# HV MV Switchgear Procedures



## micromind (Aug 11, 2007)

when working on a de-energized transformer that has a winding that normally operates at more than 600 volts, the first thing to do after it has been de-energized and tested for no power is to ground out the MV or HV winding. 

It'll hold a charge (for a long time), and if you are the first path to ground.....POW!!!!

If any work involves overhead lines that are open circuit, remember; if it ain't grounded, it ain't dead. Wind and low humidity will cause static voltage to build up; I've seen arcs 6" long when I grounded them. No real current to speak of, just a nice SNAP!

If you're closing in a cut-out, especially onto a circuit of unknown status, wear your earmuffs. If the circuit is faulted, it'll sound a lot like a 12 gauge shotgun, but louder. 

If at all possible, operate MH and HV breakers from a remote location. Especially when closing them. 

A good part of MV breakers I work with have cap-trips. These are a capacitive device that stores enough energy (for a long time) to operate the trip coil of the breaker. When the control power is off, the trip circuit is very likely still energized. 

When racking a MV breaker in or out, get it done. Don't stop in the middle. 

Never force a SF-6 breaker open when the gas pressure is low. To do so will almost always result in an explosion. There is a reason why the electrical controls will lock it out on low gas pressure. 

That's all I can think of off the top of my head.

Rob


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## nitro71 (Sep 17, 2009)

Thanks! If you think of more things let me know. I'm going to start compiling some check lists and procedures. 

Was on one site where our lead was closing a fused switch with a hot stick and the whole thing just seemed unsafe. In that situation are you supposed to shed the downstream loads first before energizing or is it SOP to close them under load?


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## micromind (Aug 11, 2007)

nitro71 said:


> Thanks! If you think of more things let me know. I'm going to start compiling some check lists and procedures.
> 
> Was on one site where our lead was closing a fused switch with a hot stick and the whole thing just seemed unsafe. In that situation are you supposed to shed the downstream loads first before energizing or is it SOP to close them under load?


I've closed lots of cut-outs in with load connected downstream. Of course, it's always better to bring the load on in steps, but usually it's just slammed in with the load connected. 

On a similar note, it an elbow is not rated for load-break, don't pull it out if there's any load on. Even the primary of a transformer with no load on the secondary will cause it to blow up.


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## Big John (May 23, 2010)

micromind said:


> ...On a similar note, it an elbow is not rated for load-break, don't pull it out if there's any load on....


I'll add that applies to air-break switches as well. Many are only designed for isolation and not load interruption, make sure the equipment is intended to do what you're trying to do with it.

A lot of MV equipment, especially overhead, will arc significantly during normal operation. So just just because something looks like it can be operated by hand doesn't mean you should. Pulling elbows, closing cutouts, operating oil switches, even applying grounds, should always be done with a hot stick. The more distance, the better.

Good list, Rob. :thumbsup:

-John


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## Zog (Apr 15, 2009)

nitro71 said:


> Was wondering if anyone had any safety, operating procedures for MV/HV switch gear, transformers. Maybe something you've worked up for your own plant or operation that you wouldn't mind sharing. I'm just trying to add some new knowledge to my skill set.


What type of breakers, switchgear. transformers, etc.. do you have? An answer to your questions can take weeks to answer being generic. I used to design custom courses that were equipment specific for facilities asking what you are asking and the classes were usually 40-80 hours long. There is a lot to cover and a generic answer or answer based on different equipment can be dangerous for you to use.


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## nitro71 (Sep 17, 2009)

Zog said:


> What type of breakers, switchgear. transformers, etc.. do you have? An answer to your questions can take weeks to answer being generic. I used to design custom courses that were equipment specific for facilities asking what you are asking and the classes were usually 40-80 hours long. There is a lot to cover and a generic answer or answer based on different equipment can be dangerous for you to use.


I'm just working on broadening my knowledge base. There isn't going to be any jumping into working on this stuff without further training on my part.

Some years back our lead pulled a cutout with a hot stick and we proceeded to wire in a disconnect on the load side of a transformer that it fed. Just from what has been mentioned so far it sounds like we should have grounded the primary on that transformer before working on it. 

Just trying to learn some more. Most of the "qualified" electricians I've worked with aren't really qualified..


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## Zog (Apr 15, 2009)

The first place to look is OSHA 1910.269. Covers many procedures that everyone working on power systems needs to know.


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## frenchelectrican (Mar 15, 2007)

Nirtro71.,

Those guy did hit right on the spot and also if you ever run into double or triple switchgear you better watch your arse most case they will have kirk key system or interlock to prevent any major mess show up.

I have deal few of MV/ HV system from time to time as other guys mention my golden rules anything is not Terra'ed then watch your back and ase on them.



> Never force a SF-6 breaker open when the gas pressure is low. To do so will almost always result in an explosion. There is a reason why the electrical controls will lock it out on low gas pressure.


This part is true what Rob mention SF-6 Breakers I have see two blow up allready.

Also just be aware some oil switches are only for isolating as well.

I know Zog have few good source of infomation you are looking for.

Merci,
Marc


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## Zog (Apr 15, 2009)

Take a basic substation course like this. 
http://avotraining.com/training-course-details.php?cn=230


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## mrmike (Dec 10, 2010)

The biggest safety issue is to work with someone experienced in working with it. The books are good but not a self-training guide. Don't ever try something with HV without someone with prior experience.
Other than Rob's suggestions which are great especially the racking in & out. One that I can add is never to trust a Tic Tac without first trying it on something live....... Even after racking out HV, Never put you Dic%Skinners on anything with out checking it with a voltmeter first........


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## JIMMAC (Nov 15, 2011)

Check out this site there is a lot of good information on saftey, grounding, etc. 
http://www.usbr.gov/power/data/fist_pub.html


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