The issue is not the main breaker itself. the point is available incident energy at the secondary side of transformer which is at the main breaker bus bar . This prevents any type of work carried out on the breaker , such as opening or closing. Breaker can not be remotly operated., so this option is out of question.
The only option is finding a way to reduce the arc flash. primary has a fuse disconnect switch combination., however available short circuit rating is more than switch rating to open under fault.
despite the other practical situation, I need more fault current here to operate the fuse faster.
Ok Zogzog. This was great. suppose they can open it. How about closing it.
there is no electrical charging mechanizm on this breaker. so it needs to be manually charged.
Thanks for the links.
Oh Humble!! You need replace your old breaker to new one
with close and trip coil option. Isnt joke, Im serious.
Its simple and cheaper.
Regards.
Slava
You manually charge it then hook up the remote operator and close it remotely, just like other plants that use this system do.
Best I can tell from info in your posts you have an (indoor?) substation with a transformer of unknown size and type, delta-wye connected, I assume MV/LV. It sounds like you have a fused disconnect switch(?) on the primary fed from an unknown source. The secondary of this transformer feeds a main breaker of unknown type with unknow protective devices to some design of switchgear lineup.
Your problem is a problem at every industrial plant I have been in and there are several solutions, the more details about your actual problem the more we can help recommend a solution. We understand the coord issue you are having, it is very common.
Replacing the low side breaker does not help, as Humble has already pointed out. Faster high side protection is needed, such as a breaker, circuit switcher, or transrupter. I wonder if you could use the flash detector to initiate the closing of a high side grounding switch and shave a few ms. You did say you needed more fault current.
Or work it dead. See my posting in thread238-210239 for a suggestion for getting around the catch 22 involved in de-energized work in this situation.
How do you get the system dead? You have to open the breaker, possibly rack it out to remove key for primary switch, and verify dead with a meter. Arc flash rules apply for all of these so "Work it dead" dosent remove arc flash concerns.
Yes I did, he is saying you have a reduced arc flash hazard on the primary and is right but you need to open the secondary main forst (Might even be key interlocked with the primary switch) and need to follow arc flash rules to do so.
While stevenal's method is safer for the voltage check and grounding part, you still have a breaker operation on the seconday side.
Common practice in the field is also to ground and test both the primary and seconday side of the transformer prior to work, grounds on the primary side of a transformer may not protect a worker on the seconday side from a backfeed on the secondary.
Lots of speculation here. A keyed interlock that increases the arc flash hazard is no longer acceptable and should be removed or redesigned.
NFPA allows a reduced amount of PPE for breaker operation with doors closed or covers on. If still unacceptable, downstream loads can be removed one by one. Or move upstream to find a suitable device. Or use the remote switch operator you suggested. Once the primary is opened, tested, and grounded, assuming there are no other sources, the manual recharging can occur without PPE.
Talk about speculation!! NFPA allows for reduced protection if you are using the tables and you can only use the tables if you are within the tables fault current and clearing times listed which we obviously are not here with such a high Ei.
I am not speculating anything, you need to open the main breaker before you open the primary switch. Thats why I suggested the remote operator in the first place!!!
After I suggested the remote operator you came in with the work it dead idea (Which as I pointed out is a fine idea but you still have the problem on the LV side for opening the breaker)then you suggested removing an interlock as a safety suggestion??
Ok. Guys. I just found out that according to safety codes, if the upstream device has an load intrupting rating ,key intelock is not required.so there is no interlock present.
However, the breaker needs to charge mechanically, so it means working on a breaker withing the boundary even if I use remote trip device.with high calory incident energy.
Is charging the breaker allowed without using PPE?
Right, if it is load break capable than you dont need an interlock, but if there is an interlock then advising to remove those interlocks is a bad idea IMHO.
As far as chraging the breaker goes, that is a grey area, the tables refer to breaker operations, which implies per IEE def of operations opening and closing, no mention of charging. The 2008 70E will use the term "Interact with switchgear: which implies charging is interacting. I have asked the 70E committe (Some members) in an open forum about charging operations and got some answer like "If it presents a hazards the PPE should be worn". What dies that mean? I dont know.
I am on a special risk assessment group that will be looking at these types of items, I will report our findings. But I believe (Again, my opionon) that charging would not produce a signifigant arc flash hazard, I believe racking from disconnect to removed and vice versa does not either. It is the making and breaking of a circuit that poses the hazard.
Now there is a possibility that when charging the breaker it could close on you (Charging latch failure or misadjustment), it is a long shot but possible.
What working distance are you assuming for the switchgear (LV side)Ei calcs?
Zogzog,
My handbook only says to perform an analysis, not specifying how the analysis is done. The tables imply the presence or not of covers or doors and the nature of the task may come into play. Not as clear cut as it could be, I agree.
Seems Humble does not need to open the breaker first.
My comments regarding the speculated interlock were not meant for anyone with a wrench, but for engineers familiar with evolving codes and safety issues qualified to make the call.
If work practices mandate testing and grounding all sides of a transformer prior to clearance, the catch 22 will remain.
