Best Practice High Voltage switch

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cornbread

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We recently had a electrcial safety audit done and one of the recommendations was to lock the high voltage switches in their intended operating position. Theory being if the swithes are locked this will prevent a un-qualified person from trying to operate the switch. I can see that point but in the case of a emergency I don't want to be tracking down keys and going thru a lock removal.

Looking for opinions, what is the best practice:?
 
cornbread said:
We recently had a electrcial safety audit done and one of the recommendations was to lock the high voltage switches in their intended operating position. Theory being if the swithes are locked this will prevent a un-qualified person from trying to operate the switch. I can see that point but in the case of a emergency I don't want to be tracking down keys and going thru a lock removal.

Looking for opinions, what is the best practice:?
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Are you refering to the MV switches that feed your transformers in your MV/LV substations?
 
Well they likely have kirk key interlocks to prevent operation unless the 480V main breaker for that transformer is open and/or racked out.

Kirk key switch to main.jpg

Is this what you have?
 
Ours transfomers are dual fed with no Kirk keys, they do have a Kirk system for the tap changer. Our transformers typically run on one feed but we can parralle and swap feeds as needed.
 
cornbread said:
Ours transfomers are dual fed with no Kirk keys, they do have a Kirk system for the tap changer. Our transformers typically run on one feed but we can parralle and swap feeds as needed.
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You sure about that? For a M-T-M configuration you should also have these. They are often located behind a door.

Kirk key main tie main.jpg
 
cornbread said:
Ours transfomers are dual fed with no Kirk keys, they do have a Kirk system for the tap changer. Our transformers typically run on one feed but we can parralle and swap feeds as needed.
Click to expand...

The purpose of the Kirk keys is to disallow paralleling that would cause the fault current to exceed the interrupting rating of breakers and such in the system. In the last 5 years or so we have been buying Switchgear and MCCs rated to withstand the paralleled condition so we do not need the Kirk keys for temporarily paralleling feeders like you're talking about. Most manufacturers want to install Kirk keys by default and require a written statement from the owner stating that they are aware of the interrupting capabilities of the equipment, have completed the short circuit study, and understand the implications of removing the Kirk keys.
 
cornbread said:
JD, do you lock the switch in its normal operating position?
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I think you are missing the point, as JD said you usually have to special order and provide a written statement to order without kirk keys, which are there to prevent the exact situation you are describing. Locking these switches open is a very poor recomendation for several reasons:

1. Finding a key in an emergency as you mentioned
2. You should already have a interlock system in place to prevent operating this switch out of the proper sequence, regardless of the person being qualified or not
3. The substations these are in should be locked or access controlled from unqualified persons anyways.

I still think you have a kirk key system as I described but are not looking in the right spot. You already mentioned there are kirk keys for the tap changer, meaning you will have a empty lock on your tap changer and the key for that will be in the primary switch that gets released when the switch is in the open position.
 
cornbread said:
JD, do you lock the switch in its normal operating position?
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It depends. We have gone away from using metal enclosed switches or oil switches on transformer primaries for the last 25 years or so. Now we try to have a circuit breaker on the primary so we can install differential protection so faults will clear faster, which limits equipment damage in addition to lowering the arc flash incident energy (sometimes, depending on the CT location - transformer differential can be installed such that the arc flash incident energy is not meaningfully lowered - differential protection is not a magic solution).

We installed one set of main-tie-main 4160V switches a year or two ago. We purchased 400A load break switches and operate them with the tie normally open. The fault current in this location is such that when the tie is closed none of the equipment is over-dutied from having too much fault current available - in other words it is safe to parallel momentarily so we can do switching without dropping the load.

There are two safety issues here:
1. Keeping electrically-knowledgeable folks from causing unintentional damage by getting a switching procedure out of order, missing a step, using a non-load break disconnecting means to disconnect a load, etc. Kirk keys can serve this purpose.
2. Keeping non-electrical people from tampering with equipment they are not trained to operate and shouldn't be touching. Kirk keys may help here but don't totally address the problem - padlocks are typically used.

We safeguard against #1 this by designing a system that has load break switches, and with any switch combination the short circuit availability is within the ratings of all affected equipment. We do not design intentional safeguarding against dropping the load - that is a local operational decision basically saying we are confident our electricians will follow written switching procedures and not cause any unintentional outages.

We safeguard against #2 by liberally locking substation doors, transformer air terminal chambers, padmounted transformers, switchgear doors, etc. with a "Refinery Electrical" padlock that all electricians have keys for. This way we don't impede emergency access since anyone trained to operate the equipment has the "Refinery Electrical" key. Anyone who doesn't have the key shouldn't operate the equipment even in an emergency because they aren't trained on it and can cause an even bigger emergency if they operate it improperly.

It sounds like you may have both concerns 1 and 2 above - there is a possible unsafe switching arrangement that needs to be addressed, and possibly the switches are in areas that non-electrical personnel could operate them if they are not padlocked in position. We may be able to come up with ideas to help with #1 (other than kirk keys) if you can post a single line of part of the system.
 
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Further thoughts & questions about your safety audit issues . . .

Further thoughts & questions about your safety audit issues . . .

Cornbread,

First, I concur with JD?s general operational procedures ? the are very sound. I?d like to emphasize that:
  1. No ?Unqualified Persons? should have access to your switches or any medium or high-voltage equipment that is not NEMA rated and constructed as ?tamper-proof?. That means a normal, say, utility-type pad-mounted transformer is fine to be out in the open where ?unqualified persons? can walk up to it and touch it but a unit substation transformer or metal-enclosed medium-voltage switch does NOT meet that criteria. From the sound of your safety person?s audit, I am strongly sensing that your switches are open to general personnel. That does not have to mean general public. Your site could still have restricted security access but if it is accessible to persons not specifically meeting the definition of ?qualified?, then it should be fenced with locked access.
  2. Regarding the key issue, you did not reveal any details but presumably you have a reasonable size industrial installation. That should mean that you have very well-established key control procedures with (preferably) one key for all electrical personnel. Occasionally, there are good reasons for two or three different keys (e.g. one for low-voltage equipment and personnel, etc.) but your concern about finding a key in an emergency by your qualified personnel should NOT be an issue.
Having said all that, proper procedure then should be that your personnel are required to have a key to get into the area of the equipment (switch, in this case) anyway, the only reason I can possibly think of (which you did NOT cite) for locking a switch is to preclude feeding from the other supply which might have substantially higher available fault current, thereby negating all of your downstream arc flash study short circuit values on utilization equipment. Other than that, there is really no need to lock the switch in a certain position except to preclude accidental paralleling by qualified persons.

While there have been comments in this thread about proper use of Kirk keys, I have not seen a response from you as to why you would have them on your tapchangers. I?ve been thinking about that and wondering where you other Kirk-keyed lock is located???
 
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