I.L. 41-490H
12
or inserted by locking two nuts on the stud and then
turning the proper nut with a wrench.
For detail information on the FT case refer to I.L.
41-076. The relay contacts should stay open with
panel de-energized.
9.
EXTERNAL CONNECTIONS
Figure 19 shows the connections for 3-zone protec-
tion utilizing the TD-4 timer. Figure 24 is similar to
Figure 19 except that the TD-52 timer is used in-
stead of the TD-4. Figure 20 and Figure 21 show the
use of a 15/5 auxiliary current transformer so that the
CT neutral may be formed elsewhere.
Ac connections for additional applications are shown
in Figures 20, 21, 22 and 23. Three of these, Figures
20, 21, and 22 apply when the transmission line is
terminated in a power transformer, and when low
side voltage and current are used to energize the re-
lays. In calculating the reach setting, the bank im-
pedance must be added to the line impedance.
For the case of a wye-delta bank (Figures 21 and 22)
the voltages and currents are phase-shifted by 30;
however, this fact should be ignored, as the KD-10
a n d K D - 1 1 r e l a y s a r e n o t a f f e c t e d b y t h i s
phase-shift.
Figure 23 shows a KD-10 and TD-5 relay connected
for generator back-up protection.
10. SWITCHBOARD TESTING WITH
KD-10 AND KD-11 RELAYS
Immediately prior to placing the relay in service, the
external wiring can be checked by manipulating the
current and voltage applied to the relay. If such a
check is desired, refer to Appendix A for the proce-
dure.
10.1 Current Voltage Relays with Mutual
Reactor Precautions
Relays which include compensators to modify the
applied voltage (such as the KD types) will produce
an output at their voltage terminals when the current
circuits are energized.
Thus, it is possible to pull potential fuses and still
have v oltage a ppear o n the relay side of the fuses.
The magnitude of this voltage is dependent on mag-
nitude of load or fault current, relay settings, relay
impedance, and other potential circuit burden con-
nected in parallel with the relay containing the com-
pensator.
To avoid any difficulties due to interaction between
current and voltage circuits, it is recommended that
when PT fuses have been pulled to permit work on
voltage circuits, that these circuits should not be
considered safe until the current circuits have been
de-energized, or until the voltage circuits have been
shorted on the relay side of the fuses.
11. ACCEPTANCE TESTS
KD-10 and KD-11 relays have a very small number
of moving parts which might become inoperative.
Acceptance tests in general consist of:
a. A visual inspection to make sure there are no
loose connections, broken resistors, or broken re-
sistor wires.
b. An electrical test to make certain that the relay
measures the balance point impedance accurate-
ly.
11.1 Electrical Tests
An adjustable source of three-phase voltage and an
adjustable single-phase current along with a means
for varying the phase relation between current and
voltage are required for testing the relay. The volt-
age source may be either “open delta”, “closed del-
ta”, or “wye” connected. However, the relay operates
only on delta quantities since it has no neutral con-
nection.
Check electrical response of the relay using test
connections shown in Figure 25. Figure 26 features
the same connections except shows the use of addi-
tional switches that facilitate fast switchover from
“phase-to-phase” fault mode to “three-phase” fault
mode. Test connections, referred to in the test pro-
cedures, are the same on both drawings. Accuracy
of the test results will depend to large degree on the
accuracy of the instrumentation used. In general, it is
advisable to restrict instrument readings to the last
20 percent of the scale. For most accurate phase an-
gle readings use phase-shifter scale. This method
requires calibration of the scale using accurate watt-
meter (at 90
°
–0 watts and at 0
°
–maximum watts), or
an accurate phase angle meter.
