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Home » Applications » AC drive for water supply pump in power plant
AC drive for water supply pump in power plant
Recently, power generating cost is increasing with the price of power and coal rising. In order to reduce power consumption rate, after full investigations, we decide to reform with technology of variable frequency to heighten competitive power.
There are three sets of 220t/h boilers equipped with four medium voltage water supply pumps. Pumps' inlet fetches water from the public pipe of deaerator, and the outlet water flows into the same pipe. The supply water is adjusted by the governing valve. Some water might flow back deaerator by opening the recycling valve if there is much deviation of water supply. However, the self-circulation would result in waste of water and power so that there is great potential for energy-saving.
Before the reform, the water flow is adjusted by opening of valve. Actually it is adjusted by the pressure loss, not the output of motor. After the reform, in full-opening state of valve, flow is controlled by adjusting motors' speed with great potential of energy saving. In 2005, we made a lot of field surveys and researches, finally we choose Gozuk which takes the largest market share in Chinese medium voltage AC drive field.
Main circuit
The system is type of one drive one. AC drive directly connects with the 6kV power cable to drive the motor. To improve the reliability, a bypass circuit might be needed.
The bypass circuit is composed of 3 medium voltage isolator switches QS1, QS2 and QS3 (QF is the original medium voltage breaker). It requires that QS2 and QS3 can not be closed together and they are interlocked mechanically. When the motor is driven by medium voltage AC drive, QS1 and QS2 are closed and QS3 is open; when the motor is in direct on line, QS3 is closed and QS1 and QS2 are open.
For the purpose of protecting, medium voltage AC drive is link locked with the switch QF. Once medium voltage AC drive faults, QF will switch off. In direct on line state, medium voltage AC drive allows QF switch-on and cancels the switch-off signal to enable the motor to start.
Parameters of water supply pump
Parameters of motors
Parameters of pumps
Parameters of circulating pump
Drives Type choosing
According to operating experience, the max work current of water supply pump's motor is less than 150A, we choose Gozuk drives. The rated output current is 170A which fully meets the need of site. In a similar way, we choose the AC drives for motor of circulating pump.
Site control of AC drive
The output frequency of AC drive is controlled by a 4~20mA standard industrial signal which is from a LU-900M intelligent monitoring instrument with PI controller. The instrument input a 4-20mA pressure signal of pipe. Adjust set value through the meter panel which can implement non-disturbance switch for open/close loop control. The system figure as below:
Energy saving effect
The motor's current of water supply pump is about 120~130A before reform, and 90~110A after the reform.
Flow is basically same. Current of heat supply network circulating pump is about 55A, After the reform, it comes to 45A.
Other effects of the application
Conclusion
Since the AC drive was used, it has been running stably and greatly. It improves the site operating state, and reduces the working strength of the operators. Most of all, the station service labour decreases obviously. In 2006, for better effect we purchased four sets of AC drive for the boilers' fans again. We do believe more and more AC drives would be used in thermal- power corporations for building a more conservation-minded society.
There are three sets of 220t/h boilers equipped with four medium voltage water supply pumps. Pumps' inlet fetches water from the public pipe of deaerator, and the outlet water flows into the same pipe. The supply water is adjusted by the governing valve. Some water might flow back deaerator by opening the recycling valve if there is much deviation of water supply. However, the self-circulation would result in waste of water and power so that there is great potential for energy-saving.
Before the reform, the water flow is adjusted by opening of valve. Actually it is adjusted by the pressure loss, not the output of motor. After the reform, in full-opening state of valve, flow is controlled by adjusting motors' speed with great potential of energy saving. In 2005, we made a lot of field surveys and researches, finally we choose Gozuk which takes the largest market share in Chinese medium voltage AC drive field.
Main circuit
The system is type of one drive one. AC drive directly connects with the 6kV power cable to drive the motor. To improve the reliability, a bypass circuit might be needed.
The bypass circuit is composed of 3 medium voltage isolator switches QS1, QS2 and QS3 (QF is the original medium voltage breaker). It requires that QS2 and QS3 can not be closed together and they are interlocked mechanically. When the motor is driven by medium voltage AC drive, QS1 and QS2 are closed and QS3 is open; when the motor is in direct on line, QS3 is closed and QS1 and QS2 are open.
For the purpose of protecting, medium voltage AC drive is link locked with the switch QF. Once medium voltage AC drive faults, QF will switch off. In direct on line state, medium voltage AC drive allows QF switch-on and cancels the switch-off signal to enable the motor to start.
Parameters of water supply pump
Parameters of motors
| Motor type | YK1600-2/990 | Rated voltage (U0) | 6KV |
| Rated power (Pdn) | 1600kW | Rotate speed (n0) | 2980r/min |
| Rated current (I0) | 186.5A | Power factor | 0.86 |
Parameters of pumps
| Pump type | DG230-140 | efficiency | 76% |
| Shaft power | 1200kW | Rotate speed (n0) | 2960r/min |
| Rated flow | 230t/h | lift | 1470m |
Parameters of circulating pump
| Circulating pump motor type | Y400-4 | Rated voltage (U0) | 6KV |
| Rated power (Pdn) | 500kW | Rotate speed (n0) | 1480r/min |
| Rated current (I0) | 59A | Power factor | 0.87 |
Drives Type choosing
According to operating experience, the max work current of water supply pump's motor is less than 150A, we choose Gozuk drives. The rated output current is 170A which fully meets the need of site. In a similar way, we choose the AC drives for motor of circulating pump.
Site control of AC drive
The output frequency of AC drive is controlled by a 4~20mA standard industrial signal which is from a LU-900M intelligent monitoring instrument with PI controller. The instrument input a 4-20mA pressure signal of pipe. Adjust set value through the meter panel which can implement non-disturbance switch for open/close loop control. The system figure as below:
Energy saving effect
The motor's current of water supply pump is about 120~130A before reform, and 90~110A after the reform.
Flow is basically same. Current of heat supply network circulating pump is about 55A, After the reform, it comes to 45A.
Other effects of the application
- After the reform, it only needs to adjust the speed of the motor in the control room so that the valve is not need to be changed. By AC drive, speed starts from zero and rises gradually. Thus, there is no large starting current which could protect the motors.
- Reduction of the maintenance. After the reform, it could avoid vibration caused by pumps' deviation from working area in valve control mode. Generally, the application of AC drive is for reducing the speed of pump. Because of slow start-up and low-speed running, it correspondingly prolongs the lifetime of the components, such as the hermetic seal, shaft.
- Reduction of working strength. For the interlocks between the running devices and back-up devices, system implements protection and malfunction alarm automatically, so it greatly reduces the working strength, improves productivity and provides reliable guarantee for the optimizing operating.
- Reducing the impact of grid side. In direct on line state, the starting current is about 6~7 times of rated. After the reform, soft-start becomes a reality. Starting current is about rated. Starting time is prolonged correspondingly so that there is not too much impact on the grid side. At the same time it could prolong the lifetime of the motors.
Conclusion
Since the AC drive was used, it has been running stably and greatly. It improves the site operating state, and reduces the working strength of the operators. Most of all, the station service labour decreases obviously. In 2006, for better effect we purchased four sets of AC drive for the boilers' fans again. We do believe more and more AC drives would be used in thermal- power corporations for building a more conservation-minded society.
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