsthe operating current around the pole windings, pre-venting the overcurrent unit from developing torque.If the directional unit should pickup for a fault, thisshort-circuit is removed, allowing the overcurrentcontact to commence closing almost simultaneouslywith the directional contact for high speed operation.

2.3 OVERCURRENT UNIT TRANSFORMER

This transformer is of the saturating type for limitingthe energy to the overcurrent unit at higher values offault current and to reduce ct burden. The primarywinding is tapped and these taps are brought out to atap block for ease in changing the pickup of the over-current unit. The use of a tapped transformer pro-vides approximately the same energy level at a givenmultiple of pickup current for any tap setting, result-ing in one time curve throughout the range of therelay.

Across the secondary is connected a non-linearresistor known as a varistor. The effect of the varistoris to reduce the voltage peaks applied to the overcur-rent unit and phase shifting capacitor.

2.4 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 t he 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 tar-get to 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.

3.0 CHARACTERISTICS

The relays are available in the following currentranges:

The tap value is the minimum current required to justclose the overcurrent relay contacts. For pickup set-tings in between taps, refer to Section 7.0 “ADJUST-MENTS AND MAINTENANCE.”

3.1 TYPE KRD RELAY

The type KRD relay utilizes a directional unit similarto the KRC relay in conjunction with the directionalunit and phase-shifting circuit of the KRP relay.

The current-polarized directional unit of the KRDrelay operates on residual voltage and residual cur-rent.

3.2 TYPE KRP RELAY (PHOTO ON PAGE 2)

The KRP relay is designed for potential polarizationand has its maximum torque when the current lagsthe voltage by approximately 60 degrees. The shift-

Range Taps

0.5-2 amps1-42-84-1610-40

0.51.02410

0.751.53615

1.02.04820

1.252.55924

1.53.061230

24.081640


4

ing of the maximum torque angle is accomplished bythe use of an internally mounted phase shifter asshown in the internal schematic.

The directional unit minimum pickup is approximately1 volt and 2 amperes at its maximum torque angle forthe 0.5 to 2, 1 to 4 and 2 to 8 ampere range relays.For t he 4 to 16 and 10 to 40 ampere range, the mini-mum pickup is 1 volt and 4 amperes.

3.3 TYPE KRC RELAY (PHOTO ON PAGE 2)

The KRC relay is designed for current polarizationand has its maximum torque when the operating cur-rent leads the polarizing current by approximately40°.

The directional unit minimum pickup is 0.5 ampere ineach winding at the maximum torque angle for the0.5 to 2, 1 to 4 and 2 to 8 ampere range relays. Forthe 4 to 16 and 10 to 40 ampere range, the minimumpickup is 1 ampere.

For the 0.5 to 2, 1 to 4 and 2 to 8 ampere rangerelays, the minimum pickup of the current polarizedunit is 0.5 ampere in each winding at the maximumtorque angle. The minimum pickup for the voltagepolarized unit is 1 volt and 2 amperes with the currentlagging voltage by 60°.

For the 4 to 16 and the 10 to 40 ampere range relays,the minimum pickup is 1 ampere for the current-polarized directional unit, and 1 volt and 4 amperesfor the voltage-polarized directional unit.

4.0 TIME CURVES

The time curves for the KRD relay are shown in fig-ures 5 and 6. Figure 5 consists of three curves whichare:

1. Directional Unit opening times for current andvoltage polarized.

2. Directional Unit closing time for current and volt-age polarized.

3. Directional Unit closing time for 1 volt, voltagepolarized.

Figure 6 shows the instantaneous overcurrent unitclosing time.

The voltage polarized curve B begins to deviate fromcurve A for less than 5 volts.

Both the directional unit and the overcurrent unitmust operate before the trip circuit can be completed.Hence, the unit which takes the longer time to oper-ate determines when the breaker will be tripped. Theovercurrent unit contacts cannot operate until theback contacts of directional unit open; therefore, thetotal time for overcurrent unit to operate is its closingtime given in figure 6 plus the directional unit openingtime given in figure 5. The total closing time for thedirectional unit is given in figure 5. The two examplesbelow will serve to illustrate the use of the curves.

EXAMPLE1. Using the formulas and definition of symbols on

figure 5, we have –

Let: lpol = 2 ampslop = 2.31 ampsTap Value (T) = 0.5 ampØ = 0°

For current polarized relay:

Referring to figure 5 at multiples of productpickup of 14.2, the directional unit opening timeis about 12.2 ms, and the closing time for thisunit is 58 ms.

