138KV switching

[Prairie Dog]

Looking for some input here...I recently posed this question to my fellow troublemen, "Why are we manually switching 138KV substation switches wearing 20KV gloves?" No one had an answer, nor had anyone ever questioned it. Now, they too, are asking the same question. I understand that the switch is grounded but grounding can fail. There are no insulated links in the mechanism. I've suggested motor-operation would solve the issue but as I've been reminded, "That all costs money". For those troublemen who switch subs, how is it done at your outfit?

[Pootnaigle]

Umm we dunnit the same way you are n summa it wuz 230KV I member one swtch that wuz operated with a wheel (stiff as heck) and when them blades started movin the noise it made wuz recorded ferever in yer brain. seemed like it took ferever fer that stuff to seperate and the switch itsself wuz only bout 12 ft bove our lil punkin heds

[lewy]

You are standing on a mat that is bonded to the ground in some way I hope, the reason for the gloves is in the event something goes wrong your feet will be at the same potential and the handle or wheel is also suppose to be at the same potential, but because of all the linkages they feel there could be a difference in potential. This is all dependant on you staying on the matt while everything is going to hell in a hand basket around you. I leave that up to you on whether you would start running.

[loodvig]

We stood on matts and everything had insulated links. I did a 230kv once with the big wheel and yes it took forever for the arc to break!

[thrasher]

We were told the idea of the class 2 gloves was there was a chance of some connections between the handle and the mat having measureable resistance and possibly producing several hundred to a couple of thousand volts between the handle and the mat, and class 2's would protect against this.
It's standard procedure at both Cooperatives that I have worked at, and in 34 years don't know of anyone being hurt doing it this way.

[copperlineman]

I've never heard of a voltage building up between the handle and mat (platform). The switching linkage, handles, platforms, ground connections and everything else is built to specifications to provide protection for the worker depending on voltage and max loads. The handle/platform configuration provides an "equal-potential zone" for the worker so he is not exposed to a difference of potential between hand and feet , and therefore would be a path for current to flow. Plus it's grounded to the grid for a quicker trip-out, but it's never quick enough. The use of 20kv rubber gloves usually complies with a companies procedures and practices. Using 20kv gloves to protect you from 138kv doesn't make sense, but who knows, it may prevent a fatality under certain conditions. I too have never seen or heard of an accident with this equipment in over 40 years. I'd like to hear the details if any have happened. As for the crank switches, they provide cheap entertainment. They put on a good show, especially after dark!

[Prairie Dog]

Thanks for the replies. I've been on the end of a 34.5kv sub switch that didn't open all the way. It failed to break arc and went to ground between my feet. The ground blast blew me about 6' from the handle. The recloser operated but the breaker never locked out. The arc was huge and never went out until a fellow troubleman opened an airbrake out on the line. My jeans were scorched and my boot laces were melted. I walked away without even a flash burn. The company investigation (I had to force that issue) determined that the ground bond was intact. They also said the breaker was working fine. Now, us troublemen know one of those two factors weren't working as designed. This got me thinking...if that's how things are "supposed to work" what would have happened while operating one of the 138kv switches? All that we do in this line of work has multiple layers of protection. Where's the protection against a failed ground bond in this case?

[copperlineman]

It sounds like you had one those exciting evenings. I agree that something didn't work as planned, or did it?
Your first post asked about 20kv gloves on 138kv. This event involves 34kv which is a different animal altogether. Some companies use 34 as distribution and the parameters for reclosers, relays, breakers, etc. are set differently from high voltage transmission. Our 138kv was set so tight that if a conductor came down, it was dead by the time it hit the ground, let alone have fault current develop from it. I've seen things happen on 34, and they are huge and dramatic, that you wouldn't see on 138 and higher.
A few things had to go right for you to walk away without even a flash burn. And the fact your partner opened an air-break switch to drop fault current was in itself a minor miracle. We would never open an air-break switch under fault current. Any arc you see on the ground will come out of that switch as you open it. it can, and has, destroyed switches. Maybe he caught it while the recloser was operating. But...you did the right thing in having an investigation and trying to find out what happened. I hope you can come to a conclusion, but remember, things can and do happen in this work and the best we can do is get the odds in our favor before we act and have our protections in place. Sounds like you did that to come out without a scratch.

[T-Man]

138 being a Transmission voltage, has a way more sensitive set of protection relays and is in lock out during a fault to ground in 3-4 cycles (that's fast)

34.5 has a subtransmission set of relays and act much slower. So to that end, being in a substation which is set on a ground grid under the whole station, I feel safe switching always in rubber gloves and proper PPE anytime. You do have to know there will be some barking when opening some switches.

[rob8210]

Does anyone still use a portable ground gradient control mat any more? Whenever I have switched on air brakes I have used a portable mat connected to the pole ground and rubber gloves, usually my class 4 gloves. All our air brake switches have a ground grid installed with 3 ground rods, but who knows how long they have been there and how good the connections are without digging then up. Its the way I was taught and it doesn't seem like a lot of extra work. I know of a case that happened during a strike many years ago, a 44kv feeder was out, the general foreman had just operated a switch , then the general manager closed the breaker back in. The problem was a broken insulator on the switch structure, the foreman had stood there leaning against the pipe when the circuit energized, across the broken insulator down the pipe. The general foreman blew a couple of toes off!

[lewy]

Rob the only time I wear my class 4s is when I am actually rubber gloving 27, all other times class 2 at the most.

[rob8210]

Yeah , Lewy, I am a firm believer in only wearing my rubber gloves when needed, especially my class 4's. It does make good sense to me to use them when operating an air brake or LIS though , but I only wear them when actually operating the handle, and I don't hang around the area when I am done, just in case it goes boom!

[T-Man]

Yeah , Lewy, I am a firm believer in only wearing my rubber gloves when needed, especially my class 4's. It does make good sense to me to use them when operating an air brake or LIS though , but I only wear them when actually operating the handle, and I don't hang around the area when I am done, just in case it goes boom!

Rob, cant count the times getting ready to throw the switch and took a good look around and devised an escape route away. Nothing ever happened,(as if I was faster that lightening :eek:) but in some cases the station gates were on the other side of the station behind the Transformer I was reenergizing. We didn't always have the option of a remote closing point especially on customer stations.

[HiStrung]

You have had a lot of response to your question, but I will validate what "Thrasher" was trying to say. The reason you wear gloves, even those rated below the switched voltage, has to due with resistance.
Ideally, the mat is at the same potential as the switch-handle (equal-potential). If you are within your equal-potential zone then no current will flow through your body (if your feet are at the exact same potential as your hands). However, if there is a compromised connection in the grounding, then the gloves would increase the resistance of current flow through you. Electricity takes the path of least resistance. Those 20kV gloves have a high-resistance value.
You are correct, that 20kV gloves won't protect against 138kV, but you are not in series with the circuit. If something catastrophic happens during the switching sequence, then more than likely, it will find an alternate path to ground. Nothing in this world is certain, but at least you are putting forth an effort.
Oh, and the statement about a few hundred volts on the handle is accurate too. Check your voltmeter; you might be surprised!

[Prairie Dog]

Thanks for additional inputs. Currently, we do not use a portable ground mat. Most of our 138KV switches are in transmission subs and are bonded to a ground grid. We have been assured that the grid provides sufficient grounding. However, I hesitate to trust the findings of the same group that inspected the ground grid at the failed 34.5 air break and deemed them "intact and in perfect working order". I'm still concerned with catastrophic failure of overhead hardware, porcelain, etc... Again, I saw all of this with the 34.5 failure and don't want me, or my co-workers in that "line of fire".