Phasing

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dogman

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Location
Woodward,ok
2 3? circuits to phase in, both off of the same sub. 14,400 is the voltage. When they phase this in, they have 2000 volts difference on all ?s. A to A, B to B, C to C. Question is, is this safe to put together? Thank you, Bob
 

broadgage

Senior Member
Location
London, England
Without more detailed information, I would say no way !
2000 volts is a very significant difference.

If the two supplies are dervived from the same transformer, then if unloaded they should not differ by even one volt.
If the supplies were differently loaded then the voltages would differ, but only by a few % due to the voltage drop in the wires.

If we are talking about two transformers energised from the same source, then if correctly selected, and with the same tappings on each transformer, I would expect voltages to be within 1%

More detail required, but for now I would advise against it.
 

richxtlc

Senior Member
Location
Tampa Florida
2 3? circuits to phase in, both off of the same sub. 14,400 is the voltage. When they phase this in, they have 2000 volts difference on all ?s. A to A, B to B, C to C. Question is, is this safe to put together? Thank you, Bob
2000 volts is a significant difference. How are you phasing these two circuits? Direct measurement or through the use of the PTs? If you are using PTs, have you checked that they are wired properly and that the phase rotation is correct?
 

dogman

Member
Location
Woodward,ok
phasing

phasing

Same transformer, they used phasing sticks. Checked voltage ? to neutral and had 14400 volts. So the sticks were working. They are worried about putting this together with the 2000 volts difference. I agree. Thank you, Bob
 

Phil Corso

Senior Member
Dogman...

2kV between like-phases is about 7% of the ph-to-ph voltage. Do you have an idea about the physical distance between the two sources, even though they are fed from the same sub?

Regards, Phil Corso
 

dogman

Member
Location
Woodward,ok
phasing

phasing

I don't know, they are fairly new sticks. 6 months ago we had 2 other sets of sticks and they all read the same, with these sticks. I don't know on the length. Contractor is working at another coop. and called and asked if I have ever ran into anything like this.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Where are you trying to put this together at? Are you trying to put it together at the end of the runs?
Example, If one three phase line is 1 mile long, the other three phase line is 10 miles long, and you are trying to put it together where the two come together, that could explain the difference.
How are you wanting to put this together? GOABS, solid blades, or VWVE?
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
There was a book written by O.C. Seevers with this condition listed in it. The title was "unique power systems problems solved". I wish I had a copy handy. It is about midway through the book.
 

mivey

Senior Member
There was a book written by O.C. Seevers with this condition listed in it. The title was "unique power systems problems solved". I wish I had a copy handy. It is about midway through the book.
Problem #6. It was a 69 kV line. The difference was 10 kV. The separation was 100 miles.

The speed of light yields one degree per 8.61 miles because (186,000 miles/s) / (60 cycles/s) / (360 degrees/cycle) = 8.611111 miles/degree

100 miles / 8.61 miles per degree = 11.6? = 8.04 kV.

The 2 kV in the 14.4 kV case gives us 7.964? or a distance of 68.6 miles. So if we are talking about a loop difference of about 70 miles, that would be about right assuming a vaccum. Probably 180,000 miles per second is closer for the wave propagation and yields about 66 miles for our problem.

The problem is, the OP is not going to have a 60-70 mile 25 kV line. Even allowing for some voltage drop would still be too long for this voltage level (around 52 miles if we allowed a 3% drop and have a remaining 6.24?)

I would not tie it.

My first guess was measurement error, but we need additional information on the circuit configuration and loading to figure out where the 6? to 8? is coming from. Any regulators or capacitors in the line?
 

dogman

Member
Location
Woodward,ok
phasing

phasing

It is a double deadend, with no switches. They wanted them to hook it up with macs. I think the sticks are ok. I will call the contractor and find out more information. Thank you, Bob
 

dogman

Member
Location
Woodward,ok
phasing

phasing

They checked with both digital and analog phasing sticks. 7 or 8 miles on both from sub. until they meet. Don't know about the taps that come off of both circuits, he thinks there is alot. On Wednesday they hooked all of the capacitors on, one of the circuets. Thank you, Bob
 

mivey

Senior Member
I noticed you said they got 14,400 for L-G. Did they get that for all six or did they just check one to see if the stick was working?

I'm trying to determine the contribution from voltage drop, but for a rough guess I'm getting a high case of around 1,000 volts. Still does not get us to the 2,000 volts we are looking for, plus one circuit would have to have all the load and the other practically none.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Problem #6. It was a 69 kV line. The difference was 10 kV. The separation was 100 miles.

The speed of light yields one degree per 8.61 miles because (186,000 miles/s) / (60 cycles/s) / (360 degrees/cycle) = 8.611111 miles/degree

100 miles / 8.61 miles per degree = 11.6? = 8.04 kV.

The 2 kV in the 14.4 kV case gives us 7.964? or a distance of 68.6 miles. So if we are talking about a loop difference of about 70 miles, that would be about right assuming a vaccum. Probably 180,000 miles per second is closer for the wave propagation and yields about 66 miles for our problem.

The problem is, the OP is not going to have a 60-70 mile 25 kV line. Even allowing for some voltage drop would still be too long for this voltage level (around 52 miles if we allowed a 3% drop and have a remaining 6.24?)

I would not tie it.

My first guess was measurement error, but we need additional information on the circuit configuration and loading to figure out where the 6? to 8? is coming from. Any regulators or capacitors in the line?

Yea, I brought the book home today from work, was going to try and figure what you did. Thanks though for giving me a reference to check my calcs against. :thumbsup:
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
My first guess was measurement error, but we need additional information on the circuit configuration and loading to figure out where the 6? to 8? is coming from. Any regulators or capacitors in the line?

I also thought this would be a regulator issue. 2000 volts would be 120 volts and 103 volts
 

mivey

Senior Member
I also thought this would be a regulator issue. 2000 volts would be 120 volts and 103 volts
There is something not adding up. Unfortunately, we may not be able to get the info we need over the internet.

I sure would not tie it until I had a reasonable explanation. How many times have you seen a tie-line change and two circuits are no longer fed the way you remember them being fed? That is just one of the possibilities that would need to be eliminated before I reached my happy place.
 

Joshuas

New User
Location
USA
Occupation
suggestion
In the event that we are discussing two transformers invigorated from a similar source, at that point if accurately chose, and with similar tappings on every transformer, I would anticipate that voltages should be inside 5%
 
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