Space Charge Measurement and Electroluminescence of Aged LDPE

Polymeric insulation aging is related to the change of its different properties. An attempt is tried to relate the Fourier transform infrared (FTIR) absorption spectra, space charge distribution and electroluminescence (EL) behaviors of aged polymers. Low density polyethylene (LDPE) samples are aged in a thermal aging oven with different periods, and the FTIR absorption spectra is used to analyze the change of their molecule structure. There are mainly two new elements at ~1725 and 3380μm corresponding to carbonyl and hydroxyl groups occurred due to the oxidation. The pulsed electro-acoustic (PEA) method is employed to measure the space charge distribution under different electric field intensity and for different aged materials. A sensitive photon counting module (PCM) is employed to measure the weak EL emission from each sample under 50 Hz ac electrical stresses. All EL experiments are performed in a vacuum chamber to avoid the influence of gases or impurities absorbed on the sample surface. It is found that aged LDPE samples show a relatively lower EL initial voltage than that of sample without aging. New products resulted from aging would act as the traps to capture charge carriers, possibly leading to the differences of space charge distribution for different aged samples, and henceforth affecting the light emission from different LDPE samples.