phase angle setting for syn check
phase angle setting for syn check
(OP)
Let's say there are three systems - A, B & C. They are all interconnected in a ring form A-B-C-A. Our system is A. System C is very weak and has limited generation. So, A & B are delivering power to system C. Whenever the system C & A are disconnected, the transmission system becomes a long radial line. Whenever, we tried to reclose the breaker between C & A, we have a huge phase angle difference even though all three systems are tied together. The breaker is located at the generation station at system A.
I was told that the generators in system A only can withstand 10 deg phase difference during switching. So, I always set my relay sync check angle at 10 deg. For the above case, we can't close the breaker between C & A because of the sync check relay. Typically, our linemen don't use the sync check relay (bypass it) and manually close the breaker. So far, our generators are still running.
Anyone wants to chime in on this situation. How can I find the generators tolorence on phase angle differences during switching at the generating station.
I was told that the generators in system A only can withstand 10 deg phase difference during switching. So, I always set my relay sync check angle at 10 deg. For the above case, we can't close the breaker between C & A because of the sync check relay. Typically, our linemen don't use the sync check relay (bypass it) and manually close the breaker. So far, our generators are still running.
Anyone wants to chime in on this situation. How can I find the generators tolorence on phase angle differences during switching at the generating station.






RE: phase angle setting for syn check
Do you have any recordings that show large generator current excursions when the breaker closes? Does the floor jump? Can the plant operators even tell it is happening? If not then there probably is not a problem.
My idea may be wrong. I'll check some of my analysis books for an answer.
RE: phase angle setting for syn check
RE: phase angle setting for syn check
On a small plant with 350 KW and 600 KW machines I have seen consistent closing at 30 deg phase angle. A little more and the breaker tripped. A little more than that and a coupling would shear a key. This happened once or twice a year. I found a hardwired phase angle error of 30 degrees in the synchroscope circuit. I am happy closing at 15 degrees error.
Bill
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"Why not the best?"
Jimmy Carter
RE: phase angle setting for syn check
In your case the impedance of the interconnection line acts to soften the shock because it limits the amount of synchronising current (and thus torque) that system C can impose onto the generators of systems A and B. If system C has very little generation then you could possibly (and very crudely) model system C as a lumped load through a series impedance.
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If we learn from our mistakes I'm getting a great education!
RE: phase angle setting for syn check
We had a good topic on the issue.
Please see attached
http://www.eng-tips.com/viewthread.cfm?qid=259102
Good Luck
Slava
RE: phase angle setting for syn check
RE: phase angle setting for syn check
Assuming we're talking about HV system, what happens when you have a trip and some automation is trying to reconnect?
In some utilities for heavy loaded 400 kV lines, the reclosing automation will check synch at 60 deg close to power plants.
May you grow up to be righteous, may you grow up to be true...
RE: phase angle setting for syn check
These three systems are relatively small compared to most of the systems. I should have said that they are interconnected with the subtransmission lines such as 230kV between A & B, 115kV between A & C and B & C. The load in system C is around 180 MW and they have only 40 MW of generations.
To answer ScottyUK's question, yes 10 deg is the sync check relay phase angle difference allowance.
To answer stevenal's question, yes you may consider as one big system. Please note that they are 4 or 5 gas generators in system A, 4 or 5 gas generators in system B and 2 small Hydro generators in system C. Are you saying, since they are in sync between those generators, the phase angle difference doesn't matter.
To answer m3ntosan's question, I was thinking exactly. Raise system B & C generations and close the phase angle gap between A & C and close the breaker. However, I need to know how much the pahse angle differences the machines in system A can take. I don't know where to find this information. Is it something that I need to get it from the manufacturers?
I drew up some diagrams below for your visual aid.
Before BKR close
B
/ \
/ \
/X ___\
A C
After BKR close
B
/ \
/ \
/_____\
A C
RE: phase angle setting for syn check
There's a problem for generators when you're synchronizing separate systems with difference in frequency and the shock in the system will trip units.
May you grow up to be righteous, may you grow up to be true...
RE: phase angle setting for syn check
May you grow up to be righteous, may you grow up to be true...
RE: phase angle setting for syn check
I don't see how you would be able to change generation to reduce the angle across the open breaker. As long as there is load flowing from A to B to C, there will be phase angle differences.
RE: phase angle setting for syn check
Power angle is influenced by active power flow, impedance path and voltage magnitude as per P (δ) relation/diagram.
May you grow up to be righteous, may you grow up to be true...
RE: phase angle setting for syn check
http://www.o-t-s.com/synchronizing.html
As you can see in the link, Scenario #2 is very similar to my situation. The article suggests that we need to make sure the phase angle and voltage magnitude differences are within acceptable limits. My guess is the generators' limits.
What do you guys think about it?
The angle of separation between A & C is 25 deg when the breaker is open.