Typical application case: from June to July in 2007, HARSVERT sold 18 sets of high voltage VFDs to Shanshui Group. Most of them are applying on high temperature fans, kiln head coal mill fans, kiln head surplus fans, raw mill circulating fans and so on. Two production lines with daily productivity 5000T in Zibo Shanshui Cement Company and Pingyin Shanshui Cement Company. By VFD, the two production lines achieve ideal energy-saving effect.

2 The shortcomings of original hydraulic couplers

1) Hydraulic coupler is mechanical adjusting speed equipment. It has 5-8% speed loss. Power loss is converted into heat, so a great mount of cooling water is needed to cool oil.

2) The oil temperature is above 95 degree in the actual operation, the water of cooling equipment is easy to scaling and plugging, which results in trouble.

3) Because the hydraulic couplers deliver power by hydraulic pressure oil, its speed control is not stable, the power factor and accuracy of speed adjusting is bad.

4) Because of the low efficiency of the whole hydraulic couplers, low power factor, inaccuracy of speed adjusting, big speed adjusting loss, a large amount of maintenance and high costs, energy-saving effect is not significant .

3 Introduction of high voltage adjusting speed system

Asynchronous motor adjusts speed by changing the supply power frequency of stator to realize variable frequency adjusting speed. It can maintain small speed disparity during the process from low speed to high speed, so the small consumption speed disparity power and high efficiency is the most reasonable method of adjusting speed for asynchronous motor.

At present, the variable frequency adjusting speed is main adjusting speed method for asynchronous motor; it is widely used in many fields.

High voltage variable frequency speed adjusting system has many significant advantages as following:

(1) A lot of expenditure loss caused by load tailgate or valve adjustment will disappear after VFD reconstruction;

(2) The power factor of asynchronous motor rises from 0.85 to above 0.95 after using VFD;

(3) The high voltage VFD has smallest loss and the efficiency of the whole equipment is 97%;

4 The comparison of VFD and hydraulic coupler

(1) Speed adjusting range of HARSVERT-A high voltage VFD is from 0 to100%. Speed adjusting range of hydraulic coupler is from 40% to 95%, and it has 5% speed loss at high speed range. This will affect output power of equipment.

(2) The efficiency of HARSVERT-A high voltage VFD is high in the whole adjusting speed range ( more than 96%), but the efficiency of hydraulic coupler decreases with adjusting speed decreasing, this results in a lot of loss. Energy-saving decreases sharply.

(3) HARSVERT-A high voltage VFD realizes soft-start for motor. It solves start impact problem thoroughly. If needed, motor can start frequently in a short time. Hydraulic coupler can\'t solve the start impact problem. Motor still starts directly and needs starting device. It also has big start impact and can\'t start frequently in a short time.

(4) When HARSVERT-A high voltage VFD drives motor, the motor only needs to be separated from original switch and electrical connection cable. Then connect it to high voltage VFD. It is no need to change connection of motor or change any basic mechanism. When hydraulic coupler puts into service, it must be connected in series with motor and mechanical connection axis. Basic equipment needs to be moved and re-casted. These modifications may be not permitted in some sites.

(5) HARSVERT-A high voltage VFD is high-technology equipment with high reliability and free maintenance. Hydraulic coupler is mechanical equipment with oil pipeline, water pipeline and many sets of systems, so it has high failure rate and heavy maintaince, which shortens the effective production time.

5 Variable frequency reconstruction of high temperature fans

According to the load parameters and operation condition provided by cement plant, HARSVERT-A06/300 (rated voltage is 6kV, rated current is300A) is applicable to the plant.

The power and the heat diffusion of high voltage VFD is much. In order to ensure adequate ventilation cooling, Leader&Harvest designs wind duct on the top of VFD cabinet and power cabinet respectively. They connect to outlet as a whole, discharging the heat outside, ensuring the reliable ventilation effect.

8 The statistic of energy saving

1) The comparison table between Zibo shanshui cement no.1 and no.2 kiln fans before and after reconstruction.

8 sets of HARSVERT-A VFDs in different occasions as follows:

From above data we see energy-saving efficiency of each kiln system fan after reconstruction.

Taking the calculation of the fans in line 1 kilns for example:

energy-saving power:

（790－661）+（774－681）+（2221－1777）+（348－247）＝767（kW）

yearly energy-saving:

767kW×7392h＝5669600kW·h

yearly energy-saving: