ABB Power T&D Company Inc.Power Automation and Protection Division

Coral 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 is desiredby purchaser regarding this particular installation, operation or maintenance of this equipment, the local ABBPower T&D Company Inc. representative should be contacted.

Printed in U.S.A.

I.L. 41-496K

Supersedes I.L. 41-496J, Dated February 1988

( ) Denotes Change Since Previous Issue

Before putting protective relays into service makesure that all moving parts operate freely. Inspectthe contacts to see that they are clean and closeproperly. Operate the relay to check the settingsand electrical connections.

1. APPLICATION

The KDXG relay (Figure 2, page 2) is a high speedsingle phase distance relay of reactance type. ThreeKDXG relays are used in conjunction with a grounddirectional unit-timer relay, and an auxiliary currenttransformer Type IK for transmission line protectionfrom a single phase-to-ground fault within 3 zones ofprotection.

A ground directional unit-timer relay is required withthe KDXG relays. Either KRT or KDTG relay providesthis function.

The KDTG should be used to avoid incorrect direc-tional sensing where zero sequence system isolationmay occur and zero sequence mutual exists. It isinsensitive to line energizing transients and does notrequire zero sequence current for its operation.

Where relay current for a ground fault within thereach of the relay is less than approximately 3amperes, or where a third zone reach in excess ofapproximately 10 ohms is required, the KRT relay isused.

Both the KRT and the KDTG relays contain a direc-tional unit (dual polarized in the case of the KRT andKD-10 phase to phase unit in the KDTG) and a statictimer that switches the KDXG reactance unit fromzone 1 to zone 2 and 3 after the preset time delays.

The IK current transformer, in addition to its ratioingfunction for reactance unit current, may also be used

to compensate for adjacent line (or lines) zerosequence mutual effect.

A type ITH instantaneous ground over-current relaymay be used to supplement the ratio discriminatorsso that the KRT timers may be started at the incep-tion of a distant fault. Refer to Figure 6 (page 6). TheITH will speed the clearing of faults where the faultcurrent is less than about twice the load current flow.Otherwise, for these cases the timer starting will besequential after remote breaker has opened to redis-tribute fault current or cut off load current flow.

2. CONSTRUCTION

2.1. Compensator

The KDXG relay consists of two single air gap trans-formers, one of which acts as a reactance compensa-tor and the other as a ratio discriminator transformer,one tapped auto-transformer, a cylinder type reac-tance tripping unit, a polar relay unit, 2 telephonerelays for zone switching, diode bridge assembly witha filter network, and a maximum voltage type resistor-diode network.

The compensator is a three winding air-gap trans-former, (Figure 3, page 3). There are two primarywindings, one designated “TL” and the other TO.” “TL”winding is energized by the phase current, and “TO”by the residual current. Each winding has taps whichterminate on the tap plate. Values between taps aremarked 0.3, 0.2, 0.6.

Current flowing through the primary coils provides aMMF which produces magnetic flux in the core. Avoltage is induced in the secondary which is propor-tional to the primary tap and current magnitude. Thisproportionality is established by the cross sectionalarea of the laminated steel core, the length of an airgap which is located in the center of the coil, and thetightness of the laminations. All of these factors whichinfluence the secondary voltage proportionality havebeen precisely set at the factory. The clamps which

! CAUTION

Type KDXGGround Distance Relay

Effective: June 1997

I.L. 41-496K

3

hold the laminations should not be disturbed byeither tightening or loosening the clamp screws. Thesecondary winding has a single tap which divides thewinding into two sections. One section is always con-nected subtractively in series with the relay terminalvoltage. Thus a voltage which is proportional to theline current and leads the current by 90° (jXIR) is sub-tracted from, voltage (VLG) Figure 5a (page 5). Thesecond section becomes connected in series withthe first section when the reactance unit is switchedto zone 3 setting, thus increasing the secondary volt-age output of the compensator by a factor of 2.5.

2.2. Ratio Discriminator Transformer

Ratio discriminator transformer is similar in construc-tion to the compensator except that it has a singleprimary winding and a single secondary winding thatproduces a voltage proportional to the magnitude ofthe phase current.

2.3. Autotransformer

The autotransformer has ten taps MC which are num-bered (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) and ten taps MFnumbered (.1, .2, .3, .4, .5, .6, .7, .8, .9, 1.0) MCtaps represent ten percent autotransformer outputtaps, and MF taps are one percent.

2.4. Reactance Tripping Unit

The reactance unit is a four pole induction cylindertype unit. The direction of operating torque of this unitdepends on the angle between the current and therelay terminal voltage as modified by the compensa-tor voltage.

Mechanically, the cylinder unit is composed of fourbasic components:

■ A die-cast aluminum frame an electromagnet.

■ A moving element assembly and a moldedbridge. The frame serves as a mounting structurefor the magnetic core.

■ The magnetic core which houses the lower pinbearing is secured to the frame by a locking nut.

■ The bearing can be replaced, if necessary, with-out having to remove the magnetic core from theframe.

The electromagnet has two sets of two series con-nected coils mounted diametrically opposite oneanother to excite each set of poles. Locating pins onthe electromagnets are used to accurately positionthe lower pin bearing, which is mounted on theframe, with respect to the upper pin bearing that is

Figure 2. Internal Schematic of the TypeKDXG Relay in FT-42 Case

Figure 3. Compensator Construction

187A120Sub 1

v

*Sub 7185A189

AIR GAP

PRIMARY SECONDARY LAMINATED

V

I

CORE

I.L. 41-496K

4

threaded into the bridge. The electromagnet issecured to the frame by four mounting screws.

