Single phase power and 3 phase power are terms we hear quite frequently in the electrical world. But what are the differences between them? In the latest episode of Electrician U, Dustin explains the differences and benefits to each in a never-ending pursuit to answer our followers’ questions.
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Let’s start off by defining them. Single phase is referring to a single loop of current flow. One big loop! One can also think of single phase as two hots (typically A and B phase or Black and Red). Current is flowing TO the load on one wire (say the black wire) and returning TO the source on the other wire (say the red wire). They are also alternating back and forth between pulling and pushing the current flow. Try to conceptualize the sine wave chart. As one of the conductors is pushing the current (black), the other is pulling (red). Until they both get to the neutral (or zero point) where it begins to go the other way. Black will pull and red will push.
Three-phase on the other hand is referring to 3 loops of current flow from 3 separate generating sources. Same type of general concept except that they are tied together. As before with single phase, current left on the black, travelled thru the load, and returned on the red. Here in three phase, current leaves on the black, travels thru the load, and returns on the red. However, that red ALSO happens to be powering the one side of its own generator as well that will leave on its red conductor and return on another conductor (blue). This blue is ALSO tied to ITS own generator that current will leave on the blue, travel thru the load, and return on the black, and we start the sequence all over again! So, they are all separate loops but tied together to form another loop so they can share the load amongst themselves.
The terms Primary and Secondary also come into play here. Primary refers to the conductors on the side Feeding the transformer, Secondary refers to the conductors on the other side that will be utilized by us. Transformers operate by induction. When we push/pull current thru the transformer on the primary side of the coil, it induces movement of current on the other secondary coil (transformers have coils that are close to one another but not touching) and that current flow is what provides us the stepped down power we need.
One of the big reasons WHY we would use 3-phase for some applications is due to efficiency. Remember our sine wave chart? On single phase, work is being done when the points are at their farthest distances apart from one another. But when they both come back to the zero point (at the same time, remember), there is no work being done at all as they are both at zero. On a 3-phase system, when one of the 3 phases is doing ALL the pushing, the pulling action on the other end is being shared equally by the other 2 phases. And that alternates between all three of the sets. So, on a sine wave chart, when one conductor is at its highest point, the other two are not exactly opposite of it because they are sharing the work. And, then THEY alternate also. So, at no point is anything sitting idle on a three phase, thus more efficient for larger scale type items like factories, plants, warehouses, etc.
We can also get motors in either single phase or three-phase. Same type of concept and for the same reasons. Efficiency! The three-phase motors share the work among the three points of power.
We hope this answers the age old question of the differences between single phase and three phase. Please continue to follow Dustin and Electrician U as we are constantly adding new content to bring clarity to the electrical trade!
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