Description
Overview of Microprocessor-Based Resonance Eliminator
- Developed specifically for power systems, the Microcomputer Resonance Elimination Device effectively prevents severe faults including burnout and explosion of voltage transformers (PT) triggered by ferromagnetic resonance.
- The Microprocessor-Based Resonance Eliminator displays system clock and PT open delta voltage components at 17Hz, 25Hz, 50Hz and 150Hz in real time. It identifies overvoltage, ferromagnetic resonance and single-phase earth faults, and features communication ports to upload fault information, perfectly suitable for unattended substations.
Technical Parameters of Secondary Resonance Elimination Device
- Operating Power Supply: DC/AC 170～240V
- Power Consumption
- Power circuit: ≤10W
- AC voltage circuit: ≤1VA
- Secondary zero-sequence voltage of busbar PT connected to device: 3U0 ≤ 200V (AC effective value)
- Resonance judgment delay: 500ms, resonance elimination time: 60ms, interval time: 1s
Operation Criteria of Ferromagnetic Resonance Elimination Device
- Resonance Criteria: 17Hz harmonic voltage ≥17V, 25Hz harmonic voltage ≥25V, 150Hz harmonic voltage ≥33V, fundamental frequency voltage ≥150V.
- Earth Fault Criteria: Fundamental voltage ≥30V and ＜120V.
- Zero-sequence Overvoltage Criteria: Fundamental voltage ≥120V and ＜150V.
- Reset Coefficient: 93%, reset value of fundamental frequency resonance: 148V.
Technical Features of PT Secondary Non-Linear Resistor Device
- Adopts ultra-low power consumption 32-bit ARM CPU, perfectly adapted to industrial environments. Modular circuit board design simplifies maintenance. It features fast speed and high precision in data acquisition, calculation, logic judgment and control output. Equipped with watchdog circuit, it owns strong self-checking and automatic recovery capability.
- Equipped with wide-temperature graphic LCD with Chinese menu, which displays abundant and intuitive data.
- Adopts advanced intelligent software technology with stable performance and high operational reliability.
- Real-time display of system clock, calendar and effective value of PT open delta voltage.
- Eliminates ferromagnetic resonance of four frequencies: 17Hz, 25Hz, 50Hz and 150Hz.
- Accurately distinguish overvoltage, ferromagnetic resonance and single-phase earth fault.
- Output alarm signals for all faults, meanwhile display and store relevant fault records.
- Non-contact resonance elimination component with large output power, built-in permanent breakdown protection function.
- Parameter setting via Chinese interface and panel keys for easy commissioning and maintenance.
- Simple wiring and convenient field installation.
- Applicable to PT in 3kV ~ 66kV power systems.
- Support communication connection to transmit fault data to integrated automation system, suitable for unattended substations.
Application Conditions
- Indoor installation only
- Altitude: ≤2km
- Ambient temperature: -20℃ ~ 50℃
- Relative humidity: ≤90%
- Atmospheric pressure: 80~110kPa
Working Principle
- The Microprocessor-Based Resonance Eliminator monitors PT open delta voltage and calculates four frequency components of zero-sequence voltage. It identifies fault types once abnormalities occur. In case of ferromagnetic resonance, it rapidly activates resonance elimination components in accordance with preset procedures to eliminate resonance, meanwhile displays, stores fault data and outputs alarm signals.
- It adopts three-stage resonance elimination mode with three operations per stage. Each thyristor conducts for 3 cycles with an interval of 1 second. After the first stage, it checks elimination effect. If all harmonic voltages drop below reset values, resonance elimination terminates without triggering the second stage.
- Similarly, after the second stage completes, resonance elimination of the third stage will not be triggered if resonance voltage is lower than the reset value.
- If resonance still exists after the third stage, it will be judged as permanent fault, alarm resonance elimination failure and stop relevant operation.
- The resonance elimination function will be re-enabled 10 seconds after all resonance voltages drop below the reset value.
Simulation testing
Earth Fault Test
- Apply voltage to the zero-sequence voltage terminal via single-phase autotransformer with voltmeter for accurate reading. Raise voltage gradually from below 30V to 30V, the device activates: earth fault indicator lights up, and fault info can be queried and uploaded via serial port.
- Gradually lower the voltage. Due to reset coefficient, the fault state remains and indicator stays on when voltage is above 27.9V. The fault resets once voltage drops below 27.9V. Alarm logs shall record the exact fault occurrence time.
Overvoltage Test
- Apply voltage to the zero-sequence voltage terminal with a single-phase autotransformer fitted with a voltmeter for precise voltage reading. Gradually raise the voltage from below 120V up to 120V, the device triggers action: the overvoltage indicator lights on, and fault information can be queried and uploaded via serial port.
- Slowly reduce the voltage. Due to the reset coefficient, the fault state persists and the indicator remains lit when the voltage is no lower than 111.6V. The fault resets automatically when the voltage drops below 111.6V. The alarm records shall keep the exact time of fault occurrence.
Resonance Test
- Apply voltage to the zero-sequence voltage terminal of the device by a single-phase autotransformer (connect a voltmeter for accurate voltage observation). Gradually increase the voltage from below 150V to 150V.
- The device will act: resonance indicator and resonance elimination indicator light up, alarm relay closes with its contacts conducting when measured by multimeter, and the buzzer sounds. Fault data can be checked and uploaded via serial port. Meanwhile, resonance elimination components start working with visible bulb flashing. The resonance elimination indicator turns off after completion of three-stage elimination.
- Gradually lower the voltage. Due to the reset coefficient, the fault state remains and the resonance indicator stays on when voltage is no less than 148V. When voltage drops below 148V, the resonance indicator goes out, the alarm relay breaks after 1-second delay, and the resonance elimination function restores after 10 seconds. Alarm records shall store fault occurrence time and resonance elimination failure information. If voltage falls below 148V during three-stage elimination, resonance elimination is judged successful.
- The test methods and working phenomena for 17Hz, 25Hz and 150Hz are basically the same. Replace the autotransformer with relay protection tester or other professional instruments. Since the corresponding voltage is low and output power is insufficient, bulb flashing cannot be observed. Do not test without series-connected bulbs, otherwise temporary conduction of resonance elimination thyristors may damage test equipment. Strictly ensure equipment and personal safety during the whole test process.
FAQ
Q：What are the differences between a Microprocessor-Based Resonance Eliminator, a PT measurement and control device, and a PT parallel connection device?
A:The Microprocessor-Based Resonance Eliminator eliminates PT ferromagnetic resonance and suppresses overvoltage to protect voltage transformers. The PT monitoring device collects voltage data, monitors grid anomalies and realizes remote communication. The PT paralleling device switches and parallels secondary circuits of busbar PTs to ensure stable voltage supply during switching operations.
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