The moving element assembly consists of a spiralspring, contact carrying member, and an aluminumcylinder assembled to a molded hub which holds theshaft. The hub to which the moving contact arm isclamped has a wedge-and-cam construction to pro-vide low-bounce contact action. A casual inspectionof the assembly might lead one to think that the con-tact arm bracket does not clamp on the hub as tightlyas it should. However, this adjustment is accuratelymade at the factory and is locked in place with a locknut and should not be changed. Optimum contactaction is obtained when a force of 4 to 10 gramspressure applied to the face of the moving contactwill make the arm slip one-fourth of its total freetravel. Free travel is the angle through which the hubwill slip from the condition of reset to the point wherethe clamp projection begins to ride up on the wedge.The free travel can vary between 15° to 20°.

The shaft has removable top and bottom jewel bear-ings. the shaft rides between the bottom pin bearingand the upper pin bearing with the cylinder rotating inan air gap formed by the electromagnet and the mag-netic core. The stops are an integral part of thebridge.

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. This

stationary contact has .002 to .006 inch follow whichis set at the factory by means of the adjusting screw.After the adjustment is made the screw is sealed inposition with a material which flows around thethreads and then solidifies. The stationary contacthousing is held in position by a spring type clamp.

When contacts close, the electrical connection ismade through the stationary contact housing clamp,to the moving contact, through the spiral spring andout to the spring adjuster clamp.

2.5. Polar Relay Unit (RD)

This unit consists of a rectangular-shaped magneticframe, an electromagnet, a permanent magnet, andan armature with two contacts. The poles of the cres-cent-shaped permanent magnet bridge the magneticframe. The magnetic frame consists of three piecesjoined in the rear with two brass rods and silver sol-der. These non-magnetic joints represent air gapswhich are bridged by two adjustable magneticshunts. The operating winding is concentricallywound around a magnetic core. The armature is fas-tened to this core at one end and floats in the front airgap at the other end. The moving contact is con-nected to the free end of a leaf spring.

2.6. Telephone Relays

The telephone relay units T2X and T3X are of fastoperate type. In these relays an electromagnetattracts a right angle iron bracket which in turn oper-ates a set of make and make before break contacts.All contacts are of bifurcated type for high reliability.

Figure 4. Tap Plate

X10T

MC MF+-----------------------=Mc MF

TO

4

3

2

1

.3

.2

.6

0

Z1 Z2

2.5Z3

5

9

8

7

6

TL

.6

.5

.4

.3

.2

.3

.2

.6

.1

1.0

.9

.8

.7

Z1 Z2

25Z3

dtp illustration

I.L. 41-496K5 Figure 5. Voltage, Current and Flux Conditions for the Reactance Unit for Faults at Various Locations

Sub 2407C687

I.L. 41-496K

6

Figure 6. External Schematic for Type KDXG Relay with KRT

Sub 14407C602

I.L. 41-496K

7

2.7. Diode Bridge Assembly andAssociated Network

Diode rectifier bridge assembly is a full-wave typeusing silicon medium power type diodes. DC outputof this bridge is filtered by a capacitor and a chokenetwork.The input to the rectifier bridge is shunted bya varistor and resistor combination to limit the inputvoltage at high current level.

2.8. Maximum voltage Network

Maximum voltage network consists of a tapped resis-tor (600, 2160, 2160 ohms taps) and 3 blockingdiodes.

2.9. Operation Indicator (OI)

The operation indicator (OI) is a small clapper-typedevice. A magnetic armature is attracted to the mag-netic core upon energization of the indicator. Also,during this operation, two fingers on the armaturedeflect a spring located on the front of the switch,which allows the operation indicator target to drop.The target is reset from the outside of the case by apush rod located at the bottom of the cover.

3. OPERATION

The relay is connected and applied to the system asshown in Figure 6 (page 6). The reactance unitcloses its contacts when the reactive components ofthe impedance of the protected line becomes smallerthan the relay setting. The ratio discriminator oper-ates on single-line-to-ground faults in the faulted

phase only.

The companion type KRT relay, contains a direc-

Figure 7. General System Used for Describing Type KDXG Relay Operations

Figure 8. Response of Ratio Discriminator to GroundFaults, Assuming All Impedances in Phase

Sub 1185A503

* Sub 3290B798

* Denotes change

I.L. 41-496K

8

tional ground unit that provides the scheme with directional characteristics and a timer for zone 2 and zone 3operation.

All three units, reactance, ratio discriminator and the ground directional unit operate simultaneously for singleline-to-ground faults located within zone 1 of reactance unit setting.

For reversed single line-to-ground faults the scheme does not trip since the directional unit will have its contactopen. For 2-phase-to-ground faults, or phase-to-phase faults, and 3-phase faults, tripping is blocked by theratio discriminator. Additional blocking is obtained by the ground directional unit on phase-to-phase and 3-phase faults.

For zone 2 and 3 tripping, the reach of the reactance unit is switched by the timer. The timer is started by T1relay that operates after the directional unit and ratio discriminator close their contacts.

Figure 6 shows device 50N used as an optional means of starting the timer if the D contacts of the 32T deviceare closed. This path bypasses the ratio discriminator contacts during low fault current periods. The use of thisground over-current unit allows tripping with no added delay if the ratio discriminator operates sequentially fordistant faults.

3.1. Fundamentals of Distance Measurement

Figure 7 shows a typical two-circuit transmission system with a source of power at both ends of the line.Assume that a KDXG relay is installed at the shaded breaker location. For a ground fault on phase A the phaseA reactance unit will see the following conditions.

Definition of Terms:

VAG = phase A-to-ground voltage at bus H.

K1 = portion of total positive-sequence or negative-sequence fault current flowing through relay location.

KO = portion of total zero-sequence fault current flowing through relay location.

Z1L = positive and negative-sequence impedance of the protected line.

IA1 = total positive-sequence fault current.

IA2 = total negative-sequence fault current.

I0 = total zero-sequence fault current.

I0E = adjacent line zero-sequence current.

Z0M = mutual zero-sequence impedance between the two lines.

Z0L = zero-sequence impedance of the protected line.

