Changing phasing on motors

[lcrjr]

I am rephasing some taps to balance load on a feeder. The taps are V phase (2 phases) and there are downline 3PH motors served from two pot banks. If I rephase the taps as designated below, will I reverse motor rotation?

1. change AC to AB
2. change AC to BC

 

[rcwilson]

1. change AC to AB
2. change AC to BC

Looks like there either is a typo or all phases are shorted by changing AC to both AB & BC.

No phase rotation change if:

Move A to B, move B to C, move C to A, or

Move A to C, B to A, C to B.


Any other swap of the ABC terminals will change phase rotation.

 

[Smart $]

I am rephasing some taps to balance load on a feeder. The taps are V phase (2 phases) and there are downline 3PH motors served from two pot banks. If I rephase the taps as designated below, will I reverse motor rotation?

1. change AC to AB
2. change AC to BC

Your description is open to at least a couple different interpretations. Let's start over. You have a 3?, 3-wire feeder. This feeder is tapped how many times, and how many conductors for each tap? What loads or equipment do the tap conductors serve... 1? or 3? loads, or a combination thereof?

If your taps serve only 1? loads, you will not affect any rotation. If they are 3-wire and serve 3? loads, see below...

 

[Hv&Lv]

I believe I understand what you are saying. You have 2 phases of primary feeding two open delta banks, producing three phases of secondary. you presently have A&C primary feeding the open delta banks, and would like to feed them with A&B primary, or B&C primary. correct?

 

[Hv&Lv]

I can't see the problem, to tell you the truth. No matter what is said here, if the rotation is reversed, go to the bank and switch two of the secondary wires. In order to do the balancing, you are going to have to interrupt their power. Take a rotation reading at a disconnect, not at the bank. I say this because sometimes someone will check rotation at the transformer and forget to have the rotation meter clips stay with the original wire it was checked on.

Have someone at the bank, and a man at the disconnect. Check rotation, leave the meter hooked up. change the phasing,. call, and if the rotation is wrong, swap the wires at the bank. You have to have an idea of the phase you want to switch if you have already took your amp readings for balancing.

 

[Smart $]

I believe I understand what you are saying. You have 2 phases of primary feeding two open delta banks, producing three phases of secondary. you presently have A&C primary feeding the open delta banks, and would like to feed them with A&B primary, or B&C primary. correct?

This only makes sense if the feeder is 4-wire wye. The OP made no mention of a neutral.

No change to rotation will occur if line conections are simply rotated. If connected A-N-C, flopping to B-N-A, or C-N-B, will not change roatation of the motors.

One way to look at it is, because the last connection of the existing "lags" by 240?, keep the revised last connection the same "lagging" by 240?. I put lags / lagging in quotation marks because the last connection may actually lead the first, but as long as the original order ABC is maintained, rotation will be maintained regardless of the original CW or CCW rotation.

Perhaps an easier way is whatever number of connections you rotate the first connection forward or backward in the ABC cycle (i.e. ABCABCABC...) the last connection gets rotated the same number of connections. For example if rotating first connection A to B, that's rotating one connection forward or two connection back, so the last connection rotates from C to A, which is also one connection forward or two connections back.

 

[Hv&Lv]

This only makes sense if the feeder is 4-wire wye. The OP made no mention of a neutral.

No change to rotation will occur if line conections are simply rotated. If connected A-N-C, flopping to B-N-A, or C-N-B, will not change roatation of the motors.

One way to look at it is, because the last connection of the existing "lags" by 240?, keep the revised last connection the same "lagging" by 240?. I put lags / lagging in quotation marks because the last connection may actually lead the first, but as long as the original order ABC is maintained, rotation will be maintained regardless of the original CW or CCW rotation.

Perhaps an easier way is whatever number of connections you rotate the first connection forward or backward in the ABC cycle (i.e. ABCABCABC...) the last connection gets rotated the same number of connections. For example if rotating first connection A to B, that's rotating one connection forward or two connection back, so the last connection rotates from C to A, which is also one connection forward or two connections back.

