Medium Voltage Frequency Inverter for Power Plant
This application introduced Gozuk inverter Power Plant, made comparison for energy saving, explained application prospect of variable frequency drive.
There are 4 sets of generators in power plant. Capacity of 1#, 2# units is 125MW. Capacity of 3#, 4# units is 135MW. Before reconstruction, 1# and 2# FD fans adopted damper adjusting, this caused much energy wasted. In order to save energy and improve adjustment quality, we finally chose variable frequency technology after long term discussion. Variable frequency technology is advanced and drive is installed easily. It only connects between MV breaker and motor, without modification for motor and load. In October 2006, we installed two frequency inverters in A, B sides 1#FD fan. Inverter realizes stepless adjustment, wide adjustment range, high adjustment precision and high efficiency, soft start. The frequency inverter saves energy and reduces maintenance.
Motor parameters:
Bypass cabinet is designed to keep system reliability. When inverter is broken, motor is switched to direct on line manually. Bypass circuit is composed of three isolators. QS2 and QS3 are double throw isloators and they are interlocked. In variable frequency state, QS1 and QS2 close, QS3 opens; in direct on line state, QS1 and QS2 open, QS3 closes.
Inverter link locks with MV breaker. In case of frequency inverter fault, MV breaker trips off. In direct on line state, inverter cancels signal of breaker trip-off. Motor starts/stops by breaker normally.
PLC communicates with DCS. Start/stop, frequency adjustment are controlled by DCS. Meanwhile, inverter status feeds back to DCS.
Energy saving effect
1) inverter parameter
2) motor parameter
3) Calculation
For fan and pump: Q∝n ,H∝n2,P∝n3
n---speed;
Q---flow;
H---pressure;
P—shaft power
When motor speed decreases to 80% of rated speed, input power of system (inverter + motor) decreases to 51% of that in rated speed. Thus, energy saving effect is more obvious when speed is low.
Make comparison in same working conditions:
The reconstruction cost can be recovered within 18 months.
Air-water cooling system
The site is very hot in summer, so we installed air-water cooling system to ensure reliability.
Hot air from inverter enters cooling device through air channel. There is 33℃ cooling water tube which makes heat exchange with hot air. Heat is taken away by circulating cooling water. Air from cooling device is cold, which keeps inside temperature less than 40℃.
2 sets of cooling devices are equipped with inverter. Single device fault causes little influence. From practical application, inside temperature keeps about 30℃.
By calculating, cost of air-water cooling system is 50% of air conditioner cost.
Conclusion
Inverter saves much energy, especially in low load, frequency inverter realizes soft start, prolongs motor lifetime, eliminates surge, reduces wear and tear.
2 inverters have been running stably since they put into service. The reconstruction is very successful.
There are 4 sets of generators in power plant. Capacity of 1#, 2# units is 125MW. Capacity of 3#, 4# units is 135MW. Before reconstruction, 1# and 2# FD fans adopted damper adjusting, this caused much energy wasted. In order to save energy and improve adjustment quality, we finally chose variable frequency technology after long term discussion. Variable frequency technology is advanced and drive is installed easily. It only connects between MV breaker and motor, without modification for motor and load. In October 2006, we installed two frequency inverters in A, B sides 1#FD fan. Inverter realizes stepless adjustment, wide adjustment range, high adjustment precision and high efficiency, soft start. The frequency inverter saves energy and reduces maintenance.
Motor parameters:
- Model :Y500-4-6
- Rated current :118.8A
- Rated power: 1000kW
- rated frequency: 50Hz
- rated voltage: 6kV
- rated speed: 990r/min
Bypass cabinet is designed to keep system reliability. When inverter is broken, motor is switched to direct on line manually. Bypass circuit is composed of three isolators. QS2 and QS3 are double throw isloators and they are interlocked. In variable frequency state, QS1 and QS2 close, QS3 opens; in direct on line state, QS1 and QS2 open, QS3 closes.
Inverter link locks with MV breaker. In case of frequency inverter fault, MV breaker trips off. In direct on line state, inverter cancels signal of breaker trip-off. Motor starts/stops by breaker normally.
PLC communicates with DCS. Start/stop, frequency adjustment are controlled by DCS. Meanwhile, inverter status feeds back to DCS.
Energy saving effect
1) inverter parameter
Model |
Gozuk inverter |
Input vlotage | 6kV |
Rated current | 130A | Rated power | 1000kW |
2) motor parameter
Rated power | 1000kW | Rated voltage | 6kV |
Rated speed | 990rpn | Rated current | 118.8A |
3) Calculation
For fan and pump: Q∝n ,H∝n2,P∝n3
n---speed;
Q---flow;
H---pressure;
P—shaft power
When motor speed decreases to 80% of rated speed, input power of system (inverter + motor) decreases to 51% of that in rated speed. Thus, energy saving effect is more obvious when speed is low.
Make comparison in same working conditions:
Load | inverter before | inverter after | Energy saving rate |
125MW | 70A | 48A | 25% |
100MW | 55A | 29A | 40% |
The reconstruction cost can be recovered within 18 months.
Air-water cooling system
The site is very hot in summer, so we installed air-water cooling system to ensure reliability.
Hot air from inverter enters cooling device through air channel. There is 33℃ cooling water tube which makes heat exchange with hot air. Heat is taken away by circulating cooling water. Air from cooling device is cold, which keeps inside temperature less than 40℃.
2 sets of cooling devices are equipped with inverter. Single device fault causes little influence. From practical application, inside temperature keeps about 30℃.
By calculating, cost of air-water cooling system is 50% of air conditioner cost.
Conclusion
Inverter saves much energy, especially in low load, frequency inverter realizes soft start, prolongs motor lifetime, eliminates surge, reduces wear and tear.
2 inverters have been running stably since they put into service. The reconstruction is very successful.
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