A three-phase induction motor is a type of motor which is driven by an alternating current (AC). It operates on a three-phase supply (phase is the number of separate electric currents that activate coils situated around the stator). It is the most widely used motor when it comes to 3-phase AC operation because it is a self-starting motor and does not require any starting device. In this motor, the rotor normally rotates at the same speed as the revolving field in the machine.
On the other hand, a variable frequency drive (VFD) is an adjustable-speed drive. It controls the speed of an electric motor that is driven by an alternating current (AC) by varying the frequency supplied to the motor. By using a 3-phase induction motor with VFD, you are able to get much better torque and speed control along with greater power efficiency than alternatives.
Let’s understand induction motors then uncover why a three-phase induction motor should be used with your AC variable frequency drive.
Induction Motors
Induction Motor is an AC electric motor. It contains an electromagnetically induced current in the rotor. It neither requires a separate excitation nor self-excitation or mechanical commutation for transmitting all or part of the energy to the motor from the stator. Induction motors are used in almost every process but are mainly used in water pumps, fans, kitchen appliances, and air conditioners, automobiles and common industrial machineries like boiler pumps and compressors.
These motors work using electromagnetic fields. The rotor speed in an induction motor differs, depending on the fluctuating magnetic induction. This fluctuation leads to turning the rotor at a lower speed than that of the stator’s magnetic field. They are categorized in several phases.
There are two types of Induction Motors.
- Single-phase motor
- 3-phase motor
The Single-phase motor is used for smaller loads like household appliances such as fans.
When it comes to a three-phase induction motor, three currents are used in it for energizing three or multiples of three coils. These motors are self-starting and don’t need any external DC source.
Conditions That Impact the Rotor Speed of an Induction Motor
In general, there are three conditions to impact the rotor speed of an induction motor. These conditions are the frequency of the AC supply, the number of coils that include the stator and the load on the motor.
The higher the load, the greater the difference (slip) between the speed of the rotor and the speed of the rotating magnetic field. AC supply frequency needs to be used to control the speed of the AC induction motor drive. This is what the main objective of a Variable Frequency Drive (VFD).
Three Phase Induction Motor and VFD
If a VFD is added to a three-phase induction motor, it alters the motor speed in conformity with the load and saves energy for the motor. Frequency and voltage are supplied in an accurate way when the motor starts. This is leads to many benefits such as.
- Elimination of energy waste
- ● Increased AC motor lifespan
- ● Economical speed control
- ● Lower maintenance than DC controlled motor
Today, there is a great demand for three-phase induction motors. These motors are extensively used because of their quality of self-starting, efficiency, and powerfulness. If motors are controlled with VFD, it allows efficient and smooth running of motors with the availability of a high-energy server.