Principle that WXL harmonic filtering device governs harmonic WXL harmonic filtering device could effectively filter out five times and seven times, and at same time, it also provides approximately 120 kvar reactive power compensation amounts, and the maximum absorbing harmonic currents: five times harmonic current 200A. Seven times harmonic current 130A. Because of adopting single adjusting filter principle and the unique Q-conditioning technology, it makes filtering device filtering properties of long-term, stable and reliable, and WXL a harmonic filter devices to meet the harmonic treatment of middle frequency smelting users of transformer --capacity of 315 KVA. WXL harmonic filtering device filtering is parallel way, without affecting users middle frequency furnace operation, Instead of users voltage compensation to be upgraded, providing electric furnace in the course of operation at more efficient operations, obvious effects of reactive power compensation and about 2% of active power saving efficiency. Start and the closure of harmonic filtering device by the fully automated, without manual operational users. The device has a series of function of an automatic detection, self-protection, prevention of excessive vibration, and automatic limited flow. Device control unit of device can show the real-time status of the voltage, current, reactive power, the active power and apparent power, and other parameters, and Vice Control Unit has completed detected the harmonic current and controlled loop filter