For overcurrent unit:

Multiples of pickup =

Entering the curve in figure 6 at multiples ofpickup equal to 4.6, the closing time for the over-current is 21.5 ms. However, the total operatingtime for the overcurrent unit is 21.5 plus 12.2,which is the opening time of back contacts of thedirectional unit, or 33.7 ms total operating timefor overcurrent unit. The total time for directionalunit is 58 ms; and, since this is the longest time,58 ms is the total operating time of the relay.

MPPlop lpol φ 40–( )cos

.25----------------------------------------------------=

MPP2.31 2 0.766××

.25------------------------------------------ 14.2= =

lopT

--------2.310.5

----------- 4.6= =


5

Let: lpol = 20 ampslop = 23.1 ampsTap Value (T) = 1 ampØ = 0°

Entering figure 5, the directional unit closing timeis 12 ms and the opening time of its back con-tacts is 1 ms.

For overcurrent unit:

Multiples of pickup =

Referring to figure 6, the overcurrent unit contactclosing time is about 12.8 ms. Therefore, thetotal operating time for this unit is 13 plus 1 or 14ms. In this case the total operating time of relayis 14 ms.

4.1 TRIP CIRCUIT

The main contacts will safely close 30 amperes at250 volts dc and the seal-in contacts of the indicatingcontactor switch will safely carry this current longenough to trip a circuit breaker.

The indicating contactor switch has a pickup ofapproximately 1 ampere. Its dc resistance is 0.1ohm.

4.2 CYLINDER UNIT CONTACTS

The moving contact assembly has been factoryadjusted for low contact bounce performance andshould not be changed.

The set screw in each stationary contact has beenshop adjusted for optimum follow and this adjust-ment should not be disturbed.

5.0 SETTINGS


The only setting required is the pickup current settingwhich is made by means of the connector screwlocated on the tap plate. By placing the connector

screw in the desired tap, the relay will just close itscontacts at the tap value current.

For blocking carrier relaying the carrier trip overcur-rent unit located in the type KRP, KRC or KRD relayshould be set on a higher tap than the carrier startovercurrent unit located in the type KA-4 relay at theopposite end of the line.

CAUTION!Since the tap block connector screw carriesoperating current, be sure that the screw isturned tight.

In order to avoid opening the current transformercircuits when changing taps under load, the relaymust be first removed from the case. Chassisoperating shorting switches on the case willshort the secondary of the current transformer.Taps may then be changed with the relay eitherinside or outside the case. Then reclose allswitch blades making sure the RED handles areclosed LAST.

NOTE: When the voltage polarized unit of theKRD is not used, terminals 4 and 5 mustbe shorted. When the current polarizedunit is not used terminals 7 and 8 are leftopen.

5.2 DIRECTIONAL UNIT (D)

No setting is required.

6.0 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 two mounting studsfor projection mounting or by means of the fourmounting holes on the flange for the semi-flushmounting.

Either of t he studs or the mounting screws may beutilized for grounding the relay. The electrical con-nections may be made directly to the terminals bymeans of screws for steel panel mounting or to termi-

MPPlop lpolcos(φ 40 )–

.25--------------------------------------------------=

MPP23.1 20 0.766××

.25--------------------------------------------- 1415.6= =

lopT

--------23.1

1----------- 23.1= =


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nal studs furnished with the relay for thick panelmounting. The terminal studs may be easily removedor inserted by locking two nuts on the studs and thenturning the proper nut with a wrench.

For detailed information, refer to Instruction Leaflet41-076.

The external ac connections of the directional over-current relays are shown in figures 7, 8 and 9. If novoltage polarizing source is to be connected to theKRD relay, short-circuit the voltage polarizing circuitat the terminals of the relay.

7.0 ADJUSTMENTS ANDMAINTENANCE

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 section 5.0, “SETTINGS”,should be required.

7.1 ACCEPTANCE CHECK

The following check is recommended to insure thatthe relay is in proper working order.

7.1.1 Overcurrent Unit (I)

Contact Gap – The gap between the stationary andmoving contacts with the relay in the de-energizedposition should be approximately .020”.

Minimum Trip Current – The normally-closed con-tact of the directional unit should be blocked openwhen checking the pickup of the overcurrent unit.

The pickup of the overcurrent unit can be checked byinserting the tap screw in the desired tap hole andapplying rated tap value current. The contact shouldclose within ±5% of tap value current.

