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Caraway, AR | Can someone explain Grounded 3 phase. In the fuse box it has a copper pipe in place of fuse in the center fuse position. Also on the contactor coil has 480v to ground rather than 240 to ground and 480 across poles? Makes it more complicated to hook up a shut off timer. Thanks, John |
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Wyoming | Hang on a sec - let's back up and talk about what is up on the pole:
Is your 3-phase system a "Y" type system or a delta-type system? |
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Caraway, AR | Well, I'm not an electrician, so I'm not sure. I think the grounded phase has two pots and the regular 3 phase has three. Entergy uses grounded phase on only 40 hp or less. Coop uses grounded phase uses it on up to 60 hp that I have. The copper pipe in place of a fuse in the center fuse position is what has me confused. And alse the 480 to ground on the contactor coil. This is something the power co's are doing, not something us rednecks have come up with. Thanks, John |
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Wyoming | Is this a wild leg system? |
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Agent Orange: Friendly fire that keeps on burning. | John, It's a grounded Delta setup. You have 3 transformers on the pole that are hooked in a Delta. One corner of the Delta is grounded. In the fuse box, that grounded phase will have a shorting bar instead of a fuse. Since there is no center tap on any transformer, you have 480 on phase A to B, 480 on phase B to ground, and 480 on phase A to ground. If you google ISBN 0-538-33550-5 you'll get some hits for a decent book on this stuff that is written for someone that's not an Electrical Engineer, and covers all the different situations. Here's one link for a used book that seems reasonably priced: http://search.barnesandnoble.com/used/productMatches.asp?r=1&PEAN=0538335505 |
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Princeton,IN | It won't have a wild leg. That would reqire a center tap on one transformer, and ON A DELTA BANK, YOU ARE ALLOWED ONE, AND ONLY ONE, REFERENCE TO GROUND. Center tap won't work with a grounded phase. Has to be straight power. |
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Princeton,IN | In order not to confuse yourself, when measuring three phase voltage, always check first phase to phase.
This is going to read 480 three times.
The grounded leg , when checked to ground, will be Zero. It is grounded. There is no difference of potential. (It isn't dead, it is grounded). |
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Caraway, AR | I don't think it is a wild leg system. They have been installed (irrgation pumps) but not turned on, so I can't check. I was trying to figure out some "spring wound off timers" when my electrician said he thought the coil wire voltage would be 480 to ground instead of 240 to ground and 480 phase to phase(I hope I'm saying this right).I called power co engineer and he verified that the coil wires would be 480 to ground. I assume phase to phase would have to be 480 still. 0-12 hr spring wound timers that will handle up to 277 volts are common, but I can't find one that will handle 480 V. I hope my laymans terms arn't confusing the issue. Let me make this clear:I won't be doing the work myself, only trying to run down the parts. I do some 220 3phase at my grainery, but this is out of my league and I know it. Thanks, John |
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Princeton,IN | How about 277 phase to ground , and 480 phase to phase,
Grounded leg to ground will read zero.
CANCEL THAT.
After the last post just came on, this is built with three, 240/480 transformers. 480 three times on the voltmeter, phase to phase.
Edited by pjt 5/16/2008 23:44
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Agent Orange: Friendly fire that keeps on burning. | I agree. Many/most folks don't understand the isolation characteristics of a transformer and that's what makes this situation work. Even though it is grounded, it's a phase -- 120° out of sync with the other legs of this delta. |
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Agent Orange: Friendly fire that keeps on burning. | Sounds like a 480/277 Wye. Big brother to the 208/120 Wye that is more commonly used in shops. |
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Princeton,IN | nothing like a fast moving thread for confusion. Think your power co. engineer made a mistake when he said 480 to ground. I can't think of powerbank that will read 480 phase to phase, AND 480 phase to ground.
Edited by pjt 5/16/2008 23:49
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Caraway, AR | More than likley I'm the one that got his explaniation wrong Thanks, John |
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Somerville, Indiana | you aren't the only one. :( |
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SW Ohio | If I wanted to do timers and relays (control circuits) I would first use a small transformer (sized to load...relays and timers don't pull much) to get 110 VAC. Then there are hundreds of options, timers relays programmable controllers. You can make it do what you want and work in a safer voltage. The coils of most contactors can be changed out to 110 VAC. Or a 110 VAC relay with 480 rated contacts could be used. Then you don't need all the transformer info, just control logic. But the time may be right to get an electrician to keep it safe. Sometimes what you do works and is logical to you but hurts the next guy who expects it to be wired to certain standards.
Good Luck
Dave
Edited by L8Bloomer 5/17/2008 00:07
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| John..neAR - 5/16/2008 22:31
Can someone explain Grounded 3 phase. In the fuse box it has a copper pipe in place of fuse in the center fuse position. Also on the contactor coil has 480v to ground rather than 240 to ground and 480 across poles? Makes it more complicated to hook up a shut off timer. Thanks, John
I would call your friendly utility and have them explain what you have or a local electrician should have lots of experience with it.
