sets until synchronization is accomplished.
Exercise extreme care not to
This relay is identical to the K16 relay used
touch exposed electrical connec-
in the mode II relay box assembly. Refer
tions when working inside precise
relay box with generator set
d. The electronic components assembly
(A6) consists of C1, R4, and R5. The
assembly connects to the governor control
Remove cover from precise relay
unit and acts as a feedback circuit to pro-
box to gain access to test points,
stabilization. This assembly is identical
1. With the generator set at rated
to the A6 assembly used in the mode II relay
speed and voltage, measure the voltage
from terminal 1 to terminal 2 of the K12
e. The governor paralleling control is
relay. Nominal voltage is 120 VAC.
a rheostat (R28) which permits initial
2. If the voltage at terminal 1 and 2
matching of the governor paralleling cir-
is normal and fault light is still illuminated,
cuits for sets operating in parallel. Its
remove the wire from terminal 6 of K12
function is to ensure proper real load shar-
relay and reset fault 1 amp. If fault lamp
ing. It has a slotted shaft with locking
can be reset, relay K12 is defective.
device which when rotated counterclockwise
will cause an increase in signal appearing
3. If the voltage at terminals 1 and
2 is normal and the contactor CB2 will not
erator to assume a greater share of the
close, measure the voltage from terminal
load. This rheostat is identical to the R28
3 of K12 to TB3-1. Voltage should read
20-32 VDC, with the contactor switch S3
rheostat used in the mode II relay box as-
in the closed position. Measure the volt-
age from terminal 4 of K12 to TB3-1.
6-1880 50/60 HERTZ UNDER FREQUENCY
Voltage should read 20-32 vdc with the
contactor switch S3 in the closed position.
If no voltage, is present, replace relay K12.
6-189. ON EQUIPMENT TEST.
4. Reduce frequent y below 54 Hz
a. Symptom and Isolation of Malfunc-
(45 Hz for 50 Hz sets); relay should trip.
tion. A malfunction of the underfrequency
If not, replace relay.
relay K12 is usually indicated by the illu-
mination of the UNDER FREQUENCY fault
light or by failure of the load contactor to
tag, then disconnect wiring to the under-
frequency relay. Remove the four screw
normal. To isolate the malfunction, pro-
assemblies securing the relay in posi-
ceed as follows: