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Anonymous Poster #1

Changing the single bus Panel to double ended with bus tie

11/22/2022 2:51 PM

Is it true that installing a tie breaker reduces the fault current?

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#1

Re: Changing the single bus Panel to double ended with bus tie

11/22/2022 4:02 PM

"A Tie Breaker is a type of circuit breaker that connects two sections of electrical bus serving different power sources. When closed, current can pass in either direction between them."

I don't see how it would....It would allow you to isolate the fault without complete power shutdown though...

https://www.ascopower.com/us/en/resources/technical-briefs/increasing-power-redundancy.jsp#:~:text=A%20Tie%20Breaker%20is%20a,in%20either%20direction%20between%20them.

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#4
In reply to #1

Re: Changing the single bus Panel to double ended with bus tie

11/23/2022 8:07 AM

I was under the impression that a "tie breaker" is only necessary when the scores of the teams playing in the game are the same and the game playtime has already lapsed..

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#5
In reply to #4

Re: Changing the single bus Panel to double ended with bus tie

11/23/2022 10:06 AM

When it's England playing soccer, and the tie breaker is a penalty shoot out: then the fault current increases dramatically.

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#6
In reply to #5

Re: Changing the single bus Panel to double ended with bus tie

11/23/2022 11:17 AM

Its typical for all soccer teams, especially the European teams..

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#2

Re: Changing the single bus Panel to double ended with bus tie

11/23/2022 1:34 AM

It doesn’t sound plausible.

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#3

Re: Changing the single bus Panel to double ended with bus tie

11/23/2022 3:13 AM

If the bus tie is closed between two healthy supplies then the fault current available will be some value greater than the single feed and as high as the maximum available, likely double, having regard for the system impedance limiting the fault current.

From my experience the neutral of each supply needs to be Routed through a pole of the bus tie breaker, usually a 4 pole breaker. The only time the bus tie should be closed is before the incomer to the switchboard of either supply is opened and for the shortest time possible.

A suitable switching sheet needs to be available for the whole process where all calculated faults and switching duration needs to be specified. Suitable hazard analysis needs to address the design fault capacity of the switchboards.

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Anonymous Poster #2
#7

Re: Changing the single bus Panel to double ended with bus tie

11/25/2022 7:44 AM

Why would it?

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#8

Re: Changing the single bus Panel to double ended with bus tie

11/28/2022 2:19 PM

AP1,

In my experience, No. As others said, a tie breaker can allow power to flow in either direction between the two buses that are joined when the breaker is closed. The available fault current on either bus depends on many factors, such as the physical distance between them, the type of connection (wire, size, number, conduit, etc), and the presence of motors on either of them (which can contribute to the fault current when running and a fault occurs upstream).

If both buses are energized when the tie breaker closes, an instantaneous fault can occur if the two are not synchronized in phase and at about the same voltage. This would create a fault current as high as the sum of the two separate fault currents for each of the two separate buses.

Proper switching controls will prevent this from happening.

The most common use of tie breakers, in my experience, is to allow one source of power to be turned off without leaving the load off for any more than the time needed to close the tie to the other source. This is best done with mechanical interlocking (such as "Kirk" keys) and/or electrical interlocking.

--JMM

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