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Wet Induction Motor Symptoms

Induction Motor

Pouring water on an Induction Motor may stop it working, due to the lowering of the insulation resistance of the internal motor coil windings.

The coil windings are located inside the metal case of the induction motor, and are what generates a magnetic field, which makes the motor turn.

This article will focus on what are known as ‘three phase’ Induction Motors, which have three sets of coil windings inside the motor.

The internal motor windings are wound together in a component known as a ‘Stator’.

Each winding is electrically separated by an insulation layer on the copper wire that makes up a stator winding.

Therefore there should be a high level of electrical resistance between each of the three coils.

This ‘Insulation Resistance’ is typically above 2 Mega Ohms in a correctly operating Induction Motor, however for marine Induction motors 0.5 Mega Ohms is the stated (Solas) minimum.

If the coil windings become wet, then the insulation resistance would drop to a low level, which would prevent the motor from operating, due to a short circuit between the coil windings.

The good news is that induction motors can usually be dried out, and therefore returned to having a high insulation resistance between the Stator coils.

It is of course vital that the motor is disconnected from the electricity supply, and that only a qualified person carries out the work.

On land based industrial installations a damp or wet  Induction Motor, should trip the safety circuit breakers (RCD), and isolate the supply.

This is because on land, the priority is to safeguard the safety of people and livestock.

On board ships and Super-yachts however, the priority is to maintain the ships important systems, such as Steering gear.

Therefore ships electrical systems are designed to tolerate a single earth fault, without shutting down the whole circuit.

A wet Induction Motor would cause an earth fault to be detected by the ships ‘fault panel’, but not trip the whole circuit.

Yesway has experience of working on Marine Induction motors, and years of related experience.

Monitoring Using Radio Communications

Radio communications technology can be used to monitor the condition of induction motors.

Sensors can be attached or even integrated into induction motors, to monitor motor conditions.

Induction motor parameters that can be monitored by sensors are:

Phase Current

Motor speed RPM

Vibration

Torque



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