7.1.2 Directional Unit (D)

Contact Gap – The gap between the stationary con-tact and moving contact with the relay in the de-ener-gized position should be approximately .020”.

Sensitivity – The respective directional units shouldtrip with value of energization and phase angle rela-tionships as indicated in Table 1 (Directional UnitSensitivity).

Spurious Torque Adjustments – There should beno spurious closing torques when the operating cir-cuits are energized per Table 2 (Directional Unit Cali-bration) with the polarizing circuits short-circuited forthe voltage polarized units and open-circuited for thecurrent polarized units.

7.1.3 Indicating Contactor 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 be between 1and 1.2 amperes. The indicator target should dropfreely.

The contact gap should be approximately 5/64”between the bridging moving contact and the adjust-able stationary contacts. The bridging moving con-tact should touch both stationary contactssimultaneously.

8.0 ROUTINE MAINTENANCE

All relays should be inspected periodically and theoperation should be checked at least once everyyear or at such other time intervals as may be dic-tated by experience to be suitable tot he particularapplication.

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

CAUTION!The use of abrasive material for cleaning con-tacts is not recommended, because of the dangerof embedding small particles in the face of thesoft silver and thus impairing the contact.

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 section 7.1“Acceptance Check”).


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1. The upper pin bearing should be screwed downuntil there is approximately .025 clearancebetween it and the top of shaft bearing. Theupper pin bearing should then be securely lockedin position with the lock nut. The lower bearingposition is fixed and can not be adjusted.

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.Advance t he stationary contact until the contactsjust close. Then back off the stationary contact2/3 of one turn for a gap of approximately .020”.The clamp holding the stationary contact housingneed not be loosened for the adjustment sincethe clamp utilizes a spring-type action in holdingthe stationary contact in position.

3. The sensitivity adjustment is made by varying thetension of the spiral spring attached to the mov-ing element assembly. The spring is adjusted byplacing a screwdriver or similar tool into one of the notches located on the periphery of the springadjuster and rotating it. The spring adjuster islocated on the underside of the bridge and isheld in place by a spring-type clamp that doesnot have to be loosened prior to making the nec-essary adjustments.

Before applying current, block open the normallyclosed contact of the directional unit. Insert thetap screw in the minimum value tap setting andadjust the spring such that the contacts will closeas indicated by a neon lamp in the contact circuitwhen energized with the required current. Thepickup of the overcurrent unit with the tap screwin any other tap should be within ±5% of tapvalue.

If adjustment of pickup current between tap set-tings is desired insert the tap screw in the nextlowest tap setting and adjust the spring asdescribed. It should be noted that this adjustmentresults in a slightly different time characteristiccurve and burden.

8.3 DIRECTIONAL UNIT (D)

In the type KRP and KRC relays the directional unit isthe lower unit. In the type KRD the directional unitsare the lower and middle units.

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. Contact gap adjustment for the directional unit ismade with the moving contact in the reset posi-tion, i.e., against the right side of the bridge.Advance the right-hand stationary contact untilthe contacts just close. Then advance the sta-tionary contact an additional one-half turn.

Now move in the left-hand stationary contactuntil it just touches the moving contact. Thenback off the stationary contact 3/4 of one turn fora contact gap of .020” to .024”. The clamp hold-ing the stationary contact housing need not beloosened for the adjustment since the clamp uti-lizes a spring-type action in holding the station-ary contact in position.

3. Insert tap screw of overcurrent unit in highesttap. The sensitivity adjustment is made by vary-ing the tension of the spiral spring attached to themoving element assembly. The spring isadjusted by placing a screwdriver or similar toolinto one of the notches located on the peripheryof the spring adjuster and rotating it. The springadjuster is located on the underside of the bridgeand is held i place by a spring type clamp thatdoes not have to be loosened prior to making thenecessary adjustments.

The spring is to be adjusted such that the con-tacts will close as indicated by a neon lamp in thecontact circuit when energized with the requiredcurrent and voltage as shown in Table 1, (Direc-tional Unit Sensitivity). This table indicates thatthe spring can be adjusted when the phase anglerelationship between the operating circuit and thepolarizing circuit is at the maximum torque angleor when the circuit relationship has the operatingand polarizing circuits in phase.

4. The magnetic plugs are used to reverse anyunwanted spurious torques that may be presentwhen the relay is energized on current alone.

