Three-phase motors are widely used for industrial purposes because of their simple structure, less cost, ease of maintenance, and operation. Normally three-phase power supply(3 ph 220v, 380v, 400v, 415v, 480v, etc.) is used to run three-phase motor. Three-phase motors, on the other hand, necessitate a three-phase power supply to function. Three separate alternating currents of equal frequency, peaking at alternating points in time, power these motors. Three live wires and a neutral are used in a three-phase motor.
Household appliances, usually have a single-phase supply (1 ph 110v, 220v, 230v, 240v, etc.)instead of a three-phase supply. In this article, we are going to discuss how to run a three-phase motor using a single-phase connection.
How to connect two AC motors in parallel?
Different methods of running three-phase motor
There are three different methods to run 3 phase motor by using a single-phase power supply. They are
- By using Rotary Phase Converter
- By using a VFD
- Rewinding the motor
By using Rotary Phase Converter
From a single-phase power source, a Rotary Phase Converter can run three-phase equipment at full rated power.
The most common and universal type of phase converter is the rotary phase converter. The rotary phase converter is made up of two parts. A “control panel” and an “idler generator.” A start circuit is included in the control panel to start and stop the idler generator, as well as capacitance to balance voltages between phases. The idler generator is powered by a rotating mass spun by single-phase power. This rotation creates a third power line, which is combined with the two single-phase lines to create three-phase power.
Rotary phase converters are classified into three categories:
- Standard Rotary Phase Converter
- Digital Rotary Phase Converters
- Rotary Converter Control Panels
By using a VFD
A variable frequency drive (VFD) converts each pair of phases to dc and then inverts the dc to power for the three-phase output, allowing a VFD to operate a three-phase motor with a single-phase input. Manufacturer support varies, so it’s best to reduce the drive by one divided by the square root of three (about 58 percent ). Also, because VFDs are rated by current, the hp/kW rating is there for convenience in sizing drives.
Using a VFD to operate the existing motor from single-phase power is a better idea than buying an expensive single-phase motor, changing the controls, and dealing with speed control and starting torque issues. A suitable VFD can be purchased for much less than the cost of rewinding a three-phase motor and providing the necessary controls for many applications up to 5 hp (4 kW).
A three-phase motor is typically less expensive to purchase, the controls do not require replacement or modification, and the VFD has the added benefit of providing speed control. Best of all, you won’t have to waste a weekend assisting someone who doesn’t fully comprehend what you’re doing.
To understand more about VFD Click Here
Rewinding the motor
Rewinding a three-phase motor is another way to make it run on single-phase power. Single phasing is another name for this technique. It entails using capacitors to rewind the electric motor. Three symmetrical sine waves bring three-phase power into the system. These waves are 120 degrees electrically out of phase with each other.
Two of the three phases of a three-phase motor are connected to the single-phase power supply to convert it. Capacitors are used to create a Phantom leg for the third phase. Between the auxiliary and main windings, the capacitors force a 90-degree electrical offset. The capacitors used must have the appropriate capacity for the load in order for the current to be balanced.
Comparison of different methods
| Rotary Phase Converter | VFD | Motor Rewinding |
|---|---|---|
| The conversion is aided by a phase converter, which adds an extra leg to the two single-phase lines. | VFD allows variable speed control when it converts frequency. | Use capacitors to rewind the motor |
| Less wiring needed when compared to VFD and motor rewinding | Need more wires than rotary phase converter and lesser than motor rewinding | Complex in structure than rotary phase converter and VFD |
| Can run multiple devices simultaneously | Can run the only single three-phase motor at a time | Need to rewind each and every motor we are using |
| Produce less heat | Produce less heat | Produce a high amount of heat |
Some useful Questions
1) What are the four sections of VFD?
- Rectifier
- Intermediate DC link
- Inverter
- Controlling circuit
2) Which is better a rotary phase converter or VFD?
Phase converters work machines with modest performance increase and low voltage controls, such as freezers and trailer equipment, benefit from VFDs, on the other hand, are ideal for devices that require greater control, such as saws and pumps.