Study On Interturn Short Circuit Fault Online Monitoring Technology For Dry-type Air-core Reactor

Reactor is an important high-voltage device in power system.It is mainly used to limit the short-circuit current,compensate the reactive power,and filter higher harmonics.The dry-type air-core reactor has a simple structure and other advantages such as low loss,low noise and good linearity.It is widely used in power systems for good quality and easy maintenance.During the long time operation,the failure rate of dry-type air-core reactor is continuously increased due to the insulation aging,and 60% fault was caused by the inter-turn short circuit.However,the existing monitoring technology of dry-type air-core reactors has the problem of low sensitivity,and it is hard to detect early inter-turn short-circuit faults.Therefore,it is of great significance to develop a new kind of high-sensitivity short-circuit on-line monitoring technology.Firstly,the equivalent circuit model of dry-type air-core reactor is established in this paper.The power angles of the reactor under normal and inter-turn short circuit fault conditions are calculated through analytical method.Analyzed the characteristics of power factor angle change under a short circuit fault are analyzed either.Based on the change of power angle,an on-line monitoring method for the short-circuit fault of dry-type air-core reactors is proposed.Harmonic analysis method is used to calculate the power angle,and the sampled signal is processed by the modified ideal frequency sampling method.The effective combination of the two solves the effects of system frequency fluctuation and harmonic wave on the measurement accuracy of the power angle.Secondly,according to the characteristics of the power factor angle before and after the inter-turn short circuit fault occurs in the reactor,a dry-type air-core reactor on-line monitoring device is designed.The monitoring device obtains the secondary side voltage and current signals of the reactor bus through a high-precision voltage transformer and current transformer.The signal passes through the modulate circuit and uses the STM32F407ZGT6 chip as the core controller to control two AD7656 s to achieve the synchronization of 6 voltage signals and 3 current signals.The collected data is uploaded to the reactor IED via Ethernet.The software adopts the modular concept,the signals are digitally converted,filtered,and stored.At the same time,the power factor angle was obtained to calculate the power factor,performs fault interpretation according to the thresholds and historical data,and implements fault alarms.Finally,a high precision signal source and three CKGL-40/10-6 reactors were used to set up a test platform to undertake the power factor angle accuracy measurements,inter-turn short circuit fault simulation,and the electromagnetic compatibility tests.The device was installed to test the performance at a 500 k V substation in Shanxi province,and the results of tests and operation show that the method and designed online monitoring device can quickly detect the occurrence of short circuit faults in the early stage,the change of power factor angle is related to the number of short circuit turns and the short circuit position.As the number of short-circuit turns increases or the position of inter-turn short-circuit fault moves from the end to the middle,the reactor power factor angle gradually decreases,and the power factor increases continuously.