Good Luck,
Bob |
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Bovina, TX | Ed is right on. 480 leg to leg. 480 to ground on two legs. 0 to ground on the "dead" leg. We use 480 volt timers here all the time. What is the timer going to be used for? |
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Agent Orange: Friendly fire that keeps on burning. | I seriously doubt what John has is an open Delta setup. Nothing mysterious here; it's just a corner grounded Delta setup, as I previously mentioned. Here's some drawings of different configurations of Delta setups and how they can be grounded. I vote for drawing B in John's case. A to ground (or C phase) 460V, B to ground (or C phase) 460V, C to ground 0V, A to B 460V 
Drawing C is a 4-wire Delta. A to ground is 120V, C to ground is 120V, B to ground is 208V, any phase to another is 230V, and of course all three are 3-phase 230V |
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Caraway, AR | We always check our wells and change sets on 12 hr intervals, but sometime we need to run a few hrs extra to finish a run. We need a timer to dial in from 0-12 hrs then shut off. Don't need one to turn on, we do that part. Thanks, John |
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Caraway, AR | Bob, Ark-mo has been gone a long time. They are now called Entergy. They are doing one for me that is 40 HP. That is as big as they will go with grounded phase system. Co-op (REA) is doing 60 HP with grounded phase (2 transformers) This 2 transformer 3 phase is some what new around here, at least on the farm. Will post pics when I figure out how. Thanks, John |
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Caraway, AR | Well a thousand words from me anyway. A pic of the two.... yes two tarnsformers and the copper pipe in place of the fuse in the panel. Why are they using two transformers.....saving money? Is this something new or something old? Thanks, John
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| John..neAR - 5/17/2008 12:41
Well a thousand words from me anyway. A pic of the two.... yes two tarnsformers and the copper pipe in place of the fuse in the panel. Why are they using two transformers.....saving money? Is this something new or something old? Thanks, John
Bob |
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Wyoming | That's why I thought it was a wild leg setup - you said way back up the thread that there were only "two pots" up on the pole. The only way you get three phases with two transformers is what we have here - open delta, or wild leg. The power company is bringing in only two phases and a neutral. That's what I see in your picture up on the pole.
BTW - you get only about 58% (if my memory is correct) usable power of the aggregate power rating of these transformers if they were in a true delta or wye setup, or 87% of the sum of the two transformers up on the pole.
The "cost savings" here is in not supplying you with a third transformer, and not carrying all three phases through to your service location. There's lots of terms EE's have to describe this setup. Not many of them can be used in polite company. |
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| NVDave - 5/17/2008 17:47
That's why I thought it was a wild leg setup - you said way back up the thread that there were only "two pots" up on the pole. The only way you get three phases with two transformers is what we have here - open delta, or wild leg. The power company is bringing in only two phases and a neutral. That's what I see in your picture up on the pole.
BTW - you get only about 58% (if my memory is correct) usable power of the aggregate power rating of these transformers if they were in a true delta or wye setup, or 87% of the sum of the two transformers up on the pole.
The "cost savings" here is in not supplying you with a third transformer, and not carrying all three phases through to your service location. There's lots of terms EE's have to describe this setup. Not many of them can be used in polite company.
Bob |
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| Power company here has moved away from the open delta and started using corner grounded delta for safety. Looking aside from the voltage on A and B to ground, the reason for the copper pipe is a safety issue to assure the system will always be grounded. |
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Caraway, AR | I just hope it is safe (after the new wears off) and that the motors will run efficiently and have a good service life running on this half way system. Ed, I ordered the book. I figure in about a week I'll be an electrical engineer. But still.........my redneck logic tells me : that if one transformer=single phase and three trans=three phase, then 2 trans would = 2 phase???..... Ya'll have put forth a good effort to explain it and appreciate it. Thanks and have a good Lord's day, John
Edited by John..neAR 5/18/2008 09:14
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Princeton,IN | Always,always,always when checking voltage on three phase, CHECK IT FIRST PHASE TO PHASE. If you have three voltages measured phase to phase, things are good
When you measure phase to ground, and see a zero on your voltmeter, your mind starts working in overdrive, and you may imagine problems you don't have. REREAD paragraph one.
If you had a three wire,three phase system without the ground (straight power)you would have voltage registered three times when checking phase to ground. REREAD paragraph one. BELIEVE paragraph one.
If you had straight power( a three wire, three phase system with no neutral), and you developed an accidental ground on one phase, it would continue to function and you would never know the difference, until
1). You checked voltage phase to ground, OR
2). You developed an other ground on either of the two OTHER phases.
Situation two, you would recognize from fire, smoke, and no power.
Now:
One transformer=single phase
Three transformers=three phase
TWO transformers=three phase, also.
Don't worry about two transformers. You ain't an engineeer, and I ain't either! I are a LINEMAN. Don't worry if it causes the engineeers problems,(it might), or if the power company is cheap(they are).
YOUR only worry is: will the power bank do the work I need it to do? Tell the power company straight up what you plan/need to do, and tell them if you have any growth/changes planned, also.
As to the copper tube in the fuse panel: You don't fuse your ground wire do you? It is confusing. It is grounded, but it is also a phase.
Also:
Do not confuse a two transformer bank with a three transformer bank with a grounded phase system with a straight power system.
REREAD paragraph one.
Confused is what I was when grounded phases where explained to me, and when it was explained how to build them. I remember thinking "you want me to do WHAT?"
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Agent Orange: Friendly fire that keeps on burning. | That there was such a thing as 2-phase. 2 transformers and 4 wires to transmit the power. Still some transmission lines by the Fort Peck Dam. I believe it was used to run the pumps and diggers on the dredges used to move the fill material to build the earthen dam. |
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Mobile | MCEC uses this system ,I like it because it will not try to single phase with you if you loss a leg. Call C&C Irrigation in Osceola for help with problem. |
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Wyoming | There indeed was/is a two-phase power. It dates back to the very first AC systems set up by Tesla at Niagra Falls. The phases are offset by 90 degrees. There's four wires just as you say. This allows for self-starting AC induction motors. Again, Tesla was the guy to identify that you need more than one phase to self-start an induction motor. Today, we use a cap to shift a single phase to start a single-phase induction motor. I'm hoping you're not constrained to 25Hz power at Ft. Peck. That would be carrying the homage to Tesla just a wee bit too far. ;-) |
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Electrical :Grounded 3 phase