RG = fault resistance.

IA = (1)

VAG = (1A)

K1I A1 K1I A2 KOI O+ +

K1I A1nZ1L K1I A2nZ1L K0I 0nZ0L I oEnZ0m 3I 0RG+ + + +

but from (1)

then:

VAG =

=

(2)

Now, let the relay current IR be:

K1 I A1 I A2+( ) I A KOI O–=

I AnZ1L KOI OnZ1L– KOI OnZOL I OEnZOM 3I ORG+ + +

nZIL I A KOI O

ZOL ZIL–( )ZIL

----------------------------- I OE

ZOM

ZIL-----------+ + 3I ORG+

I.L. 41-496K

9

IR =

(3)

then (4)

The first term nZ1L is directly proportional to the dis-tance from the fault to the relay and is independent ofconditions external to the protected section.

The second term is a function of fault resistance, RG,and has an effect of pure resistance if IO is in phasewith IR. This will be nearly true, since in general allthe impedances involved in equation for ZR will havenearly the same phase angle, unless line resistancesare very large, and also since IA, IO, and IOE are usu-ally nearly in phase for this type of fault. Assumingthat this term is resistive the reactance unit ignores itby sensing only the imaginary component of ZR, jXR,

thenjXR = jnX1L

The relay current

IR =

is obtained by supplying the reactance unit currentcircuit with line current, residual current, and theresidual current from parallel line. The correction ofresidual currents by factors

is done by means of taps on the auxiliary currenttransformer type 1K. The factor 3 is needed sinceIO = 1/3 residual current in the protected line andIOE = 1/3 residual current in parallel line.

3.2. Principle of Operation of Reactance Unit

The reactance unit is an induction cylinder unit hav-ing directional characteristics. Operation of this typeof unit depends on the phase relationship betweenmagnetic fluxes in the poles of the electromagnet.

One set of poles is energized by two pairs of currentwindings, where one pair receives the line currentand the second pair the residual current from the pro-tected and parallel lines as modified by auxiliary cur-rent transformer tap settings.

The second set of poles is energized by the line-to-ground voltage as modified by the compensator volt-

age.This compensator voltage determines the reachof the reactance unit.

Compensator T is designed so that its mutual reac-tance, X, has known and adjustable values asdescribed under “CHARACTERISTICS ANDSETTINGS” . The mutual reactance of a compensa-tor is defined here as the ratio of secondary inducedvoltage to primary current and is equal to T. the sec-ondary compensator voltage is in series with the line-to-ground voltage as modified by the autotransformersetting. The flux in the voltage-energized poles is soadjusted that it is in phase with the resultant voltage,V1, (see Figure 5a, page 5). Cylinder connectionsare such that it closes its contacts whenever the fluxin the voltage polarized poles lags the flux in the cur-rent polarized poles.

Figure 5a illustrates the operation of the reactanceunit. Here VLG is the line-to-ground voltage leadingthe line current by an angle α. Compensator voltageis shown here as –jXLIR. øV is the flux due to the volt-age (VLG – jXLIR). øI is the flux due to the relay cur-rent. Since flux øV is the flux leading øI the cylinderunit will have restraining torque keeping its contactsopen.

The balance will occur when flux øV will be in phasewith flux øI. For this to happen, compensator voltagejXLIR must be equal to VLG sinα– the magnitude ofthe reactive component of the relay voltage, asshown in Figure 5b, page 5.

For faults inside the protected zone (see Figure 3c,page 3) the compensator voltage will be larger thanthe V sinα value, this makes the flux øV lag the flux øIand cause the relay contacts to close. For faultsbeyond the balance point (Figure 5d, page 5) com-pensator voltage will be smaller than VLG sinα. Thiswill make the voltage flux øV lead the current flux øIand restrain relay from contact closing. For faultsbehind the relay or for reverse power flow the reac-tance unit will keep its contact closed (Figure 5e,page 5) since the current flux will always lead thevoltage flux independent of the value of compensatorvoltage.

3.3. Principles of Operation of RatioDiscriminator

The ratio discriminator unit (RD) is a polar type relayoperating on a voltage derived from the line currentin the transformer DT. Before this voltage is appliedto the polar unit (RD) it is rectified, filtered, andapplied across the voltage divider resistor (RS). 70percent of this voltage is tapped off the RS-resistorand applied to the polar unit coil. This coil (RD) isconnected in series with a diode (D3) in conducting

I A KOI O

ZOL Z1L–( )Z1L

----------------------------- I OE

ZOM

Z1L-----------+ +

ZR

VAG

I R---------- nZ1L RG

3I O

I R---------+= =

I A I OKO

ZOL Z1L–

Z1L------------------------ I OE

ZOM

Z1L-----------+ +

ZOL Z1L–

3Z1L------------------------ and

ZOM

3Z1L------------

I.L. 41-496K

10

direction. The full voltage developed across RS-resistor is applied to the ratio discriminators networksin the two adjacent phases through diodes D1 andD2. with no line currents in the adjacent phase relaysthe polar unit will operate on a minimum of 1 ampereof current flowing through the primary of the DT-transformer. If there is a line current in any one of theadjacent phases, the full voltage developed acrossRS-resistor in those relays is applied to the blockingside of the diode D3 through Terminal 11 so that ifthis voltage should become a higher positive poten-tial than the operating voltage applied to the RD-coil,the diode D3 becomes non-conducting, the RD-unitwill be prevented from operation. This means that inorder for an operating unit to trip, current in its line

must be at least = 1.43 times the larger of the

adjacent phase currents. Conversely, the adjacentphase current required to block tripping should bemore than 0.7 times the faulted phase current. Thisnominal value of 0.7 varies from 0.5 to 0.75 depend-ing upon the magnitude and phase of fault currents(see Figure 11, page 11).

