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Inverse definite time relay

Inverse definite time relay

Inverse definite time relay

(OP)
What is a inverse definite time relay? How does it work?

RE: Inverse definite time relay

Have you tried Google? Or one of the protection texts available to download free-of-charge in FAQ238-1287: What are good references for a Power Engineer?? You will learn far more from them than we can post in a text-only forum.
  

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If we learn from our mistakes I'm getting a great education!
 

RE: Inverse definite time relay

jgrimard,

Inverse definite minimum time relay - a European term? Plenty hits on Google, although I doubt you will learn much if you understand how an 'inverse time relay' from your patch works.
  

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If we learn from our mistakes I'm getting a great education!
 

RE: Inverse definite time relay

Some devices, for example S&C Vista (electronic fuses), do allow a definite minimum time delay to an otherwise inverse time curve. This is to allow coordination with downstream devices. Perhaps some other relays do the same.

Rafiq Bulsara
http://www.srengineersct.com

RE: Inverse definite time relay

If I may be so bold, I think the point ScottyUK was getting to was that if someone needs to ask this question, they are either A) a student, in which case they are violating the forum rules, or B) not an EE (or one with a power background), in which case they have no business dealing with this issues as this is not a good "learn-as-you-go-on-the-job" discipline.

In other words if you have to ask that question, close the cabinet door and walk away slowly, then call someone who knows what they are doing...

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln  
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies  

RE: Inverse definite time relay

Go to the FAQ listed above, follow the link for GE's Art and Science of Protective Relaying... open the PDF, and search for "Definite Time". "Inverse time" is also explained on that page.

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(2B)+(2B)'  ?

RE: Inverse definite time relay

jraef,

LPS. wink
  

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If we learn from our mistakes I'm getting a great education!
 

RE: Inverse definite time relay

Quote:

If I may be so bold, I think the point ScottyUK was getting to was that if someone needs to ask this question, they are either A) a student, in which case they are violating the forum rules, or B) not an EE (or one with a power background), in which case they have no business dealing with this issues as this is not a good "learn-as-you-go-on-the-job" discipline.
Or they are not familiar with UK/European/IEC nomenclature.  IDMT (inverse definite minimum time) is not a common nomenclature in the USA.  We think of relays as either inverse-time or definite-time.
 

RE: Inverse definite time relay

The 'definite minimum time' name goes back to induction disc relays: however hard you drive them there is still a finite response time before a trip is initiated. With numerical relays the minimum time could be made very small, but they are typically programmed to mimic the standard set of curves dating back to the days of electro-mechanical relays and they retain the IDMT name.
  

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If we learn from our mistakes I'm getting a great education!
 

RE: Inverse definite time relay

The book "Protective Relays" (1922)  by Victor H. Todd defines the inverse definite time relay as:

"In this type of delay the latest practice is obtained by having the protective relay give a time delay which is inversely proportional to the magnitude of the overload up to about 1,000 per cent of load, but which becomes a definite time limit upon any greater overload than this."

Relays available from (it)micro, for example: http://www.itmikro.com/catalog/mk204a.pdf

Looks very much like an ordinary inverse time relay.

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