When is PPE Required on Secondaries?

We have taken the stance that any large 480V secondary transformers (over 500 kVA) must be de-energized before working on them. The trouble is, to de-energize the transformer, the doors have to be opened and the switch has to be fliped. Does this acation constitute work, and therefore can't be done since work isn't allowed on the secondary side of large transformers? Wondering what the general feeling out there is on this type of scenario.

You shouldnt work on any transformer live, regardless of the size. As far as your switching question, it isnt "work: but still requires the correct PPE.

What "work" are you doing on these transformers?

If you are a utility the NESC does not prohibit live work.

Since your company made the rules not to do the work over 500 kVA, I would say it is up to your department that put the rules in place. What do they call work?

Many utilities are choosing not to do any energized pad transformer work. Some are limiting it to voltage and size.

I should clarify here, yes we are working in the NESC world. Say we have a 3-Phase 480V 1000kVA transformer that is loop fed and want to de-energize the secondary side. To do this we have to open the door and flip the switch, but since we decided it best not to do anything on transformers of this size we find ourselves in a conundrum since once the doors are open, there are exposed live parts from the secondary. In order to follow our rule, we'd have to kill the whole line section, go in and flip the switch, and turn the line section back on. As you may guess this could cause some heart burn for clients that get their power turned off every time we have to kill someone else's transformer. I think the point is I don't want someone getting to close to a live transformer, but they have to get at that switch somehow.

UPDATE: We have decided to take the stance that as long as the door to the secondary side is closed that there are no live exposed parts, and thus the switch can be operated "safely". Now I know that door won't stop an AF, but we consider it close to the same idea as walking by a transformer and it blowing up at that time...not much you can do about it.

I am very familiar with the type of installation. The problem you have is that while you will not be in violation of the NESC if you open the doors and use a stick to operate the switch assuming proper PPE, you might well be in violation of your own company policy! That policy may or may not be consistent with the standard (doesn't matter for the purpose of the discussion), but it still seems your question should be to those who made your company rules.

They may allow the doors to be open and the switch to be operated.....don't know what they intended. I would ask for a clarification.

FYI we are just finishing up a design for a new remote operator for thee switches that allow you to operate them from 30 Ft away. Already have many on backorder from utilities all across the country.

cnordquist,

Please clear up my confusion. You are saying that the switch can be operated as long as the secondary door is closed. Every pad transformer I have seen requires the secondary door to be opened to get the primary door open, with the locking penta-head bolt on the primary door. I have never tried to latch the handle on the secondary door closed with the primary door open.

Can it be done? Just curious.

Alan

You have a metal petition wall between the primary and secondary correct? The switches are on the primary side, oil submerged, and can be operated with a shotgun? If yes to both, then you need PPE for sure, but many institutions would consider this within acceptable norms - or at least what used to be. The policy may need review. Oil filled transformers pose an addition risk worse than just the arc blast because they can seriously fireball and spray flammable oil.

But as Alan said, you have to open the secondary compartment to expose the penta-head bolt that allows opening the primary compartment. I also do not think that the secondary door can be latched while the primary compartment is open. For large padmounts, the incident energy on the secondary side will be more than 40 cal/cm² even at hotstick distance.

If you have to open the secondary door to then open the primary, consider shutting down and performing modifications to the door so that you can at least securely refasten the secondary door with the primary open. If you consider that the secondaries are probably 30" into the transformer, and a man stand 12" away, you would then calc IE at 42" for purposes of opening the secondary door. But at that distance it should be reasonable, may even be the same as what you are using for the primary. Opening the doors on a transformer secondary are low risk. Once the secondary door is secured its a metal enclosure so you can switch off the primary to deenergize. Now, with that said, switching on the primary even with the secondary doors closed takes on a lot more risk. I always worry about an internal short that causes the casing to exploded and spew buring oil. Even if you have a shotgun I would probably want Level 4 for energizing.

If you do this frequently you should formulate a procedure and teach that procedure.

If this is a utility style padmount transformer it would be an unwarranted liability to modify the door without factory testing and approval; utility transformers exposed to the public are tested for things like car accidents and vandalism.

Regarding the hot oil risk, utilities have been energizing transformers for over a hundred years and managed this limited risk prior to NFPA 70E. And the guidelines given in NFPA 70E are for protection against radiated energy, the PPE is not rated for hot oil.

We have the same transformer setup and our company requires full PPE for operating the primary side switching. As someone else said, arc flash is not the only problem. We consider the primary side compartment as having exposed conductors even though they are on pull offs. They can fail and the very operation of opening the primary door could have surprises behind it. It would not be the first time we found a hot primary connection or a ground wire floating loose in the cabinet.

Interesting post. We are in a similar situation. Our transformers are 34.5KV primary with a 575V secondary. Could someone tell me what would the proper PPE would be to just open the doors for a visual?

To Switch the padmount we do require a 40 cal suit class IV gloves etc. until an Arc Flash study is completed by the owner.