Hybrid Generator Grounding
Hybrid Generator Grounding
(OP)
I am checking a New 25 MW generator specifications and I am evaluating the options for ground fault protection. This generator will be installed in parallel with two ones that are already installed (since 10 years ago).
Is the Hybrid generator grounding protection the best for this fault? Do I have to consider the same type of protection that the old ones?
Thanks for your opinions
Is the Hybrid generator grounding protection the best for this fault? Do I have to consider the same type of protection that the old ones?
Thanks for your opinions






RE: Hybrid Generator Grounding
Normal practice for a generator of that size is to use a single phase grounding transformer with a resistive burden on the LV side sized to limit stator ground fault current to 5 or 10A in order to protect the stator core.
What did you have in mind?
----------------------------------
Sometimes I only open my mouth to swap feet...
RE: Hybrid Generator Grounding
When there is a ground fault in the generator stator windings or associated bus connections to the generator breaker, the ground (87GD) and possibly the phase (87G) differentials will operate to initiate a high-speed generator shutdown. As part of the shutdown, the ground interruption device in series with the low-resistance ground path is tripped, disconnecting the low resistance ground source. This reduces ground current from 200 to 400 Amps to less than 10 Amps during the coast-down period, greatly reducing ground fault damage.
Taken from : htt
RE: Hybrid Generator Grounding
I've never seen such a system in use on an HV generator in the UK. A 200 - 400A ground fault would cause severe damage to the stator core even if it was cleared quickly. UK practice, in common with many other countries, is to limit the ground fault to 10A or so as a maximum. It is simple to detect a ground fault using a modern relay from any of the major manufacturers: Areva, ABB, GE, Siemens, etc. There seems no reason risk causing unneccessary damage to a very expensive capital asset like a stator core, unless you have a situation with an embedded generator on an existing MV network such as that shown on the sketch in you linked to.
Can you describe your generator's connection a little more? I had assumed - perhaps wrongly - that this was a utility generator connected into the HV network via its own GSU transformer. 25MVA is quite large for an embedded generator.
----------------------------------
Sometimes I only open my mouth to swap feet...
RE: Hybrid Generator Grounding
I think the decision will depend pretty heavily on how the existing generators are grounded. If they are high-resistance grounded, I don't see much reason to do anything different. If they are low-resistance grounded, there might be some benefit in using the hybrid scheme on the new generator, but ideally, you would want to convert them all.
Probably should check with the insurance company. Insurers have been one of driving forces behind the move toward the hybrid system.
RE: Hybrid Generator Grounding
RE: Hybrid Generator Grounding
I'd realised what the scheme was from the diagram on the Beckwith website - the system is fairly unusual over here as far as I'm aware. The reasons behind the research are interesting - it's good to see insurers actually trying to reduce the risk rather than just loading premiums to cover it. I probably didn't put much emphasis on the "...unless you have a situation with an embedded generator on an existing MV network..." comment in my post. My bad. Embedded machines aren't really my field and they're subjected to some quite different conditions compared to the big central generating station machines I'm used to.
The 87GD looks like a 64 REF function from what I can work out between the diagram and the description. Am I somewhere near? The 87GD designation isn't something I've seen before. Presumably the 87G is a standard stator diff scheme?
----------------------------------
Sometimes I only open my mouth to swap feet...
RE: Hybrid Generator Grounding
RE: Hybrid Generator Grounding
http://www
----------------------------------
Sometimes I only open my mouth to swap feet...
RE: Hybrid Generator Grounding
- Is this system proved enough?
- Is the system very expensive? For sure this equipment will not have any insurance, so the project has to handle the risks. And maybe, we have to suggest the same instalation on the rest of the generators
RE: Hybrid Generator Grounding
RE: Hybrid Generator Grounding
No insurance? Why would anybody spend that kind of money and not insure the equipment?
RE: Hybrid Generator Grounding
RE: Hybrid Generator Grounding
Old fashioned REF was pretty much always Hi-Z for stability reasons and normally required a dedicated set of CT's. The modern low burden uP-based relays allow a Low-Z scheme to be used and share the CT's used by the rest of the protection. Sounds like 64 and 87GD are very close cousins if not identical.
----------------------------------
Sometimes I only open my mouth to swap feet...
RE: Hybrid Generator Grounding