Substation high side protection - breaker vs circuit switcher 1

[cmfowler3]

What is the difference between using a 115kV circuit switcher versus a 115kV circuit breaker in a distribution substation? I understand a circuit switcher takes up less space and costs less but I am not sure what is sacrificed when using a circuit switcher instead of a breaker. Thanks!

 

[davidbeach]

With the circuit switcher you have a lot fewer CTs to work with.

With a breaker, you will have the bus zone extend to the transformer side of the breaker and the transformer zone start on the bus side of the breaker.

With a circuit switcher, you will have the protection zone boundary between CTs on the high side bushings of the transformer.

 

[stevenal]

Some switchers will provide a staged visible opening as well. The breaker (and some circuit switchers) will require a separate disconnect to achieve a visible opening.

 

[cranky108]

Depends on the system configuration.
Cost comes to mind, number of CT's, number of bushings to flash over, having to add disconnect switches, zone of protection and what is tripped, maintenance.

So it depends on what your system constraints are. Be more specific on your question for a more specific answer.

 

[krisys]

Circuit Switchers are not popular in IEC World.
However, if the installation is simple and not supplying the critical area, probably you can use. Also make sure the fault level at the point of Circuit Switcher application is relatively low.

 

[bacon4life]

Many manufacturers offer live tank circuit breakers with comparable fault ratings to dead tank breakers. We make the choice between live tank and dead tank based on physical space restrictions and a need for CTs. If you are getting product quotes, make sure you specify whether you want a live tank breaker per c37.06, or a circuit switcher per C37.016. Since the margin to move up to a live tank breaker is pretty small, some manufacturer quit building C37.016 circuit switchers and just bid their live tank breakers as higher quality circuit switchers.

 

[cranky108]

The difference being that some circuit switchers have visual opening blades, where live tank breakers do not. So a live tank breaker would require a switch.

 

[Overvoltage]

One thing I haven't seen mentioned is that depending on the switcher, you may have to trip elsewhere for a fault. That is, the switcher may not be able to interrupt fault current, while the breaker will be able to. This could force you to trip remotely to clear a fault downstream of the switcher. This may or may not be an issue depending on other parts of your system configuration.

 

[DTR2011]

I see circuit switchers often in my neck of the woods. Often used as transformer high side or HV cap bank applications (~115-138kV).

The 2 manufacturers I see most are S&C and Southern States. Previous generations of circuit switchers have had limited interrupting capability, which
had led to some interesting relaying schemes. I believe the more modern designs have overcome this.

In my experience installing, maintaining and repairing these devices, there are a few things to consider.
First would be that access to the control cabinet can either be from a single front door, or cabinets that have front and both sides available to
open. In general the control cabinets are much smaller than a circuit breaker of a similar rating, and thus any changes, or repairs can be significantly more difficult if only a front door is available.

Second would be that the controls themselves tend to follow motor control (ladder logic), which is not an issue, but may be confusing for maintenance folk who are used to certain wires on breakers being trip, close etc.

The 52a/52b contacts often need to be adjusted to the desires of the system operators (via SCADA), as there is a longer time required for the integral disconnect switches (if so equipped) to come to their final position.

The controls generally speaking, require a much longer pulse for closing (from either the control switch or SCADA), as the "trip coil" and "close coil" are actually contactors. With modern relays, this is not an issue. With manual operation from the control switch, the switchmen need to understand to hold the control switch until the position change is indicated.

In a circuit breaker control scheme, the traditional red light not only provides breaker position information, but also the red light, if designed properly, provides TCM. I have not seen a circuit switcher control scheme designed this way, but have seen optional accessories for S&C units that do provide true TCM, which is not the main trip, but the shunt trips that open the interrupters, and not the main unit.

As mentioned earlier, there aren't CT's normally included in a circuit switcher. I have seen a few applications at lower voltages (35kV - cap bank), where unconventional CT's were applied. I believe Southern States has a few application notes available. Often times the transformer high side CT's are utilized for relaying.

In the territory I work in, Circuit Switchers have been applied extensively since the late 1970's-1980's. Many are still in service, although as mentioned are overdutied. In these applications, either through the 86T or a SEL (or equivalent) relay, they either trip for all faults, or if overdutied, will transfer trip the remote end.

There are many stations that previously had fuses (~69kV) on the transformer high side. Substation modernization programs are replacing this with a circuit switcher / with disconnect switch and associated relaying. The circuit switchers require a single concrete pad for the integrated unit and can fit into tight areas. The biggest installation hassle is getting the disconnect switches installed / adjusted properly, but this is an issue with any disconnect switch.

Hope this helps.