Partial Discharge Tester

Additionally, the operating bias voltage (threshold voltage) between the Gate and Emitter or between the Gate and Source of each module may be provided by individual transformers. These transformers may have a high voltage difference with high frequency between their primary and secondary sides. When the insulation capability between the primary and secondary sides of a transformer is insufficient, the surges of continuous abnormal discharge may interfere with the digital control operations and result in transistor failure.

Although the wires used in the transformers may have sufficient withstand voltage capabilities (e.g., 3000V) by themselves, when the coils/wires on the primary and secondary sides are very close to each other, it may appear that the wires can withstand a relatively high voltage (e.g., 6000V). However, in fact, after operating a period under the typical voltage (e.g., 1000V), insulation failure may occur. Because the permittivity of the general wire’s insulation layer is much greater than that of air, the voltage division ratio across the air gaps between the wires is relatively high. When the voltage across the air gap between the wires is >350V (the discharge inception voltage for the shortest air distance at 1 atm), PD begins to occur on the partial surface between the wires. Because the insulation layer of the wires does not deteriorate or get damaged immediately, the insulation layer gradually carbonizes after continuous use over a period of time, ultimately leading to a short circuit on the primary and secondary sides of the transformer (Figure 4).

Photocouplers and digital isolators are used in various environments that require isolation. When the isolation voltage is applied across insulation materials that contain voids or cracks, the voltage across the voids or cracks may be sufficiently high to cause PD. After long-term degradation, the voltage isolation fails due to the insulation failure of the insulation material (Figure 5).