Earth fault protection
Earth fault protection
(OP)
I want to know the basic difference between Neutral Earth fault and Stand-by Earth fault protections please
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RE: Earth fault protection
RE: Earth fault protection
Please search in the Forum, we had a lot of threads on the topic.
Shortly, I suggest: neutral EF protection, it's mean. residual connection of three phase CT to the additional CT input, and stand-by earth fault protection it's additional protection is connected to toroid CT on the trafo neutral.
Alehman, it are same 50N, 51N, 50G, 51G with lot of mix additionals, SEF-stand by earth fault or also used sensetive earth fault protection, BEF-back-up earth fault.
Once with toroid on the transformer neutral, once with toroid on the all 3-phases, once with residual/holmogren connection. Once it's toroid CT, once balanced core CT, once ZS CT.
So much terms about same
Best Regards.
Slava
RE: Earth fault protection
It's definitely a UK term, possibly European too from what Slava has posted. In UK practice the standby E/F relay is usually a IDMT type, possibly with a high set, connected to a plain CT on the neutral earthing conductor. It backs up a faster relay which is often in a residual connection.
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RE: Earth fault protection
Operation of Stand by Earth fault protection is wired to trip the upstream (Trafo primary) breaker in addition to the Trafo secondary breaker. Some times, Stage-1 element of the protection is also set and wired to open the bus coupler (in case of 'bus coupler closed' operation)
RE: Earth fault protection
Your explanation conform with what I know. But what of Neutral Earth fault?
RE: Earth fault protection
I think the question is not correctly worded or its comparing apples to oranges.
A proper (answerable) question would be what is the difference between Neutral overcurrent (51N) and ground (earth) fault overcurrent (51G) protection.
OR you can ask what is the difference between a earth (ground) fault protection and a backup (standby, if it a real term) earth fault protection. You can deploy either kind of protection as primary or backup (earth or neutral) overcurrent protection. Only thing that a standby or back up protection will have higher (slower) setting than the primary settings so failing primary, the backup protection would come in picture.
As for 51N and 51G, the way modern relay manuals proposes, 51G actually measures the current in neutral using a CT (residual CTs), where as 51N is where current in neutral is calculated by vector sum of the 3 phase over currents by the relay.
RE: Earth fault protection
ScottyUK has given a pretty good defintion. A CT on the Star point of the transformer will directly measure an earth fault, but it has no idea which feeder it is on, so it trips the transformer.
Therefore it is set slower than all other e/f protection devices, and hopefully something else should always operate first.
RE: Earth fault protection
There is neutral overcurrent and there is earth (ground) over current.
RE: Earth fault protection
You are correct, when you think about it, it is a confusing term, but in our organisation we all know what it means.
By the way, 51G can mean either measured e/f or calculated e/f, as can 51N.
For SEL 51G is the calculated e/f & 51N is the measured
For GE UR Relays 51G is the measured e/f, 51N is the calculated.
RE: Earth fault protection
The code recommends use of suffix "G" when the CT is located in transformer / generator etc. neutral circuit.
RE: Earth fault protection
Other relays have 51N and/or 51G elements that can be assigned to either a measured or calculated value (eg Basler)
It is not correct to make a general statement that 51N is a calculated value (or vice versa). It depends on the relay, or the person who has put it in the drawing/document.
But getting back to the orginal question
RE: Earth fault protection
The moral of the story is that it doesn't matter what the term is, it is the application that counts.
I am sure most of us have seen different terms used for the same application, and also the same term used for different applications - I certainly have on many occaisions.
Haisa, could you please give us some more detail of your questions application or context.
RE: Earth fault protection
I prefer the terms residual current and neutral current. No confusion. Either can be backup (standby?), depending on settings.
RE: Earth fault protection
See thread238-212004: The advantage of a residual overcurrent relay vs a ground fault relay
RE: Earth fault protection
http://www.basler.com/downloads/transfguide.pdf
RE: Earth fault protection
In this relay, the 51N element can be assigned to either the Ig CT input, or a vector sum of the phase CTs.
So you can make the 51G function (as defined in the Basler guide) using a 51N element. You can also make a 51N function (as defined in the guide) using the same 51N element of the relay depending on how you set it.
Thanks for helping me make my point
RE: Earth fault protection
Not sure what your point is. Plus I was not trying to make any point.
You can play with electrical wiring and schemes and make it work, that has nothing to do with accepted conventions per IEEE. I can write much longer repsonse as to where 51G and 51N designations come from but I have no apetite for it.
The flexibility of digital relay may have blurred some lines to some. But if you were to use only discrete or electromechanical relays, you would appreciate the difference.
I have seen and used residual CT connection in 51G input, but it still amounts to measured current.
RE: Earth fault protection
jensendrive had a pretty good explanation but maybe it would be best to forget semi-ambiguous terminology and stay with 3-line diagrams!
RE: Earth fault protection
Just by seeing 51N or 51G (or any other designation) written, it doesn't mean a great deal without looking into the detail.
I was trying to politely say this statement is not always true.
RE: Earth fault protection
RE: Earth fault protection
This must mean the SEL products are not modern relays.