A brief discussion on the significant energy-saving effect of high-voltage VFD (Variable-frequency Drive)

【Abstract】At this stage, energy conservation and emission reduction have become issues that must be considered for the sustainable development of every steel company, and the widespread application of high-voltage VFD (Variable-frequency Drive) can save electricity and reduce energy consumption.

【Key words】High voltage frequency conversion energy saving effect analysis

Through the development in recent years, high-voltage variable frequency speed regulation technology has become increasingly mature and has begun to be widely used in various fields. A large number of fans, water pumps and other equipment in steel companies have been running at power frequency, and gate valves need to be used to control air volume and flow. , thus losing a lot of energy, and after changing to variable frequency speed regulation, the air volume and flow rate are adjusted by changing the motor speed (that is, changing the motor output power), reducing resistance consumption, thereby achieving the purpose of energy saving.

The following is a detailed analysis of the energy-saving effect of high-voltage frequency conversion technology, taking the frequency conversion renovation project of two 75T gas boiler induced draft fans in the power plant of Xingtai Iron and Steel Co., Ltd. as an example.

1. Project Overview

The power plant's own power station currently has two 75T gas boilers, which are equipped with high-pressure induced draft fan motors of 400kw. The original operation mode is power frequency operation. In order to keep the negative pressure in the boiler furnace basically constant, it needs to be controlled by adjusting the inlet damper. The actual opening of the inlet damper is 36%-40%, and it moves frequently, so a considerable part of the power consumption is wasted on the damper. In order to change this situation, develop a circular economy, achieve energy conservation and environmental protection, and ensure the sustainable development of the enterprise, frequency conversion transformation of the two high-voltage motors began in May 2008.

The implementation of frequency conversion transformation of high-voltage motors means changing the speed of the motor (that is, changing the output power of the motor) through different frequencies output by the VFD (Variable-frequency Drive) to adjust the fan air volume so that the negative pressure in the boiler furnace is basically kept constant; imported The damper is in a fully open state to reduce resistance consumption, and the motor runs at a state far below the rated power, thereby achieving energy saving. By adding a bypass cabinet as a backup, when the VFD (Variable-frequency Drive) fails, the motor can be switched to power frequency operation, which not only takes advantage of the energy-saving advantages of the VFD (Variable-frequency Drive), but also ensures safe production. The adjustment and control function of the inlet damper is also limited to the power frequency operating state.

Through the selection of technical solutions and comparison of economic applicability, Sunwoele Co., Ltd. was selected as the general contractor for this project, and the installation was completed at the end of May. According to the production situation and planned maintenance arrangements, the first (4#) high-voltage motor with frequency conversion transformation was connected (connected) to the line on June 10, and the second (5#) high-voltage motor with frequency conversion transformation was connected (connected) on July 10. ) line operation.

2. Project investment (financing) methods

This project adopts the energy-saving rebate model for project construction. Xingang Steel provides initial operating equipment and on-site (platform) conditions. The other party is responsible for designing, providing equipment, and advancing funds for installation and construction. The cash flow of the project is used as a guarantee to achieve financing and put into operation. Afterwards, both parties share the electricity saving expenses in proportion, achieving a mutually beneficial win-win situation: Xingshan Iron and Steel saves electricity bills and reduces costs; the other party's equipment and construction costs are paid from its dividends and can make profits; at the same time, the energy conservation and environmental protection of the project benefit the country and the interests of the country. People and benefit society.

3. Project operation

Equipment transformation and operation: On June 10, 2008, the #4 boiler was taken advantage of the overhaul opportunity to install a VFD (Variable-frequency Drive) on the #4 boiler induced draft fan motor and conduct wiring. It was put into trial operation without load at 21:00 on June 11 . At 17:35 on June 14, the boiler was officially put into operation. The boiler negative pressure is set to -60Pa, and the actual negative pressure fluctuates ±15 Pa. The operation is relatively stable, and the operating frequency is 37-39Hz. The operating power is 152-175KW, with an average of 160KW, which is only 45.6% of the power frequency operating state. The average operating power under power frequency is 351 KW. The actual operating data statistics of power frequency and variable frequency are as follows:

4# induced draft fan motor power frequency operation record

Date and time Electricity meter bottom current transformation ratio voltage transformation ratio coefficient electricity average power 5.3015:009111.2275/56000/100900