grounding old distribution system
grounding old distribution system
(OP)
Guys,
I have to change the old gear in the following system and design the grounding system for that.
Problem is that the old system is not grounded and I can not touch the old T1.
Any idea for grounding the new system? Adding new 2MVA transformer looks an expensive option!
I have to change the old gear in the following system and design the grounding system for that.
Problem is that the old system is not grounded and I can not touch the old T1.
Any idea for grounding the new system? Adding new 2MVA transformer looks an expensive option!






RE: grounding old distribution system
If you can't use high resistance, use a zig-zag grounding transformer.
RE: grounding old distribution system
Connect them in wye:delta. The secondary voltage is relatively unimportant as long as the three are the same.
Ground the wye point through a 2760 Ohm resistor and you will have a 5 Amp High resistance grounded system.
You may also ground the wye point directly and insert a suitable resistor in the delta.
5 Amps at 13.8 kV = 69 KVA
You could probably accept that overload on 50 KVA transformers. The overload will only be present during ground faults.
Another option is corner grounding.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: grounding old distribution system
Is this mean, I should design my grounding current for only 400A?!
RE: grounding old distribution system
For 480Volts,
400 Amps x 480 Volts = 192 KVA grounding transformers. These will probably accept a substantial overload for short time duty. With this in mind, you may select smaller than 200 KVA grounding transformer(s).
5 Amps x 480 Volts = 2.4 KVA
A zig=zag transformer may be a special order.
You may be able to source 13.8 Volt distribution transformers in stock somewhere. They will probably be cheaper than a zig zag transformer and more readily available should a transformer need to be replaced in the future.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: grounding old distribution system
The delta/delta is for utility (we can't touch it). We also, don't want to pay for another main transformer (2MVA) just for grounding purpose.
What do you mean by grounding transformer? Do you mean Zig-Zag?
RE: grounding old distribution system
"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic ù and this we know it is, for certain ù then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". û Nikola Tesla
RE: grounding old distribution system
Sizing ground grid for 5A of zig-zag doesn't look right because, at least we have lightning to consider.
Do you have any idea how to size the ground grid if I only have a HRG zig-zag?
RE: grounding old distribution system
RE: grounding old distribution system
RE: grounding old distribution system
"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic ù and this we know it is, for certain ù then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". û Nikola Tesla