Phase rotation
- Thread starter erwin71
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If you're looking at the voltages at any point in a system, phase rotation is the order in which they peak. If at some point in time phase A hits its maximum voltage, after 120 degrees (1/180 second) one of the other two phases will hit its maximum voltage, then another 120 degrees after that the third phase hits its max. So, there are two possible outcomes - A then B then C, or A then C then B. Any other sequence is just rearranging one of these two.
Where the "rotation" part comes in is primarily in motors. Say you make the connections from your phase conductors to three motor leads (regardless of how other motor leads are tied together and whatnot). If the phase sequence changes, the magnetic field in the stator will rotate in the opposite direction, making the motor rotate the other way. That's my explanation of where the rotation part comes in.
Where the "rotation" part comes in is primarily in motors. Say you make the connections from your phase conductors to three motor leads (regardless of how other motor leads are tied together and whatnot). If the phase sequence changes, the magnetic field in the stator will rotate in the opposite direction, making the motor rotate the other way. That's my explanation of where the rotation part comes in.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
First, it only applies to three-phase systems. Secondly, it has to do with the timing of the rising and falling of currents (or voltages) in each of the three wires.
Consider three conductors that are run across a room, from a power source to a motor. They are run in open air, supported every few feet or so, and you can see all the conductors. Label one of them ?Phase A,? one of them ?Phase B,? and one of them ?Phase C.? Put a clamp-on ammeter on each conductor, and run the signal cables to a computer display. Suppose you see that, at one moment in time, the current in Phase A is about to reach its peak, and the currents in the other two phases are much lower. A short time later, you observe that the current in Phase B reaches its peak, and a short time after that the current in Phase C reaches its peak. Then the pattern repeats itself. The pattern is A, B, C, A, B, C, A, B, C. . . .
It is just as possible that, after Phase A reached its peak, the next one to reach a peak might have been Phase C, with Phase B coming next. The pattern would then be A, C, B, A, C, B, A, C, B . . . .
Those are the only two possible phase rotation patterns. The most significant difference between the two is that one will spin a motor clockwise, and the other will spin the same motor counter-clockwise.
Consider three conductors that are run across a room, from a power source to a motor. They are run in open air, supported every few feet or so, and you can see all the conductors. Label one of them ?Phase A,? one of them ?Phase B,? and one of them ?Phase C.? Put a clamp-on ammeter on each conductor, and run the signal cables to a computer display. Suppose you see that, at one moment in time, the current in Phase A is about to reach its peak, and the currents in the other two phases are much lower. A short time later, you observe that the current in Phase B reaches its peak, and a short time after that the current in Phase C reaches its peak. Then the pattern repeats itself. The pattern is A, B, C, A, B, C, A, B, C. . . .
It is just as possible that, after Phase A reached its peak, the next one to reach a peak might have been Phase C, with Phase B coming next. The pattern would then be A, C, B, A, C, B, A, C, B . . . .
Those are the only two possible phase rotation patterns. The most significant difference between the two is that one will spin a motor clockwise, and the other will spin the same motor counter-clockwise.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Beat me to the draw, will you JD? I'll just have to send my tiger over for a visit! :wink: :grin:
I suppose that is what I get for being long-winded.
I suppose that is what I get for being long-winded.
quogueelectric
Senior Member
- Location
- new york
Phase rotation is the sequence in which the voltage rises on a feeder which in turn causes current to flow which in turn causes the magnetic field which in turn spins the 3 phase motor in a specific direction.
rather than getting involved in a which came first the chicken or the egg. The most common application for an electrician is to check which way a motor is spinning and how to reverse it if it is not.
The best way to check is with a phase rotation meter the leads must be hooked up the same way each time and to to the same wire.
For example If I am changing a service to a building I would hook up my meter red white blue to a-b-c when I reinstall the new service I want to make sure the rotation direction is the same or I might damage equipment.
Some equipment cannot be run backwards without causing damage and the direction of some equipment can cause other thing to get locked out downstream with phase reversal relays.
If you are just hooking up say a fan motor and want to check rotation you could just bump the motor on briefly and see which way it wants to spin if you need to reverse the direction for proper air flow (notice I didnt say direction)
you can swap any two line side wires and it will reverse the direction of the motor. A-B-C-A-B-C-A-B-C-**********swap any 2 say b with c and now you get C-B-A-C-B-A-C-B-A see now it is runnung backwards. This ought to get you started.
rather than getting involved in a which came first the chicken or the egg. The most common application for an electrician is to check which way a motor is spinning and how to reverse it if it is not.
The best way to check is with a phase rotation meter the leads must be hooked up the same way each time and to to the same wire.
For example If I am changing a service to a building I would hook up my meter red white blue to a-b-c when I reinstall the new service I want to make sure the rotation direction is the same or I might damage equipment.
Some equipment cannot be run backwards without causing damage and the direction of some equipment can cause other thing to get locked out downstream with phase reversal relays.
If you are just hooking up say a fan motor and want to check rotation you could just bump the motor on briefly and see which way it wants to spin if you need to reverse the direction for proper air flow (notice I didnt say direction)
you can swap any two line side wires and it will reverse the direction of the motor. A-B-C-A-B-C-A-B-C-**********swap any 2 say b with c and now you get C-B-A-C-B-A-C-B-A see now it is runnung backwards. This ought to get you started.
quogueelectric
Senior Member
- Location
- new york
I was within armslength of the tiger that attacked Roy at the mirage. When I was seated the waitress asked me what was in the bag I had. I asked her why she wanted to know and she replied. You will be very close to the tigers and I want to make sure you dont have food in the bag. I replied "you did feed them tonight didnt you??" Moral of the story DONT mess with a tiger.charlie b said:Beat me to the draw, will you JD? I'll just have to send my tiger over for a visit! :wink: :grin:
I suppose that is what I get for being long-winded.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
erwin71 said:
I'm curious what the different answers would be???
quogueelectric
Senior Member
- Location
- new york
Do tell. We promise we wont pounce on you.
frenchelectrican
Senior Member
- Location
- Nord'est Wisconsin et Paris France
Electric motors .,,, gas engines .,, diesel engine even turbines they all work very simuair manner.,,
get 3 cylinder engine [ same idea with 3? motors ]
start at #1 lit it off at #1 hole the piston move down while other two piston move the #2 pistion move up to next spot then lit off #2 piston that piston move down and thrid piston move up and lit off #3 piston it will move down the #1 will come back up and do it all over again it the same idea with electric motor.
but kinda off topic but same idea how go foward and reversing engine do.http://www.youtube.com/watch?v=ebvD1RnX7LY
this basicially how the engine go foward and reversing it the same idea with electric motor reversing.
Merci, Marc
get 3 cylinder engine [ same idea with 3? motors ]
start at #1 lit it off at #1 hole the piston move down while other two piston move the #2 pistion move up to next spot then lit off #2 piston that piston move down and thrid piston move up and lit off #3 piston it will move down the #1 will come back up and do it all over again it the same idea with electric motor.
but kinda off topic but same idea how go foward and reversing engine do.http://www.youtube.com/watch?v=ebvD1RnX7LY
this basicially how the engine go foward and reversing it the same idea with electric motor reversing.
Merci, Marc
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