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dilbert247365
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High Resistance Grounding

02/18/2014 12:32 PM

What are the pros/cons of high resistance grounding versus solid grounding and low resistance grounding? What is the preference for different applications? What complications does high resistance grounding introduce in drive system applications?

Thank you.
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user-deleted-1105
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#1

Re: High Resistance Grounding

02/18/2014 12:48 PM

Errrr surely high resistance grounding isn't grounding at all???
Del

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jack of all trades
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#2
In reply to #1

Re: High Resistance Grounding

02/18/2014 1:05 PM

I think he is referring to situations where a series resistance would be placed in the ground path to limit the fault current, for example transformers protected by a NER (Neutral Earthing or Grounding Resistor).

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Isti80
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#6
In reply to #2

Re: High Resistance Grounding

02/18/2014 3:18 PM

You mean the (1Mohms) resistor via which the earth-mat is connected to ground on benches...?

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jack of all trades
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#8
In reply to #6

Re: High Resistance Grounding

02/18/2014 7:13 PM

Well I was thinking more of 22kV 500A neutral earthing resistors connected to transmission sized grid transformers (the other end of the spectrum) for example.

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#3

Re: High Resistance Grounding

02/18/2014 1:08 PM

Many if not most situations have the grounding method dictated by local electrical standards, in which case you have to use one over the other.

What do you mean by "drive system applications"?

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PeterT
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#4

Re: High Resistance Grounding

02/18/2014 1:18 PM

Some good resources on neutral grounding theory and practice including resistance grounding are available at Post Glover's (recently merged with IPC Power Resistors) technical library site. Check out the documents at the following link, especially the "Historical Development of Neutral-Grounding Practices" by John Dunki-Jacobs, one of the most recognized names in the field.

Post Glover Technical Library

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lyn
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#5

Re: High Resistance Grounding

02/18/2014 1:35 PM

What is the subject of your question?

Grounding or drives or just a general electrical interview topic?

The question seems rather broad, unless you have a specific application in mind.
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#7

Re: High Resistance Grounding

02/18/2014 3:27 PM

There is a whole article in Wikipedia on earthing systems. Doesn't that warrant a look-in?

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msamad
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#9

Re: High Resistance Grounding

02/18/2014 10:59 PM

Here copied from one of my previous replies (http://cr4.globalspec.com/comment/642965):

There are primarily three types of grounding system which are:

(1) Solid grounding - The neutral point of the system is grounded without any resistance. If the ground fault occurs, high ground current passes through the fault. Its use is very common in low voltage system, where line to neutral voltage is used for single phase loads.

(2) Low Resistance grounding (LRG) - This is used for limiting the ground fault current to minimize the impact of the fault current to the system. In this case, the system trips for the ground fault. In this system, the use of line to neutral (single phase) is prohibited. The ground fault current is limited to in the rage from 25A to 600A.

(3) High Resistance Grounding (HRG) - It is used where service continuity is vital, such as process plant motors. With HRG, the neutral is grounded through a high resistance so that very small current flows to the ground if ground fault occurs. In the case of ground fault of one phase, the faulty phase goes to the ground potential but the system doesn't trip. This system must have a ground fault monitoring system. The use of line to neutral (single phase) is prohibited (NEC 2008, 250.36(3)) in HRG system, however, phase to neutral is used with using the additional transformer having its neutral grounded. When ground fault occurs in HRG system, the monitoring systems gives alarm and the plant operators start the standby motor and stop the faulty one for the maintenance. This way, the process plant is not interrupted. The ground fault current is limited to 10A or less.

There are other two types such as Corner Grounding (for Delta system) and Ungrounded system but they are not commonly used.

- MS

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Yusef1
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#10

Re: High Resistance Grounding

02/19/2014 8:26 AM

Hope you are not sitting at your exam desk texting and hoping for an answer.....

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#11
In reply to #10

Re: High Resistance Grounding

02/19/2014 8:38 AM

Good point. The exam would be over before anything useful arrived! :-D

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#12
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Re: High Resistance Grounding

02/19/2014 9:10 AM

Exactly!

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