I am thinking of a two phase (V phase) line, say 14400L-G volts primary. This V phase line is tapped off a three phase pole. This V phase line goes a couple of miles and feeds a few single phase transformers, and two open delta two pot banks somewhere down the line.

The V phase line is presently fed from A & C phase. In order to balance the circuit from the substation, he wants to switch C&B, as in the first example, or A&B as in the second example.

From a utility (POCO)standpoint, What I wrote makes perfect sense. Check out the OP's profile... I think what he want to know is when he switches the primary phasing, how will it affect the secondary rotation on an open delta two pot bank. see if the picture helps [.

 

[Smart $]

I am thinking of a two phase (V phase) line, say 14400L-G volts primary. This V phase line is tapped off a three phase pole. This V phase line goes a couple of miles and feeds a few single phase transformers, and two open delta two pot banks somewhere down the line.

The V phase line is presently fed from A & C phase. In order to balance the circuit from the substation, he wants to switch C&B, as in the first example, or A&B as in the second example.

From a utility (POCO)standpoint, What I wrote makes perfect sense. Check out the OP's profile... I think what he want to know is when he switches the primary phasing, how will it affect the secondary rotation on an open delta two pot bank. see if the picture helps.

You are describing, and the picture depicts exactly what I am saying, only I am telling him how to change connections and maintain the same rotation.

Scenario -

Available Primary: Four-Wire, Grounded Wye (A, B, C, and N=G)
Two 1? POTS
Secondary: Open Delta 3? 3- or 4-W

Existing Primary Connections:

Pot 1: H1-A, H2-N
Pot 2: H1-C, H2-N

Alternate connections to maintain same rotation...

Pot 1: H1-B, H2-N (B is one connection forward from A in rotation cycle)
Pot 2: H1-A, H2-N (A is one connection forward from C in rotation cycle)


or

Pot 1: H1-C, H2-N (C is one connection backward from A in rotation cycle)
Pot 2: H1-B, H2-N (B is one connection backward from C in rotation cycle)

 

[Hv&Lv]

You are describing, and the picture depicts exactly what I am saying, only I am telling him how to change connections and maintain the same rotation.

OK. I was refering to the comment in post 6 where what you stated what I wrote didn't make sense unless in was 4 wire wye. If we are on the same page, then we both make sense.

Scenario -

Available Primary: Four-Wire, Grounded Wye (A, B, C, and N=G)
Two 1? POTS
Secondary: Open Delta 3? 3- or 4-W

Existing Primary Connections:

Pot 1: H1-A, H2-N
Pot 2: H1-C, H2-N

Alternate connections to maintain same rotation...

Pot 1: H1-B, H2-N (B is one connection forward from A in rotation cycle)
Pot 2: H1-A, H2-N (A is one connection forward from C in rotation cycle)


or

Pot 1: H1-C, H2-N (C is one connection backward from A in rotation cycle)
Pot 2: H1-B, H2-N (B is one connection backward from C in rotation cycle)

I see what you are saying. I know what you have shown will work, simply from learning from your previous posts on a variety of subjects and respecting your opinions.:thumbsup: The only problem is he will have to cross stingers in order to connect the transformers like you have shown. Either that, or make wierd rolls at the three phase pole where the V phase takes off. I highly doubt that will be acceptable. What he needs to do would to be to switch the secondary connections. No need to make it harder than it should be.

 

[Smart $]

OK. I was refering to the comment in post 6 where what you stated what I wrote didn't make sense unless in was 4 wire wye. If we are on the same page, then we both make sense.

Yes, we are on the same page. Its not that what you wrote didn't make sense, it's more that the OP'er left out some details which opened the door to other possibilities, especially because I hadn't read his profile at that point.

I see what you are saying. I know what you have shown will work, simply from learning from your previous posts on a variety of subjects and respecting your opinions.:thumbsup: The only problem is he will have to cross stingers in order to connect the transformers like you have shown. Either that, or make wierd rolls at the three phase pole where the V phase takes off. I highly doubt that will be acceptable. What he needs to do would to be to switch the secondary connections. No need to make it harder than it should be.

