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Electric Motor Condition Monitoring

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Motor Condition Monitoring Aids
Water Company Pump Test

Whitelegg Ltd was recently contacted by Knowlton & Newman Ltd, a family-run motor rewinding specialist, based in Portsmouth.

One of K & N customers had requested a test on two 120kw pump motors, at a remote pumping station. The two pumps (one being on standby) are used to maintain water levels in the nearby water-ways.

The Baker Explorer online, motor monitoring unit was used to test both motors by looking at a range of potential problem areas.

The Explorer works by measuring the voltage and current of all three phases of a motor and calculates a host of information including speed, torque, and percentage load and operating efficiency. Additionally, it can highlight rotor bar issues, power quality problems, stage 3 and stage 4 bearing problems, and other mechanical problems imparted by the load.

The main series of tests did not highlight anything untoward on either motor, so a transient analysis test was performed, whereby the voltage and current draw, and the torque profile are all plotted against time, whilst the motor runs from standstill to operating speed.

The engineer conducting the tests was informed that soft-start units had recently been installed, both to conserve energy and to help protect the motors from the stress of starting direct-on-line.

To their surprise, it was found that the results provided by the Explorer were more typical with a direct-on-line start. This was seen to be the case on both pumps.

On the current graph, it can be seen that the current peaked at 561 Amps after approximately 1.5 seconds, before gradually reducing to around 114 amps over the following 12 seconds or so.

Results seen on both pumps

Results seen on both pumps