NGR Vs Dedicated Solid Earthing

With NGR you most likely refer to a Neutral Ground Resistor.

If you do an internet research you will find lots of good information to read and comprehend. After you have done so you might be able to write that comparison on the fly. Without the proper knowledge you will get stuck in your sentences and fail your customer.

I am of the opinion the customer is always right, so why even opposing them?

Dear @IdeaSmith

As i am trying to search though internet but always it looks that I should install NGR (neutral ground resistor) for transformer.

But due to space limitation and price variations we are not going to provide. So i need back up to prove my statics. Plz help out

Sorry I can not help here. For me it sounds a bit (and forgive my frankness) you are going "cheap".

Space limitations around a transformer that usually comes with a NGR seems like an excuse and "price variations" puts you in the corner of "quoted not enough" to get the job.

You are on your own with this one!

If Google keeps finding sites that recommend the use of NER (NGR) and none against there use then maybe it's giving you a hint.

Think along the lines of limiting earth (ground) fault currents.

That's why i choose this forum to Help me out. I know the benefits of NGR. But in our case we are not using and need to justify.

That's a commercial decision. CR4 is for technical matters.

Actually, this is a technical matter. The decision on solid grounding vs. resistance grounding has impacts on equipment and protection choices, as well as system operation.

For the OP's situation (medium voltage system), low-resistance grounding is a very common practice, to limit fault currents to levels that can be withstood by the electrical apparatus until the fault can be detected and cleared.

There are good resources available from several of the NGR manufacturers that explain the differences between the various grounding schemes and how/when to apply them. You can get (free) literature from the following:

Post Glover

I-Gard (formerly IPC Power Resistors)

These companies are long-time manufacturers of grounding resistors, and are respected in the industry. I would suggest that the OP contact them for technical recommendations.

I've only worked on solid earthed 3.3KV up to 2MVA
Above that all our 3.3KV systems were via NER's.

NER's make sense to me. What doesn't make sense is designing a system and then trying to fit the circumstances to the decision.
I think someone has got things a bit back to front and is trying to dig themselves out of a hole.

I share that notion!

If you are providing the transformer protection but are not providing a NGR then are we to assume that you are providing alternative protection for the transformer instead?

If so, detail that offer to the customer as a variation, if not tell the customer they will need to change their protection scheme to work with your offering. Either way the customer must approve the variation.

If you don't know or cannot show why your offering will meet the customers requirements then you have a problem and shouldn't have offered this solution.

Grounding the neutral through Resistor and thus limiting the earth fault current to low levels (typically 300A) is worldwide practice for MV systems. IEEE Red book explains the practice saying

• Medium Voltage systems ranging from 3kV to 15kV are basically for supplying motors and the resistance grounding of these systems ensures that no damage is done to the stator core laminations (in the event of stator earth fault).

The above can only be waived,

• if the owner maintenance practice doesn't include repair / rewiding of motors (instead go in for outright replacement of faulty motor)
• if the 22/3.3kV transformer rating is small and that too with higher %Z as to limit the expected earth fault current to desired low levels
• if the owner's 3.3kV system doesn't include motors and has only step-down transformers connected to the busbars.