The reversing of the spurious torques is accom-plished by using the adjusting plugs in the follow-ing manner:


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a) Voltage circuit terminals on the voltagepolarized relays (KRP and KRD voltagepolarized unit) are open-circuited.

b) The polarizing circuit of the current polarizedrelays (KRC and KRD current polarized unit)are open-circuited.

Upon completion of either “a” or “b”, current isapplied to the operating circuit terminals as perTable 2.

Plug adjustment is then made per Table 2 suchthat the spurious torques are reversed. Theplugs are held in position by upper and lowerplug clips. These clips need not be disturbed inany manner when making the necessary adjust-ment.

The magnetic plug adjustment may be utilized topositively close the contacts on current alone.This may be desired on the same installations inorder to insure that the relay will always trip thebreaker on zero potential.

8.4 INDICATING CONTACTOR SWITCH (ICS)

Adjust the contact gap for approximately 5/64” (-1/54”, +0).

Close the main relay contacts and check to see thatthe relay picks up and the target drops between 1and 1.2 amperes dc.

To increase the pickup current remove the moldedcover and bend the springs out or away from thecover. To decrease the pickup current bend thesprings in toward the cover.

9.0 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.


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OVERCURRENT UNIT BURDEN DATA AT HIGH CURRENTS

AMPERE RANGE 1 - 4

Tap Value Current 1 2 4

Multiples ofTap Value Current

20 40 60 80 10 20 30 40 5 10 15 20

VA† 56 176 330 560 27 76.8 156 236 12.4 40 85.2 136

P.F. Angle‡ 41° 35° 27.2° 23.°6 35.6° 28.8° 23.8° 21.5° 24.3° 22.7° 19.9° 16.1°

† Voltages taken with Rectox type voltmeter‡ Degrees current lags voltage

ENERGY REQUIREMENTS – 60 HERTZDIRECTIONAL UNIT POLARIZING CIRCUIT BURDEN

RELAY TYPE RATINGVOLT

AMPERES†POWER FACTOR

ANGLE‡

KRC 230†† amperes 1.45 8° Lag

KRP 208‡‡ volts 11.2 28° Lead

KRD Current Unit 230†† amperes 1.45 8° Lag

KRD Voltage Unit 208‡‡ volts 11.2 28° Lead

† Burden of voltage polarized units taken at 120 volts. Burden of current polarized units taken at 5amperes.

‡ Degrees current leads or lags voltage at 120 volts on voltage polarized units and 5 amperes on cur-rent polarized units.

†† One second rating.‡‡ 30 second rating. The 10 second rating is 345 volts. The continuous rating is 120 volts.


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ENERGY REQUIREMENTS – 60 HERTZTYPE KRD RELAY

AMPERE RANGE TAP VA at Tap Value† P.F. Angle‡ VA at 5 Amps† P.F. Angle‡

.5-2

.5

.751.01.251.52.0

0.420.510.630.780.971.44

39.539.539.540.040.040.0

28.3019.8014.5012.1010.608.80

47.043.041.040.040.040.0

1-4

1.01.52.02.53.04.0

0.651.011.482.103.854.56

39.039.540.040.541.041.5

15.2011.009.108.257.757.25

40.040.040.040.541.041.5

2-8

234568

2.013.445.367.7510.7118.40

46.044.042.542.042.042.0

12.759.508.407.757.457.15

45.543.542.542.042.041.5

4-16

4689

1216

2.864.837.589.0914.7025.00

40.034.032.031.030.030.0

4.453.342.902.782.582.40

40.034.031.031.030.030.0

10-40

101520243040

10.522.037.855.284.0149.0

30.029.529.029.028.528.0

2.602.402.352.302.252.24

30.029.529.529.529.529.5



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ENERGY REQUIREMENTSBURDEN DATA OF OPERATING CURRENT CIRCUIT – 60 HERTZ

TYPE KRP RELAY

AMPERE RANGE

TAP VA at Tap Value† P.F. Angle‡ VA at 5 Amps† P.F. Angle‡

.5-2

.5

.751.01.251.52.0

0.400.450.530.620.730.96

36.835.334.133.132.332.1

26.1016.7012.109.437.946.06

42.336.933.933.131.631.1

1-4

1.01.52.02.53.04.0

0.530.720.961.251.632.55

31.129.128.728.729.630.1

12.507.996.095.044.573.99

31.228.227.828.128.930.0

2-8

234568

1.552.263.204.395.789.31

38.335.533.232.832.431.8

9.546.254.984.404.053.62

37.634.833.132.732.132.4

4-16

4689

1216

2.052.944.094.777.3011.5

42.838.535.734.833.332.0

3.242.031.591.461.241.11

42.038.035.735.534.334.2

10-40

101520243040

5.2310.517.624.136.864.9

30.930.330.329.430.128.9

1.331.151.071.050.990.97

30.831.330.829.931.631.9



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ENERGY REQUIREMENTS – 60 HERTZKRC RELAY

