Electric motors typically account for 60% to 70% of the electricity consumed in an industrial environment. The cost of labor and lost downtime to replace or repair even a small motor can be excessive.
Protecting a motor from destruction and controlling a process are completely different requirements. For example, using a standard motor starter with thermal or bimetallic overload protection downstream from a circuit breaker will often prove insufficient to protect the motor from sustained overload conditions. These overload devices are designed to trip only after a prolonged period and excessive current rise. Typically, after an overload situation does occur, the operator will most likely press the reset and start buttons repeatedly until the equipment is back up and running. With time, over-heating and winding failure is imminent.
Underload conditions can also cause unwanted expense, downtime, and compromised performance and safety. A broken or slipping drive belt, a loose or sheared shaft coupling, a restricted pump intake or open pump discharge, or a clogged filter or screen are among the most common causes for underload motor conditions to occur.
Monitoring the current of an industrial load using current sensitive relays is a simple way to detect problems before they cause equipment and process breakdowns. Whether the problem creates an over-current or under-current condition, the information derived from these simple and reliable sensors can save labor and capital dollars. This article discusses a variety of predictive maintenance methods for both AC and DC loads using these simple, yet valuable additions.