Corona discharge tester
XT-281

Overview

According to the evolution of power electronics and growing demand of energy saving, the inverter driven motor is largely produced as the motor of air conditioner, washing machine and refrigerator and so on. Recently the production of the motor started, beyond the appliance, for the automotive such as Electric car.
The conventional insulation test was done with direct current and commercial frequency. But the impulse voltage comes out repeatedly from the inverter so that new measurement method and test equipment is required.
The product or part driven with inverter is used not only for motor of air conditioner and refrigerator but also for power source of fluorescent lamp and air cleaner and so on.
Accordingly, the measurement using impulse voltage is essential for the part such as transformer, coil, printed circuit board, connector, connecting cable used for these products.
The corona discharge tester XT-281 performs the discharge test applying the test voltage similar to that of repeated impulse voltage of the real inverter.
The corona discharge tester XT-281 detects Flashover and Corona Discharge.
The Flashover accompanies light and sound consuming high energy so that gives large damage to the target product and part resulting operation failure instantly or in short time.
On the other hand, Corona Discharge is generated with the ionization of air and the action is weak so that the operation of the product or the part will rarely fail in short time. But due to the oxidation with ozone generated at Corona discharge or damage with heat, the insulation degradation occurs according to time that leads the Flashover to generate the operation failure

Operation

When gate voltage is kept ON for a set interval, the current flowing through IGBT increases with time. The flowed electric energy is stored in internal inductance mainly as magnetic energy and also stored in the coil when the DUT (Device Under Test) is inductive.
When IGBT is turned off, magnetic energy is converted to high voltage electric energy and resonates in the circuit composed of internal inductance, internal capacitor and the DUT and the oscillating waveform attenuates with time.
When resonant frequency becomes high with only the stray capacitance of the DUT, the oscillating frequency may be adjusted by the internal capacitor.
When the DUT is capacitive between coil and core, an attenuating sine wave can be generated by the internal inductance.

XT-281 detects the presence of Corona Discharge and Flashover each time an intermittent test signal is applied.

Corona DischargeCorona Discharge is detected in the current flowing through the DUT.
The discharge rate (0-100%) is displayed when Corona Discharge is detected (See “Discharge rate” in Section 8). (It is not indication of electric charge)

FlashoverFlashover is detected with the voltage change in the applied test signal.
The count (0-127) is displayed when Flashover is detected.