Testing of Transformers
Testing of Transformers
Testing of Transformers
Preliminary Tests
•
• %Z = (test voltage/rated voltage) x (rated current/test current)x100
• While measuring load loss and impedance at
different tap positions, readings should be taken
quickly, and the interval between measurements
at different taps should be adequate to avoid
significant errors due to momentary temperature
rise of windings
• The difference in temperature between the top oil
and bottom oil should preferably be small to
enable the average temperature to be determined
accurately
• Three wattmeter method should be used
instead of two wattmeter method to avoid
large value of wattmeter multiplier constant
• The power factor during load loss test can be
less than 0.1 and wattmeters suitable for such
low power factors should be used
• Tolerances
4. Measurement of no load loss and current
• For normal flux densities and frequencies of 50Hz and 60Hz, P 1 and
P2 are each 0.5 for grain oriented steel
• P1 and P2 are 0.7 and 0.3 , respectively, for no-grain oriented steel
5. Measurement of Insulation Resistance