Appendices
25
5.3 SENSIBLE ADDITIONAL CHECKS
5.3.1
BEFORE SWITCH ON, ENSURE that
a) All the Oil Shut-Off Valves are OPEN and Draw-Off Valves are
CLOSED.
b) All Thermometer Pockets are near filled (85%) with oil.
c) Oil is at correct level in the Bushings, Conservator, etc.
d) Desiccant colour in breather is blue for blue silica-gel or yellow /orange
for envirogel.
e) Earthing Connection of Main Tank, Neutral Bushing, Marshalling Box,
Control Gear Box, Cable Box, Arcing-Horn, etc., are correctly made.
f) Bushing arcing horn gap is set correctly.
g) All CT Secondary Circuits are closed.
h) All Air-Release Plugs of Main Tank, Radiator, Conservator, Buchholz
Relay, Bushings, etc., are free of air pocket / bubbles.
Note: After Oil-Filling or Before Commissioning, AT LEAST 12hrs
should be allowed for the oil to settle-down and air is released from all
points at 2 hourly intervals.
5.3.2
It is recommended that the transformer is initially energised at NO-
LOAD only and checked for any abnormalities for the next 6 to 8 hours.
5.3.3
AFTER SWITCHING on no-load, if the Primary Side Circuit Breaker is
tripped, investigate the cause thoroughly and re-energise the transformer
ONLY AFTER ensuring that the fault is properly cleared.
5.3.4
If satisfactory (transformer on No-Load) then apply load gradually and
observe for any abnormalities for the next 6 to 8 hours.
5.3.5
If the transformer is satisfactory on-load up to 50% for the first 4-8
hours, shut-down the transformer and ensure that all air-release plugs of tank,
radiator, conservator, buchholz relay, bushings, etc., are free of air pockets
which might have developed during initial loading.
A - 7
