HV Load Interrupter Switch

Depending on application, there may not be a circuit breaker at all, which can result in cost savings...but the pro and con aspects must be carefully evaluated.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

I don't think I've ever seen a load interrupter switch in a HV switchyard. I'm not sure a true load interrupter goes beyond MV. Everyone has a slightly different definition of HV vs. MV, so I'm assuming greater than 69kV for HV.

Are you thinking of a circuit switcher with integrated motor operated switch?

If this is what you are referring to, the horizontal interrupter between the middle and right vertical insulators is a SF6 circuit breaking device. It operates first on a trip (electrically and mechanically), then the motor operated switch opens. Closing is the opposite. Some use these on Transformers or Cap banks. Notice the external Live Tank CT's. Some may call a circuit switcher a poor mans circuit breaker. The vertical interrupter design are sometimes handy when space is a premium in front of a transformer. Generally the transformer has internal CT's for 87T and 87B applications.

I've seen a defective disconnect switch used to pick up an unloaded 138 kV transformer. We were warned to stay back as the arcing whips / horns were known to be missing. It was dark and I was young and still jumped a bit.

I think of this when breaking HV..

500kV Switch

In my not very vast experience, load break switchs (LBS) are only attached to a HV circuit for its functionality under normal grid conditions (to change the circuit configuration) being more economic than a circuit breaker (CB). The breaker usually is still needed for protection.

This is helpful in circuits with some complexity (with more LBSs than CBs) and doesnt seems needed for, lets say, a single feeder.

Also, from another point of view:
Historically the pair "disconnect switch (DS) - CB" is (or was?) the way to go in HV because the DS will add a safety element to the circuit (even in the single feed example) providing visual disconnection.

A load breaker switch its kinda an "upgrade" to the disconnect switch and probably has took its place in some cases, though Im not sure about the safety issue with this change.

The LBS is never considered as a CB backup.

Hope it helps.

I’m guessing you talking about a circuit switcher. Something like an S&C mark IV or a Mark V.
We and many others still have these in service. Like mentioned above, load breaks inside an SF6 bottle, then the switch opens.

[sub]To perform Interrupting a circuit in the HV substation imposes heavy thermal and dielectric stresses in the protective device. This combined with the need for maximizing the availability and system reliability, HV substation is required to perform reclosing particularly in transmission lines.[/sub]

a) Circuit breakers [sub]are designed to perform heavy interrupting duties within the design parameters with high interrupting capacity(40, 63, 80 & 90 kA), fast clearing time (as low as 2 to 3 cycles) and used up to UHV[/sub].

b) Circuit switchers [sub][sub][sub](Horizontal or Vertical)[/sub][/sub] are an intermediate interrupting device slower than circuit breakers and do not have reclosing capability designed up to 345 kV. Commonly used for transformer and UG feeders protection.
[/sub]

c) Vacuum switches:

d) Disconnect switches have limited current interrupting (In a low single-digit).

[sub]Some utility facing an economical dilemma and provide a low-cost alternative using a disconnect switch with load-break capability using breaking accessories with mixt results like the following devices added in the switchblades:[/sub]

* High-Speed Whip: Typically used attached to air switch to interrupt transformer magnetizing and line charging current.

* Quick Break Whip: Difficult to specify the exact level of interrupting capability. Increase switch line dropping capability by increasing the speed of contact separation during the opening of a switch.

* Single Bottle Vacuum: Load break capability up to 34.5 kV. Above that, only add the capability of loop splitting < 2000 Amps on systems up to 230kV. Link

* Load break interrupter: It is a switch attachment using an SF6 fill device that could provide limited ampacity capabilities in the 100's to low 1000's for load breaking, line dropping, and loop splitting.

Cuky nailed it.