Air Gap Question

[EmpireWind]

Reading through the NESC code section Part 4, working around energized and de-energized equipment in the switchyard, one of the precautions for approach especially voltages above 72.5kV, the control measure is to include blocking reclosing, prohibiting switching during live line work, using protective air gaps etc.

So in switchyards that are open to air, there is a disconnect switch along with a ground switch on both sides of the 52 breaker. My questions are as follows:

1. Is this more of a best practice or is this based on the interpretation of OSHA 1910.269 and NESC?

2. In the event of a gas insulated switch-gear how is the air-gap requirement satisfied as outlined in Table 441 1 through 4.

3. Does the disconnect switch and ground switch inside the GIS enclosure satisfy the air-gap requirement or is a separate disconnect switch outside the GIS needed to meet the air-gap requirements?

Would appreciate your feedback.

 

[EmpireWind]

No response?

 

[Hv&Lv]

Reading through the NESC code section Part 4, working around energized and de-energized equipment in the switchyard, one of the precautions for approach especially voltages above 72.5kV, the control measure is to include blocking reclosing, prohibiting switching during live line work, using protective air gaps etc.

So in switchyards that are open to air, there is a disconnect switch along with a ground switch on both sides of the 52 breaker. My questions are as follows:

1. Is this more of a best practice or is this based on the interpretation of OSHA 1910.269 and NESC?

2. In the event of a gas insulated switch-gear how is the air-gap requirement satisfied as outlined in Table 441 1 through 4.

3. Does the disconnect switch and ground switch inside the GIS enclosure satisfy the air-gap requirement or is a separate disconnect switch outside the GIS needed to meet the air-gap requirements?

Would appreciate your feedback.

1) I would guess it’s a convenience thing on an old breaker.
We will not use them and I have only looked at three in a switchyard one time. Thought it was a bad idea personally.

2) It’s not.

3) No, you need a separate disconnect beyond the switch to provide a visual opening. An open breaker doesn’t mean anything if you can’t see the visual opening.

 

[EmpireWind]

In response to answer to point (3), is that an interpretation of code or regulation. Can someone point me to the correct reference?

 

[Hv&Lv]

In response to answer to point (3), is that an interpretation of code or regulation. Can someone point me to the correct reference?

I have a question.
Is there a switch before and after the breaker, with a bypass above for breaker maintenance?
If the answer is yes, then: (emphasis mine)
1926.961(c)(2)
Open disconnecting means. The employer shall ensure that ALL switches, disconnectors, jumpers, taps, and other means through which known sources of electric energy may be supplied to the particular lines and equipment to be deenergized are open. The employer shall render such means inoperable, unless its design does not so permit, and then ensure that such means are tagged to indicate that employees are at work.

In which case a grounding switch on a breaker will be useless.

 

[EmpireWind]

Thank you for pointing that out. Doesn't 1926 relate to construction. Is there a similar clause in 1910.269?

And the answer to your question about switch on either side of breaker, no. The vendors are proposing a disconnect on the upstream side of the 52 breaker but the downstream side which is being connected to the HV bushing of the transformer, no. They are just providing an earth switch. I have been challenged to provide a compelling code requirement that would need to be satisfied. I have always taken this for granted based on my previous utility experience that required disconnect switches for isolation.
If this were an open air switchyard, I would use NESC Table 441 requirements but this is a GIS setup and am finding a hard time coming up with a standard, safety code or OSHA requirement. Glad you mentioned 1926. I was looking at the 1910 sections which would apply for operations phase.

 

[Hv&Lv]

The 29 CFR 1926 standards apply to construction, alteration, and/or repair, including painting and decorating, as those terms are defined under the Davis-Bacon Act, U.S.C. 276a, which authorizes the Secretary of Labor to set wage standards for federal contracts for construction, alteration, and/or repair, including painting and decorating.

 

[Hv&Lv]

I’m curious as to how this breaker will be tested and maintained without a way to isolate and or bypass it?
when testing or maintenance is due, the load will be able to be interrupted and or shut down for however long repairs or tests take to complete?

My mind is trying to put this in a substation or switchyard setting.
Im sorry if I’m picturing this wrong.

 

[EmpireWind]

You are right about that. Which is my concern too, hence I flagged it to the equipment vendor. I have to provide a reference to code. Since I was looking at 1910 and 1926, I did not see explicit reference to disconnect.
My concern is also with regards to working on transformer and isolation between the GIS and the xfmr bushings. So thanks for taking time to answer my questions.
Any experience with three way disconnect/ground switches?

 

[Hv&Lv]

You are right about that. Which is my concern too, hence I flagged it to the equipment vendor. I have to provide a reference to code. Since I was looking at 1910 and 1926, I did not see explicit reference to disconnect.
My concern is also with regards to working on transformer and isolation between the GIS and the xfmr bushings. So thanks for taking time to answer my questions.
Any experience with three way disconnect/ground switches?

No. Only saw them in an old station.
Didn’t like them then either.
Seems to me if your buying the equipment you don’t have to cite code to any vendor.
They should provide by your specs or find another vendor.