Electric motors consume 60 to 70% of the energy used in the industrial environment. The cost of replacing even a small motor needs to be carefully analyzed.
1. Labor to access and remove failed or damaged motor.
2. Repair or replacement cost.
3. Labor to reinstall motor.
Often Murphy strikes and the motor is virtually inaccessible, and/or is connected to the pump shaft or gearing. Because it affects thruput, that loss is added to the repair/replacement cost.
Standard motor starters with thermal or bimetallic overload protection are often insufficient to prevent damage to the motor. These overloads are designed to trip and remove the protected load in 10, 20, or 30 seconds after the current reaches 600% of rating. When an overload reaches only 150% of rating or target load the starter overloads take from 4 to 12 minutes to trip. This causes heat which can be dissipated through the rotor and stator cores assisted by the motor housing and shaft fan BUT very few operators will stop the process to wait for cooling. Usually they will press the reset and start buttons repeatedly until the system runs again, often causing severe overheating and even winding failure.
It is important to realize that protecting the pump motor and controlling the process are completely different objectives. The application will always determine the product and protection selection. If the pump load is critical to process, thruput, or output the fastest and most accurate protection is a must!
Basically, the motor current drawn represents the load on the pump at any time. A CURRENT TRANSDUCER will monitor current flow accurately and instantly WITHOUT cutting into the conductor insulation. The output of the CT is fed to an analog or digital indicator or more sophisticated network or programmed logic controller (PLC).
Applications requiring very precise control can use a POWER TRANSDUCER that provides additional voltage and power factor to monitor.
A GROUND FAULT SENSOR should always be added to provide safety for the pump and the employees. This device will measure ground leakage currents as low as 5 milliamps.