1.Overview

The XFLD power plant has 3155MW generator sets (steam engine) and 4520t / h boilers, with two functions: one is to generate electricity for the production needs, and the other is to supply the steam needed by the alumina plant. Each boiler is equipped with two centrifugal induced draft fans, dragging the motor selected YKK630-4 motor, rated power: 2000kW, rated voltage: 6kV, rated current: 226A, power factor: 0.89, rated speed: 1490 r/min, by changing the opening of the fan air valve to adjust the air volume. Using hydraulic coupler speed regulation, its disadvantages are: low efficiency of the fan, large loss, especially in low speed operation, lower efficiency. Because the liquid coupling often fails, so it is basically in the constant speed state for a long time.

The power generation load of the power plant is usually adjusted and changed between 50% and 100% of the rated load. For the change of generator output power, the related equipment of boiler system should also be adjusted accordingly with the change of load. The air supply volume and air supply volume of the boiler change accordingly, and the output adjustment of the induced draft fan is adjusted by changing the opening degree of the fan air valve. Thttling loss is large, especially in low load operation, the motor output power of a lot of energy consumption on the baffle, the throttling loss is greater. The starting current of the asynchronous motor generally reaches 5~8 times of the rated current of the motor, which causes a large impact on the motor and power cable, and has a certain impact on the stable operation of the power system. At the same time, the powerful impact torque and impact current shorten the service life of the motor and fan machinery. Through a large number of applications shows that the application of high voltage frequency inverter conversion speed control device to change the motor speed, to meet the process requirements of different loads, is an effective means to solve the above contradictions.

In order to reduce the power consumption rate and reduce the operating cost of the unit, the power plant leaders of the company decided to use 4 sets of 2000kW / 6kV FD5000 high voltage frequency inverter produced by FGI on the 3 # and 4 # generator sets to transform the induced draft fans of the 3 # and 4 # generator sets respectively.

2.Implementation plans

In terms of the main body operation, DCS control and RS485 monitoring are adopted to improve the safety performance of the system. The operating state of FD5000 high voltage frequency inverter is controlled by the existing DCS in the power plant, and the operating parameters of FD5000 high voltage frequency inverter are monitored in multiple places through RS485 communication.

In the control system of boiler induced draft fan, frequency conversion operation mode is divided into manual control and furnace negative pressure PID adjustment automatic control. Under normal circumstances, the A and B frequency conversion induced draft fans are put into operation at the same time. In the induced draft control system, the air valve of the induced draft fan is fully open, and the PID regulator stabilizes the negative pressure of the furnace by controlling the speed of the induced draft fan.

When a single frequency inverter fails to trip, the high voltage switch at the top of the system joint jump frequency inverter realizes the switch of the original chain action logic of the induced draft fan, and the boiler joint jump of the single side draft fan, and realizes the control logic of automatic load reduction of the furnace. 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. After the trip of the single-side induced draft fan of the system, in order to meet the rapid response characteristics of the system, the furnace negative pressure automatic regulation system automatically adjusts the PID control parameters, so as to improve the response speed of a single induced draft fan and ensure the control quality of the furnace in the variable load operation.

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.