Electric motors convert electricity to useful make machinery work. It is estimated that 70% of all electric energy used in the manufacturing sector in the US is consumed by motor systems.
Knowing that most of the equipment used by a facility employs some type of electric motor, it is important to lay out a systematic plan to perform preventive maintenance. First, let's take a look at what these different types of motors look like.
What are the different types of motors?
Electric motors differ based on the type of current that drives the motor – direct current (DC) or alternating current (AC). Motors are then categorized as either DC motors or AC motors.
What are DC motors?
DC motors use the interaction of magnetic fields and a direct current (DC) supply. These types of motors allow more speed control, and they usually power variable-speed applications such as machine tools. In a DC motor design, communicator assemblies supply an electric current but go through significant wear over time.
What are AC motors?
AC motors similarly convert electrical energy to mechanical energy, except the supply is in the form of an alternating current (AC). Their design allows the current to evade direct contact with commutator assemblies. AC motors tend to last longer because they have fewer deteriorating components. Due to their rugged and simpler construction, AC motors more widely-used in equipment.
What are the key components of a motor?
Because of design differences, the key components of a DC motor differ from that of an AC motor.
The key components of a DC motor are:
- Field pole – the component that creates a steady magnetic field within the motor.
- Armature – the rotating component of the motor. This becomes an electromagnet when current passes through, causing it to rotate as it interacts with the surrounding magnetic field.
- Commutator – the contact points that supply the current from the power source to the armature. It allows the direction of the current to be overturned in order to continuously drive the rotational motion.
On the other hand, the key components of an AC motor are:
- Rotor – the outside part of the motor, wound with coils that transmit the alternating current.
- Stator – the part of the motor that is coupled with the output shaft.
Note: Depending on the type of AC motor, the configuration of the coils on the rotor and the stator may take different forms and patterns.
What are the common causes of motor failure?
The moving components of motors are susceptible to usual wear after long durations of use. However, the rate of deterioration accelerates when certain components experience localized stress. Voltage imbalances due to improper insulation, increased friction from lack of lubrication, thermal stresses, or even dirt and moisture accumulation all contribute to motor wear.
To increase the precision of identifying any operational symptoms, some diagnostic equipment can assist further than the usual preventive maintenance tasks.
What is some diagnostic equipment for motors?
Use infrared thermometers to assess temperature profiles.
Use ultrasonic to isolate distinct sound patterns around bearings.
Vibration analysis is particularly great for rotating components.
Preventive Maintenance Checklist for Motors
The U.S. Department of Energy provides a guide for maintaining assets such as electric motors. With a checklist at hand, it then helps to have an idea of the types of motors usually found in a plant, as well as the components that you can expect each type to have.
Along with a preventive maintenance checklist, the use of diagnostic equipment can provide targeted insights on implementing maintenance strategies for electric motors.