132kV Switchgear Ground Clearance in Substation 2

[Yogima]

Dear experts,

I hope you can provide some insight with an issue I have.
My organisation is supervising a new substation that will import 50MW via 132kV transmission line and transformerd into 66kV for reticulation to the existing grid.

While reviewing the drawings for the 132kV switchyard, I have found out the support structures the contractor has proposed is 2.6m. Per IEC 60071-1 the minimum air clearance for phase-phase and phase to earth for rod-structure is 1,300mm. All switchgear comply with the clearance from the live terminals to the earth terminals.

We have proposed to reduce the structure heights from 2.6m to 2.1m after discussing with our operations and maintenance personnel to accommodate their requirement for ease of access to the mechanical boxes as well as operating the isolator switch handles.

I however am cautious about the safety implications of this. Apart from safe working distances, could the experts advise what other risks there are despite the minimum earth clearance being complied with which I may be overlooking.

Thank you.
Yogima

 

[7anoter4]

For general information see attached about 138 kV Substation design:

https://r5.ieee.org/houston/wp-cont...-HV-Substation-Application-Design-Oct-2-3.pdf

 

[bacon4life]

I do not quite understand exactly which clearance you are asking about.

I have found that using the minimum code required clearance does not provide adequate clearance for routine maintenance activities. In particular, having higher elevation provides additional room for driving crew vehicles and for vegetation maintenance personal(who may not be qualified electrical workers). I have been in stations that have extra internal fencing around bus work that was built without sufficient additional margin over of code minimums.

It is important to mount operating handles at an ergonomic height for the operator.

 

[waross]

Looking at my code, the clearances to grounded surfaces are comparable to your figures, however:
For system voltages below 120 kV
For areas accessible to pedestrians the vertical clearance must be increased to 3.5 meters.
For areas accessible to vehicles the vertical clearance must be increased to 5.5 meters.

For system voltages above 120 kV
For areas accessible to pedestrians the vertical clearance must be increased to 4 meters.
For areas accessible to vehicles the vertical clearance must be increased to 6 meters.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Yogima]

Hi 7anoter4,
I have downloaded the file and it has been very helpful.

Hi bacon4life,
The clearance I was referring to here was the Ground Safety Clearance (vertical). I live in PNG and we exclusively use the IEC and AS standards, I have settled on the ground clearance set out in the AS2067 in the absence of a local code and appreciate your input to input here.

Hi Waross,
Thank you for the response. The vertical clearances allowed for in the AS2067 are comparable to what you have proposed in general therefore I am convinced now to forgo the plan to reduce the ground clearance heights and maintain what is in the standard until such time we devel a local code to suit us.

Pleasant day to you all.

 

[stevenal]

Another IEEE/ANSI/NESC perspective here, so not sure how this will translate to IEC. The distance above ground to live parts is important, but also look for the distance above ground to parts of indeterminant potential (like porcelain). NESC allows guarding by height or by barrier, so the fenced off low bus that bacon4life mentioned is not necessarily in violation.