Alternating current reverses flow 60 times a second. Three phase power provides alternating current separated by one third cycle or 1200 verse 180 degrees for single phase power.
Transmission of Electricity from Power Plant to Home
Household’s power delivery is 220 to 240-volt single phase alternating current at 60 cycles per second (60 Hz or Hertz). It uses a two-phase wire system with a ground. 120-volt power is through one delivery leg and a neutral two wire system. Thus, the homes power provisions are the 240 and 120 volt circuits in the house. A breaker spans the two legs to provide 240-voltage power to ovens, electrical water heaters and other high voltage appliances.
How is Electricity Delivered to Commercial & Industrial Systems?
Commercial-Industrial systems prefer the triple or three phase power delivery through a three-wire system. Triple phase is the most economical and efficient way to provide power and many industrial systems are three-phase systems. Because of the phase shifts two wires provide the return leg while the third wire is power or phase leg. For industrial application three phase power is very consistent, very efficient and allows heavy triple phase motors to draw less current than a single-phase motor. One aspect of alternating current is that is can be transmitted over longer distance than direct current. Another consideration is that during transmission the higher the voltage the better. Generally, those machines in the industrial sector operate at 480 volts, the most common in power used in the US, however in Canada 600 volts is more likely. The voltages go up to 4,160 volts at the load. Transmission line voltage can go from 69,000 volts up to 765,000 volts.
Three Phase Generator to Single Phase Conversion
Conversion from triple phase to single phase will decrease the wattage by about a third, thus a 150kW triple phase line will be reduced to 100 kW single phase line. Changing voltage is interesting. The U.S. and a lot of Asia use 60 Hz while much of Europe is 50 Hz. You can change 600 volts 3-phase to 480 but not the reverse, 480 to 600 doesn’t work. A shop with significant investment in three phase equipment that is in a location due to a move may find itself in a single phase only delivery. Three phase motors can run on single phase, but cannot start on it, though it shortens the life of the motor. Static Phase Converters have charge capacitor that fires providing the third leg and starts the motor rotating on single phase power. A rotary phase convertor consists of a three-phase idle motor, runs with no load on the supplied single-phase power. A static phase convertor starts the motor which is powered by the single-phase supply. A motor being spun is a generator and supplies its own third leg out putting triple or three phase-power. The con to all this is that you need to have a 2-1 start up advantage. This translates into the requirement that the convertor must be twice the load horsepower. You need a 10hp converter to start a 5hp motor. As in all things a rotary phase converter gets more expensive with higher output. For many shops a conversion to single phase 240-volt power may prove to be more economical, depending how much equipment needs conversion.
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A variable frequency drive uses similar technology as 12-volt DC to 120-volt AC inverters and synthesize three phase power. The inverters create a separate AC power source from its power source it can create output frequency that varies and can be used to tune the speed of motor for fine control. Of course, industrial level gensets can be had to pump out three phase power and provide standby or emergency power. Environmental Power Solutions offers clean running diesel generators for lease, rent or sale. Contact us for more info today.