Simultaneous observation of electroluminescence and dissipation current waveform in LDPE film

Polyethylene (PE) is widely used as an insulating material for power cable. Recently, the simultaneous observation system for electroluminescence (EL) and dissipation current waveform has been developed by authors. By using this system, the simultaneous observation in low-density polyethylene (LDPE) film was carried out at 50, 100 and 200 Hz, respectively. From the results of experiments, the relation between the time and spatial distributions of EL and the dissipation current waveforms were carefully examined. At the 1^st 50 Hz electric field application, the plenty number of EL pulses have occurred. Also, at the consecutive experiments at 100 and 200 Hz, the number of EL pulses shows the positive frequency dependence. However, at the 2^nd 50 Hz electric field application just after that at 200 Hz, the number of EL pulses extremely decreased compared with 1st application. On the other hand, the nonlinearity of dissipation current at the 1^st 50 Hz application seems to small compare with that at the 2^nd application. The fundamental component itself at 1^st one is smaller than that at 2^nd one. The EL images showed that EL occurred at the multiple weak points within the circular observation area. The spatial distributions of EL are almost same for all frequencies. It is considered that a lot of recombination center in material will exist in initial. But the long period ac high field application makes the number of recombination center decrease. This decrement due to occupation by carrier leads the carrier density increase and it may cause the nonlinearity of dissipation current waveform.