transformer neutral grounding resistance

[nandarora]

I am working in an industry where my technicians have to short the bus bars on regular basis (manually) for some maintenance purposes.

I want to add high neutral grounding resistance to the incoming supply transformer to limit the Line to ground fault. Presently the neutral has been solidly grounded. What will be the disadvantages of high resistance neutral grounding?

We are using neutral for some (single phase) welding and grinding purpose.

Can I have res in K ohms. I do have earth fault relay

 

[Sahib]

There shall not be any single phase load directly on the secondary of high resistance grounded transformer...........

 

[GoldDigger]

There shall not be any single phase load directly on the secondary of high resistance grounded transformer...........

Code section?

mobile

 

[Sahib]

250.36

 

[texie]

There shall not be any single phase load directly on the secondary of high resistance grounded transformer...........

The issue is not single phase loads but rather line to neutral loads.

 

[gray.one]

No reason to worry about maintenance attaching safety grounds to the bus bars.

The single phase line to neutral loads are a problem. There is no neutral in and HRG system. Everything is line to line voltage.

If you have any loads incorrectly tied to building steel, then you will find all of them after switching to HRG.


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[Fnewman]

So, if I had a 480 volt Y secondary with a HRG, it would require an isolation transformer if I wanted to serve some 277v loads from that substation?

 

[Ingenieur]

So, if I had a 480 volt Y secondary with a HRG, it would require an isolation transformer if I wanted to serve some 277v loads from that substation?

Yes
basically a seperately derived neutral

they shunt live phases to ground?
or 'short the bus bars' as in to each other?
on a 480 system 5-10 A nrg is low for an industrial application
inmining at times we gonas low as 600 mA
or 3.25 A on 4160
you have to ensure nrg is 2 or 3 times larger than cap charging currents
and you have to have open ngr protection

 

[gray.one]

they shunt live phases to ground?

I think he is talking about grounding busbar for safety of the electricians after the breaker has been locked out.

It's not relevant to HRG.


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[Ingenieur]

I think he is talking about grounding busbar for safety of the electricians after the breaker has been locked out.

It's not relevant to HRG.


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Kind of what I figured
not related to nrg

as far as why no neut loads
277/480/3
Assume a 10 A ngr 28 Ohm
put another 10 A load (28 Ohm) on it
total 56 Ohm or 5 A draw
139 vac across each, the ngr and the load
Device would not function

 

[Tony S]

I think you will find under the Indian Code of Practice for Electrical Installations you can’t use a NER for low voltage supplies where the neutral is used.

 

[Sahib]

as far as why no neut loads
277/480/3
Assume a 10 A ngr 28 Ohm
put another 10 A load (28 Ohm) on it
total 56 Ohm or 5 A draw
139 vac across each, the ngr and the load
Device would not function

I think there are single phase transformers with HRG.

 

[Ingenieur]

I think there are single phase transformers with HRG.

how would that work?
you have a line L1, L2 and a N
the ngr is in the N leg?
do you have Lx - N loads?

 

[Sahib]

how would that work?
you have a line L1, L2 and a N
the ngr is in the N leg?
do you have Lx - N loads?

Single phase L and N transformer and not a L1, L2 and N single phase transformer

 

[Ingenieur]

Single phase L and N transformer and not a L1, L2 and N single phase transformer

Show me a diagram please