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Application of Medium-voltage VFD on condenser pump
Abstract: This article focuses on the application of China-made cell-cascade multi-level medium-voltage frequency drive system in the Zhangshan Power Company on 2 # Unit Condensate water system, makes a comparison of energy saving before and after the reform. The results showed that the main auxiliary equipment in power plant using medium-voltage frequency drive system is feasible, with quick pay-back and other characteristics. VFD has a positive significance to reduce power consumption .
Key word: Medium voltage frequency drive condenser pump Application

1.Preface
Zhang Shan power plant has two units of air-cooling system of of 300MW. VFD is manufactured by Beijing Leader&Harvest Electric Technologies Co., Ltd. Pump adopt mode of "one work, one standby". Water level of deaerator is adjusted by damper. We have a discussion about VFD application according to the actual situation of # 2 Unit condenser Pump reform in Zhangshan Power Plant.

2.Operating Conditions
to ensure continuous and stable operation of condenser pump is an important factor of power generating units security. Condenser system is shown in following.

Principle of system is shown in following

After the VFD reform, during normal operation, adjust VFD output frequency to change the speed of Condenser pump, to adjust flow and control the water level of deaerator. Following is condenser control programe.

3.The effect of Energy-saving
(1)The power saving is remarkable in the plant
As shown in Table 1:

Unit Load(MW) 200 210 220 230 240 250 260 270 280 290 300
Pump Current(Before Reform) 81.8 84.2 85.4 88.0 90.6 91.1 93.9 94.5 95.0 95.8 98.2
Pump Current(After Refore) 29.0 30.5 36.0 43.0 48.0 50.0 52.0 56.0 70.0 72.0 82.0
Reduce the current A 52.8 53.7 49.4 45.0 42.6 41.1 41.9 38.5 25 23.8 16.2

Table 1:VFD current before and after the reform

Units power consumption kW·h power saving kW·h
#1(direct on line) 307000
#2(variable frequency) 186000 121000

Table 2:Saving Statistics

As each unit run 300 days a year, according to the power price 0.25 yuan / kWh. 605000 yuan (USD 88970) is saved.
(2)Reduce the impact current when the motor starts
Observing the load curve, we find no impact current when the VFD starts. The current rises from zero with speed increasing and never exceeds the rated current in any cases. Therefore, VFD solves the large current impact issue when the motor starts, eliminates a large starting current to the motor, significantly reduces the costs of routine maintenance. Here is starting current trend (Initial Speed: 900r/min).

(3)Extend equipment life
Using the VFD can change the motor speed along the condenser pump characteristic curve, extend the life of the bearing. Data shows that reducing condenser pump speed can prolong life of condenser pump. So cost would naturally be reduced.
(4)Reduce noise
After the reform, not only pump speed is down but also the noise dramatically lowers. Condenser pumps operating conditions have improved significantly.

4.Conclusion
The successful application of VFD on condenser system fully shows that VFD control technology has a broad application prospects and development potential with significant energy-saving effect, good system response and quality of control. It has a positive significance in improving the competition power of enterprises and reducing cost.

From the Editor:
For VFD reform project in Zhang Shan Power Plant 2 × 300MW units, Beijing Leader-harvest electric technologies Co., Ltd makes full electrical system design, DCS logic design, system commissioning, construction and other technical services. Leader Harvest provides a comprehensive and effective technical support services for the implementation of the project to achieve energy-saving. Leader Harvest VFD optimizes the system operation process, protects system security, improves energy efficiency and other economic benefits.

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