Research And Development On Interturn Insulation Test Device Of Iron Core Reactor Based On Variable Frequency Resonance

Dry-type iron-core reactor is an important device in power system.It has the functions of eliminating power frequency overvoltage,limiting switching current,power filtering and so on.With the development of the power system,the use of iron-core reactors has increased year by year.At the same time,iron-core reactors have been affected by manufacturing processes,materials and switching over voltage,so the interturn insulation damage often occurs.Due to the problems of iron saturation and uneven distribution of capacitance parameters in iron-core reactors,the lightning impulse test method and the induction withstand voltage detection device of dry-type hollow reactors are not suitable for iron-core reactors.Therefore,developing a turn insulation withstand voltage detection device of high-voltage drytype iron-core reactor is necessary.Firstly,this thesis analyzes the existing interturn insulation detection methods and related standards of iron-core reactors at home and abroad,and proposes a method for detecting the interturn insulation resonance induction withstand voltage of iron-core reactors based on the principle of variable frequency resonant technology.According to the maximum output capacity of the device,this thesis calculates,analyzes and selects the hardware parameters of the rectifier unit,boost unit,inverter unit,and voltage and current sampling unit.This thesis gives the recommended values of resonance frequency and matching high-voltage capacitors for typical iron-core reactors,and determines the output frequency range of the developed device is 50Hz-2k Hz and the maximum output capacity is 200 k VA.This thesis theoretically analyzes the change law of the inductance of reactors and the current rate of change of reactors when the reactor turns short-circuited.Then,using software to simulate the topology of the overall circuit of the device,the simulation results are consistent with the theoretical derivation.The simulation study finds that when the resonance condition is broken,the reactor terminal voltage drops and the loop current decreases.Therefore,while ensuring the safety of the test,the voltage or current drop can be used as an interturn short-circuit detection indicator to judge the winding interturn insulation short-circuit fault.In terms of hardware development,a single-phase full-bridge inverter topology is used as the core of the frequency conversion circuit,and the inverter is driven by a central main control unit to output sinusoidal pulse width modulation waves and square wave voltages of different frequencies,which are applied to the test circuit to make the reactor reach the test voltage value by resonance.The DC part of the inverter power supply of the device uses three-phase rectifier and BOOST circuit,through controlling the boost duty cycle to adjust the variable-frequency resonance output voltage,and determine that the DC-side voltage of 900 V can basically meet the test requirements of existing iron-core reactors.Based on the above hardware platform,this thesis has developed an interturn insulation real-time monitoring application software platform that can realize test detection control,test waveform acquisition,fault judgment,historical data recording and basic parameter settings.The software adopts the graphic G Language of LABVIEW platform to realize the MODUS protocol communication between the monitoring host computer and the underlying hardware device unit.In this thesis,the variable-frequency resonance interturn insulation detection device of Iron-Core Reactor is used to carry out insulation detection tests in laboratories,reactor manufacturers test stations and substation sites,and the test results meet the needs of field testing.