As a matter of general consensus it is known that a 4160 VAC generator, in this case an emergency diesel generator, should not be solidly grounded. We have a new installation at one of our facilities where Contractor has idea of solidly grounding the neutral point of a wye connected generator with 300:5 CT on neutral going to 51G electronic protection relay. Would this be an acceptable alternative to the resistance types of grounding ?

 

Had a typo. The CT would be connected to a 50G instantaneous

 

IKE43
1. What is Generator Capacity?
2. What is load?
Regards, Phil Corso

 

IKE43
1. What is Generator Capacity?
2. What is load?
Regards, Phil Corso

It is a 1250 kw Standby generator, wye wired, feeding three 4160/480 transformers for approximately 1000 amps load at 480 VAC.
oh and thanks for your reply Mr.Corso

 

IKE43
3. By "Standby" do you mean it is "Portable", i.e., carried from one place to another.?
4. Or do you mean "Mobile", i.e., moved on wheels from one location to another?
5. Are the three Transformer secondary's Delta or Wye Connected?
Phil Corso

 

Emergency Diesel Generator at a Power Plant. Yes all three transformers are 4160/480

 

IKE43
3. By "Standby" do you mean it is "Portable", i.e., carried from one place to another.?
4. Or do you mean "Mobile", i.e., moved on wheels from one location to another?
5. Are the three Transformer secondary's Delta or Wye Connected?
Phil Corso

It is an Emergency Diesel Generator at an Industrial Plant in a fixed location. The transformers are all 4160 Delta and 480 wye

 

IKE43
6. How is the emergency system's 480-V output transferred to the 480-V system requiring it:
a) connecting jumper cables, or b) transfer switch?

 

IKE43
6. How is the emergency system's 480-V output transferred to the 480-V system requiring it:
a) connecting jumper cables, or b) transfer switch?

The generator is tied to the buss on the 4160 switchgear that feeds those transformers. Those transformers feed separate MCCs

 

IKE.
1) Since the situation is an emergency... 2) It's location is permanent... 3) In a plant having knowledgeable personnel... 4) Already connected to the load it's servicing... 5) And (in my words) requires simple closure of a Breaker at each MCC involved, then, NFPA-70 (NEC) Articles 250, and 712 apply.
But here's the kicker, whether or not the Generator-Neutral should or shouldn't be grounded, is up to the Authority Having Jurisdiction!
Personally, I would spend the money to properly protect this rather large Generator using the Distribution Transformer technique!
Regards, Phil Corso