1. Transformer DC resistance test

Measurement purpose: welding quality of winding joints; short circuit and open circuit between winding turns; tap switch contact;

Apparatus and principle: DC resistance bridge and constant current source R=U/I balance bridge

Note: Poor contact of tap changer: switch contacts are not clean; electroplating layer is off, spring pressure is not tight; poor welding; poor external contact;

2. Transformer ratio group test

Purpose of measurement: the accuracy of the winding turns ratio; the accuracy of the tap switch gear position; whether the winding has short-circuit between turns; whether it can be operated in parallel;

Use instrument and principle: ratio electric bridge; U1/U2

Note: Tap switch wrong gear: wrong tap switch position indication; short circuit between winding turns;

3. Transformer insulation resistance test

Measurement purpose: check the insulation status of the transformer;

Apparatus and principle: digital megohmmeter, insulation resistance tester; electric field force

Note: The surface is dirty; the interior is damp;

4. Transformer dielectric loss factor test

Measurement purpose: to check the overall dampness and insulation aging of the transformer; deterioration of oil quality; concentrated defects of small-capacity equipment;

Apparatus and principles used: QSI Xilin bridge, dielectric loss bridge; balanced bridge

Note: The surface is dirty; the interior is damp; the oil quality is degraded;

5. Transformer DC current leakage test

Measurement purpose: check porcelain insulation cracks; local insulation looseness and fracture; deterioration of oil quality;

Use instrument and principle: DC device; rectifier circuit

Note: The surface is dirty; discharge in time after the test;

6. Precautions for transformer insulation resistance test and dielectric loss factor test

1. Current transformer with and without final screen;

2. End shielding method of electromagnetic voltage transformer;

3. Self-excited method of capacitive voltage transformer;

Seven, transformer AC withstand voltage test

Measurement purpose: An effective method to check the insulation strength of transformers, which is very effective for defects such as insulation moisture, cracks, loose windings, insufficient lead distance, and impurities in the oil;

Use instrument and principle: series resonance

Note: The last screen is not grounded; the quiet time is not enough; the distance between surrounding leads and other objects;

8. Transformer partial discharge test and induction withstand voltage test

Measurement purpose: to detect whether there is partial discharge in the internal insulation of the transformer; to check the longitudinal insulation of the transformer

Use instrument and principle: series resonance, parallel resonance

Note: The last screen is not grounded; the silent time is not enough; use a pressure equalizing cover;