×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Flying Grounds for Transmission Line Protection

Flying Grounds for Transmission Line Protection

Flying Grounds for Transmission Line Protection

(OP)
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?

RE: Flying Grounds for Transmission Line Protection

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

RE: Flying Grounds for Transmission Line Protection

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.

RE: Flying Grounds for Transmission Line Protection

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.

RE: Flying Grounds for Transmission Line Protection

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

RE: Flying Grounds for Transmission Line Protection

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

RE: Flying Grounds for Transmission Line Protection

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources