Research On The Influence Of Sampling Resistance And Transformer Type On The Insulator Leakage Current Acquisition Results

Sampling resistor method is widely used in the laboratory to collect the insulator leakage current and in this method the non-inductive resistor acts as a kind of sensor while the test transformer as power supply. Practically the resistance of the resistor distribute in a wide range, from a few ohms to more than 10 thousand ohms. Though the specific influence is still unknown it does effect the leakage current acquisition results. Meanwhile different scientific institutions are usually equipped with transformers of different types and capacities and what effects of all this differences will lead to on the leakage current acquisition results are still unknown. Therefore, in this dissertation systematical study are carried out on the matter of the resistance and transformer selection in the sampling resistor method.An insulator leakage current acquisition system was constructed and sampling resistors with resistance from 1 Ω to 10 kΩ were used to measure the leakage current of dry and clean insulator, water drops attached insulator as well as the wet and contaminated insulator, power supplied by 4 transformers of different types and capacities. The types of the transformers in use are YDTW-1200/300, YDTW-50/250, YDTW-10/100 and YDJ-5/50 respectively. The impulse component is extracted from the acquired leakage current signal through the median filter algorithm. The influence of the sampling resistance on the impulse amplitude is analyzed and the relationship between the impulse amplitude and the resistance is fitted by the least-squares fitting. A preliminary mechanism analysis of the influence of the sampling resistance on the leakage current acquisition results is introduced, which is validated by experiment. Based on the data acquired through the 4 different transformers, the leakage current parameters including the maximum values of the leakage current, the RMS values of the leakage current, the maximum values of the pulse component, the RMS values of the steady-state component and the ratio of the 3rd harmonic to the fundamental and the 5th harmonic to the fundamental of the leakage current are extracted and the effects of the different transformers on the aforementioned parameters is analyzed.The results reveal that the sampling resistance has significant effect on the impulse component of the leakage current. The difference between the impulse waveform obtained by different sampling resistance is distinct. The impulse amplitude will decrease as the resistance increases and they satisfies power function, based on which the leakage current acquisition results are expected to be corrected. It is also discovered that under the same external conditions, the difference between the leakage current parameters obtained by the different transformers are distinct. The steady state components of the leakage current from the 4 different transformers are almost the same. Yet, the transient impulsive components are more severely affected by the transformer type and capacity than the ratio of the 3rd harmonic to the fundamental and the 5th harmonic to the fundamental. Transformer selection has great influence on the reliability of the related experiment results.