Threshold electric field of conductance and space charge in PMMA under DC field

PMMA is the standard sample of space charge detection in IEC/TS 62758–2012, but its reference electric field has a wide range of recommended values at room temperature and does not involve high temperature environment. Based on the space charge response and high field conductance detection of PMMA under DC electric field, the threshold electric field of charge accumulation and conductance in samples at different temperatures is analyzed, and the correlation between the two parameters is discussed. The results show that obvious space charge accumulation occurs in the sample when the electric field intensity is higher than about 14.95kV/mm at 30°C. At 50°C, the polarization electric field threshold of space charge accumulation in the sample is about 10.24kV/mm. With the increase of the electric field intensity, the heteropolar charge near the cathode gradually increases, while a large amount of homopolar charge accumulates first and then is partially replaced by heteropolar charge near the anode, finally manifesting the accumulation of homopolar charge. As the temperature rises, the conductivity of PMMA tends to increase, while the polarization electric field threshold of obvious space charge accumulation inside the sample decreases, which indicates that the increase in temperature will promote the impurity dissociation inside the sample and the hole injection at the electrode side. In addition, it is advisable to observe charge accumulation at a threshold electric field lower than 10kV/mm to reduce the measurement error under higher temperature test conditions.