Manufacturer of Low and Medium Voltage Switchgear

Overview, Working Principle

Many components in the power system are inductive or capacitive, such as power transformers, transformers, generators, and arc suppression coils are inductive components, and parallel or series capacitor banks for compensation and parasitic capacitance of high-voltage equipment are capacitive components. However, there are both longitudinal inductance and transverse capacitance between the wires of the line and the wires. These components form a complex LC oscillation circuit. Under the action of a certain energy, the circuit with specific parameters will resonate.

The following excitation conditions can cause ferromagnetic resonance:

  • Sudden input of voltage transformer
  • Single-phase grounding occurs in the line
  • Sudden changes in system operation or switching of electrical equipment
  • Large fluctuations in system load
  • Grid Frequency Fluctuations
  • Unbalanced changes in load, etc.

The resonant overvoltage caused by the voltage transformer is very frequent, but after some switching operations such as the closing of the circuit breaker or the disappearance of the ground fault, due to the different inductance saturation of the three-phase inductor after resonance, the resistance to the ground is different. Balanced, it forms a resonant circuit with line-to-ground capacitance, which may excite ferromagnetic resonance overvoltage. The ferromagnetism caused by the saturation of the iron core of the voltage transformer is the most common internal overvoltage that causes the most accidents. In the actual operation of equipment, due to the low insulation of equipment in the neutral point ungrounded power grid, single-phase ground faults are relatively frequent. Generally speaking, single-phase ground faults are the most common excitation method for ferromagnetic resonance.

In the power system, there is no matching with the nonlinear inductance of the voltage transformer and the capacitance of the line to the ground, which causes iron resonance overvoltage, which directly threatens the operation of the power system, and in serious cases, it will cause the explosion of the voltage transformer (PT) and cause an accident. The ferromagnetic resonance of the voltage transformer must be supplied by the power frequency power supply to maintain it. If this part of energy is suppressed or consumed, the ferromagnetic resonance can be suppressed or eliminated. The usual solution is to add a resistor to the open delta winding. Theoretically speaking, the lower the frequency, the smaller the resistance should be for the ferromagnetic resonance. However, too small a resistance will affect its normal operation on the PT open delta. In severe cases, the PT will be burned. Therefore, the frequency of ferromagnetic resonance is often not single, so it is difficult to eliminate all resonances by this method.

In response to the above situation, some manufacturers have successively developed some frequency division and harmonic elimination devices. These devices all adopt the principle of analog frequency selection, which has a single function and is only effective for the resonance of a single frequency. Since the resonance in the power grid often exists with multiple frequencies at the same time, its applicability is poor. Compared with the computer, the frequency selection effect of the analog circuit is also poor, and sometimes the excessive process of the power grid will also cause misoperation.

The KCXQ microcomputer harmonic elimination device uses the fast and accurate data processing capability of the 80C196 single-chip microcomputer to realize Fourier analysis, and the frequency selection is accurate. By collecting the triangular voltage of the PT opening, it can quickly analyze various frequency components when the power grid resonates, and can accurately identify: single-phase grounding and power grid resonance. If it is resonance, the instruction issued by the computer makes the resonance elimination circuit put into operation, consumes the energy supplied by the power supply for resonance, suppresses the ferromagnetic resonance overvoltage, realizes fast resonance, and perfectly solves the harmonic amplitude of each harmonic of the power grid in the power system , can be widely used in power plants, substations and power systems of large-scale factories and mines such as steel, coal, petrochemical and other enterprises.

Device Features

  • Automatically identify and eliminate ferromagnetic resonance of different frequencies in the system, and output an alarm at the same time
  • Real-time display of the system clock and the running status of the monitored PT, real-time cycle monitoring of the PT opening triangle voltage
  • Using LCD display and Chinese menu, the information is intuitive and rich
  • No need for setting and debugging, it automatically enters the running state after starting up, and the equipment maintenance is low
  • The ARM chip has strong anti-interference ability and high data acquisition accuracy
  • It can be divided into ferromagnetic resonance, overvoltage, and single-phase grounding; accurate diagnosis, rapid harmonic elimination, and 100% correct action rate
  • Multiple fault information can be stored, and the data will not be lost after power failure, for recall and display
    Configurable communication interface (RS48 or RS232); with self-diagnosis fault, automatic recovery function

The main technical indicators of the device

(1) Working power: AC220V±15% or DC220V±15%, power consumption of the whole machine: ≤20W
(2) Number of busbar sections: 1~4 sections; Ambient temperature: -10℃~50℃
(3) relative air humidity: ≤95%; communication interface: RS232/RS485
(4) Resonance elimination 17Hz (1/3 frequency division), 25Hz (1/2 frequency division), 50Hz (power frequency), 150Hz (3 times frequency).

Software configuration of the device

The device adopts 80C196 assembly language to compile software, and the software is mainly composed of the monitoring program, floating-point calculation library, diagnostic software, harmonic elimination, recording, and other parts. The tasks of voltage detection, sampling, diagnosis, harmonic elimination, clock, keyboard command, and display are completed by the real-time monitoring program.

Scroll to Top
× How can I help you?