Stand-Alone Relaying CTs for Use With Circuit Switchers

[111R]

I'm looking for model recommendations (commonly available in USA) for stand-alone relaying CTs (C400 or higher) that can be used for protection applications with circuit switchers. Circuit switcher manufacturers never seem to provide slip on CTs as an option similar to circuit breakers. Combo units with PTs/CTs would be the most convenient since PTs are needed also, but the CTs provided in combo units are usually made for metering accuracy applications and not relaying accuracy.

Thanks

 

[davidbeach]

Circuit switchers are for where CTs aren’t required. Breakers are for where CTs are required. Circuit switchers work for transformers with bushing CTs or as switching devices otherwise controlled. Breakers every where else.

 

[cranky108]

At one time the cost difference between breakers and circuit switchers was such that unless you had CTs on other devices, it was not worth the price.

That said, I have seen bladeless circuit switchers used for line sectionalizing, where it required sync-check to close a switch.

Besides, what David said, a circuit switcher is not a very good option for reclosing.

I do know you can use a circuit switcher, with a pre-insertion resistor for a capacitor bank. But the one I am looking at now also uses a breaker for tripping and holding the CTs.

 

[dpc]

Couldn't you use a slip-over CT on the circuit switcher bushing? That said, we've found costs for euro-style circuit breakers to be roughly equivalent or even less than an S&C circuit switcher. You might be surprised.

 

[davidbeach]

Any more, many circuit switchers are essentially live tank circuit breaker. The fact that they can be installed vertically, saving space, makes them attractive where space is constrained and where connecting transformers to simple bus the transformer and bus protection can use the CTs on the transformer bushings saving the cost of more CTs. Interrupting ratings similar to breaker ratings are available.

 

[bacon4life]

Slipover CTs are design for operation at ground potential. A circuit switcher is a live tank device, so conventional slipover CTs are not applicable to circuit switcher applications.

There are experimental nonconventional CTs that use either optical sensing or magnetic field sensing. Among other, Southern States has developed ICS sensors to go along with their circuit switcher offerings.

 

[111R]

cranky108 - that is correct. The desire is to use circuit switchers with pre-insertion resistors for cap banks rather than expensive sync close breakers, but also have the ability to trip the individual switchers based on input from relaying class CTs.

 

[cuky2000]

Circuit breaker class C2 (formerly "Definite Purpose Breakers") are rated per IEEE Std C37.09a & IEC Std 62271-100 to withstand a wide range of cap-bank interruptions without synchronous control.

Beware that the trend in the power industry is moving away from using insertion resistor due to high O&M cost and reliability concerns.

Below is an illustration of transient analysis of a Class C2 Breaker rate for 72.5 kV(69 kV) for switching a single 32.4 Mvar cap-bank.

 

[cranky108]

In times past there were air core reactors used 35kV capacitor banks. I don't know why something like that can't be used for transmission size banks.

FYI, I don't believe those air core reactors are still made, but it is possible to have something made.

Sync-breakers are no solution for complete inrush prevention between banks on different buses in the same substation. A reactor on one of them is a better solution.

 

[cuky2000]

Cranky: dry core reactors (Transient Limiting Inductors - TLI) are available for HV Transmission system up to 345 kV and expected to be available shortly at 500 kV. TRENCH, GE and ABB could provide dry core reactors.

Awareness of Drawbacks of Installing Cap Bank Reactors (TLI):
Below is an example of dry core reactor (Transient Limiting Inductor) for a 230 cap bank application.
.>>>>>>>

 

[cranky108]

The TLI was not the type I was talking about, but thanks for the information.

 

[scottf]

What voltage class?