MV variable frequency drive in Thermal Power Plant
The application of the medium voltage variable frequency drive in the large-sized asynchronous motor is just at the initial stage in China, which, however, has been pretty popular in the developed countries. As the development of the electronic components, types of the medium voltage VFD become very diverse. By the topological structure, the medium voltage VFD can be classified as IGBT module serial-connection type, tri-level type and multiple power unit serial-connection type with voltage superposition.
Considering that there will be just a little pressure change, we decided to only reconstruct the 2# water supply pump with the variable frequency drive.
Close-loop control
Shut down the by-pass valve of each pump, and realize close-loop control by the VFDs PID function, and the DCS system will provide the given 4~20mA corresponding to 0~10MP. And the press transformer on the pumping main will feed back the 0~10MP press signal to the VFD, and to control output torque by PID, so as to adjust the water flux.
Efficiency
According to the characteristics of the pump, it can be found that the flux varies due to different motor speed. On condition that less water is needed in operation, we can decrease the motor speed through the VFD rather than the valve, thus we can save a lot of electricity.
Conclusion
In recent years, Chinese government has been shifting focuses on energy saving and environmental protection, issuing a series of preferential policies to encourage its enterprises to save energy. Chinese companies, pretty active to respond to the government's appeal, are endeavoring to enhance their management level on energy use, reduce production cost and strengthen their competitiveness, which indirectly promotes the expansion of the VFD.
Considering that there will be just a little pressure change, we decided to only reconstruct the 2# water supply pump with the variable frequency drive.
- Adopt the mode of one VFD to control one pump, and no need to add power frequency bypass system
- Take 4~20mA current of the pressure transmitter from the pumping main as the feedback signal, and obtain the given frequency from the DCS system
- Run signal and stop signal are given by the DCS system
- The condition signal of the medium voltage VFD is sent from the control cabinet to the DCS system for the purpose of instantaneous detection
- The pressure value of the pumping main can reach or overrun the requested 6.8MPa after reconstruction
- Shut down the by-pass valve of each pump, and the appropriate flux can be produced by adjusting the speed of the motor through the medium voltage VFD
Close-loop control
Shut down the by-pass valve of each pump, and realize close-loop control by the VFDs PID function, and the DCS system will provide the given 4~20mA corresponding to 0~10MP. And the press transformer on the pumping main will feed back the 0~10MP press signal to the VFD, and to control output torque by PID, so as to adjust the water flux.
Efficiency
According to the characteristics of the pump, it can be found that the flux varies due to different motor speed. On condition that less water is needed in operation, we can decrease the motor speed through the VFD rather than the valve, thus we can save a lot of electricity.
Conclusion
In recent years, Chinese government has been shifting focuses on energy saving and environmental protection, issuing a series of preferential policies to encourage its enterprises to save energy. Chinese companies, pretty active to respond to the government's appeal, are endeavoring to enhance their management level on energy use, reduce production cost and strengthen their competitiveness, which indirectly promotes the expansion of the VFD.
