How is dielectric loss measured?

The transformer dielectric loss tester under HV Hipot Electric Co., Ltd. can help many power workers conduct various power tests more conveniently.

1. Safety Preparation

De-energize & Ground: Completely isolate equipment from power. Verify de-energization, discharge all test points, and apply safety grounds.

Environment: Humidity ≤80%, clean and dry surfaces.

2. Instrument Selection

Use a digital tanδ tester (select VFDS variable-frequency model for high-interference areas).

Test voltage typically 10kV (do not exceed equipment rated voltage).

3. Connection Modes

Windings/Capacitors: Direct mode (HV lead → test object HV terminal, measurement lead → LV terminal).

Bushing Taps: Reverse mode (HV lead → bushing conductor, instrument ground → tap).

CVTs: GST/Guard mode (excitation via secondary winding).

4. Procedure

① Connect HV lead to test object HV terminal, measurement lead to LV terminal. Ground instrument and equipment chassis.
② Set parameters: Voltage (10kV), frequency (50Hz or variable 40-70Hz), connection mode.
③ Start measurement. Record stabilized tanδ and capacitance (Cx) (takes ~1-3 minutes).
④ Temperature correction: Convert readings to 20°C reference (tanδ ≈ increases 1.5x per 10°C rise).

5. Anti-Interference

Always use variable-frequency mode near live equipment (avoid 50Hz noise).

Keep test leads short with shields grounded.

6. Result diagnosis

Normal: New equipment tan δ<0.5% (at 20 ° C).

Exception:

Tan δ increases by more than 30% compared to historical values → insulation degradation

Cx significantly increases → moisture intrusion

Cx reduction → insulation layer delamination risk

Critical value: tan δ>2% or doubled compared to previous tests.

7. Safety Warnings

Never touch leads during test!

Immediately re-ground bushing taps after measurement.

De-energize and discharge before disconnecting leads.