Thus for single line-to-ground fault on a simple radialsystem there will be operating voltage on the relay ofthe faulted phase only, with little or no blocking (dueto load current) from two other phase relays. For two

100%70%--------------

phase-to-ground faults, equal currents will restraineach other, and the unfaulted phase will experienceall blocking and no operating voltage.

Similar conditions will exist on phase-to-phase faults,except additional selectivity is provided by theground directional unit since it will not operate in theabsence of zero-sequence quantities.

For 3ø faults or loads, equal or nearly equal currentswill produce the same restraint in all 3 units, andground directional unit will provide additional selectiv-ity.

For most complicated networks, where only a part ofthe total zero or positive sequence fault current flowsthrough the protected line, the ratio discriminatorresponse is analyzed below:

Let K1= fraction of the total positive-sequence andnegative-sequence fault current flowing inthe protected line.

KO = fraction of the total zero sequence fault cur-rent flowing in the protected line.

For Single Line-to-Ground Fault (Figure 8)

For Figure 8a

Phase A operates since all fault currents flowsthrough the faulted phase

For Figure 8b

This case corresponds to the extreme conditionwhere there will be no positive sequence current flowon the relay side of the protected line. Equal zerosequence currents will flow in all three phases andratio discriminator is shown in Figure 9, page 10. Thearea above the curve represents the tripping zone ofthe ratio discriminator.

For (Figure 8c)

This case corresponds to the extreme conditionwhere there will be very little or no zero sequencecurrent on the relay side of the protected line. The

response of ratio discriminator as function of

ratio for different current level is shown in Figure 9.The area above the curve represents the trippingzone of the ratio discriminator.

For Two Line-to-Ground Faults

For correct operation of the ground distance schemeon the two line-to-ground type of faults the ratio dis-criminator should block the tripping.

K1

KO------- 1=

K1

KO------- 0=

K1

KO------- ∞=

K1

KO-------

Figure 9. Typical Operating Characteristics of the RatioDiscriminator as a function of Current Distribu-tion Factor Ratio and Operating Current

Sub 1187A121

I.L. 41-496K

11

Figure 10. Typical Operating Time Curve of the Ratio Discriminator Unit

Sub 1187A122

Figure 11. Typical Ratio Discriminator Trip Characteristic (Ires/Iop) as Function of Operating Current LOP

Sub 1187A123

I.L. 41-496K

12

For (Figure 8d)

Blocking is obtained by the two faulted phases block-ing each other, and the unfaulted phase.

For (Figure 8e)

This case corresponds to the extreme conditionwhere little or no positive sequence current flows onthe relay side of the protected line. Since equal cur-rents are flowing in all three phases, all discrimina-tors block the tripping.

For

A) (Figure 8f)

B) (Figure 8g)

Here Z′0, Z′2 are total system zero and negative-sequence impedances including fault resistance. Alldiscriminators will block tripping.

4. CHARACTERISTICS

The type KDXG relay is available in 48, 125, and 250dc rating.

4.1. Reactance Unit

The minimum reach of the reactance unit is 0.2ohms. The relay has five basic settings:T = 0.2, 0.3, 0.5, 0.8, 1.1 ohms. These settings byuse of auto-transformers taps are expanded by a fac-tor of 10.

The range settings for the reactance unit are tabu-lated below and show the range of settings obtainedfor zone 3 if the zone 1 and zone 2 are set within thefollowing range:

By use of auto-transformer taps the maximum reachfor zone 1 is 11 ohms.

The reactance unit is accurate within ± 3 percent forthe range 5° -- 90° over the following current range:

The reactance unit has a minimum sensitivity of 0.7amp with zero volts for TL = TO = .2 setting (voltage ter-minals short circuited) and 0.3 amp for TL = TO = 1.1.

The speed of operation of the reactance units isshown on Figure 16 (page 19). The curves indicatethe time in milliseconds required for reactance unit toclose its contacts for tripping after the inception of afault at any point on a line within the relay setting, linecurrent and residual current circuits connected inseries.

The reactance unit has continuous rating of 77 voltsand 5 amp ac. The one second current rating is 140amp.

4.2. Ratio Discriminator

The ratio discriminator has a minimum pickup currentof 1 amp with no restraint from other relays. It hascontinuous rating of 5 amp ac. The time-current oper-ating curve for the ratio discriminator unit is shown inFigure 10 (page 11). The one second current ratingis 140 amp.

4.3. Auxiliary Current Transformer (Type IK)

Auxiliary current transformer (Figure 12, page 13)has taps representing the part of the complete wind-ing. There are two windings: one marked “protected

line” has taps that represent factor and

the second winding marked “parallel line” has taps

representing factor . The taps are marked

as follows: 0 – 0.1 – 0.2 – 0.4 – 0.7 – 1.0.

4.4. Trip Circuit

The main contacts will safely close 30 amperes at250 volts dc, and the seal-in contacts of the indicat-ing contactor switch will safely carry this current longenough to trip circuit breaker. The operational indica-tor unit has a 1 ampere pickup and a coil resistanceof 0.1 ohm dc.

Table 1:

If zone 1 and zone 2 range is: Zone 3 range is:

0.2 - 2.0 ohms 0.5 - 5.0 ohms

0.3 - 3.0 ohms 0.75 - 7.5 ohms

0.5 - 5.0 ohms 1.25 - 12.5 ohms

0.8 - 8.0 ohms 2.0 - 20 ohms

1.1 - 11 ohms 2.75 - 27.5 ohms

K1

KO------- 1=

K1

KO------- 0=

K1

KO------- ∞=

qZ′0

Z′0 Z′2+--------------------- 0= =

Z′0Z′0 Z′2+--------------------- 1=

Table 2:

0.2 – 0.3 reactive basic ohms 6 – 75 amp.

0.5 reactive basic ohms 5 – 60 amp.

0.8 – 1.1 reactive basic ohms 2.5 – 40 amp.

CZ0L Z1L–

3Z1L------------------------=

C1 ZOM

3Z1L------------=

I.L. 41-496K

13

type IN1095 diodes. The diodes have 0.75 amp con-tinuous rating, leakage current of 0.5 MA at ratedpeak inverse voltage of 500 volts, at 50°C. Forwardvoltage drop at 0.75 amp current, at 50°C, is below 1volt. The D3 diode consists of two Germaniumdiodes type IN93. The IN93 diode has maximumpeak inverse voltage rating of 300 volts, and 75 mAcontinuous current rating.

5. SETTING CALCULATIONS

5.1. Reactance Unit

The reactance unit is set according to the followingequations:

for zone 1 and zone 2

for zone 3

Where:

X110T

MC MF+-----------------------=

X125T

MC MF+-----------------------=

X1 = The positive sequence reactance ofthe zone to be protected. T = TL = TO arecompensator setting values(0.2, 0.3, 0.5, 0.8, or 1.1). TO is set toequal TL.

MC, MF are auto-transformer output volt-age taps. Coarse tap settings, MC, canbe made in steps of 10 percent and finetap settings, MF, can be made in 1 per-cent steps.

The setting calculations procedure is asfollows:

1. Choose a value of T = TL closest tothe desired positive sequence value(X1) for the desired zone of protec-tion, but never larger than X1.

2. Find MF and MC setting for eachzone by using the following equa-tions:

for zone 1 and zone

2

for zone 3

where T is tap value selected above.The whole number part of the

MC MF+ 10TX1

----------=

MC MF+ 25TX1

----------=

answer represents the MC setting and the deci-mal fraction part represents the MF tap setting.

5.2. Sample Calculationsfor Reactance Unit Setting

Determine the settings for the protection of the fol-lowing line: (All values in percent)

5.2.1. Section 1: 14.5 Miles Long

Z1 = 3.29 + j 11.40

ZO = 9.50 + j 39.2

ZOM = 6.23 + j 25.4 (to a parallel line)

5.2.2. Section 2: 18.93 Miles Long

Z1 = 5.63 + j 15.70

ZO = 13.93 + j 48.32

All line constants are in percent on a 138 kV, 200MVA basis. RV = voltage transformer ratio = 1200:1.RC = current transformer ratio = 600:5.

Figure 12. Outline — Drilling Plan for Type IK Auxiliary CT

*Sub 4187A151

* Denotes change

CLEARANCE FOR.250 SCREW(4 HOLES)

xx

x

xx

xC1

C

1234

56

I.L. 41-496K

15

5.2.2. Section 2: 18.93 Miles Long

Z1 = 5.63 + j 15.70

ZO = 13.93 + j 48.32

All line constants are in percent on a 138 kV, 200MVA basis. RV = voltage transformer ratio = 1200:1.RC = current transformer ratio = 600:5.

A. Compute the reactive relay ohms.

=

X1 (ohms) = (0.0952)X1% = relay ohms whereX1% values are based on 138 kV and 200 MVA.

B. Compute setting for zone 1 (80% of section 1to be protected).

Desired setting:

X1 = 0.0952 (11.40) x 0.8 = .868 ohms* Select T, MC, and MF taps.

1. T setting closest to .868 ohms is:T = TL = TO = .8

2.

3. Zone 1 should be set:TL = TO = 0.8MC = 9.0MF = 0.2

C. Compute setting for zone 2 (100 percent pro-tection for section 1, and 50% protection forsection 2).

Desired setting:

X1 = 0.0952 [11.4 + 15.7 (0.5)] = 1.83 ohm

1. Select MC, MF taps

2. Now use the same T = TL = TO = .8 setting as forzone 1.

3. Zone 2 should be set:

MC = 4.0

MF = 0.4

D. Compute setting for zone 3 (100 percent pro-tection for sections 1 and 2.

X1 = 0.0952 (11.4 + 15.7) = 2.58 ohms.

1. Select MC and MF taps

2. Using T = TL = TO = 0.8 (same as for zone 1)

3. Zone 3 should be set:

MC = 7.0MF = 0.8

All settings will be within 1.0% of desired setting.

5.3. Auxiliary Current Transformer IK

The auxiliary current transformer winding marked“protected line” (terminals 1 and 2) is set according tothe formula:

where ZOL represents the zero sequence impedanceof the protected line, and Z1L the positive sequenceimpedance of the protected line.

The coefficient C represents the portion of the resid-ual current of the protected line that has to be addedto the relay current to compensate for effect of zerosequence current.

One winding of the auxiliary CT (terminals 3 and 4)(Figure 12, page 13) is connected in series with relayresidual current circuit. The residual current circuit ofthe protected line (terminals 1 and 2) is connectedacross the taps of the same winding so that differ-ence between taps will be equal to coefficient C.

If the ZOL and Z1L impedances have the same anglethe relay will correctly measure the reactive compo-nent of Z1L. If there is a wide difference between thetwo angles, use reactive components of Z1L and ZOLto compute C coefficient. In this case

The second winding of the auxiliary current trans-former marked “parallel line” (terminals 5 and 6) isset for compensation of the effects of residual currentin the parallel line due to the zero sequence mutualimpedance between the two lines.

X1(ohms)10 KV( )2

KVA---------------------- Rc

Rv------

X1%( )=

10 138( )2120( )

200 000 1 200,( ),----------------------------------------- X1%( )

MC MF+ 10TX1

----------10 0.8( )×

0.868------------------------ == = 9.22 9.0 0.22+=

MC MF+ 10 0.8( )+X1

------------------------ 81.83---------- 4.37 4.0 0.37+= = = =

MC MF+ 25TX1

---------- 202.58---------- 7.75 7.0 0.75+= = = =

CZOL Z1L–

3Z1L-------------------------=

CXOL X1L–

3X1L--------------------------=

I.L. 41-496K

17

The necessary setting is computed according to thefollowing formulas:

or

where Z0M = mutual zero sequence impedancebetween two lines.

