Perspectives: Energy Saver

Optimize Electrical Systems, Part II

Take a closer look at electric motors and plugged-in loads for potential energy savings.

By Ven V. Venkatesan, Energy Columnist

Improving motor efficiency is the most common opportunity to save electricity. Several factors can decrease motor efficiency: poor maintenance and lubrication, misalignment, frequent starting and stopping, and improper sizing. Under-sized motors draw excessive current to do the work and eventually fail due to overheating. Generally, motors are correctly sized, but if change in loading conditions makes the motor under-sized, it needs to be replaced with suitable-sized unit. Over-sized motors can draw more current than required for the work, wasting energy. In such a case, reducing the motor speed with a variable frequency drive could lower the power draw to deliver the same work. For correctly sized motors, installing ammeters would help to ensure the motor is not overloaded continuously.    Installing a variable frequency inverter on AC induction motor drives is the most common energy savings project to reduce electricity consumption, especially for plants operating a large number of centrifugal pumps and fans. In the normal plant design, most of these pumps and fans are coupled with discharge-side flow control valves to meet the exact process requirement. However, discharge-side valve or damper control is inefficient for fluid flow control. Varying the speed of the centrifugal pump or fan is much more efficient.

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