Comparison of single-phase and three-phase generators
Generators are much more common in our daily life than other machinery. When we buy generators, we often talk about single-phase generators and three-phase generators.
Single-phase generators.
How a single-phase generator works
In a single-phase generator, multiple windings of the stator are connected in series to form a single circuit through which the output voltage is generated.
The voltages on all stator windings of the same phase are equal
For example, in a 4-pole generator, the four poles of the rotor are evenly distributed across the stator frame. At any given point in time, the position of each rotor pole relative to the stator winding is the same as any other rotor pole. Thus, the voltages induced in all stator windings have the same value and amplitude each time and are in phase with each other.
Series connection of stator windings
In addition, since the windings are connected in series, the voltages generated in each winding are summed to produce a final generator output voltage that is four times the voltage on each individual stator winding.
Common voltage of a single-phase generator
- 120
- 240
- 120/240
Three-phase generators.
Principle of operation of a three-phase generator
In a three-phase generator, the three single-phase windings are spaced apart so that the voltage induced in each stator winding has a 120° phase difference. These three phases are independent of each other.
Star or Y configuration
In a star or Y-configuration connection, one lead of each winding is connected as the neutral wire. The other end of each winding, called the terminator, is connected to a line terminal. This produces a line voltage that is greater than the individual voltages on each winding.
Delta Configuration
In a delta configuration, the start of one phase is connected to the end of an adjacent phase. This produces a line voltage equal to the phase voltage. Electric utility and commercial generators produce three-phase power.
Configuration
Common voltages for three-phase generators
- 208
- 120/208
- 240
- 480 (the most common voltage for industrial generators)
- 277/480
- 600 (mainly used in Canada)
When deciding which type of generator is best for your environment, one of the main concerns should be to make sure you get the correct electrical configuration. The electrical configuration usually includes the phase, voltage, kilowatts and hertz that are best suited for your application.
For small single-phase loads, single-phase generators typically do not exceed 8 kilowatts. They are typically used in residential settings. Three-phase generators are primarily used for larger industrial power generation. These generators can provide both single-phase and three-phase power to run higher horsepower industrial equipment. They are typically used in a commercial setting.
You can convert single-phase power to three-phase power and sometimes you can get about 20-30% of the rated output in kilowatts. You can also convert from three phase to single phase, which will reduce your rated output by about 40%. For example, a 100 kW three-phase generator will drop to about 60 kW when converted to single-phase.
When we buy generators, we often talk about single-phase generators and three-phase generators.