Development of Measurement System for DC Integrated Charge at High Temperature

We have proposed a “direct current (dc) integration charge (DCIC-Q(t)) method” as a new degradation diagnosis technique that can be applicable to various insulating materials used for electrical equipments. In our previous work, we evaluated the reliability of the measurement results obtained using the DCIC-Q(t) method by comparing with results obtained using PEA (pulsed electro acoustic) method at room temperature. While the results obtained at room temperature were corresponded each other, however, in recent years, a demand of diagnosis at high temperature has been increased, and it is necessary to apply the DCIC-Q(t) method to the measurement at high temperature. Therefore, we tried to improve the system to be applied to a high temperature measurement. Using the improved system, we measured the Q(t) in film samples of polypropylene (PP) and polystyrene (PS) at 80°C under dc stress from 20 kV/mm to 80 kV/mm. Furthermore, to confirm the measurement results of DCIC-Q(t), space charge accumulation behaviors in them were also observed using PEA method under the same condition. As a result, charge injection and accumulation were clearly confirmed in the results obtained using the both methods. Thus, by these measurement results, it is confirmed that the improved DCIC-Q(t) measurement system for high temperature is effective for the diagnosis of insulating materials.