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Vertical roller mill in Cement industry Case - Medium Voltage Inverter
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Summary:In this paper, through introducing INVT GD5000 medium voltage inverter applied to vertical roller mill in the Pakistan, in order to illustrate VFD transformation of the feasibility and economy. Especially it can increase raw milling production, input power factor and other benefits.

Keyword:GD5000 medium voltage inverter, Vertical roller mill, increase raw milling production;

1. Introduction
Modern urban infrastructure construction cannot leave the participation of cement, and cement production needs all kinds of equipment to work together. Vertical roller mill machine is a very important device in the cement factory.
Along with development of energy control technology, nowadays mostly motors are driven by inverter instead of old traditional technology such as soft starter for smarter control and energy saving purpose.

2.Project Analysis
Flying cement is a cement capacity 5000 tons/day factory. Right now they use soft starter to drive vertical roller mill.

Figure 1.The original main electrical circuit diagram

Detailed motor parameters are list as follow:

Motor Model


Rated Voltage

Rated Current

Rated Speed

Power Factor

Load Type







The Vertical mill

Table 1.Vertical Motor Parameters

The system work method: when the medium voltage power is ready, close the QF; Secondly soft starter work slowly driving vertical mill motor; Finally the grid power drive vertical mill motor directly.

INVT suggest VFD solution:

VFD Model


Rated Voltage

Rated Current






Manual Bypass Cabinet

3. System Configuration
3.1 VFD system instruction.
According to the demand on site, the variable frequency driver consists of transformer cabinet, power unit cabinet, control cabinet and manual bypass cabinet. This GD5000 MV VFD has the functions of local/remote button, emergency stop button and power frequency/variable frequency indicators on control cabinet.


Figure 2 The main circuit electrical diagram

The system work process as below:

Firstly, when the medium voltage power is ready, close the QF; Secondly, after VFD is charged run VFD to drive motor; Thirdly, based on actual need running VFD; Fourthly, if VFD is fault, the grid power from bypass cabinet and soft starter to drive motor.


3.2 Cooling system introduction:

3.3 Air conditioner requirement calculation.
The VFD model is GD5000-A3550-6.3-D. The VFD rated power is 2800KW. The efficiency of VFD
is 96%.So the power consumption is 2800KW*4%=112KW.
Based on simulation calculation value that is 1KW air conditioner can cool 3 KW heat. So the air conditioner rated power is : 112KW/3=37.3KW.
Finally we suggest customer choose air conditioner rated power is 40KW.

4. Application and Advantage
After using VFD, here are some advantages as follow,
1. Higher power factor. Over 0.95,  
2. Increase raw milling production. The vertical mill motor running at 60Hz, which is faster than before, so it can increase raw milling production.
3. Very low torque pulse without causing the resonance between the motor and other mechanical devices, and reducing the transmission mechanism wearing.
4. Perfect output waveform, less than 4% of distortion.
5. Easily controlled by DCS system;
6. Reduce the loss of shutdown maintenance and save plenty of maintenance costs.

5. Conclusion
Compared with original vertical roller driven method, the VFD method has much more advantages. The VFD system is easily controlled by DCS and the VFD running speed can automatic adjusted from 0Hz to 60 Hz. The upgraded inverter system works very well, customers are satisfied and investment payback period about 6 months by saving power energy.

[1] GD5000 Series High-voltage Variable Frequency Speed Control System Manual.    Shenzhen Invt Electric CO., LTD.

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