The taps of the “parallel line” winding are connectedin series with the residual ct circuit of the parallel line.

The taps are set so that difference between the tapsis equal to the desired C1 value.

The desired tap settings should be made to the near-est tap value.

NOTE: Terminal 5 and 6 of auxiliary currenttransformer, IK, should be left open cir-cuit when not connected to the parallelline ct’s.

5.4. Sample Calculations of IK-Settings

Using the same line as for the reactance unit samplecomputations, compute constants C and C1.

A. Coefficient C is computed for zone 1 only sincezone 1 should be set as exactly as possible.Since the coefficient represents the ratio of twoimpedances, use percent quantity directly.

Hence, the auxiliary transformer setting for pro-tected line C = .8.

B. Coefficient C1 is calculated as follows:

Hence, the auxiliary current transformer setting forthe parallel line is:

C1 = 7

5.5. Ratio Discriminator

There is no setting to be made on the ratio discrimi-nator. The operating unit will operate at 1 amp withno restraining current in two other units.

6. SETTINGS

The KDXG relay requires two compensator settings,TL and TO, three autotransformer settings (one foreach zone), and one for two auxiliary current trans-former settings, C and C1.

! CAUTION

Since the tap block screws carry operating cur-rent, be sure that the screws are turned tight.

In order to avoid opening current transformer cir-cuits when changing taps under load, start withRED handles FIRST and open all switchblades.Chassis operating shorting switches on the casewill short the secondary of the current trans-former. Taps may then be changed with the relayeither inside or outside the case. Then reclose allswitchblades making sure the RED handles areclosed LAST.

6.1. Compensator Settings

TL and TO are set for the value calculated under“Setting Calculation.” Each setting is made by con-necting the two links between taps so that the sum ofthe numerals between the two tap screws is equal tothe desired setting. For instance, if TL = TO = .8ohms, as computed in the sample computation, thetwo lines on each side of the tap plate are connectedso that T = .8 is set as sum of .2 and .6.

6.2. Autotransformer Settings

MC and MF settings are made for each zone. Theautotransformer taps MC and MF are brought out toterminals on the tap plate and are connected to thevoltage circuit of the reactance unit by means ofleads marked “Z1”, “Z2”, and “2.5Z3”.

These Z1, Z2 and 2.5Z3 leads come out on each sideof the tap plate inside the circles formed by MC andMF taps. The MC circle of taps is located on the left-hand side of the tap plate when facing the relay andthe MF circle of taps is on the right-hand side of thetap plate.

The Z1, Z2, and 2.5Z3 leads should be connected toonly that circle of MC or MF which surrounds themand should never be interchanged. There may be asmuch as three connections made to a single tap on

C1 Z0M

3Z1L------------= C

1 X0M

3X1L-------------=

CZ0L Z1L–

3Z1L------------------------ 9.50 J39.2 3.29– J11.4–+

3 3.29 J11.4+( )-------------------------------------------------------------------= =

C28.49 77.4°∠35.6 73.9°∠------------------------------- 0.80 3.5° 0.80≈∠= =

C1 Z0M

3Z1L------------=

Z0M 6.23 J25.4+( )=

Z1L 3.29 j11.4+=

C1 6.23 j25.4+( )

3 3.29 j11.4+( )-------------------------------------- 26.2 76.2°∠

35.6 73.9°∠---------------------------- 0.736 2.3° 0.738≈∠= = =

I.L. 41-496K

19

the rear mounting stud or studs for projection mount-ing. Either a mounting stud or the mounting screwsmay be utilized for grounding the relay. The electricalconnection may be made directly to the terminals bymeans of screws for steel panel mounting or to theterminal studs furnished with the relay for thick panelmounting. The terminals’ studs may be easilyremoved or inserted by locking two nuts on the studand then turning the proper nut with a wrench. Fordetailed Flexitest case information refer to I.L.41.076.

8. ROUTINE TEST

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

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

8.1. Visual Check

Give visual check to the relay to make sure there areno loose connections, broken resistors, or brokenwires.

8.2. Reactance Unit Check

1.Connect relay as shown in Figure 13 (page 14)and make the following settings:

MC, zone 1 = 9.0

MF, zone 1 = 1.0TO = TL = 0.2 ohm

Adjust the voltage for 2.4 volts and the phaseshifter for current lagging voltage by 90°.

Increase current until the contacts just close.This current should be within ±5% of 7 amperes,(6.65 – 7.35).

2. Make the following settings:

A. MC MFFor: Zone 1 2.0 0.5

Zone 2 1.0 0.8Zone 3 9.0 1.0

B. Set TO = TL = 1.1 ohms = .3 + .2 + .6

This setting corresponds to

This equation is used for testing purposes only.the two TO and TL settings are added only, whenfor test purposes, the same current is passedthrough line current circuit (terminals 16 and 17)and the residual current circuit (terminals 19 and15). Therefore, relay reach during test is dou-bled. In normal operation line current passesthrough only one current circuit (IL), and theresidual current circuit (IO) is used for compensa-tion for the effects of zero sequence quantities

X1.1 1.1+( )10

2.5-------------------------------- 8.8 ohms for zone 1= =

Figure 16. Typical Operating Time Curves of the Reactance Unit

Sub 2187A124

I = X =( MC+MF)/10(Current Times Reactive Ohm Setting times (MC+MF)/10)

I.L. 41-496K

20

only.

3. Zone 2 and zone 3 switches open.

4. Adjust the phase shifter for 90° current laggingthe voltage.

5. With terminal voltage at 44 volts, increase cur-rent until contacts just close. This current shouldbe within ±6% of 5 amps. (4.7 - 5.3 A).

6. Adjust phase shifter for 45° current lagging thevoltage and adjust voltage for 44 volts, increaseuntil contacts just close. This current should bebetween 3.30 and 4.1 amperes, if the phaseangle meter is accurate within ±2 degrees.

