Jat Power Blog Switching Generators Power from Single Phase to 3 Phase

Converting Generators to Supply Single-Phase or Three-Phase PowerBesides ensuring that the frequency of a generator matches that of the appliances or grid, the following conditions must also be fulfilled:i.The generator output frequency must match that of the appliances, or the grid powered by the generator.ii.No phase difference must occur between the generator voltage and that of the grid.To have a better understanding of the conversion of a three-phase generator to a single-phase type and the other way round, we have to look briefly at the internal configuration of single-phase and three-phase generators.Single-Phase GeneratorsIn this kind of generator, the stator has certain windings serially connected to form a single circuit through which the output voltage is produced.The same voltage across all stator windings are in phase with each other: For example, in a 4-pole generator, the four rotor poles are spaced evenly around the stator frame. Each rotor pole at any time has the same position relative to the windings of the stator, just like any rotor pole. So the voltages induced in all the windings of the stator have equal value and amplitude, also they are also in phase with each other every time.Series connection of stator windings: As the windings connections are in series, the produced voltages in every winding increase to yield a final output voltage that is 4x the voltage across each of the individual stator windings.Use of single-phase power distribution is common in both residential areas and rural areas where there are small and uncommon loads, and because setting up a three-phase distribution network is expensive.Three-Phase GeneratorsIn this kind of generator, spacing of three single-phase windings are done in such a way that there is a phase difference of 120° among the induced voltages in individual stator windings. These three phases don't depend on each other.Star or Y Configuration: In a star or Y connection, lead from every winding is attached together to form neutral. Each winding opposite end called finish end, is attached to each line terminal. This yields a line voltage that is more than the individual voltage across each winding.Delta Configuration: In a delta configuration, the start end of one phase is connected to the finish end of the adjacent phase. This produces a line voltage that equals to the phase voltage. Electrical utilities and commercial generators produce three-phase power.Phase Conversion in Generators1.Reconfiguring Coil Connection You can covert a three-phase generator to that of a single-phase one by changing the connection between the generator stator windings, either outside or inside the head of the generator. For example, in a three-phase generator, there are 6 leads. Bigger generators usually have 12 leads from six coils, and all the wires originate from the generator, easing the generator's configuration in various ways as follows:Serial connection of the coils will convert your generator to a single-phase generator.Serial connection of opposite coils doubles the output voltage.A parallel connection will increase the current flow twice.The tricky part of generator reconfiguration relies on mapping the wires coming out from the generator, to the coils that the wires are connected to. It is of necessity to have the documents of the manufacturer, or else, you have to study the wiring of your generator and work backwards from that point.2.Centre-Tapping Single-Phase Loads To Three-Phase GeneratorsA 3-phased generator is believed to be a grouping of three single-phase units together. The following are the various ways single-phase loads can be connected to a three-phase generator:Connect the load between the system neutral and a phase conductor. This is commonly done for loads with low power.Connect the load across two live phase conductors in a phase-to-phase connection. This is commonly carried out for loads of high power like heaters or air conditioners, and produces 208 Volts. But this may result to unimpressive performance because appliances require 240V to operate, and they would be operating at 75% of the capacity they were rated for at 208V.3.Phase ConvertorsA RPC (rotary phase convertor) can be connected directly to a single-phase generator to yield a three-phase power. RPC needs a simple configuration consisting of two input connections called idler inputs from a single-phase generator. There is production of a voltage on the third terminal that is unconnected to the supplied single-phase power. The voltage varies in phase from the voltage on the two other terminals by 120°.4.Variable Speed Drives (VSDs), Variable Frequency Drives (VFDs), Or Inverters These ones are like rotary phase convertors. The VFD and single-phase generator combo is known to be the most effective when only 20 horsepower or less is required.Selecting between Single-Phase and Three-Phase GeneratorsSingle-phase generators have a general output that is limited to 25kVA. At a very high rating, drawing single-phase power supply from a three-phase generator is less expensive than buying dedicated single-phase generators for higher loads.The choice between the two generators depends solely on the appliances or grid to power. Single-phase generators can provide single-phase power while both single-phase power and three-phase power can be produced by three-phase generators. If all your appliances run on single-phase power, it is sensible to select a single-phase generator. A three-phase generator would be the best for appliances working on different phases. Although, accounting for load balance is important when converting a single-phase generator to a three-phase one.