Faults of Electric Motors: Electrical and Mechanical Problems
Faults in electric motors can be either electrical or mechanical. If the issues are related to the electrical part, the cause usually lies in the winding. Common electrical faults in motors:
- short circuit between windings;
- winding break;
- inter-turn short circuit;
- winding shorted to the casing.
Methods for Eliminating Electrical Problems
Many of these problems can be resolved by rewinding the electric motor.
Mechanical Failures of Electric Motors
Mechanical faults in electric motors are usually related to the failure of individual elements of their construction. Causes of mechanical failures may include:
- wear of bearings and the occurrence of severe friction;
- interference of the rotor with the stator;
- slipping of the rotor on the shaft;
- damage to the cooling fan (in this case, the motor will not stop working, but will overheat, reducing its operational lifespan);
- damage to the housing (which can occur due to improper installation, mechanical impact, or exceeding permissible loads).
Protection of Electric Motors
Among the main means of protecting electric motors, the following can be highlighted:
- thermal relays;
- motor starters;
- thermistors;
- thermal relays;
- electronic protection relays;
- frequency converters.
Motor starters and thermal relays detect excessive current in the phases of the electric motor and disconnect it when permissible parameters are exceeded. The motor starter can independently disconnect the motor, while the thermal relay only interrupts the power supply to the circuit.
Electronic protection relays use microprocessors to monitor voltage readings in real-time, allowing for automatic disconnection of the motor or indication of problems.
Thermal Protection
Thermal protection is represented by thermal relays and thermistors, which are the last line of defense for the electric motor if the thermal protection fails during overload. Once the permissible limit of parameters is exceeded, the protection activates, and the motor is switched off.
Frequency Converters
These devices have several types of protection for the electric motor. Protection may activate in case of exceeding voltage, torque, and current. They also provide limits on torque and current, which reduces the voltage applied to the motor in case of overload. Although the motor does not stop, the operator receives a notification about the occurrence of problems.
At the input of the frequency converter, it is necessary to install a protection switch, and at the output — a thermal relay and thermistor protection.