Trouble-Shooting - ABB UZE Repair Manual

Error condition
1ZSE 5492-128 en, Rev. 4
Fault finding procedure
1. After a pressure relay trip, the on-load tap-changer
and the transformer must be carefully investigated.
That means that the on-load tap-changer must be
drained and the front cover opened. Faults, if any,
must be repaired before the transformer is energized.
If both the on-load tap-changer and the transformer
are functioning properly, continue with the next step.
2. Carry out the insulation test of the pressure relay.
Proceed as follows:
Remove the cover of the relay housing. Disconnect
from the terminals all wires coming from the control
cabinet of the transformer.
Connect terminal NO (identified 61) on the pressure
relay block to earth. Terminal C (identified 62) should
be electrified with the megger (500-2000 V for one
minute).
Connect the pressure relay housing to earth. Short-
circuit the four terminals and apply test voltage 500-
2000 V on them for one minute. Remove the shortcir-
cuit from the terminals and reconnect the wires from
the control cabinet.
If the pressure relay does not withstand the electri-
cal stress, the pressure relay should be replaced, see
section 3.6 Replacement of Pressure Relay.
3. Carry out the function test. Proceed as follows:
a. Set the valve handle to the test position as shown
on the information plate.
b. Connect the air pump and the pressure gauge to
the test tap on the pressure relay. (Thread R 1/8").
c. Raise the pressure until the pressure relay trips the
circuit breakers of the transformer.
d. Read the pressure on the manometer and check
against the pressure stated on the information
plate.
Max. permitted deviation is ±10 %. If the deviation
is greater, the pressure relay should be replaced.
e. Check that the signal disappears when the pres-
sure is released.
f. After finishing the check, turn back the valve
handle to service position.

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