# Closing of an open ring

1. Feb 8, 2010

### bigjoe5263

hi guys,

just want to ask, an open loop has three points A,B, C and each point serving a load. there is only one source (a subtransmission 69kV line from a substation), connected at point A. The loop is open at line segment AC (the circuit breaker at point C, connecting the segment AC is open). The voltage at point A,B and C are almost equal, or there is only a small difference in magnitude. my question is this:

Since there is only one source, which means the frequency (60Hz) is the same at all points, is it possible to close the loop (circuit breaker) at point C? What would be the effect of closing? what are the standards parameters?

2. Feb 9, 2010

3. Feb 9, 2010

### bigjoe5263

S--x----------x--A--x----------x--B--x----------x--C---
l l
x------------------------------------x

where:

S = source
A,B,C = interconnection (bus)
x = circuit breaker
-- = transmission line 69 kV

Thanks

4. Feb 9, 2010

### bigjoe5263

S--x----------x--A--x----------x--B--x----------x--C--x---------x-->to point A

where:

S = source
A,B,C = interconnection (bus)
x = circuit breaker
-- = transmission line 69 kV
hope this will help you visualize what I have previously posted, sorry for the drawing I don't know how to make a good one here.

thanks

5. Feb 9, 2010

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6. Feb 9, 2010

### Snoogans

Going from an open ring to a closed ring can be difficult. The fault currents in the lines are increased, basically doubled as the 2 paths are in parallel. It also complicates the protection settings. I have had limited experience with HV, but from what I can gather it is only done in critical infrastructure situations where an interruption of power is not acceptable.

7. Feb 9, 2010

### dlgoff

I don't see how the fault currents in the lines are increased because it's a ring bus. Any time you switch in a line, no mater what bus configuration you have, you're going to see some disturbances.
"www.gedigitalenergy.com/multilin/notes/artsci/art12.pdf"[/URL]
See figure 13 for how the protection relaying is accomplished for a ring bus.

Last edited by a moderator: Apr 24, 2017
8. Feb 9, 2010

### Snoogans

Under fault conditions it is the impedance of the fault path and the impedance of the source that determine the magnitude of the current (assuming bolted fault). A closed ring has 2 paths from source to fault in parallel, therefore the impedance is less. Perhaps 'lines' wasn't the best word to use previously.

I am certain there is added complexity to closed ring protection systems, I'm just not sure how to describe them. I know open ring configurations are common, closed ring are not, well at least in Australia I should qualifiy.

9. Feb 9, 2010

### bigjoe5263

dlgoff, that is almost the figure, except that A, B, C are load Bus, i.e. power transformer are connected to them, and also the ring configuration are connected to those bus through the transmission lines between them.

10. Feb 10, 2010

### dlgoff

This is probably what you have in mind.

The situation is still the same as in my first reply (...you can open breakers to isolate one line without disturbing the other lines) except now your load includes a transformer. As to frequency change due to switching in the load, it takes a little time for the generators to catch up, hence there will be a slight lowering of frequency. This is call "rubber banding" I believe.

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11. Feb 17, 2010

### bigjoe5263

digoff.. thanks for the figure.

assuming there are no generators involve, and circuit breaker A is initially open,
are there parameters to be check before circuit breaker is to be closed? what are the things need to be considered? i.e. voltage difference across the open breaker, phase angle, frequency.. etc

12. Feb 17, 2010

### dlgoff

You would have to have A and B open to isolate the left transformer. If just A is open, the there will be 69kV at the same freq. and phase on either side of A.