Busbar faults
Busbar faults
(OP)
We have a legacy practice of not allowing peeople to enter live switch yard if busbar protection is out of service and wonder what is your experience or practice in this regards?
thanks for your input in advance
thanks for your input in advance






RE: Busbar faults
RE: Busbar faults
I am talking about 110 & 220kV systems and as such there are no rules or codes mandating in this regards. Its upto individual TNSPs to decide their practice.
RE: Busbar faults
RE: Busbar faults
RE: Busbar faults
RE: Busbar faults
RE: Busbar faults
First rectify the problem and then enter the substation.
Else,
Perform the Task Risk Assessment (TRA) and then if the TRA findings are safe then take a call to enter.
Like, if the weather conditions are good, no heavy wind, day time and similar factors shall be considered to be favorable.
RE: Busbar faults
RE: Busbar faults
RE: Busbar faults
Don't forget to mitigate the perceived risks and document it and take approval from the line manager before proceeding with the job. So the risk will be spread with the concerned people, instead of one person assuming all the risk.
This is how we work.
RE: Busbar faults
All of ours are dual-protection-redundant; even the really old sh*t is equipped with both a primary and back-up protection, as a minimum...
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Busbar faults
RE: Busbar faults
RE: Busbar faults
RE: Busbar faults
RE: Busbar faults
RE: Busbar faults
How do you use these bus bars or more exactly does does any single breaker have access to only one bus bar or does any single breaker have access to two buss bars? If the latter, is one bus bar a spare or are half the breakers placed on one and the other half on the other?
At minimum you can add a relay in series with the old one.
Question. How many CT windings does each current transformer have? And how many CT circuits do you bring back to the relay house from each current transformer?
RE: Busbar faults
RE: Busbar faults
RE: Busbar faults
RE: Busbar faults
Disc 1 connecting to Bus A
Disc 2 connecting to Bus B
Disc 3 connecting above disconnectors
RE: Busbar faults
In such a case it will be much harder to implement secondary protection, but in theory I guess you could feed all the CT circuits in series with another dynamic relay and wire all else in parallel. That way if one buss relay is taken out the other will still function without issue. Just remember to have CT isolation switches:
http://www.statesproducts.com/
Another possibility is if you are ok with clearing both A and B for a fault would be to convert the existing relay to a single zone which will allow a low cost substitute instead of anther (set) of pricey dynamic relays.
RE: Busbar faults
RE: Busbar faults
It's not the TSO / TNSP folks who are making the assumption of gold-plating, it's 'experts' from outside the industry who lack any depth of understanding but make up for it with their wealth of ill-informed opinion.
I'm facing similar difficulties in the oil sector where people from the chemical industry (cheap = good) are meeting us folks from the utilities (high availability = good) in a culture clash similar to two freight trains colliding. I fear that today's focus on cost-cutting to the detriment of quality may turn around and bite us very hard in the decades to come.
RE: Busbar faults
The utility I work for just got a new CEO from the Industrial Farming industry. His first statement to the company is that he wants to take us into the commodity world. Day 1 he was able to let everyone know that he has no idea about electricity. It'll never be a commodity based industry until someone figures out how to keep all the electrons inside the grain silo. Never the less we have a 'market-based' system to 'buy and sell' electricity. On a good day we give our excess power away for free to neighboring jurisdictions. On a normal day we pay them money to take it.
From what I've seen gold plating never referred to an electrical system or sub system being over-designed. It refereed to the fact that all the hand rails in the plant were made of solid brass. Some old plants actually had marble floors. That's gold plating. The only time I've seen something way-over engineered in this business were on the generator protections of one of the first nuke plants ever built in my region. I believe the reason for this was because it was the first time using these super expensive generators so they were maybe a little nervous, and the extra cost to over-design the protection was nothing compared to a failure of protection.
There's a book written by an ex-CIA guy, I believe it's called "Confessions of an Economic Hitman" or something like that. He talks about going to third world countries back in the 60's through the 80's on behalf of a North American utility companies to help build the nations power system. His alternative agenda (the CIA agenda) was to over build the power systems so much that the country would be paying interest to a N.A. company for eons to come. That's gold plating from a design perspective. Where we would normally see a Duel bus station here in N.A. some of these countries were sold Quad bus stations, with all the extra transmission circuits that would go along. Basically the systems are quad-redundant from the primary side of things. I would consider that gold-platted design, until i realized that i've just introduced that much more of a security risk to the system by adding more elements.
The Art of P&C is understanding that there's always a trade-off between security and selectivity. It would be difficult to over build a system and call it "gold platted" due to the extra security risk. Anyone who figures out how to increase both at the same time should win a Nobel prize imo.
RE: Busbar faults
RE: Busbar faults
RE: Busbar faults
The physical risks from either arc flash or step & touch potential are relatively straightforward to calculate once you figure out the zone 2 remote clearing times. The arc flash exposure is low compared to many 480V installations because 115 kV is open air (instead of a box) and because of much larger working space. Ground grids are usually designed for lengthy clearing times, so step and touch potential probably wouldn't demand bus relay redundancy.
Complying with NERC regulations rather than personnel protection is a major factor for installing redundant bus relays. Although NERC regulations might in the long run turn out to provide more dependability, in the shorter term the regulations have had detrimental effects on security and complexity.
RE: Busbar faults
We haven't seen that kind of thing in UK plants since the days of the CEGB, and even then I'm not sure we ever had a marble turbine hall. Certainly not within my lifetime.
I think what I'm seeing here is that necessity in one industry is regarded as 'gold plating' by another. I agree with you that duplicate schemes are an operational necessity rather than a luxury. Your last few words are right on the mark.
RE: Busbar faults
RE: Busbar faults
RE: Busbar faults
If you end up with a fault on a HV bus without instantaneous protection BEST case scenario is a massive over trip taking out many more zones than necessary and potentially causing system stability issues. WORST case scenario is much, much, MUCH more expensive, not to mention potential health and safety risks. The industry really looks down on killing workers these days. At least in my jurisdiction.
RE: Busbar faults
I take there is no way to configure these relays so they will trip the breakers immediately connected to the buss instead of relying on remote zone 2 breakers?
RE: Busbar faults
RE: Busbar faults
RE: Busbar faults
RE: Busbar faults
RE: Busbar faults
How about a transformer, reactor or cap bank on zone 2? Are they not a bomb?
Or how about a line position outside the bus zone? Isn't that a risk too?
RE: Busbar faults
RE: Busbar faults
If you are interacting with the circuit, you need to perform an arc flash study or use the NESC tables to determine the incident energy and appropriate PPE. At these voltages the fault current is likely to be low and the separation distance large making the IE low. Consider the effect of reclosing as well.
RE: Busbar faults
RE: Busbar faults
The NESC refers to "employees who work on or near energized lines, parts or equipment." OSHA uses similar language.
Moving about the yard normally would not be a concern. Moving about the yard carrying a long object would be. Moving about the yard to a position close to where another is working on a live circuit would be a concern as well.