Research On The Corona Inception Voltage Of Generator Stator Winding Under Simulated High Altitude Atmospheric Conditions

The corona inception voltage(CIV)is reduced due to high altitude,and the humidity also affects the external insulation characteristics of the motor winding.However,Due to the abundant water resources in the high altitude area of Southwest China,lots of hydro-power stations will be planned or constructed in these area.At home and abroad,there are few researches on the corona characteristics of stator bars or windings in high altitude areas.And some standards refer to the influence of air pressure and humidity on CIV test results with different models,which get some differences in the influence characteristic indexes.In order to explore the corona inception characteristics of stator winding in high altitude area,the electric field distribution characteristics of the whole stator and the simulated winding in laboratory test were analyzed and compared,which shows the effectiveness of the simulated winding test in laboratory.The corona pulse current method was used to detect the CIV of the simulated winding,and the corona discharge signal of the winding surface was determined by analyzing the characteristics of the solid surface and internal discharge,and the CIV obtained by ultraviolet imaging method was used for comparative verification.The corona test of the simulated winding was carried out by changing the atmospheric parameters in the multi-functional artificial climate chamber,the influence of air pressure and humidity on the CIV of the simulated winding was analyzed,the calculation formula of the CIV considering the influence of air pressure and humidity was proposed.The main conclusions are as follows:(1)The weakness of the electric field of the whole stator winding lies in the insulation spacer block at the commutation position and the"R"angle position of the high and low resistance lap joint.For the laboratory test winding,when simulating the phase insulation,the weakness of the electric field is the insulating spacer block and the"R"angle position.When simulating the same phase situation,the weakness of the electric field is at the"R"angle position.By comparing the electric field distribution of the whole stator with the simulated winding and the numerical simulation results,it can be seen that the electric field distribution of the two models has a high similarity,and the electric field distribution of the simulated winding is more strict.(2)By using UV imager to photograph the weakness of its surface electric field,it was found that the electric field near the phase insulation spacer block is relatively concentrated,which is a high incidence area of corona discharge.In this paper,the CIV was obtained by corona pulse current method.Through the simplified model test,the characteristic peak of the discharge pulse spectrum on the solid surface is less than 10MHz,while inside the solid has significant components in the range of 10-30 MHz.The positive pulse amplitude of solid surface discharge is much higher than negative pulse,and the phase of discharge pulse shall not exceed 0°and 180°.The amplitude of positive and negative pulse of solid internal discharge are both higher,and the phase of discharge pulse can exceed 0°and 180°.In this paper,the discharge pulse of the simulated winding is surface corona,which is determined by the spectrum characteristics and the discharge phase.The CIV obtained by corona pulse current method and UV imaging method is close to each other.(3)With the increase of altitude or the decrease of air pressure(The test pressure range is 98.9 k Pa to 65.6 k Pa),the CIV of the phase insulation of stator winding decreases,but with the increase of absolute humidity,the influence of altitude or air pressure decreases.With the increase of absolute humidity(The range of absolute humidity is 3.84g/m~3to 27.66g/m~3),the CIV of stator winding decreases,but with the decrease of air pressure,the influence of absolute humidity increases,and the degree of CIV decrease becomes gentle.According to the influence of air pressure and humidity on the CIV,the calculation formula of CIV including air pressure,absolute humidity and temperature was proposed,the maximum error is-9.86%,and the average absolute error is 3.39%.In addition,the calculation formula of CIV was obtained by cross parameter method,the maximum error is 8.91%,and the average absolute error is 2.22%.For the corona pulse current of the winding,the average peak-peak value decreases with the increase of absolute humidity,and increases first and then decreases with the decrease of air pressure.The results show that the peak-peak value of corona discharge pulse current is the highest when the air pressure is about 79.36 kPa.