Motor Overload Fault Means The Actual Operating Power Of A Motor Surpasses Its Rated Value

Motor overload refers to a state where the actual operating power of the motor exceeds its rated power. Typical overload manifestations include severe motor overheating and reduced rotating speed, or even stalling. The motor emits dull noise accompanied by vibration; sharp load fluctuations may also cause fluctuating rotating speed.

Common causes of overload cover phase loss operation, operating voltage exceeding the permissible rated range, and drastic speed drop or stall triggered by mechanical failures.

1 Consequences and Characteristics of  Motor Overload Operation

Overload operation seriously shortens motor service life. It directly increases operating current and causes severe heating of motor windings, leading to aging and failure of winding insulation under excessive thermal stress.

Winding conditions can serve as judgment criteria for overload faults. The insulation material turns entirely black, brittle and fragile, and may even carbonize into powder in severe cases. The insulating coating of enameled wires darkens and may peel off completely. Separation occurs between conductors and insulation of mica-covered and silk-covered wires.

Different from phase loss, inter-turn, ground and inter-phase faults that cause partial damage, overload results in overall winding aging. It also brings secondary bearing overheating. Obvious burning odor spreads around the faulty motor, and dense black smoke may emerge in extreme situations.

2 Causes of Overload Fault During Testing

Improper operations during inspection and factory tests may trigger motor overload.

Overload frequently occurs in locked-rotor tests and wiring & voltage application processes. A locked-rotor test, also known as short-circuit test, keeps the rotor stationary. Excessively long test duration will burn windings due to overheating. Insufficient capacity of test equipment leads to prolonged startup and low-speed creeping, which also damages windings from excessive heat.

Wrong wiring is another frequent error: star-connected motors wired in delta connection with rated star voltage applied will suffer rapid winding burnout. For motors designed for non-power frequency operation, test equipment only supplying power frequency power will apply excessive voltage and burn windings.

Locked-rotor tests are also high-risk links in type tests. Longer test duration and more data sampling raise overload risks when motor performance is defective or operations are improper. Unreasonable loading and inadequate load bearing capacity also induce overload faults in load tests.

3 Causes of Overload During Practical Operation

The motor operates safely under rated load. However, excessively high or low supply voltage will overheat and burn windings. Sudden load surge reduces rotating speed sharply or stalls the motor, which is a common overload scenario, especially under impact loads.

Bearing failures may cause rotor stator rubbing and motor stalling, eventually resulting in burnout due to overload.