Logically, a load that would not suffer greatly from drawing current on only two of it’s three windings (i.e. It is not entirely clear to me what the appropriate applications are for a static phase converter and every person I’vea asked about it has warned against using one. Once the motor is up to speed, the static converter simply passes through the single-phase power supply to which it is connected. At startup, a static converter temporarily provides the third leg of three-phase power by discharging starting capacitors. This comes at the price of a 2/3 reduction in the rated horsepower and a shorter life expectancy for the motor. A three-phase motor cannot start on single-phase power, but can run on it once started. Static Phase Converters: A static phase converter is really just a method for starting three-phase motors. Another disadvantage is the fairly high cost of new giant electric motors.Ģ. The main downside is that the equivalent single-phase motor (equivalent in terms of service factor and horsepower) will draw significantly more current and will be larger in size. Replace the motor with a single-phase motor: When there are only one or two machines and the motor is in a configuration that you can actually get to, this can be the easiest solution to the problem. Fortunately, there are several ways to make that equipment – often large, valuable, and quite useful equipment – come to life.ġ. Home hobbyists and small shop owners often face the problem of three-phase equipment with no three-phase service. The design of three-phase motors, with one set of windings for each phase, is highly efficient and allows three-phase motors to draw significantly less current than the equivalent single-phase motor. To electricity consumers, that consistency in power delivery is the major benefit. The three phases share a common neutral leg in most installations. What this means practically is that the total amount of power supplied by all three alternating currents remains constant.
3 PHASE POWER CONVERTER FULL
That is, the points in time at which each leg of alternating current reaches a maximum voltage are separated by 1/3 of the time in a full cycle. Three-phase power provides three alternating currents-essentially three separate electric services-uniformly separated in phase angle. While this doesn’t matter to many electrical appliances, it has significant implications on larger equipment-particularly motors. Picture a sine wave: The amplitude of the supplied voltage passes through zero twice per cycle, and at those moments the power supplied is nada. In the US and anywhere else with 60Hz power, this cycle happens 60 times per second. As it does this, the magnitude of the voltage supplied varies continuously between a positive and negative maximum amplitude. Some of the welding equipment had been running on three-phase, but can easily be re-configured to run on either three-phase or single-phase.īut first, a short explanation of three-phase power.Īlternating current does just as it’s name implies and alternates cyclically, first flowing in one direction in a circuit and then reversing to flow in the other. So what the heck is three-phase power and how can you convert machinery to go from the more common single-phase to three-phase and vice versa? Read on.įor us, the impact was limited because only the air compressor had a three-phase motor. The old shop had it and the new shop doesn’t. The actual timing is: A top, C bottom, B top, A bottom, C top, B bottom and back to A top.I recently moved my shop, and in addition to the big issues, from forklift rental to sleep deprivation, we also had to deal with things like three-phase power, a variation of power delivery often used for big equipment. The timing between cylinders (phases) is such that each one is 1/3 of a revolution (120°) after the next, A top turns on, 120° later B top and 120° later C top. Each pair of switches connected to a phase alternates between top and bottom (+ and -). The 4 switches in the previous figures make up a single-phase inverter adding 2 more switches make a 3-phase inverter. In the next two figures, DC on the top and bottom rails can create current in two different directions by turning on or off different switches.ĭepending how fast the switches are alternated, the current will alternate at the same frequency.Įach switch carries the full-load amperage while it is on. The inverter is the group of switching devices that convert DC into AC. One such question stemmed from a general comment regarding inverter sizing. Many times I’m asked to explain a technical statement to a person who is either non-technical or from a different branch of technology.
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