GIS ratings and standards
GIS ratings and standards
(OP)
Basically I am evaluating a system that requires 6 40/50/60MVA transformers with the 33kv secondaries operated in parallel. Considering the sheer amount of fault current, I plan on using standard 72.5kv (69kv) GIS gear and adapting it as needed, however I am wondering if another option exists like standard 35kv air insulted gear- and if so what the advantages would be.
Also on the same subject... the distribution load will be around 250MVA. I take it that I do not need 4000amp rated bus bars if load is even between each feeder and bus partition?
Open to all and any answer/opinion.
Also on the same subject... the distribution load will be around 250MVA. I take it that I do not need 4000amp rated bus bars if load is even between each feeder and bus partition?
Open to all and any answer/opinion.






RE: GIS ratings and standards
One thing to consider would be adding enough impedance in the neutral to reduce the current of a single-phase to ground fault down to the level of a 3-phase fault.
How many load circuits? Hopefully a multiple of 6.
One option, but it takes a bit of space, would be to insert current limiting reactors between transformer/load groups with bypass switches around the reactors. With all transformers in service there's only limited current across reactors; enough to keep the voltages uniform. When you have to take out one transformer you close some or all of the bypass switches. You might be able to keep the fault current down to 5 transformer's worth.
RE: GIS ratings and standards
I am thinking a transformer impedance around 12% at "0" tap position.
Though this is not to say I dislike your idea, if this was an over head or non networked installation the above would be an ideal solution.
RE: GIS ratings and standards
RE: GIS ratings and standards
RE: GIS ratings and standards
RE: GIS ratings and standards
RE: GIS ratings and standards
What advantage would 3 larger units give over 6? My understanding is that the X/R ratio also goes up but could be wrong about that.
Biggest desire for me is that 40/50/60 is a very common standard power transformer in addition to its smaller size and experienced ability of personnel to transport/install.
RE: GIS ratings and standards
RE: GIS ratings and standards
RE: GIS ratings and standards
RE: GIS ratings and standards
Ok, so I looked at transformer sizes and what would "roll" down the street. I'd need to get the dimensions to a 120MVA, but it looks like I can comfortably work with a 95MVA unit.
RE: GIS ratings and standards
1. What type of gear would be best to consider and why? GIS, metal clad, ect. This will be housed an indoor, roofed, dry and climate controlled substation.
2. What bus configuration, ie single breaker double bus or multiple bus sections with ties?
RE: GIS ratings and standards
RE: GIS ratings and standards
RE: GIS ratings and standards
There's a lot that would go into the decision making process. Local familiarity with the selected option is important. Make it a complex as necessary to meet the operational objectives but any more complex than that.
Make it as maintenance friendly as you can. If uptime is king you'll have something much more complex than if outages can be readily scheduled.
RE: GIS ratings and standards