79 / 2018-08-23 21:55:30

Space Charge Behavior in PE under High Pressure and High Voltage over Long Time

space charge, PIPWP, high hydrostatic pressure

Polyethylene (PE) is widely used as insulation in submarine DC cables due to its excellent dielectric property and mechanical performance. However, the problems caused by space charge will threaten the fatigue life of the insulators and the DC cables. Space charge accumulated in the bulk of dielectric materials may result in local electric stress enhancement and is indicated to play an important role in the degradation and even premature breakdown of insulators for high-voltage application. Yet the behavior of space charge under high hydrostatic pressure in insulating materials has not been extensively studied though they may have an important influence on charge injection and charge trapping. Considering the extremely harsh undersea environment such as the very high pressure, it is significant to study the space charge behavior on these conditions. In this paper, behavior of space charge over a long period of time was detected by PIPWP method.

Nowadays, with the wide use of polyethylene in electrical insulators, especially in power cables, the problems caused by space charge have attracted increasing attention. The effect of micro-voids in insulating materials has not been extensively studied though they could have a dramatic influence on charge injection and charge trapping in insulating materials. Considering the extremely harsh undersea environment such as the very high pressure, it is significant to study the space charge behavior on this condition. Thus, based on Piezoelectric Induced Pressure Wave Propagation (PIPWP) method, a pressure device and measurement system were designed and improved.

A dedicated setup comprising a Piezoelectric Induced Pressure Wave Propagation (PIPWP) measurement system, consists of static pressure generating device, high speed periodic pulse power, acoustic pulse generator, sample bin and measuring circuit, has been developed. With this setup, linear low density polyethylene (LLDPE) planar samples are subjected to 100 MPa.

Space charge distribution has been measured by the PIPWP measurement system with the sample applied 10 kV for 25h at standard atmospheric pressure and 100MPa pressure, then short-circuited The measurement results show the space charge distribution applied for 10kV for 25h after the short-circuit.

In this paper, a dedicated setup comprising a Piezoelectric Induced Pressure Wave Propagation measurement system inclosed with the sample between two steel mold and subjected to high hydrostatic pressure has been developed. The typical experimental results revealed that the system is suitable and reliable to monitor the internal charge distribution. The hydrostatic pressure may have a direct influence on reducing the charge injection or the charge trapping. Over long period of time measured by the device, compared to standard atmospheric pressure, the injection of space charge is obviously less under high hydrostatic pressure (100MPa). With this system, further research about space charge behavior under high hydrostatic pressure will be carried on in the future.