Test on Power Transformer Before Commissioning

  

There are following test to be performed before commissioning of power transformers as per Indian Standard Code.

Inspection	Junction box and marshalling kiosks Control panel, relay panel etc.
Primary injection test	To check operation and stability of earth fault relay on high voltage side and low voltage side line directional elements of high voltage relays Over-current relays on low voltage side Over-current relay on high voltage side ( when current transformers are not in transformer bushings ) Earth fault relay on low voltage side Test on high speed neutral ammeter Voltage compensation
Secondary injection	Performed on transformer protection relay
Ratio test	When 415 V applied on high voltage side, measure the voltage between all phase on low voltage side for every tap position of high voltage Measure the voltage         A to a , b and c        B to a , b and c        C to a, b and c  Where A, B and C are three phase terminals of high voltage side whereas a, b and c are terminals of low voltage side Magnetic balance test
Tripping tests	High voltage Low voltage Inter-tripping tests Winding temperature trips
Calibrate earth resistance
Buchholz relays	Check that there is no air in protector before commissioning When energizing transformer, close in on – trip – etc. Test for angle, air injection etc Check for stability when oil pumps are started – at ambient temperature and at winding temperature of 80 degree or above
Alarm circuit	Buchholz relay Oil and winding temperature thermometer Cooling gear failure
Fan & pumps	Check that oil valves are open in cooling circuit. Check that rotation of pumps, automatic starting overloads devices etc. Check stability of Buchholz relay
Tap changing test	Check mechanism, indication, buzzer , lamp etc.
Phasing tests	At 415 V Between transformers in a bank To prove internal and external connections for parallel operation On auxiliary supply and voltage transformers
Insulation test	High voltage winding and low voltage winding On current transformer and voltage transformers
Oil test	Check oil level Dielectric test Volume resistivity Acidity Tan delta Water content
Load test	Voltmeter and ammeter on both high voltage and low voltage side Over current No spill in high voltage star point No creeping of contacts on both high and low voltage earth fault relays Directional elements – low voltage directional over current and earth fault relays Voltage compensation
Voltage compensation test ( If compensating CTs are fitted )	Primary injection test Load test
Check neutral earthing switches are closed before connect with live
Check transformer on equal taps before switching in	For transformer in bank For transformer in parallel
If necessary, arrange temporary protection for soaking and switching in ( example – unrestricted earth fault, if soaking from low voltage side 113 V and 213 V open )
Tap changing test on load over full range of taps
When transformer rating above 1000 MVA, energizing of transformer for the first time, voltage should be build up gradually
Low voltage excitation current measurement
Single phase magnetic balance test

 

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