Ring Bus or Breaker and a Half? 3

[rockman7892]

Looking at the attached one-line would others consider this as a ring bus, or a breaker and a half arrangement?

Although this appears to be setup line a breaker and a half seeing that this has (5) terminals between (6) breakers this would appear to be more of a ring bus configuration. To be classified as a breaker and a half I would expect to see 1.5X the number of feeders/terminals which in this case would just be (4) terminals.

It almost looks like this was originally a breaker and a half and then with a new line added to Bus 3 it became somewhat of a ring bus.

Appreciate input on how others see this.

Thanks

 

[cranky108]

It looks like someone was trying to save some money. The original plans may show what was intended, but it looks like a ring with an empty bay.
There appears to be no attempts to add another leg, so I would not say it is a breaker and a half.

 

[davidbeach]

It's a five position ring with six breakers. Rather than alternating lines and GSUs they put two breakers between the two lines. There might be some physical constraint the forced that arrangement, or an extra breaker was found to be preferable over the line crossings that would be needed to get the lines away from each other and only use 5 breakers. If there was just one breaker between the lines, a line fault with breaker failure could take out both lines. This way no single breaker failure takes out both lines.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[davidbeach]

Besides, you can't really have BAAH until you get to three bays. Two bays of BAAH is simply a six position ring in which two of the positions have bus protection. A third (or more) bay provides the means of alternate current paths that a ring doesn't.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[bacon4life]

It is somewhat common in my area to configure stations such that they can be converted from ring buses to BAAH at a later date if it ever needs more than 6 terminals. If the expansion for this bus from 5 to 6 terminals is less than 10 years away, I would probably push for all 6 breakers to be install initially so that very little rewiring is needed. In locations where future expansion might be more than 10 years away, it might may sense to install the physical bus to allow for eventual reconfiguration, but not actually install breakers. I have some locations where we installed a spare circuit breaker foundation during the initial substation build, but then placed a simple bus support structure where the future breaker could go.

One other potential reason for two breakers between line bays is that it eliminates a mode of inadvertent relay operations. The 321 relays have a single set of CT inputs, so in the case of a single shared breaker between lines, there is a risk of incorrect shorting of the combined CT circuit during breaker maintenance.

 

[Kiribanda]

The practical maximum number of CBs for a ring configuration is four. Therefore, anything more than four
is an expanded version of the ring bus. Your SLD shows six breakers meaning it is one step above the
standard four breaker ring bus scheme. Therefore, your SLD depicts a standard one-half-breaker bus arrangement.
The next higher step is one-third-breaker scheme with four breakers controlling three feeders.

 

[bacon4life]

Kiribanda-What limits the practical maximum number of terminals on a ring bus in your area? I my area, stations with fiver or six terminals are more likely to be configured as ring buses than breaker-and-a-half buses.

 

[Kiribanda]

To my knowledge it does not depend on the area that someone is working. Basically it is substation design engineer's choice considering equipment layout issues, bus bar configuration & also protection scheme etc.

 

[cuky2000]

The majority of the power utility practices observed in the USA use ring-bus (RB) from 3 up to 6 positions for substations rated 69 kV to 230 kV. BAAH; typically is used for 6 or greater elements or if 4 or more transmission lines are considered.

The drivers behind this general rule of thumb are to meet conflicting parameters such as reliability, allowable planning outage - -maintainability, operation flexibility, NERC & ISO outage restrictions, economics, the importance of the substations, and other factors.

Below are some generic indicator data from different sources that may help support the decision to go from RB to BAAH configurations.