This article is about Energization of Transformer and precautions to be taken before Energization of Transformer.
Preparation for energization
Prior to energizing verify the following:
a) The oil level in the oil filled compartments
b) The drying agent and the oil level in the dehydrating breather
c) Check that all valves are set at the right position
d) Check that the transformer, the control cabinet and all accessories are cleaned and touch up painted if needed.
e) Check that the heating element in the control cabinet is connected and in operation.
f) Check that the gas-operated relay is purged of air.
g) Check possible leakage. If the transformer has been stored more than two months after the assembly, all sealing joints must be retightened.
h) Check that connections to lines, bus-bars and earth are properly made.
i) Check that the distances between phases and phase to earth are sufficient.
j) Check that the covers are installed on the test taps and/or potential taps (if no potential device is connected) of the bushings to assure proper grounding of the taps.
k) All temporary protective grounds have been removed from conductors.
I)All protective and alarm circuits are operational and placed into service before the transformer is energized.
m) Get confirmation that all installation procedures have been completed successfully.
n) Get confirmation that there are no current transformer secondary open circuits.
o) Set the cooling controls for automatic operation.
p) The control selector-switch for the on-load tap changer in the control cabinet is set on REMOTE position.
The transformer is ready for service upon the successful conclusion of the tests and completion of the set time.
Energization of Transformer
If possible the transformer should be energized in such a way that the voltage is increased step by step up to the rated voltage. This may be done by connecting the transformer to a generator by which the voltage is slowly increased. The higher the rated voltage, the more important to energize the transformer as described. If it is not possible to use a generator, the transformer may be connected directly to a live transmission line at no load.
After energizing, the transformer has to be kept under careful observation for the first 12 hours. Check and record the oil temperature, the winding temperature, its instrumentation, the tank pressure (if applicable) and ambient temperature. Watch particularly for any sudden changes.
When the transformer is successively loaded, observe carefully the transformer for a few hours, especially the temperature gauges and the gas relay.
The observation should continue on a daily schedule for seven days and then weekly for the first month of operation.
An oil sample should be taken after the first and twelfth month of operation for Gas-In-Oil Analysis. The results of these two analyses should be sent to the ABB representative as soon as they are known. This analysis should then be repeated annually. Energization of Transformer
Shut down and re- energization of transformers with lnertaire or Sealedaire Oil Preservation System
When you de-energize the transformer and plan to have it out of service for any reason, no special start-up/shut-down provisions are needed unless the transformer is provided with oil pumps. For FOA transformers follow this procedure:
De-energize the transformer. Run one half of the pumps until the unit reaches temperature equilibrium with the ambient. Do not run any of the cooling fans during this cool-down cycle. This procedure moves the oil past the interface with the gas blanket to speed up the release of nitrogen from the oil. Running just one half of the pumps will reduce the static charge build up and not running the fans prevents too rapid cooling.
Starting up after Shut Down
Run one half of the pumps for 15 minutes to one hour and then de-energize these pumps and run the other half of the pumps for 15 minutes to one hour. This will dislodge any pockets of nitrogen in the oil and move the gas past the oil to gas blanket interface. Do not run both sets of pumps at one time because this may cause static charge buildup.
Within twelve hours after running the second set of pumps, energize the transformer and set the cooling controls for automatic operation. This will allow the cooling to be initiated as required by the increasing winding temperature. Energization of Transformer
Shut down and re- energization of transformers with COPS Oil Preservation System
Transformers equipped with COPS oil preservation systems do not require the special shut down and start up procedures because there is no gas blanket on the transformer. Energization of Transformer