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The insulation system of HV apparatus deteriorates due to partial discharges (PD). PD tests are carried out successfully in shielded laboratories to verify the insulation quality and to rectify defects left during the manufacturing process. A variety of techniques exists for this purpose. It is also desired to monitor the insulation when equipment is in operation. Unfortunately, the performance of PD test equipment is adversely affected by interference signals. The sinusoidal signals of low and high frequency, due to their correlation, make the measurement difficult and sometimes even impossible. This paper describes the design of an adaptive digital filtering technique and its successful application to the on-line/on-site detection of PD current pulses generated in HV insulation in the presence of sinusoidal noise signals. The technique is based on Wiener optimal filtering theory and its characteristics are investigated. The adaptive filter of this system has a time-varying response and is self-tuning to each low and high frequency noise component. The filter remains active until the signal-to-noise ratio is significantly increased and it can be used for weak PD pulse integration. Theoretical background of the technique and the results of laboratory and field tests are presented.The insulation of HV equipment in service is usually evaluated using off-line techniques which are expensive and time consuming. Therefore, it is desired to perform Conventional narrow band and wide band detectors are commonly used to reduce the interference caused by periodical signals. Their use during on-line conditions is 1070-9878/95/ $3.00

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Frequency Response Analysis can be used to detect the transformer winding deformation. Its reliability and standard are studied. A simulation model of transformer winding i s developed. The transformer winding is equivalent to a network circuit, and electrical components in the circuit can describe distributed elements o f the winding. The components in the model are determined by the geometric and electric data of the winding. If there is any deformation i n the winding, circuit parameters in the model will be changed and thus the character o f the whole circuit will be influenced. According to the common situations of winding deformation caused by short circuit, the variation of the circuit parameters are analyzed and simulation calculated. Transfer function is used to describe the character of the model.The original frequency spectrum i s taken as reference and that after deformation is analyzed. Correlative Coefficient value is used to judge whether and how bad the deformation happens. Different kinds and levels of the deformation are simulated and the results can match the data from field experiments. Some guide criteria for the detection of winding deformation i s presented.

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