You are likely correct on the take-off connections. My experience ranges to the extremes of the industry... but there's a gap in the middle

Nonetheless, if he is attempting to shift the load on the distribution lines, changing only secondary connections will not shift any of the load to the other "feeder" line (B?). To keep the take-off acceptable, he may have to change primary connections at the transformers, in addition to changing secondary connections too, essentially swapping POTS.

 

[lcrjr]

For Clarity...

For Clarity...

I presented the question with some ambiquity, so let me clarify. It is a 3PH system and I am wanting to rephase 2 separate taps, that are both 2PH. Tap 1 is A and C phases and I want to change to A and B phases. Tap 2 is A and C phases and I want to change to C and B phases. Both taps have single phase loads as well as multiple three phase motors. I was hoping to rephase the taps without changing wires on the motors. Is this possible without reversing rotation on the motors? Thanks for the replies.. chuck

 

[lcrjr]

I am rephasing some taps to balance load on a feeder. The taps are V phase (2 phases) and there are downline 3PH motors served from two pot banks. If I rephase the taps as designated below, will I reverse motor rotation?

1. change AC to AB
2. change AC to BC

For clarity let me add to the statement above. The system is a three phase primary system. The two taps are separate two phase taps: Tap 1 is A and C - I want to change to AB. Tap 2 is A and C - I want to change to BC. Both taps have multiple single phase loads and a few three phase motors (from 2 pot banks). Sorry for the ambiquity and t hanks for the replies... chuck

 

[Smart $]

I presented the question with some ambiquity, so let me clarify. It is a 3PH system and I am wanting to rephase 2 separate taps, that are both 2PH. Tap 1 is A and C phases and I want to change to A and B phases. Tap 2 is A and C phases and I want to change to C and B phases. Both taps have single phase loads as well as multiple three phase motors. I was hoping to rephase the taps without changing wires on the motors. Is this possible without reversing rotation on the motors? Thanks for the replies.. chuck

For clarity let me add to the statement above. The system is a three phase primary system. The two taps are separate two phase taps: Tap 1 is A and C - I want to change to AB. Tap 2 is A and C - I want to change to BC. Both taps have multiple single phase loads and a few three phase motors (from 2 pot banks). Sorry for the ambiquity and t hanks for the replies... chuck

Simply put, if you only change one connection on each Tap, you will reverse rotation.

If you can "roll" the connections, you will maintain the motors' direction: Tap1 existing A to B and existing C to A; Tap2 existing A to C and existing C to B.

If you can't "roll" the connections, you can change just the one for each tap, but you will then have to change the secondary connections at the pot banks.

If a diagram would help, let me know. I could draw it up now, but not going to take the time if you already understand what I'm saying.

 

[lcrjr]

For Clarity...

For Clarity...

Please let me clarify my original question. It is a three phase system. The 2 taps are separate and independent of each other. The changes I want to make are Tap 1: A and C phases to A and B phases. Tap 2: A and C phases to B and C phases. There is multiple single phase loads on each tap AND mutliple three phase loads fed from 2 pot banks.

I would be interested in knowing what happens on secondary side of the two pot banks? I understand the L-L voltages are 240V, which means they are 180 degrees displaced. How do you have 3 voltages 180 degrees displaced from each other?

 

[Smart $]

Please let me clarify my original question. It is a three phase system. The 2 taps are separate and independent of each other. The changes I want to make are Tap 1: A and C phases to A and B phases. Tap 2: A and C phases to B and C phases. There is multiple single phase loads on each tap AND mutliple three phase loads fed from 2 pot banks.

I would be interested in knowing what happens on secondary side of the two pot banks? I understand the L-L voltages are 240V, which means they are 180 degrees displaced. How do you have 3 voltages 180 degrees displaced from each other?

I understand you have two (2) taps, herein named Tap 1 and Tap 2. Each tap consists of two actual line taps, Tap 1 A&C and Tap2 A&C... correct? What seems to be missing from your details is whether there is also a Neutral tap, and also whether the two pot banks consist of two pots each. I have been assuming such because it is the only way you can get 3? from only two line taps. See picture posted by Hv&Lv earlier...