ABB KD-10 Instruction Leaflet page 4

41-490J
V = 1.5 V
X AN
Note that 3I = 0 for 3-phase faults
0
Phase B and phase C tripping unit voltages are:
V = V
Y
V = V
Z
For a fault at A, beyond the relay operating zone, the
compensator voltage, -1.5I
voltage, reducing the voltage triangle of the tripping
unit to X-Y-Z. With an X-Y-Z rotation the tripping unit
torque is in the restraining direction.
For a fault at B the current is larger than for a fault at
A, so that -1.5I T is larger. The point X is in line with
A
points Y and Z. No torque is produced, since the
X-Y-Z triangle has a zero area.
For a fault in the operating zone, such as at C, point
X is below the YZ line. Now the rotation is X, Z, Y,
which produces operating torque.
For a fault behind the relay at D, restraining torque is
produced. Since the fault is behind the relay the cur-
rent is of reversed polarity. Compensator voltage,
-1.5 T, increases the area of the bus voltage trian-
A
gle, A-B-C. Tripping unit voltage has an X-Y-Z rota-
tion which produces restraining torque.
A solid 3-phase fault at the relay location, tends to
completely collapse the A-B-C voltage triangle. The
area of the X-Y-Z triangle also tends to be zero un-
der these conditions. A memory circuit in the KD-10
relay provides momentary operating torque under
these conditions, for an internal fault. In the KD-11
relay the winding Z in the current circuit, in conjunc-
tion with the compensator voltage, produces a cur-
rent-only torque, which maintains operating torque
under the condition of zero potential. In the short
reach relay the offset is obtained by means of an ad-
ditional compensator T
BR
The P - R parallel resistor-capacitor combina-
3A 3F
tion in the compensated phase provides correct
phase-angle relation between the voltage across the
front and back coils of Z (3φ) and the current, similar
phase shift is produced in left and right hand coils by
capacitor C . The P
3C 3A
vides control of transients in the coils of the cylinder
unit.
3.2 PHASE-TO-PHASE UNIT
Compensator primaries of T
gized by I , I and I
A B
4
-1.5 I T [Equ. 1]
A
[Equ. 2]
[Equ. 3]
BN
[Equ. 4]
CN
T modifies the phase A
A
.
-C combination also pro-
3A
and T are ener-
AB BC
as shown in Figure 19
C
Type KD-10 and KD-11 Compensator Distance Relay
(page 50). Compensator secondaries are connected
to modify their respective phase voltages (e.g., T
modifies V ). With a fault in the trip direction, the in-
AB
duced voltages in the compensator secondaries
buck the phase-phase voltages.
Vector diagrams in Figure 9 (page 41) illustrate the
operation during phase B-C faults at four locations.
The system impedances and the compensator angle
are assumed to be at 90
Prefault voltages are depicted by the large dashed
triangles. The smaller light triangle in each case is
the system voltages at the relay location during the
fault. This triangle is modified by the compensator
voltages -(I -I ) Z and -(I
A B C
sator mutual impedance. In this case I
minals of the tripping unit are designated; X, Y, and
Z. Tripping unit voltages for phase B-C faults are:
V = V
XY
V = V
ZY
For a fault at A, in Figure 9 (page 41) beyond the re-
lay operating zone, the compensator voltages
change the A-B-C voltage sequence to the X-Y-Z se-
quence. Voltages of this sequence applied to oper-
ating unit produce restraining torque.
For a fault at B, the currents are larger than for a fault
at A, so that compensator voltages are larger. Points
Y and Z coincide now and the area of the X-Y-Z tri-
angle is zero. No torque is produced.
For a fault in the operating zone, such as at C , the
compensator voltages reverse the rotation of trip-
ping unit voltages to X-Z-Y sequence. Voltages of
this sequence applied to operating unit produce op-
erating torque.
For a fault behind the relay at D, restraining torque is
produced. Since the fault is behind the relay, the cur-
rent is of reverse polarity and tripping unit voltage
has an X-Y-Z rotation. This rotation produces re-
straining torque.
Note that this unit does not require memory action,
since the sound-phase voltage reacts with the com-
pensator voltage to produce a strong restraining or a
strong operating torque, depending upon the fault lo-
cation. This is true even for a complete collapse of
t h e f a u l t e d p h a s e - t o - p h a s e v o l t a g e . T h e
phase-to-phase unit is identical in the KD-10 and
KD-11 relays.
Similar vector diagrams apply for a fault between
phases A and B or between phases C and A. Each
°
, for illustrative purposes.
-I ) Z Z is the compen-
C B C. C
= O. The ter-
A
-(I -I )Z
AB A B C
-(I -I )Z
CB C B C
AB
[Equ. 5]
[Equ. 6]