1、 Introduction
The smelting production process of steel enterprises requires a large amount of industrial gases such as oxygen, nitrogen, argon, etc. Oxygen is mainly used for smelting in blast furnaces, smelting reduction furnaces, converters, and electric furnaces; Nitrogen is mainly used for furnace sealing, protective gas, steelmaking and refining, converter slag splashing protection, safety gas, heat transfer medium and system blowing, etc; Argon gas is mainly used for steelmaking and refining. To meet production requirements and ensure stable operation, large steel mills are equipped with oxygen production stations and oxygen nitrogen argon power pipeline systems.
The steel plant where this project is located is a steel plant with an annual output of 5 million tons in a certain country. Its oxygen production workshop uses a 15000 cubic meter oxygen generator, which is responsible for the production and supply of energy media such as oxygen, nitrogen, and argon in the company's smelting system. The unit was officially put into operation in October 2015 and has been running continuously for over 100 days so far. The oxygen concentrator is driven by a 6kV12MW synchronous motor, and the speed control equipment adopts the LPMV06-15500TTP high-voltage frequency converter provided by Jiangsu Lipu Electronic Technology Co., Ltd.
2、 Variable frequency scheme
High voltage AC variable frequency speed regulation technology is a speed regulation technology for AC motors that rapidly developed in the 1990s. Variable frequency speed regulation has been recognized by users and the market for its significant energy-saving benefits, high precision speed regulation, wide range speed regulation, complete protection functions, and easy to implement automatic communication functions. In terms of reliable operation, installation, use, maintenance, and other aspects, it also brings convenience to users, making it the primary solution for enterprises to adopt motor speed regulation.
Under the application conditions of this project, by using variable frequency speed regulation technology to change the speed of the air compressor motor, the gas supply flow rate of the air compressor can be changed with the change of gas consumption flow rate, which can achieve energy-saving effects. At the same time, due to the high power of the motor, starting it through frequency conversion also reduces the impact on the power grid during motor startup, allowing for an extension of both the mechanical and electrical lifespan of the motor. In addition, the power grid in the application area of this project is extremely unstable. The input power supply often operates at 60% of the rated voltage, and the frequency of the power grid is often as low as 30Hz. By enabling the AVR function of the LPMV series high-voltage frequency converter, the effect of stabilizing voltage and frequency output can be achieved, making the power supply of the air compressor stable and unchanged.
The Lipu LPMV series high-voltage frequency converter adopts dual DSP+FPGA as the control core, adopts speed vector control technology, power unit series multi-level technology, and belongs to the high high voltage source type frequency converter. Its harmonic index is much smaller than the national harmonic standard of IEE519-1992, with high input power factor and good output waveform quality, and there is no need to use input harmonic filters, power factor compensation devices, and output filters; There are no additional heating, torque ripple, noise, output dv/dt, common mode voltage and other issues caused by harmonics in the motor, and it can also drive ordinary asynchronous motors. Specifically, the various parts of the Lipu high-voltage variable frequency speed control system are introduced as follows.