Page 270 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Testing of transformer (Fig 15)

Open circuit or no load test
Open circuit or No load test is conducted to find no load losses or core losses. The following steps are used to
conduct this test.

• Find I and find R and X
0 0 0
• HV kept open
• Easy to provide supply to LV
• Low range measuring instruments only needed

• Rated voltage is fed
• No load current is measured I 0
• No load loss/ Core loss shown by wattmeter
• OC Test
• The no load current in LV is only 2 - 10% of full load current
• HV side is open

• Copper loss in LV is negligible and nil in HV
• Hence the entire loss shown read in wattmeter is taken as CORE Loss

Fig 15

Short circuit test or impedance test (Fig 16)
The following steps are used to conduct the Short circuit test.
• LV side is short circuited
• Rated current is passed in HV side

• The voltage at HV side is only 5-10% of rated voltage.
• Flux is proportional to the voltage
• Voltage is very low, and hence flux too
• Core loss is dependent on flux setting loss

• Core loss value is negligibly small
• Wattmeter in SC test is considered as Copper loss only

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CITS : Power - Electrician & Wireman - Lesson 41-49