◆ Overview
The AT-WXZ microcomputer harmonic elimination device is a newly developed and produced generation of intelligent harmonic elimination device for the malignant accidents of voltage transformer (PT) burnout and even explosion that often occur in the power sector and users due to ferromagnetic resonance. It uses a 16 bit microcontroller as the sampling operation, logic judgment, and control center (CPU), high-power, contactless harmonic elimination components as the output, liquid crystal display (LCD), signal indicator lights, touch buttons as the human-machine interface, and intelligent software to form an advanced technology and principle, easy-to-use "foolproof" diagnostic, harmonic elimination, and recording device.
This device displays the system clock and PT open delta voltage in real-time at four frequencies: 17Hz, 25Hz, 50Hz, and 150Hz. It can distinguish between overvoltage, ferromagnetic resonance, and single-phase grounding, and can be configured with an RS485 communication interface to transmit fault information to relevant departments. It is suitable for unmanned substations.
◆Model Description



◆Conditions of Use
(1) Indoor use with good ventilation;
(2) Altitude ≤ 2Km;
(3) Environmental temperature: -10 ℃ to 50 ℃;
(4) Relative humidity ≤ 90%;
(5) Atmospheric pressure of 80-110kPa;
(6) The surrounding medium is free of conductive dust, conductive metals, corrosive gases, mold, etc. that may damage the insulation.

◆Technical Parameter
(1) Working power supply: DC/AC220V;
(2) Power consumption: power circuit ≤ 10W; AC voltage circuit ≤ 1VA;
(3) Rated AC voltage: 100V.

◆Device features
(1) The CPU adopts a 16 bit microcontroller, which has fast speed and high accuracy in data acquisition, operation, logic judgment, and control output. It also has dual "Watchdog" circuits, strong anti-interference, self checking, and self recovery capabilities;
(2) Adopting a 128 × 64 graphic liquid crystal display (LCD) for Chinese menu prompts, displaying rich and intuitive information;
(3) Intelligent software technology, advanced principle, stable performance, safe and reliable;
(4) Real time display of voltage components at four frequencies (3-division/17Hz, 2-division/25Hz, power frequency/50Hz, and 3-fold/150Hz) for the system clock, calendar, and PT open delta voltage;
(5) Can distinguish overvoltage, ferromagnetic resonance, and single-phase grounding, and quickly eliminate ferromagnetic resonance;
(6) Provide alarm signals for various faults and display and save relevant information;
(7) Has memory function, can store 10 recent fault information, and will not be lost after power failure;
(8) The harmonic elimination component has a high output power and no contacts;
(9) Through Chinese menu prompts and panel button settings, debugging and maintenance are simple and convenient;
(10) Simple wiring and easy installation;
(11) Hardware and software redundancy design, strong anti-interference ability;
(12) Suitable for PT of various voltage levels;
(13) Can be equipped with RS485 communication interface to transmit various fault information to relevant departments, suitable for unmanned substations.

◆Working principle
(1) The device monitors the PT open delta voltage and calculates the voltage components of four frequencies of zero sequence voltage. If a fault occurs, the fault type is determined. If it is ferromagnetic resonance, the harmonic elimination element is instantly activated according to the set program to eliminate it, and the fault information is displayed and saved, while giving an alarm signal.
(2) Action criteria
a. Resonance criteria: 17Hz harmonic voltage ≥ 17V, 25Hz harmonic voltage ≥ 25V, 150Hz harmonic voltage ≥ 33V.
b. Grounding criterion: Fundamental voltage ≥ 30V.
c. Overvoltage criterion: Fundamental voltage ≥ 120V.
d. Return coefficient: 93.75%.

◆simulated test
(1) Connect the wires according to the terminal diagram and apply voltages of 0-120V at four frequencies of 17Hz, 25Hz, 50Hz, and 150Hz to the PT open delta voltage circuit. The real-time displayed voltage value error should be within 2%.
(2) Slowly increasing the voltage from 0 using a voltage regulator can simulate a ground fault, and then increasing the voltage to a certain extent can simulate an overvoltage fault. The signal, display, and saved fault information should be accurate.

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