Ungrounded System to Grounded
Ungrounded System to Grounded
(OP)
Hi Guys,
Our receiving power is 69kV from our Utilty w/c passes thru our 10MVA 69kV/13.8kV Delta-wye Power Transformer. Our distribution voltage is 13.8kV. and Back-up Power is a 5 Units 2000kVA, 480V, 3P, Diesel Generating Sets which connected to our 13.8kV sytem thru 5 units Step-up Transformer 2000kVA 480V/13.8kV Wye Delta, connected individually to each generator. My Question is, How can we make our system a grounded system during Back-up power since our step-up transformer is delta on the High Side? . Some of our 13.8kV distribution is using 3- 7960/230V 1P Transformer. Is it possible to install a zigzag transformer at the step-up transformer PCC (point of common Couplin)
Our receiving power is 69kV from our Utilty w/c passes thru our 10MVA 69kV/13.8kV Delta-wye Power Transformer. Our distribution voltage is 13.8kV. and Back-up Power is a 5 Units 2000kVA, 480V, 3P, Diesel Generating Sets which connected to our 13.8kV sytem thru 5 units Step-up Transformer 2000kVA 480V/13.8kV Wye Delta, connected individually to each generator. My Question is, How can we make our system a grounded system during Back-up power since our step-up transformer is delta on the High Side? . Some of our 13.8kV distribution is using 3- 7960/230V 1P Transformer. Is it possible to install a zigzag transformer at the step-up transformer PCC (point of common Couplin)






RE: Ungrounded System to Grounded
RE: Ungrounded System to Grounded
Usual ANSI practices are covered in ANSI/IEEE C62.92.4-1991 …Application of Neutral Grounding in …Distribution
With phase-to-neutral loads on the 13.8kV bus, you are consigned to a solidly-grounded system.
[TOC (only) of C62.92.4 at http://standards.ieee.org/reading/ieee/std_public/description/surge/C62.92.4-1991_desc.html]
RE: Ungrounded System to Grounded
RE: Ungrounded System to Grounded
Is your utility transformer grounded? I assume so, otherwise you probably would not be asking this, but it can't hurt to check.
This is a 3-wire system only? No neutral? Please verify.
It sounds like you never parallel the generators and utility, please verify.
Are the utility and generators both considered separately derived systems?
What are you using for transfer switching and/or generator disconnects? 3-pole or 4-pole?
Is solid grounding a requirement, or is impedance grounding OK?
How about B-phase grounding? I've never heard of this on MV systems, but I can't find anything in NEC that would prohibit it -- I could be wrong. May not be a good idea either -- I'd be interested in any comments on that. . . .
What's the motivation for grounding? Can you just leave it ungrounded?
RE: Ungrounded System to Grounded
Maybe it would be easier to get rid of the L-N loads. I wouldn't recommend operating the system ungrounded anyway though.
RE: Ungrounded System to Grounded
Yes! the 10MVA transformer is grounded at secondary, It is a 13.8kV system 4wire wye, but during the operation of our genset which is a 480V 3P wye generators we connect to the system passing through a Step-up transformer 480v/13800v wye-delta. Which means that during emergency power our system is ungrounded
RE: Ungrounded System to Grounded
RE: Ungrounded System to Grounded