Industrial Ground Methods

[ePOWEReng]

Hello. I am trying to get information on what type of grounding methods are typically used in industrial facilities. I realize this is going to vary with the type of industry, but just trying to get a general feel. Also what type of protection elements are being used for SLG fault detection? Residual Over-voltage? Wattmetric? Residual Overcurrent? Others?

Also, does any one have information about utility distribution system grounding practices and what percentage of distribution systems might be ungrounded or high Z (or R) grounded? If so, what elements are being used for SLG fault protection?

Thanks in advance for your input!

 

[Skogsgurra]

We used to see lots of isolated neutral (hi Z grounded, IT) systems in paper mills and steel works. Other industries (batch oriented and lower power levels) usually have TN-C and TN-S.

For isolated neutral systems, the Bender isolation instruments are widely used. ABB has/had their own units. But I do not see them very often.

Due to problems with the IT systems, more and more industries are grounding the neutral, transforming them into TN-C systems.

Problems are mostly that the "early warning" when you get an SLG fault never gets cleared. So instead of having a high-impedance ground you often ended up with an unidentified system where one of the phases was more or less grounded.

There have also been problems with the Bender devices in lightly loaded (idling) drive systems with active front ends. The trickle charge makes current very sporadic and that makes the mains rectifier act as a sampling circuit, which sometimes samples so that the balance between the phases is disturbed and makes the neutral drift away so that Bender trips. Very annoying. As soon as you start one drive, the phenomenon goes away.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[dpc]

If you are talking about the US:

Low voltage (480, 600 V)solid grounding is most common, but high-resistance grounding is quite common - especially in some industries such as pulp and paper.

Medium-voltage industrial - low resistance grounding is most common. For generators with unit transformers, high-resistance. Avoid solidly-grounded industrial medium-voltage systems.

Utility systems: transmission - always solidly grounded. distribution - almost always solidly grounded (95%).

This can all be different in other countries, but no one should be solidly-grounding medium voltage industrial systems.

This is a very broad topic so let us know if you have a specific concern.

 

[RalphChristie]

South-Africa

Low voltage
TN-C-S

Distribution systems:
33kV and below
Originally reactance earthed. Older systems still may have it in use.

Current practice:
Low Resistance earthed
Either through NER or combined NEC/NER

Systems with moving equipment, (trailing cables) like in mines:
High resistance earthed

Sub-transmission systems, 42-88kV
Source neutral solidly earthed
Earthing of neutrals other than the source depends on local policy.

Transmission systems, 132kV-400kV
Neutrals solidly earthed - effective earthing

Power stations
Generators
Older subs - reactance earthing
New subs - high resistance earthing.




Regarding earth-fault protection:
Depending on type of equipment and earthing method used:

Earth-fault element in the residual connection.
Sensitive earth fault protection (Balancing core CT around conductors)
Standby earth fault protection (CT on neutral)
Restricted earth fault protection.


There might be other earthing practices (with their associated protective schemes) in use, but they are not common, due to the fact that Eskom (local electricity supplier) generates ±95% of South-Africa's power.

Regards
Ralph


[red]Failure seldom stops us, it is the fear for failure that stops us - Jack Lemmon[/red]

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[controlsdude]

Grounding and bonding
Their are a series of articles that this mag puts out this very subject. I found it very useful

Look here for your info

http://ecmweb.com/

 

[Rodmcm]

Have a look at the Schneider range of papers. google "Cahier Technique"