Electric Motor
An electric motor converts electrical energy into mechanical energy by the force of opposing magnetic fields. It consists of a field magnet, known as the stator, and an electromagnet, called the rotor. The rotor spins the shaft of the motor to generate the mechanical energy. The rotor consists of metal bars and induction coils connected to make a circuit that can be powered by three-phase power from an electric supply.
The field magnet of the stator consists of a sequence of steel alloy laminations and windings. When energized by current, the rotor turns because of the Lorentz force exerted on it by the magnet. The magnetic force of the field magnet is transmitted to the rotor by means of the coils in the armature. When the rotor reaches peak speed, its torque drops off at the rate of 1/N squared.
electric motor require a high starting current to overcome the inertia of the rotor and the large resistance in the stator windings. This high starting current can damage the motor and cause voltage spikes in the power line, potentially damaging appliances that are connected to the same line. To limit this huge initial drawing of current, the motor is equipped with a starter that limits current until the rotor and stator windings reach their normal operating temperature.
Electric Motor Troubleshooting
A problem with a starter can prevent an electric motor from starting, so it’s important to check that the starter capacitor is working properly. If the starting capacitor isn’t functioning, it needs to be replaced or repaired.
Blown fuses: A blown fuse can be one of the most common reasons an electric motor fails to start up. If a fuse blows, it’s important to replace it with a fuse of the same amperage as the old one. It’s also important to reset the breaker after replacing the fuse. Corroded control switch contacts: If the contact points on the control switches are corroded or dirty, they may not allow electricity to flow through the motor. This could be a simple fix by cleaning the contacts.
Loose or defective motor bearings: If the motor isn’t bearing correctly, it can cause the shaft to rub against the housing and wear out prematurely. A seized bearing can also be difficult to repair, and will need to be replaced. Bad starting capacitor: While not all motors use a starting capacitor, those that do need it to function properly. If the starting capacitor isn’t working properly, it’s not providing sufficient resistance and will need to be replaced.
Poor or incorrect voltage: This is another common cause of an electric motor failing to start up. A motor can be supplied with AC voltage from a single-phase or three-phase power source, but the voltage must be proportional to the motor’s rated voltage. Unbalanced load: This can cause the motor to overheat, leading to damage and failure. This can be caused by a heavy load, a high ambient temperature or inadequate cooling.