7. Close zone 2 switch.

8. Adjust voltage for 38 volts and phase shifter forcurrent lagging voltage by 90°.

9. Increase current until contacts just close. Thiscurrent should be between 3.20 – 3.5 amp.

10. Close zone 3 and zone 2 switches.

11. Adjust voltage for 27.5 volts and phase shifter forcurrent lagging the voltage by 90°.

12. Increase current until contacts just close. Thiscurrent should be between 4.7 – 5.3 amperes.

This completes the check of operation of thereactance unit.

8.3. Ratio Discriminator Unit

1. With relay in the case connected as per Figure13. Pass 0.5 amp ac current through terminals17 and 16 only. Increase current until ratio dis-criminator unit just picks up. This should occur at1 ampere (± 10%).

2. Remove 1080 ohm resistor and connect a10,000 ohm resistor in series with terminal 11. .Apply 225 volts dc across terminal 12 and the 10K resistor, and across 13 and the 10 K resistorwith plus polarity on terminals 12 and 13. Mea-sure current through terminal 11. It should bebelow 0.5 milliamperes. Reverse polarity andapply 125 Vdc. The current should be approxi-mately 9 milliamperes.

3. Remove the 10 K resistor and apply 25 volts dcfrom terminal 11 to terminal 18, with positivepolarity on terminal 11. The current should readapproximately 12 mA. Reverse the polarity andapply 10 Vdc. The current should read approxi-

mately 10 mA.

4. Apply about 3 amps of ac current to terminals 17and 16. Measure dc voltage from right-handpolar unit terminal to terminal 18, and from termi-nal 13 to terminal 18. Ratio between the first volt-age and this voltage should be ( .65 to .80).

8.4. Operation Indicator (OI)

Close the main relay contacts and pass sufficient dccurrent through the trip circuit to drop the indicatingtarget. This value of current should be not less than1.0 amperes nor greater than 1.2 amperes.

9. REPAIR CALIBRATION

Use the following procedure for calibrating the relay ifthe relay has been taken apart for repairs or theadjustments disturbed.

For best results in checking calibration, the relayshould be allowed to warm up for approximately onehour at rated voltage. However, a cold relay will prob-ably check to within two percent of the warm relay.

9.1. Autotransformer Test

Disconnect all Z1, Z2 and 2.5Z3 leads from the taps.Apply 100 volts ac to terminals 19 and 20. Checkvoltages on MC taps between the tap “0” and all suc-cessive MC taps, starting at tap “1”. Voltage readingsshould be 10, 20, 30, 40, 50, 60, 70, 80, 90 volts(±.1volt).

Then check MF taps voltage between “0” tap on MCscale and all successive MF taps starting with tapmarked “1”. Voltage readings should be 1, 2, 3, 4, 5,6, 7, 8, 9, 10 volts respectively. Voltage across taps0.1, 0.2, 0.3, 0.4, 0.5 should not vary more than±.1volt.

9.2. Reactance Unit Test (Cylinder Unit)

A. Contact Gap Adjustment

The spring type pressure clamp holding the sta-tionary contact in position should not be loos-ened to make the necessary gap adjustments.With moving contact in open position againstright-hand stop on bridge, screw in stationarycontact until both contacts just make, then screwthe stationary contact away from the moving con-tact 3/4 of one turn, for a contact gap of .022.

B. Shaft Clearance Adjustment

The upper bearing screw should be screweddown until there is approximately .025” clear-ance between it and the top of the shaft bearing.The upper pin, bearing should then be securely

I.L. 41-496K

21

locked in position with the lock nut.

C. Spring Restraint Adjustment

Adjust RM2 resistor (31/2 inch resistor located onthe right-hand side bottom) to measure 577ohms. Set TL = TO = .2, MC = 9.0, MF = 1.0.Adjust voltage to measure 2.4 volts and adjustphase shifter for current lagging the voltage by90°. Adjust the restraint spring so that the currentrequired for contacts to just close is equal to 7amperes. Deenergize relay completely — themoving contact should return to its original posi-tion against the metal stop on the right-hand sideof the bridge.

D. Core Adjustment

Apply 100 Vac to terminals 19 and 20. Relaycontacts should stay open. If the contacts areclosed, rotate core by a non-magnetic tool beinginserted into sides of core adjusters located onbottom side of the cylinder unit.

NOTE: The red dot on the core must be to therear.

Magnetic Plug Adjustment

1. Short out voltage terminals 19 and 20.

2. Jumper terminals 15 and 16.

3. Connect both TL links to a common tap insert.This will exclude the current from compensatorwinding.

4. Repeat step 3 for TO links.

5. Screw in both magnetic plugs as far as possibleprior to starting the adjustment.

6. Apply 5 amps and increase gradually to 80 ampsof current in terminal 17 out terminal 14. Read-just plug if necessary to keep contacts open. Thereactance unit need not be cooled during therough adjustment but the unit should not be hotwhen final adjustment is made. Recheck coreadjustment using 70 volts as the test level.

7. When relay contacts close to the left screw outthe right-hand plug until spurious torque isreversed and screw the right-hand plug out(approximately five turns).

8. When spurious torque is in contact openingdirection (to the right), then left-hand plug shouldbe screwed out until the spurious torque is incontact closing direction. Then screw in the left-hand plug until spurious torque is reversed and

screw the right-hand plug out five turns.

E. Phase Angle Adjustment for Zone 1 and 2

Set TL and TO links for .3 setting each. Connectrelay per Figure 15 (page 18) with test reactancemeasuring approximately 1.0 ohm and an adjust-able resistor of 10 ohms (1000 watts). There isno need for exact reactance, since reach of theunit is determined by a factory-adjusted compen-sator. Connect conventional test probe leads toZ1 leads for convenience. Close switch 1 short-ing out the resistor. Adjust current for 9 amperescurrent in the circuit. Apply Z1 leads to differentMF and MC taps. Note MC and MF taps at whichreactance unit just closes and opens. If 1 ohmreactor is used, this should occur at approxi-mately MC + MF = 6.0.

