Application of FGI FD5000 high-voltage frequency inverter in the boiler fan

1.Overview

The existing steam generator set of our factory is 3155MW (steam), and the boiler is 4520t, which is mainly used to meet the production needs and provide steam for the aluminum oxide plant. Each boiler is equipped with two centrifugal induced draft fans, drag motor is YKK630-4, rated power 2000 kW, rated voltage 6 kV, rated current 226 A, power factor 0.89, rated speed 1490 r/min, by adjusting the fan valve opening to achieve the adjustment of air volume. This paper introduces a method to adjust the speed of the fan by using the hydraulic coupler. The disadvantages of this method are low efficiency and large loss of the fan, especially at low speed. Because the liquid coupler often fails, it basically maintains a constant speed for a long time.

The load of the power plant is generally adjusted or changed within the rated load range of 50-100%. When the output power of the generator changes, the relevant devices of the boiler system should also be adjusted according to the load. On this basis, a new design scheme is designed, which is adjusted according to different air volume and air volume. The throttle loss is large, especially under small load conditions, a considerable part of the motor output is dissipated on the deflector, resulting in a large throttle loss.

The starting current of the induction motor can usually reach 5-8 times the rated current of the motor, which has a huge impact on the motor and the power supply line, and seriously affects the safe operation of the power grid. At the same time, due to its large impact torque and pulse current, the service life of the motor and fan can be greatly shortened. Practice has proved that adopting high voltage frequency inverter technology to speed regulate the motor to meet the production needs of different loads is an effective method.

In order to reduce the power consumption of the unit and reduce the operating costs, our factory has studied and used four 2000 kW/6 kV FD5000 high-voltage frequency inverters of FGI Company for Unit 3 and Unit 4.

2.Implementation plans

In the operation of the host, DCS is used for remote monitoring and monitoring through RS485 communication to enhance security. The working condition of the FD5000 high voltage frequency inverter is controlled by the existing DCS in the factory, which can monitor the FD5000 high voltage frequency inverter in multiple locations in real time through RS485 communication.

In the control system of boiler induced draft fan, the variable frequency operation mode is divided into manual control and automatic control of furnace negative pressure PID regulation. Under normal conditions, the induced draft fans of A and B frequencies run in parallel. In the control system of the induced draft fan, the air valve of the induced draft fan is fully open, and PID controller is used to adjust the speed of the induced draft fan, so that the negative pressure of the boiler can be stabilized.

When the single frequency inverter trip fails, the system connects the high pressure switch at the upper part of the trip frequency inverter to complete the conversion of the original induced draft fan chain action logic, and completes the automatic load reduction of the boiler by single-side fan trip. The negative pressure automatic regulation system of the furnace automatically increases the speed of another induced draft fan, and closes the exit baffle of the induced draft fan through the feedforward signal of the fan, so as to reduce the disturbance impact of a single induced draft fan on the negative pressure value of the furnace. When the single-end induced draft fan trip, in order to adapt to the rapid response of the system, the automatic negative pressure adjustment system in the furnace will automatically adjust the PID control parameters according to the rapid response characteristics of the system, so as to improve the reaction rate of the single-end induced draft fan and ensure the control quality of the boiler under variable load.

3.Application advantage

(1) After using FD5000 high voltage frequency inverter, the motor realizes the soft start, eliminates the impact on the power grid and the load, avoids the operation overvoltage and damages the motor insulation, and extends the service life of the motor and the fan.

(2) Using FD5000 high voltage frequency inverter adjustment, reduce the baffle throttle loss, and can uniform speed regulation, to meet the production needs, save a lot of electricity.

(3) The speed is reduced under low load, which reduces the wear and vibration of the mechanical part, and extends the overhaul cycle of the fan, thus saving a lot of maintenance costs.

(4) It has the characteristics of high control precision, strong anti-interference ability, small harmonic content, and perfect protection function, which is conducive to the safe operation of the motor and the fan.