Air compressor motor burned Case Analysis - power phase and voltage anomalies

Abnormal voltage and phase can easily destroy any motor. Supply voltage range must not exceed the rated voltage of ± 10%. Three phase voltage imbalance must not exceed 5%. High-power motors must be independent of the power supply, resulting in low voltage to prevent the same line when other power equipment up and running. Motor power cable must be able to carry the rated motor current.

If phase when the compressor is running, it will continue to run but there will be a large load current. Will soon overheat the motor windings, the compressor is thermally protected under normal circumstances. When the motor winding is cooled to a set temperature, the contactor will be closed, but the compressor does not start up, appears stalled, and enter the "stall - thermal protection - stall" death cycle.

Modern motor windings difference is very small, when the difference between three phase power supply phase currents can be ignored. Ideally, the phase voltage is always the same, as long as one phase after another protector can prevent any excessive damage caused by the current. In fact it is difficult to ensure a balanced phase voltages.

Voltage unbalance percentage is calculated as the maximum deviation of the average value of the ratio of the phase voltage three-phase voltage three-phase voltage average. For example, a nominal 380V three-phase power, measured at the compressor terminal voltages are 380V, 366V , 400V. You can calculate the average of the three-phase voltage 382V, maximum deviation of 20V, the voltage unbalance percentage was 5.2%.

As a result of voltage imbalance, in normal operation the unbalance of the load current is 4-10 times the voltage unbalance percentage point numbers. The previous example, 5.2% voltage imbalance can cause 50% of the current imbalance.