Published On: Mar 11, 2016
VSDs provide continuous control by matching motor speed to the specific demands of work being performed. They are an excellent choice because they allow operators to fine-tune processes while reducing costs for energy and equipment maintenance. Some of the known applications of VSDs are:
While VSDs prove to be a medium of saving energy consumption to a considerable extent, but they are also responsible for creating an adverse effect on the power quality. Some of the key PQ issues caused by VSDs are:
Thankfully, there are various ways of mitigating VSD generated PQ issues.
Problem Statement : Delta Paper Mill is one of the paper manufacturers in South India with three paper machines and a capacity of 51100 MT/annum of quality writing and printing papers. The paper machine section has a large number of VSDs installed and work continuously with multi drive control strategy. The plant was using 6-pulse thyristor rectifiers due to its well know advantages, however, it also emitted harmonic voltage and current.
Solution adopted : The data was recorded & measured using PQ analyser and it was observed that the considerable amount of harmonic distortion was present in both voltage and current waveforms of all the motor drives. In order to reduce the harmonic content of the motor drives, an Active Power Filter (APF) was implemented.
Benefits & Conclusion : Results were obtained for harmonic profile with APF as shown in below table:
|
% THD without filter |
% THD with filter |
---|---|---|
Voltage |
37.07% |
1.87% |
Current |
26.54% |
2.93% |
It is clear that the harmonic content has been reduced to a great extent with Active Power Filter.
Conventional motors with fixed speeds are inefficient for many industrial applications. Instead, VSDs are reliable and cost effective means to control the speed of electrical motors. Installing VSDs on electrical motor applications improves the efficiency of the system and saves a huge amount of energy. They require little maintenance, provide the most energy efficient capacity control, have the lowest starting current of any starter type, and reduce thermal and mechanical stresses on motors and belts. However, when considering using a VSD to a motor, care must be taken to ensure that the drive is really needed, that it is used in the best place and that it is being used correctly with suitable PQ mitigations to provide the best energy saving advantages to the industry.
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