*Polyimide for Electronic and Electrical Engineering Applications*

**Figure 3.**

*Schematic diagram of the space charge measurement system for high temperature up to 80 °C.*

*Space Charge Accumulation Phenomena in PI under Various Practicable Environment DOI: http://dx.doi.org/10.5772/intechopen.96786*

temperature, the P(VDF/TrFE) is used as the piezo-electric sensor. By combining the sensor and a water-cooling system, the space charge measurement at maximum 150 °C becomes possible. A band heater is fitted to the high voltage electrode unit to increase temperature of the sample. In ordinary PEA measurement, to improve an acoustic impedance matching between the sample and the metallic electrode, a semiconductive (SC) layer, which is used for power transmission cable, is used for a high voltage electrode. However, the base material of this SC layer is usually polyethylene, and it is not available at high temperature. Therefore, in such high temperature measurement, we used a SC layer made of PEEK. In all measurements, the positive voltage was applied to the sample through the upper SC electrode.
