High voltage is generated between the layers of an electromagnetic transformer. Therefore, particular care for interlayer insulation and terminal processing is required. Flashovers are easy to determine because the transformer becomes unusable when they occur. However, corona discharges are more difficult to determine because the transformer operates with few problems.
If the electric field around an electromagnetic electrode is high, the air is ionized and corona discharges start. Application of consecutive pulses causes corona discharges to grow. In general, ozone is created along with corona discharges. Ozone has strong oxidation power and contributes to the degradation of insulating material in many cases and there are concerns that over the long term this may cause breakdowns due to flashovers.
This method, unlike the thyristor method, switches IGBT to off and then applies high voltage. Therefore, there no effects for the switching element and corona discharges can be detected.
The operation of this device is explained in Diagram 1.
After moving to the switch to ON, electric current i use increases over time and is stored in L1 as magnetic energy. When the switch is moved to OFF, the stored energy generates high voltage HV in the secondary coil, and corona discharges and flashovers occur.
This device is composed of two circuits: an excitation pulse generator circuit to generate the high voltage necessary for testing and a detection circuit to count the corona discharges and flashovers created by the high voltage.
Corona discharge tester