The growing requirement for reliability of insulation systems gives researchers more responsibility to investigate new techniques of monitoring and diagnosis of dielectrics. It is well known that the presence of space charge plays an important role in premature failure of polymeric high voltage cables. Space charge surveillance is becoming the most generally used skill to evaluate polymeric materials, particularly high voltage cables. The well-known pulsed electroacoustic method (PEA) is a reliable non-destructive method. It gives a reasonable resolution about the concentration of the space charge in the insulation material. The main tasks in this project were carried out using PEA technique to measure space charge in low density polyethylene.
A sudy into space charge formation and distribution at the interface of a multi-layer sample under dc and ac applied voltage was initially carried out. Electrode materials and frequency are two important factors to determine the charge injection and distribution. It has been found that the interface between films acts as traps for charge carriers, especially for electrons. Positive charge has high mobility compared to negative charge shown from this interface study. An advanced PEA measurement system with high rate test and excellent phase resolving capability was then designed. Compared with the typical PEA system the new one can provide enhanced experimental results for transient situations, achieving high-quality diagnosis for the typical industrial conditions such as dc cable polarity reversal and transient voltage failure.