25 MVA transformer protection
25 MVA transformer protection
(OP)
Hello, I am an electrical power engineer with a strong design experience in Low and Medium voltage systems. Basically everything that is governed by the NEC. Presently working on some schematic designs for a fuel cell system that will connect to the grid at 69kv. Eventually there will be a high voltage engineer on this project, but I am working on some of the up-front design.
There will be a new 69kv primary, 13.8kv secondary, 25mva transformer to connect at the utility. Primary config may be wye or delta at utility's final decision. Secondary is wye. I can find typical IEEE protection schemes and understand what should be shown. Question is the physical location of the secondary main breaker. My experience would put the secondary breaker close to the transformer. Conceptual layouts given to me at the start of the project don't show this "local" secondary main. These documents have a piece of switchgear about a 1/4 mile away (collection switchgear for fuel cells) Am I correct in thinking there should be a stand alone main local to the transformer ? Any other thoughts on this are welcome.
JP
There will be a new 69kv primary, 13.8kv secondary, 25mva transformer to connect at the utility. Primary config may be wye or delta at utility's final decision. Secondary is wye. I can find typical IEEE protection schemes and understand what should be shown. Question is the physical location of the secondary main breaker. My experience would put the secondary breaker close to the transformer. Conceptual layouts given to me at the start of the project don't show this "local" secondary main. These documents have a piece of switchgear about a 1/4 mile away (collection switchgear for fuel cells) Am I correct in thinking there should be a stand alone main local to the transformer ? Any other thoughts on this are welcome.
JP






RE: 25 MVA transformer protection
From the transformer terminals up to this switchgear a connection of-let's say 2*3*500 MCM copper
conductor cable[see for instance Det.8 NEC Table 310.60(C)(85)]will run underground.
A Short-Circuit and Ground-Fault Protection shall be provided as per NEC 240.92(C)(1).
It is recommended to provide a breaker between transformer terminals and cable terminations.
You'll need an overcurrent protection as per NEC 240.100 also.
RE: 25 MVA transformer protection
It sounds like the only thing connected to the 13.8 kV side of the transformer will be the fuel cell system. In the event of a fault between the transformer and the 13.8 kV switchgear, your objective is to clear that fault. In this case, it shouldn't matter if the transformer is also de-energized when the fault is cleared.
Assuming that you will have a 69 kV breaker between the utility interconnection and the transformer, I would consider using that 69 kV breaker to protect from secondary faults (install an overcurrent relay that is connected to CT's at the transformer secondary bushings). Installing a relay to trip the 69 kV breaker for a 15 kV fault would be a fraction of the cost of installing a 15 kV breaker to protect a quarter-mile of line.
RE: 25 MVA transformer protection
RE: 25 MVA transformer protection
How much available fault current will a fuel cell provide?
RE: 25 MVA transformer protection
RE: 25 MVA transformer protection