Tie Breaker in Series and Bus duct

[NickParker]

We have a space constraints preventing a long switchboard, so we want to segregate the switchgear by sections Bus A and Bus B as shown in the below figure.
The questions are,
1) The link - to be connected by cables or bus ducts (distance less than 10 meter)
2) Should I have bus tie breaker at the both the ends of Bus-A and Bus-B?

 

[RRaghunath]

Busduct or cable tie - depends on the layout. If lay out permits, bus duct is preferred for obvious reasons.
Breaker at both ends or only one end - if the intent is to keep the two busses always tied / treated as a single bus, there is no need to have circuit breakers. Just one disconnector will do.

 

[NickParker]

Busduct or cable tie - depends on the layout. If lay out permits, bus duct is preferred for obvious reasons.
Breaker at both ends or only one end - if the intent is to keep the two busses always tied / treated as a single bus, there is no need to have circuit breakers. Just one disconnector will do.

The Bus A and Bus B receives power from their transformer; it is a Main-Tie-Main arrangement; Bus tie always operated in "Normally open" but has momentary parallel for Auto transfer.

 

[crshears]

Using two breakers in series provides additional redundancy in terms of being able to still break bus parallel if one bus tie breaker should fail to open on command during switching. Breaker fail schemes also benefit from having a second breaker.

However, providing two breakers in series obviously increases capital cost as well as incrementally adding to OM&A budgets.

A compromise I have frequently encountered is to have one bus tie breaker and one set of removable links, so that if tie bus maintenance is required, an outage can be taken on the section "bus x removable links x bus tie breaker" to open the removable links. Following this outage, the second bus can be returned to service and the next outage taken on the bus tie section "bus tie breaker x removable links" so as to perform the required work.

 

[mparenteau]

Not sure about your voltage...maybe a tie-breaker in your busduct link?

Mike

 

[NickParker]

Not sure about your voltage...maybe a tie-breaker in your busduct link?

Mike

It is a low voltage; 690V

 

[crshears]

And to think I was thinking 13.8 kV . . .

 

[RRaghunath]

The Bus A and Bus B receives power from their transformer; it is a Main-Tie-Main arrangement; Bus tie always operated in "Normally open" but has momentary parallel for Auto transfer.

In such a case, when the tie is open, the respective bus incomer protection acts as back up to the outgoings of that busbar and when the two buses are tied, the incomer protection will have to act as back up to all the feeders included in Bus A & B.
The tie cable or busduct will remain live from one bus with breaker open at the other end. This breaker is controlled by the auto transfer scheme when required.
Some engineers would like the small length cable / bus duct of the tie feeder (that is live from one end) to protected, especially if it happens to be cable tie. I always felt this is not necessary. Now that you confirm the system is LV, the risk is much lesser.

 

[bacon4life]

Seconding crshears suggestion to ensure you design the tie with adequate isolation points to allow for maintenance of either bus without taking both busses out of service. Beyond that, the second tie breaker adds very little value.