Application of FGI FD5000 high voltage frequency inverter in circulating pump in power plant

1.Overview

GXLD alumina and electrolytic aluminum plant belongs to the power consumption, need a lot of electricity, if only use the national grid electricity, one is high cost, another when the power production is limited, the secondary steam power plant and alumina plant need a lot of use, so aluminum electricity base generally have their own self-provided power plant.

The company's power plant has 3155MW generator sets (steam engine) and 4520t / h boilers (3 for 1 standby). Each steam engine has two circulating pumps (A and B circulating pumps), and the whole power plant has six circulating pumps. Under normal circumstances, only one circulating pump is opened, and the other pump is used as standby. The circulating pump is changed once every 3 months. The circulating water pump motor has two taps, high speed 495rpm, power 1600kW; low speed 425rpm, power 1250kW / 1120kW. Speed regulation method: large water supply in summer, high speed motor, small water supply in winter, low speed motor.

In order to reduce the power consumption rate and reduce the cost of power generation, the power plant leaders of the company decided to use 3 sets of 1600kW / 6 kV FD5000 high voltage frequency inverter produced by FGI on the 6 circulating pumps of 1 #, 2 # and 3 # generator sets.

2. Implementation plans

In terms of frequency conversion speed control system operation, there are two control methods: remote control and local control, which can improve the safety performance of the system. The operating state of the FD5000 high-voltage frequency inverter is monitored by the existing DCS of the power plant, and the frequency inverter is controlled by remote control and local control.

In order to ensure the safe operation of the generator set, in the frequency conversion operation mode, when the frequency inverter and water pump fail the high voltage circuit breaker, the standby circulating pump needs to be put into operation automatically.

The variable frequency speed control system is connected to the existing DCS system of the generator set. According to the load situation of the unit, the DCS automatically controls the boiler circulating water pump speed according to the setting procedure. The switching volume output that the frequency inverter needs to be provided to the DCS includes fault alarm, readiness indication, operation indication, high voltage closing permit, joint jump high voltage signal, pump bypass switch closing signal, frequency conversion KM1 closing signal; The switching quantity that the DCS needs to supply to the frequency inverter includes: frequency conversion start (dry node, Effective when closing), frequency conversion stop (dry node, Closed effectively), frequency conversion emergency stop (dry node, Effective when closed); The DCS needs to be provided to the frequency inverter analog quantity: 2 lines of 4 ~ 20 mA current source output, One signal is that the circulating water pump frequency given, As a given value of the rotation speed of the frequency inverter, Another signal is the circulating water pump female pipe pressure given; The analog required to DCS are: 2 lines of 4 ~ 20 mA current source output, The corresponding physical quantity of the analog output is the output frequency and the output current; The analog quantity provided to the frequency inverter is: 1 current source output of 4 ~ 20 mA, Represents the outlet pressure of the variable frequency pump.

The frequency inverter has a manual / automatic control mode. When the manual control mode is selected, the frequency inverter is not controlled through the PID controller, and by the local and remote control speed control buttons, so as to change the flow rate of the water pump and achieve the purpose of manually adjusting the condenser vacuum. When the automatic control mode is selected, the vacuum value of the condenser is set by the operator through the CRT, and the measured value of the vacuum transmitter installed on the condenser shall be taken as the feedback value of the process control variable to compare with the given value. When the measured value of the vacuum transmitter is less than the given value, the output of the PID controller increases the frequency inverter speed, and the pump flow increases the cooling and accelerates. On the contrary, the output of the PID controller reduces the speed of the frequency inverter, and the pump flow reduces the cooling and deceleration, until the measured value is equal to the given value, and the motor speed is stable at a certain value. Realize the automatic control of the circulating water pump speed, so as to achieve the purpose of the water pump regulation.

3.Application advantage

In July 2010, compared with July 2011, After using FD5000 high voltage inverter,the average load of unit # 1 is basically about 118MW, the power frequency operation data of circulating pump is: power grid voltage is 6.2kV, motor current is about 163A, power factor is 0.82, pipeline pressure is 0.2MPa, and the average vacuum degree of the unit is about 90.5%. According to the operation data, it can be seen that after the frequency conversion transformation of 1 # unit, the input current is significantly reduced, and the vacuum degree of the unit is improved, and the power saving effect is obvious.