Capacitor Voltage Transformer (CVT) TanDeltaTest

Image Credit - Pixabay: CVT test 

A Capacitor Voltage Transformer (CVT) is an essential component in high-voltage power systems, primarily used for voltage measurement and protection. Electrical testing of a CVT ensures its proper functioning, accuracy, and insulation integrity.

Here are the common electrical tests performed on a CVT:

⭕ Capacitance & Dissipation Factor (Tan Delta) Test:

 ✅ Measures the capacitance and insulation loss (dissipation factor) of the capacitor divider.

 ✅ Helps detect moisture ingress and insulation degradation.

⭕ Ratio & Phase Angle Error Test:

✅ Verifies the transformation ratio and phase displacement between primary and secondary voltages.

✅ Ensures accurate voltage measurement for metering and protection.

⭕ Insulation Resistance (IR) Test:

✅ Measures the insulation resistance between different parts (HV to ground, HV to LV,LV to ground etc.).

✅ Typically performed using a Megger at 500v .1 kV, 2.5 kV, or 5 kV.

⭕ Power Frequency Withstand Voltage Test:

✅ Applies a high voltage (50 Hz or 60 Hz) to check insulation strength.

✅ Confirms the CVT can handle system voltage without breakdown.

⭕ Lightning Impulse Test:

✅ Simulates lightning strikes to verify impulse voltage withstand capability.

✅ Usually applied as a standard 1.2/50 µs waveform.

⭕ Partial Discharge Test:

✅ Detects small insulation defects by measuring partial discharge levels.

✅ Performed at different voltage levels to assess insulation integrity.

⭕ Secondary Burden Test:

✅ Evaluates the performance of the secondary winding under load conditions.

✅ Ensures the CVT delivers accurate voltage under real-world operating conditions.

Conclusion:

CVT testing ensures accuracy and insulation integrity. Key tests include Capacitance & Tan Delta for insulation health, Ratio & Phase Angle for voltage accuracy, and Insulation Resistance for insulation strength. Other tests like Power Frequency, Lightning Impulse, Partial Discharge, and Secondary Burden verify withstand capability and performance under load.