How variable speed drives help in motor protection

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Variable speed drives branch out as a segment of motor controllers. The frequency of the drives is directly proportional to the speed of the motor. These drives are used to control the frequency (measured in RPM) to meet the requirements of the electric motor’s load. Variable speed drives help in motor protection by changing the speed of direct current of the motor as per the voltage applied to the armature, i.e. direct current motors allow the drive to change the speed by adjusting the shunt field current.

The motor failure rate is conservatively estimated at 3-5% per year and goes to as high as 12% in mining and pulp and paper industry. It majorly happens because of three main causes, i.e., electrical, mechanical and environmental factors. However, apart from the downtime or loss of production, the operators also need to pay for repair or replacement and removal and installation.

Variable frequency drives can operate as motor protection devices along with their role as motor speed controllers. The adjustable speed drive consists of an electric motor and controller that is used to adjust the motor’s operating speed. Alternatively, this setup can be created by mounting a combination of a continuously adjustable mechanical speed-changing device and a constant-speed motor.

The advancement in technology has increased the use of VFDs in all applications ranging from small appliances to large compressors. Electric motors consume about 25% of the world’s electrical energy in industrial applications. The efficiency of these operations can be enhanced by using VFDs in centrifugal load service and motor starters. However, the industries are yet to realize the need for such applications as its global market penetration is relatively small.

Power electronics based variable frequency drives are rapidly making older technology redundant. The new developments now focus on servo motors with hydraulics and air valves. The new age system comes with various feedback and performance measurement indices. Schneider Electric India has been the pioneer in the production of variable speed drives and motor protection instruments which when used in couple yields desired throughput from the operating machinery.

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