Flying Grounds for Transmission Line Protection

[fredcon]

We have a situation on some of our older 115KV:13.2KV substations where we are still using flying grounds in lieu of higher rated circuit switchers between our station transformers and our 115KV T-lines. Does anyone know the concept behind this original design and why it would be justifiable to upgrade to circuit switchers?

 

[davidbeach]

What is a flying ground? I don't recognize that term.

 

[jghrist]

It is either the use of sky hooks to support shield wires or the use of high speed grounding switches, closed by transformer protection, to cause a transmission line trip at the source.

If the latter, the justification for changing to circuit switchers is a reduction of high level faults that stress the transmission system.

The use of high speed grounding switches is better than a system used by the supplier of one of our municipal clients. The system was to open a motor-operated disconnect when the transformer protection operated, with the idea that if the current was too high to be interrupted by the switch, the arc would go to ground and cause the transmission line protection to trip at the source.

 

[apowerengr]

There are still quite a few grounding switches out there. As jghrist described the intended operation the concept motivator was economics saving the cost of the circuit switcher. Now days I can't see keeping with this concept in most applications unless you can't get a local device with enough interrupting rating to handle the faults involved. Grounding switches were expendable and the line breakers were designed to handle the faults anyhow.

With power transformer costs continuing to increase and if the physical space is available I've been suggesting installation of a circuit breaker instead of a circuit switcher as I want the zone of protection extended to CT's on the breaker in order to protect for a tank-mounted lightning arrester or high-bushing failure.

 

[slavag]

Hello Apowerengr.
This old system have two "goals"
1. Save CB's.
2. No problem with protection coordination, you have only one 50/51, 50N/51N relay installed on the source side.
This system is common practic in Russia on radial lines up to 110kV with many xfr. on the same line.( municipal and settelments applycation only, not for industrial or transmission lines).
Regards.
Slava

 

[cuky2000]

Are you referring to a switch with arcin horn with interrupting device ?
Any similarity to the one shown in the enclosed link?

http://video.google.com/videoplay?d...=31&start=0&num=10&so=0&type=search&plindex=0

 

[bacon4life]

Jgrist, what are sky hooks? Google found them as a reference to climbing hooks or gaffes.

 

[jghrist]

My reference to sky hooks was a feeble attempt at humor. We used to joke about supporting lines from the sky on sky hooks to avoid using poles.