The medium frequency furnace adopts rectification and inverter technology during operation, resulting in a large number of current and voltage harmonics in China. Harmonics have an impact on the development of power supply management system and serious environmental pollution, which can cause misoperation in the process of precision instrument analysis work and learning, and increase the loss of power supply equipment of enterprises. Let's take a look at the existing problems and solutions with cook Cooper, a manufacturer of low-voltage electric containers

1、 Load and harmonic characteristics: widely used in nonferrous metals, ferrous metals, smelting, heating and other fields. Such as smelting raw iron, ordinary steel, stainless steel, tool steel, copper, aluminum, gold, silver and alloy; Medium frequency smelting furnaces for steel parts, hot forged copper parts, extruded aluminum ingots, metal pressure regulation and quenching heat treatment are increasingly widely used in smelting, casting and other industries. The power control system of medium frequency induction furnace is the largest harmonic source in the power information system. Generally, 6-pulse medium frequency furnace mainly produces 5, 7, 11 and 13 characteristic harmonics

2、 Problems faced

1. A large number of harmonics are generated during the use of medium frequency furnace, which makes the harmonic pollution in the power grid very serious

2. Harmonics reduce the efficiency of electric energy transmission and utilization, overheat electrical equipment, produce vibration and noise, aging its insulation, reduce its service life, and even break down or burn out;

3. Harmonics will cause local parallel resonance or series resonance in China's power management system, so that the harmonic content can be amplified, resulting in the burning of capacitance compensation control equipment and other equipment;

Case 2 of harmonic control by using active power filter in medium frequency furnace

4. Harmonics will also cause relay protection and automatic misoperation of devices, resulting in confusion of electric energy measurement;

5. Outside the power system, harmonics will cause serious interference to communication and electronic equipment.

6. When the power factor fails to meet the requirements of 0.90 of the power supply bureau, a fine for adjusting the electricity charge will be imposed.

7. The power factor of medium frequency furnace is low. When a large amount of reactive power is provided by special transformer, the burden of transformer is increased.

3、 Solutions to choose fromScheme 1: centralized processing (applicable to multi IF signal electric furnaces operating at the same time; harmonic filtering device is installed in the distribution room) adopts harmonic control branch (5, 7 and 11 filtering) + reactive power regulation branch. After the filter compensation device is put into operation, the harmonic control and reactive power compensation of the power supply system meet the requirements. The reactive power compensation of power supply system can meet the requirements after using active filter (filtering dynamic harmonic frequency) and harmonic regulation branch (5th, 7th and 11th filtering) + reactive power regulation branch.

Scheme 2: local processing (install local harmonic filter device next to the power cabinet of intermediate frequency furnace) adopts different harmonics to control branches (5, 7 and 11 filtering). The operation of intermediate frequency furnace is automatic control and tracking, and the harmonics are solved locally. During production, it does not affect the operation of learning other enterprise equipment, and the harmonic reactive power reaches a standard after input Active filter (band adjustment unit) and filter branch (5, 7 filters) are adopted, and the harmonic reactive power after input meets the standard.

Scheme 3: adopt active power filter. The compensation capacity of cook Cooper active power filter is 50a, 75A, 100A and 150A