High speed grounding switch and its purpose in EHV GIS 4

[ravindranathan]

What is the use of High speed grounding switch in EHV GIS and in which location of the bay is it exactly used? Why only in line feeder bay? Some specs mention that both earthing and high speed earth switch should be able to make a fault..some specs say only high speed earth switch needs to have making capability.Pl advise.

 

[RRaghunath]

High speed earth switch is used for earthing the OHL feeder.
The high speed earth switch is capable of making the SC current, unlike the standard earth switch in outdoor substations.

 

[crshears]

What RRaghunath said.

The reason why, as I understand it, is that overhead lines that have been disconnected from their grid can still have standing voltages on them due to mutual inductance from adjacent in-service circuits, and cables can have trapped electrostatic charges on them under the same circumstances. A high-speed grounding/earthing switch can successfully drain these charges without sustaining damage. Station busses do not typically afford the same challenges, and can therefore be grounded/de-energized using standard, and therefore less expensive, ground switches.

All this being said, grounding switches are not normally closed into energized apparatus, and as such should not normally be exposed to true fault current.

CR

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

 

[Mbrooke]

What Crshears said.

 

[thermionic1]

More of an anecdote. Years ago, I was working on a GIS project. This was all new to me at the time. The OEM had their specialists supervising the installation. All over my schematics were references to Fast Acting Ground Switch (Abbreviated), as if it were part of the tripping scheme (jumpers were removed to disable the function). I finally asked the OEM guy what the purpose was and he told me (in a Swiss Accent) "well in places like Russia it is to awake sleepy protection at the other end of the line). I had a good laugh, but I think he was serious.

 

[cuky2000]

Earthing switches shall only be closed onto High Voltage conductors that are identified as de-energized from all sources by voltage and/or disconnector indication.

High-Speed-Earthing Switch (HSES) can be used for secondary arc extinction during fault or re-closing scheme.

Below are a couple of links and a comparison table among earthing switches for HV GIS application:

https://www.eng-tips.com/viewthread.cfm?qid=438187

https://www.youtube.com/watch?v=uNvpfF-ERiU

 

[ravindranathan]

Cuky and all others many thanks for the inputs.
Secondary arc is a new thing for me..Did google and could learn a new phenomena..
Thanks

 

[Mbrooke]

What is secondary arc?

 

[cuky2000]

This arc is supplied by:
1) Electrostatic:(capacitive charging coupling}proportional to the length and voltage of the transmission line.
2) Electromagnetic induction from the adjacent healthy phases.

The secondary arc current can be expressed as: [highlight #FCE94F]I_s = I_sc + I_sm[/highlight]

Where,
I_sc : Electrostatic current induced in a healthy phase.
I_sm : electromagnetic current induced in a healthy phase.

 

[crshears]

Sounds like what I said, but using numbers...

All over my schematics were references to Fast Acting Ground Switch (Abbreviated), as if it were part of the tripping scheme (jumpers were removed to disable the function). I finally asked the OEM guy what the purpose was and he told me (in a Swiss Accent) "well in places like Russia it is to awake sleepy protection at the other end of the line). I had a good laugh, but I think he was serious.

One of our 230 kV stations in the farther-flung northern reaches of the province was not provided with any means of remote or transfer circuit tripping from operations of the transformer differential protection; instead, it had a high-speed vacuum ground switch on the transformer side of the high-voltage disconnect switch, wired to close on bank diff. The circuit's reclosure time delay was a few seconds longer than it took for the primary switch to open.

Indeed, back in the day when the highest voltage on our system was 115 kV, auto-grounds were routinely used to trip off banks on differential protection; by convention, these were all wired to the blue phase to provide reasonable assurance that any circuit auto-reclosures had been initiated by a transformer diff trip somewhere out there. One would wait for the "power off" calls to come in to find out which one...

CR

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

 

[stevenal]

The original schematics for our 115 kV mobile substation show a high speed grounding switch on one phase in front of the primary fuses. The transformer has relatively high impedance, so low side faults may not clear with the primary fuses. The switch was spring charged and ready to initiate a primary fault for secondary side faults. Remote protection would then operate. Built in California, but I wasn't aware California was like Russia. See "fault switch" in Blackburn's book.

 

[cuky2000]

Notice that there is a different application for the high-speed ground switch (HSGS)for air-insulated substation (AIS) and gas-insulated substation (GIS).

The AIS HSGS are basically of two types:
a) Single pole: sometimes called fault-initiating switch, that closes to create a phase-to-ground fault to ensure that remote terminals operate for transformer faults. . See illustration below.

b) Three poles: are group operated to provide grounding for inspection, maintenance, repair, or replacement of other substation equipment such as capacitor banks, circuit breakers, circuit switchers, etc. They are available as stand-alone devices (capacitor bank grounding for example) or integrated to a group operated disconnect switches, circuit switchers, and other devices.

 

[Protection Engineer]

We, unfortunately, still utilize BUPPO ground switches (back-up protection pneumatically operated) for bank protection at a couple hydro generation sites. Cheap solution when you don't want to pay for a high-side PCB...

 

[ravindranathan]

Is it advisable to have HSES if outgoing is a Tie Line feeder which feeds power to the other end through cable?