Study On Development And Application Of Transformer Insulation Testing System Based On Recovery Voltage Measurement

Power transformer, as the core of power transmission and distribution, is one of the pivotal equipments in power system, also the most expensive and complex one. Its insulation state has direct bearing on the security and stability of grid operation. Along with the realization of west-to-east power transmission, mutual power supply between south and north and a nationwide transmission network, china’s power grid continues to expand in scale and increase in voltage class, leading to higher potential in serious accidents and upgrade in hazard levels. Once a transformer malfunctions, it may cause power blackout in large scale or even a breakdown of regional power network, resulting in huge economic losses and adverse social impact. In this sense, a research into the test method of insulation state of transformer as well as a further probe into the insulation testing system is of essential importance to guarantee an effective assessment of the running state of a transformer.Recovery Voltage Measurement (hereafter shorted as RVM), which has been popularly adopted at home and abroad in recent years, is a convenient, effective insulation testing method and harmless to the measured objects. The core of RVM is applying direct current voltage to transformer insulation system to gain wave spectrogram of transformer recovery voltage and evaluate the insulation state of transformer. However in china, the study concerning the application of RVM still remains in its theoretical stage and no perfectly workable devices that can evaluate transformer insulation states under RVM has yet been developed.By reviewing the previous researches in RVM conducted both home and abroad and with the aid of the existing devices in insulation state evaluation, this paper successfully designs and further works out a testing system of transformer insulation state on the basis of RVM. This testing system consists of six major parts:high-voltage direct current power (DC) module, switching unit, voltage sampling unit, system interface, expert evaluation system and database. Adopting RMV, the author conducts a series of tests on some transformers in Sichuan Power Grid under multi parameters. Then the author compares and analyzes the results obtained from RMV tests with those from insulation resistance and absorption ratio tests to validate the reliability of the system. He also makes a comparative analysis in the characteristic parameters (maximum recovery voltage Urmax, center time constant tcdom and initial slop Si) of the voltage curves of transformers which are tested under RVM in different years. Based on field tests, the author investigates the influence of memory effect on characteristic parameters of recovery voltage. The research enriches the database of studies conducted RVM. which offers important evidence for accurate assessment of the insulation states of transformers.