If some other reactor value is used, approximatevalues are found by using equation

where X = the available reactor value. Hereagain relay reach is doubled, since the same testcurrent is passed through the line and residualcurrent circuits. Open the switch and set testresistor for 7 ohms. Adjust current for 10amperes. Check again MF and MC taps at whichreactance unit just closes and opens. Note thetaps – they should be the same as for reactoronly value within one MF tap. If the new taps atwhich the reactance unit closes is higher than the“reactor only value” increase slightly the RM2resistance; if it is lower, then decrease slightlyRM2 resistance.

Continue to adjust RM2 until the MC, MF taps arethe same as for “reactor only” – part of test. If dif-ference in taps is too large, recheck taps with“reactor only” and use new taps value as check.Reduce the test resistor to about a half of the per-vious setting (3-4 ohms). Readjust current for 10amps. Check MC and MF taps again. The reac-tance unit should close and open again withinone MF tap. If difference in MF tap is larger thanspecified, readjust RM2 resistor until all threetests (with “reactor only”, with 7 ohms resistorand 3 ohms resistor) will close and open at thesame MC and MF taps (within one MF tap). Ener-gize T2X and T3X-telephone relays with the ratedvoltage, across terminals 5 and 6 and 5 and 4.

Zone 3 – Phase Angle Adjustment

MC MF+10 TO TL+( )

X test-------------------------------=

I.L. 41-496K

22

Set TL = TO = .8 ohms. Use test reactor that hasapproximate reactance of 5 ohms and test resistorequal to 24 ohms (250 watts). Set RM3 resistorlocated on the bottom left-hand side, to measure,1020 ohms. Follow the same procedure as describedunder Phase Angle Adjustment for zone 1 and 2,except adjust current for 3.0 amperes and use first24 and then 12 ohms resistance in series with reac-tor. The approximate tap value is computed as fol-lows:

9.3. Compensator Check

Accuracy of the mutual impedance T of the compen-sator is set within very close tolerances at the factoryand should not change under normal conditions. Themutual impedance of the compensators can bechecked with accurate instruments of the high inputimpedance type by the procedure outlined below:

1. Set TO = TL = 1.1

2. Disconnect Z1 and 2.5Z3 leads from MC and MF

taps.

3. Pass 10 amp ac current in terminal 14 out termi-nal 17 (with 15 and 16 jumpered together).

4. Measure voltage across Z1 leads. It should mea-sure 22 volts (±3%).

5. For Z3 compensator check operate telephonerelays T2X and T3X. The voltage across 2.5Z3

leads should be equal to 55 volts (±3%).

9.4. Ratio Discriminator Transformer Check

With relay connected per Figure 13 (page 14) mea-sure current in the polar element by inserting a dcmilliampere in series with polar unit coil.

With 1 amp passed through the relay the dc currentthrough the polar element should measure .70 milli-amperes (±10%).

9.5. Ratio Discriminator Calibration

1. For best results, the calibration should be donewith relay in the case. Adjust the contact screwsto obtain a .050” contact gap such that the arma-ture motion between the left- and right-hand con-tacts is in the central part of the air gap betweenthe pole faces. Tighten the contact locking nuts.Approximate adjustment of the two magneticshunt screws is as follows:

Screw both shunt screws all the way in. Then

back out both screws six turns, pass 1 ampere atrated frequency in terminal 17 out terminal 16.Screw in the right-hand shunt until the armaturemoves to the left. If the armature moves to theleft as less than 1 ampere. Screw out the fight-hand shunt until proper armature action isobtained.

Reduce the current until the armature resets tothe right. This should happen at .4-.5 amperes. Ifarmature resets at less than this value, it will benecessary to advance the left-hand shunt toobtain the desired dropout.

This in turn will require a slight readjustment ofthe right-hand shunt. Recheck the pickup anddropout points several times, and make anyminor “trimming” adjustments of the shuntscrews that may be necessary to obtain correctcalibration. If the above procedure does not givesufficiently high dropout, a small amount of fur-ther adjustment can be obtained by advancingthe left-hand contact screw a fraction of a turn.As finally adjusted, the contact gap should be atleast .45” and the action of the armature shouldbe snappy at the pickup and dropout points.

Just above the pickup current, there may be aslight amount of contact vibration. Make a finaladjustment of the two left-handed contact screwsto obtain equal vibration of both contacts as indi-cated by a neon lamp connected in the contactcircuit.

Pass 50 amperes ac for a short moment throughthe relay, recheck pickup. Readjust shunts ifthere is a change in pickup. Apply 50 amperesagain. Recheck pickup and dropout severaltimes until there is no change in pickup and drop-out before and after 50 amps are applied.

2. Remove 1080 ohm resistor. Apply 225 Vdcacross terminals (12 and 11) and (13 and 11)with plus polarity on terminals 12 and 13. Mea-sure current in series with terminal 11 and a10,000 ohm resistor. It should be below 0.5 milli-ampere. Reverse polarity and apply 125 Vdc.The current should be approximately 9 milliam-peres.

3. Apply 25 volts dc from terminal 11 to terminal 18,with positive polarity on terminal 11. The currentshould read approximately 12 mA. Reverse thepolarity and apply 10 Vdc the current should readapproximately 10 mA.

4. Apply about 3 amps of ac current to terminals 17and 16. Measure dc voltage from left-hand polar

MC MF+25 TO TL+( )

X test-------------------------------=

I.L. 41-496K

24

Figure 18. Outline – Drilling Plan for Type KDXG – Relay in FT-42 Case

* Sub 19

57D7905

* Denotes change