AMPERE RANGE

TAPVA at Tap Value† P.F. Angle‡ VA at 5

Amps† P.F. Angle‡

.5-2

.5

.751.01.251.52.0

0.420.490.570.680.811.10

36.537.936.936.036.036.4

27.5017.6013.0010.508.986.94

43.639.537.835.935.635.4

1-4

1.01.52.02.53.04.0

0.570.791.101.461.923.06

37.136.737.137.938.439.6

13.308.796.845.905.344.77

38.136.836.837.438.139.1

2-8

234568

1.682.583.755.197.0711.30

39.837.336.135.835.835.7

10.507.035.875.174.884.51

38.836.535.835.736.136.8

4-16

4689

1216

2.173.204.645.378.5213.80

42.238.035.535.834.833.7

3.372.221.801.671.461.33

42.037.836.035.735.035.0

10-40

101520243040

6.0812.220.528.743.478.3

34.032.631.831.330.428.5

1.521.341.271.241.191.16

33.934.134.534.535.435.6



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RATING OF OVERCURRENT UNIT

RANGE

CONTINUOUS

RATINGAMPERES

ONE SECONDRATING

AMPERES

.5-21-42-8

4-1610-40

588

1010

100140140200200

Table 1: DIRECTIONAL UNIT SENSITIVITY

RELAY TYPE AMPERE RATING

VALUES FOR MIN. PICKUP†

PHASE ANGLERELATIONSHIPVOLTS AMPERES

KRPKRD (Voltage Unit)

.5-21-42-8

1 2.0 l Lagging V by 60°‡

1 4.0 l In-phase with V

4-1610-40

1 4.0 l Lagging V by 60°‡

1 8.0 l In-phase with V

KRCKRD (Current Unit)

.5-21-42-8

0.5 l0 Leading IP by 40°‡

0.57 In-phase

4-1610-40

1.0 I0 Leading IP by 40°‡

1.4 In-phase

† The energization quantities are input quantities at the relay terminals.‡ Maximum torque angle.

Table 2: DIRECTIONAL UNIT CALIBRATION

RELAYRATING

CURRENTAMPERES

BOTH PLUGS IN CONDITION ADJUSTMENT

All Ranges 80Spurious torque in contact closing direction (left front view).

Right (front-view) plug screwed out until spurious torque is reversed.

All Ranges 80Spurious torque in contact opening direction (right front view). Contacts remain open.

Left (front-view) plug screwed out until spurious torque is in contact closing direction. Then the plug is screwed in until spurious torque is reversed.

NOTE: Short circuit the voltage polarizing circuit and open circuit the current polarizing circuit at the relay terminals before making the above adjustments.


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THIS SPACE RESERVED FOR NOTES


15

Figure 3: Internal Schematic of the Type KRP Relay in the FT-31 Case

*Sub 6

183A025

Figure 2: Internal Schematic of the Type KRD Relay in the FT-31 Case

Sub 2

183A412


16

Figure 4: Internal Schematic of the Type KRC Relay in the FT-31 Case

Sub 5

183A022

Figure 5: Typical Operating Times for the D-Unit of the Type KRD, KRP, and KRC Relays

*Sub 1

619617


17

Figure 6: Typical Operating Times for the D-Unit of the Type KRD, KRP and KRC Relays

Sub 2

538109


18

Figure 7: External Schematic of the Type KRC Relay

Sub 3183A968


19

Figure 8: External Schematic of the Type KRP Relay

Sub 3183A969


20

Figure 9: External Schematic of the Type KRD Relay

Sub 6183A970


21

Figure 10: Test Connections

Sub 33512A85


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THIS SPACE RESERVED FOR NOTES

ABB Inc.4300 Coral Ridge DriveCoral Springs, Florida 33065Telephone: +1 954-752-6700Fax: +1 954-345-5329www.abb.com/substation automation

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Documents

Types KRD, KRP and KRC Directional Overcurrent Ground ... · The directional unit minimum pickup is approximately 1 volt and 2 amperes at its maximum torque angle for the 0.5 to 2,