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 Post subject: Transformer Tap Changer Safety Practices
PostPosted: Tue Apr 13, 2021 8:27 am 

Joined: Mon Apr 29, 2019 5:24 pm
Posts: 11
Location: Phoenix, AZ USA
I’m currently researching the topic of tap changers on transformers to determine if we should add some “Do’s and Don’ts” information in our electrical safety procedure and training regarding them.

During my research I’ve run across a few situations where workers were killed or seriously burned when they were performing some type of work with tap changers while the transformer was still energized.

One fatality occurred in Chelmsford, UK on May 7, 2008 and the other in Kissimmee, FL on August 7, 2011. Even within the nuclear electric generating industry, we’ve had one incident at a nuclear power plant on June 1, 2015 that didn’t result in a fatality, but five workers were burned.

As most of us are aware, there’s two basic types of tap changers that go by all kinds of different names:
1. Those designed to be moved while the transformer is energized, often called “On Load Tap Changer (OLTC or LTC), On Circuit Tap Changer (OCTC)”, etc.
2. And those designed to only be manipulated when the transformer is deenergized, often called “Deenergized Tap Changers (DETC), Off Circuit Tap Changers (OCTC”), No Load Tap Changer (NLTC)”, etc.

I’ve reviewed both OSHA 29CFR 1910 and 1926 and NFPA 70E but they’re silent about transformer tap changers, other than the generic “Electrical equipment shall be used according to its listed and labeled instructions”.

NFPA 70B and ANSI/NETA MTS speaks about maintenance practices for tap changers, but the only safety information is a generic statement upfront recommending the equipment be de-energized (MTS) or placed in an electrically safe work condition (70B).

This said, does anyone have any additional information, know of any standards or thoughts about transformer tap changer safety for employees or any practices that you’ve implemented at your companies for their use?
Thanks


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 Post subject: Re: Transformer Tap Changer Safety Practices
PostPosted: Mon Apr 19, 2021 6:36 am 
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Joined: Thu Jan 10, 2008 8:49 pm
Posts: 502
Location: New England
If you are referring to automatic LTCs, then they make the next tap before breaking the existing tap, to avoid arcing. If you are referring to the manual tap selector found on building transformers, then they should only be changed when de-energized to avoid internal arcing and damage to the transformer.


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 Post subject: Re: Transformer Tap Changer Safety Practices
PostPosted: Tue Apr 20, 2021 9:57 am 
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Joined: Tue Jan 13, 2009 5:00 pm
Posts: 547
One style of low maintenance LTC employs vacuum interrupters in the design. The GE LRT200 and I believe all the Reinhausen brand LTCs are of this style. If an interrupter should fail, bad things happen. For this reason they employ a system that checks vacuum interrupter integrity. This safety system prevents only electric operation when failures occur, so the rule is never hand crank a vacuum LTC when the transformer is energized.

I once had a bulletin that described a dual fatality involving an LRT, but have lost it. Would you have more information on the fatalities you mentioned?


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 Post subject: Re: Transformer Tap Changer Safety Practices
PostPosted: Tue Apr 27, 2021 7:32 am 

Joined: Mon Apr 29, 2019 5:24 pm
Posts: 11
Location: Phoenix, AZ USA
@ stevenal

The fatality I had referenced occurred in Kissimmee, FL inside a Kissimmee Utility Authority (KUA) substation and the worker who lost her life was a Reinhausen employee under contract with KUA. Only one person was killed. The other two were seriously burned but survived.
KUA's website lists the event but contains very little information about this tragedy so I submitted a public records request for any additionally information surrounding the event. KUA responded a couple of weeks later essentially claiming as a "municipal utility" they are not under the jurisdiction of OSHA therefore they have no investigation reports of the event then referred me to OSHA.
However, I was able to glean some information from various online sources that the fatality was somehow related to tap changer work activities on an energized 230kV to 69kV transmission XFMR. But none of the threads could tell me if the tap changer was an OLTC/LTC or DETC/NLTC type.
KUA's claim sounds a little odd to me. Every publicly and privately owned electric utility company I know of are all under OSHA's authority, either on the federal level or a through state plan. The mining industry is exempt from OSHA because they fall under MSHA and federal DOE facilities who have their own federal occupational safety and health oversight are also exempt from OSHA regulations. In any case, I think they’re mistaken.
I’ve run into this same erroneous belief within the nuclear industry as well with many individuals, from front line workers to managers adamantly claiming, “OSHA has no jurisdiction in nuclear power because we’re under the NRC!”. But when I show them a Memorandum of Understanding (MOU) between OSHA and the NRC pertaining to OSHA’s authority at licensed nuclear plants, their jaws drop wide open and their cockiness instantly evaporates. :lol:

https://www.osha.gov/laws-regs/mou/2013-09-06

At my nuclear power plant, all our large XFMRs are equipped with DETC/NLTC type tap changers so we’re going to secure them in place with a padlock and if the manufacturer’s warning labels/signs are faded or illegible then we’ll add our own warning labels to the locks.
As an administrative barrier, I’m also added some information into our electrical safety procedure that tap changers shall not be changed or manipulated while the XFMR is energized then cover this in our annual training of our electricians.

https://kua.com/news/transformer-explos ... ubstation/


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 Post subject: Re: Transformer Tap Changer Safety Practices
PostPosted: Tue Apr 27, 2021 7:34 am 

Joined: Mon Apr 29, 2019 5:24 pm
Posts: 11
Location: Phoenix, AZ USA
@haze10
I was referring to moving DETC/NLTC type tap changers while the XFMR is still energized. These types of tap changers are not only limited to building transformers but large electric utility transmission XFMRs as well, such as our very large 1532 MVA 24kV to 525kV GSU's, 140 MVA 24kV to 13.8kV aux XFMRs and many others.


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