INVT Medium Voltage VFD Applied to Sugarcane Mills in Cuba

Summary: In this case，through introducing INVT GD5000 medium voltage drive applied to sugarcane mills in the Cuba to illustrate variable frequency drive transformation of the feasibility and economy. Especially can increase sugar extraction rate, upgrade sugarcane crushing technology, prevent press from getting stuck and energy saving.

Keyword: GD5000 medium voltage drive, Sugarcane mill, increase sugar extraction rate.

1. Project introduction and analysis

Cuba is the traditional sugar exporter country and has long history in manufacturing sugar industry. Due to technology of sugar manufacturing in Cuba is old and outmoded; many sugar plants are closed and stopped.

There is one sugar plant named Ciro Redondo sugar mill in Ciego De Avila city. This plant is closed many years and lots of devices are old and damaged. There are many steam turbines in sugarcane shredding and mill process.

Old sugarcane mill line which used steam turbines has below disadvantages:

1) Steam pressure instability.
Normally steam turbine control steam pressure by valve. By this way it can’t adjust pressure smoothly, so the steam pressure is instability. For this point, when sugarcane milling sugarcane is easily getting stuck and whole sugarcane mill line will be stop.

2) Low steam power efficiency.
Due to technology of boiler is old, the boiler producing steam pressure is low; it means each kw of sugarcane milling turbine need more bagasse fuel compared with high pressure boiler.

3) High maintenance costs for pipe network of steam.
From boiler to each sugarcane steam turbines, there are lots of big and long pipe network of steam in main network and branch network. Because of steam high pressure and high temperature, those pipes need much maintenance work and costs after sugarcane season.

4) Low rate of sugar extraction.
Due to steam pressure is instability and sugarcane milling running not smoothly, it will impact sugar extraction rate.

In order to increase sugar production and update sugar plant technology, AZCUBA group plan to transform this plant and restart it. The new plant sugarcane milling capacity is 5,000 tons/day.

Old sugarcane mill line:

Figure 1.The old sugarcane mill line

2. System Configuration

2.1 Motor introduction.
Detailed motor parameters are list as follow:

Table 1.No.1 sugarcane mill motor Parameters

Table 2.No.2-No.5 sugarcane mill motors Parameters

Figure 2.The sugarcane mill motors and gear units

2.2 System solution.
Based on INVT experience on sugar industry variable frequency driver renovation project, INVT can supply whole solution for the customer.
According to customer demand, the variable frequency drive (VFD) consists of buffer cabinet, transformer cabinet, power unit cabinet and control cabinet. The GD5000 MV VFD has function of local/remote button and emergency stop button on control cabinet.

INVT suggest VFD solution:
Table 3.MVD for sugarcane No.1 mill

Table 4.MVD for sugarcane No.2,3,4,5 mill

Main systme diagram:

Figure 3.The system diagram

Figure 4.The sugarcane mill VFDs

3. Application and Advantage

After using VFDs, there are some major advantages as follow:

1. Sugarcane mill stability.
Because VFD is a step-less speed regulation, the sugarcane mill can be run smoothly with wide speed rang. VFD adjusted torque automatic according to sugarcane capacity.

2. Increase sugar extraction ratio.
Due to VFD adjust speed and torque automatic, the sugarcane can be milled thoroughly and adequately. Whole system can increase sugar extraction rate.

3. Increase grid line power factor.
The grid line power factor is over 0.97. It can increase efficiency of the grid.

4. Energy saving.
The sugarcane mill is not running at full speed and power all the time. The real running situation depend on sugarcane capacity and sugar production. When it run at low speed, there is much energy saving.

5. Perfect output waveform.
Output waveform is perfect, less than 2% of distortion.

6. Prolong motor working life time.
VFD can keep motor running at optimal situation.

4. Conclusion

Compared with old technology, the VFD driven method has many advantages. Especially increase sugar extraction ratio. The transformational VFD system works very well, customers are satisfied with INVT solution and INVT VFDs met with customer’s requirements.

References
[1] GD5000 Series Medium-voltage Variable Frequency Speed Control System Manual. Shenzhen INVT Electric CO., LTD.