Experimental Study On The Partial Discharge Phenomena On Oil/paper Insulation System Under X-ray Irradiation

Insulation degradation can be caused by partial discharges (PD) in oillpaper insulation system of high voltage equipment, finally, causing IIY apparatus failur. With conventional PD measurement technique, it is difficult to increase the sensitivity of detecting PD and locate PD in the transfonners on site. Aiming at above problems, we proposed a new PD measurement technique in oil/paper insulation, calling as X-ray Inducing Partial Discharge Meaning. The limitation of conventional PD measumnent technique could be decreased by this method. The main contributions to XLPDM in the paper are as follows: l.Under AC voltage PD phenomena in cavities of oil/paper insulation induced by X-ray irradiation was investigated experimentally in this paper. It was found that PD inception voltage decreases by X-ray irradiation to cavities of oil/paper insulation. The X-ray Inducing PD Inception Voltage (XIPDLV) changes with cavity diameter and number. With X-ray irradiation the smaller cavity diameter is, and the more cavity number is, the lower XIPDIV is. When PD occurs in the cavities, the frequency and amplitixle of discharge pulses increase with X-ray irradiation under same voltage. The X-ray Inducing PD (XIPD) phenomena observed from the samples with gas cavities could be associated with photo ionization, effective electron increase for electron avalanches and decrease of the statistical time lag in cavities. These results will lead to an important significance in reducing the test voltages and improving PD sensitivity in cavities of oil/paper insulation under X-ray irradiation on site. 2.PD phenomena induced by X-ray irradiation in the oil-gaps of oil/paper insulation under AC voltage was investigated experimentally in this paper. It was found that XIPD in an oil-gap of oil/papa insulation is associated with oil-gap type. For an oil-gap wrapped by clothes, the XIPDIV changes with the oil-gap wrapped form. With X-ray irradiation, the smaller the oil-gap formed between the electrode and the wrapped cloths is, the thicker the wrapped clothes are, the lower XIPD1V is. When PD occurs, the frequency and amplitude of discharge pulses increase with X-ray irradiation at the same voltage. The XLPD observed from the oil-gap wrapped by clothes could be associated with photoelectrons which could come from the LW metal electrode with X-ray irradiation The photoelectrons were limited in the tiny oil gap by clothes and form space charges, causing partial electric field stress intensified greatly. With X-ray irradiation it is advantage to find the poor insulation where partial electric field stress is too high in oil/paper insulation. For an oil-gap without cloth wrapped, we found no effect of X-ray irradiation on PD occurs in an oil-gap under low AC voltage application. This is because photoelectrons injected into oil-gap from HV electrode could not be accumulated. 3.PD phenomena induced by X-ray iiradiation in an oil-gap wrapped in oil/paper insulation under DC voltage was investigated experimentally in this paper. PD phenomena in oil-gap wrapped in oil/paper insulation under DC voltage is different from that imder AC voltage. It is found that PD induced by X-ray irradiation is restrained and lagged under DC voltage in oil-gap of oil/paper insulation. During X-ray irradiation no P1) occurred or PD was restrained in oil-gap wrapped in oil/paper insulation. After Xiwy irradiation stopping PD occurred suddenly in the wrapped oil-gap. PD phawa~m induced by X-ray irradiation wider DC voltage Is associated with space charges in oil-g~ wrapped in the oil/p...