When are Switching Platforms Required?

[MikeVA]

Currently we require switching platforms for operators to stand on while switching all our 110KV air switches. There is no requirement to have them for our 22KV air switches. Is there a standard voltage requirement to have them? Thanks for all responses.

 

[slavag]

Hi MIke.
Sorry, I don't understand your Q.
Could you please provide more information.
Actually, operation procedures are depend on primary configuration of SS and not on the voltage level. single bus for 35kV and 350kV, are same rules for switching.
Best Regards.
Slava

 

[MikeVA]

I am talking about the grounded platform the switch operator stands on while opening and closing the switches. We require them on our 110KV bus switches but not our 22KV bus switches. I was wondering if there is some standard that indicate when they are required.

 

[msquared48]

I wonder if it could have to do with the level of induced current in the area of the gear that could give a static discharge to the operator. The greater the voltage, the greater the induced current?

In my earlier years, I was an Operator's Helper and spent many a working hour in station switchyards, regularly working in the vicinity of 4 to 115 KV circuitry. Those line trucks can pick up a whale of a static charge from the peripheral equipment.

Mike McCann
MMC Engineering

 

[racobb]

Grounding platforms are cheap. I require them, as well as, operating pipe ground straps for every high voltage switch in a station.

Alan

Alan

 

[waross]

Many switches have gradient control mats either on top of the crushed gravel or a few inches below the surface. The size and position assures that the switch operator will be standing on or over a gradient control mat when operating a high voltage switch. A platform may provide more protection at higher voltages. Both work by holding the operator at the same potential as the switch operating handle. The principle of protection is related to the Faraday cage.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jghrist]

Grounding platforms are most important where the source of fault current is external to the substation, which is normally the case at higher voltages. If the source of a ground fault is local, such as the secondary of a 110-22 kV power transformer, then current from a faulted switch has a metallic path to the source and does not flow through the earth.

As Alan says, however, grounding platforms are cheap. We specify them at all group-operated switches in a substation.

 

[Kiribanda]

MikeVA,

To my knowledge, there is no standard specifying the requirement of such gradient control mats.But IEEE STD-80 recommends that type of mats under gang operated switches.These switches at this voltage range are normally owned and operated by Utilities.Therefore, the relevant Utility codes should have some reference to the requirement of these mats.

Anyhow, I strongly feel that it is a good operating practice to have these mats below any outdoor gang operated air switches down to 1000 V.

 

[xxjohnh]

IEEE80 does not mandate them provided the proper grounding is designed and installed. I seldom see them in IEC projects, even 380Kv.
It seems to depend on local practice. It is an extra safety measure.

 

[waross]

Canadian Electrical Code,
Section 36
High-voltage installations
Voltages in excess of 750 volts
Rule 36-310 Gang-operated switch handle grounds
Gradient control mats are required to maintain touch potentials at tolerable levels as specified in Table 52

If the calculated touch voltages tend to approach the tolerable limit at higher voltages, your utility may have mandated platforms to increase operator safety at higher voltages.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jmmee97]

MikeVA,
RUS talks about operator mats in their "Design Guide for Rural Substations", bulletin 1724E-300. It is a pretty large document; over 700 pages. Figure 9-37 shows a typical switch grounding detail. Look under their website,

http://www.usda.gov/rus/electric/index.htm.

 

[waross]

By "platform" do you mean an elevated galvanized steel platform or a standard gradient control mat on a crushed rock base?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[racobb]

Bill, I you are asking me then yes they are the same, just different terminology. My term for the platform is the steel mat laying on the rock.

Maybe you are asking the OP?

Alan

 

[waross]

Yes I was asking the OP. I remember seeing steel platforms a foot or so off the ground for an operator to stand on when switching. I suppose a platform may give better protection than a mat during wet or flooded conditions. Same principal of operation as a mat.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[apowerengr]

MikeVA - from what I've seen switch platforms are required for system operating voltages greater than the insulating level provided by the rubber gloves used by the operator when operating the switch. In other words, if the operator has gloves adequate for the system voltage level switch ground mats are not required and if the system operating voltage is greater than the glove insulating rating the switch ground mats are provided.

I have seen some ground grid designs which claim adequate performance such that switch ground mats are not provide but I'm somewhat against that.

Many distribution switches don't have ground mats provided - the operators have gloves providing adequate insulation for the system exposure level.

 

[waross]

A couple of alternatives to gloves;
Some codes demand mats.
Some utilities supply portable mats to their crews. The mats are carried in the service trucks and rolled out and connected before switching.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[MikeVA]

Thanks for everybodies replies. Yes, I am talking about the platform/mats that are on the ground for the operator to stand on.