Directional Ground Relays

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mull982

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Hello

I am working on a project that requires Directional Ground Relays. I am not familiar at all with the subject of directional ground relaying, so I was wondering if anybody could give me some information on this topic, or tell me where I could find information.

Thank You

mull982
 
There are several types of protective relays for power systems. Directional relays represent one kind for unintentional ground-faults.

I would suggest you consult a power systems engineer that is familiar with these devices or the manufacturer's representative providing the equipment.
 
I did quite a bit of relaying in the distant past, and never ran into directional ground relaying. A GOOGLE search finds quite a few references to transformer protection, ungrounded system protection, etc.

You might start there.

Jim T
 
mull982 said:
Hello

I am working on a project that requires Directional Ground Relays. I am not familiar at all with the subject of directional ground relaying, so I was wondering if anybody could give me some information on this topic, or tell me where I could find information.

Thank You

mull982
Click to expand...

Refer to Protective Relaying, by J. Lewis Blackburn. Also, here is the link to Basler relay page for the 67N.

http://www.basler.com/html/pcs59-87.htm
 
No, this project is in an industrial cement plant.

We have 4160 V going to a load breaker, which then feeds a transformer stepping the voltage down to 480V to supply an MCC. However due to the plant growing, we want to add a new 4160 V crusher, and a new 480V MCC. We are going to parallel off of the existing 4160V load breaker to new 4160 switchgear which will then feed the 4160 crusher and a new transformer for the 480 V MCC. According to the one-line it looks like the directional grounding relays are going to be used for the two feeds coming of of the
4160V load breaker which feed the existing transformer and new switchgear. I was just wondering how this principle worked and why it would be used in this situation. (Both of the Transformers are resistance grounded)

Also, in researching this subject I came across some information on zero, positive and negative sequences. I've seen this before, but can someone refresh my memory on what these are.

Thanks so much for the help

mull982
 
You may struggle to understand ground relaying without a good background in symmetrical components. Positive, negative, and zero sequence networks are a way to analyze an unbalanced 3 phase system. CL Fortescue came up with a theory, symmetrical components, that said you can model an (n) phase unbalanced system with (n) sequence networks that are balanced. These networks are connected in various configurations depending on transformation and the type of fault being analyzed. It has been the curse of power engineering students since the 20's.

I bought my J Lewis Blackburn relaying book over 30 years ago when I was taking a graduate class on protective relaying. They are very valuable, but I'm not sure of their availability.

Jim T
 
Thanks alot for the course notes, I've been looking through them, and there looks like theres a lot of good information there. Very Helpful!!!

mull982
 
Take a look at the definition of IEEE Device number 67N which is an "AC Directional Overcurrent Ground" relay and please advise if this is of any help to you.
Thanks,
Dave T

The following is taken from the following EC&M "Ask the Experts":
http://expert.ecmweb.com/resistance_grounding_experts/page/50/

Q. How can I make a directional earth fault relay?
A. When an earth fault can be fed from both ends of the circuit being protected, it is necessary to determine the direction of the current flow in order to selectively trip the right breaker. A directional overcurrent protection relay serves this function. In order to determine the direction of earth fault current flow, the sensed current must be compared with a reference or "polarizing" source (either voltage or current). Often a polarizing voltage is used; for earth faults it is the zero sequence voltage, i.e. residual voltage, which is in quadrature with the earth fault current. Hence a directional earth fault relay requires additional sensors such as voltage transformers, which is why these relays are more costly to use. However, they are simple and reliable. The ANSI device number for non-directional earth fault overcurrent protection of a feeder (with adjustable time delay and pickup settings) is 51N. The device number for directional earth fault overcurrent protection is 67N. For more information, look up the website of any protection relay manufacturer, for example: GE Multilin, Schneider Electric SEPAM, Schweitzer Engineering Laboratories (SEL), Areva, Basler, Siemens, and Beckwith. For example, the following document is helpful: Cahier technique no. 181: Directional protection equipment, Schneider Electric, 1998, available at www.schneider.co.uk
 
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