Have you tried Google? Or one of the protection texts available to download free-of-charge in faq238-1287? You will learn far more from them than we can post in a text-only forum.
----------------------------------
If we learn from our mistakes I'm getting a great education!
I have heard of an inverse time relay and a definite time relay, but not an inverse definite time relay.
Take a look at the ABB CO relay instruction manual. You can see how the relay works and the difference between the CO6 Definite time curves and the CO8 Inverse time curves.
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.
----------------------------------
If we learn from our mistakes I'm getting a great education!
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.
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
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.
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.
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.
----------------------------------
If we learn from our mistakes I'm getting a great education!
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."
![[wink]](/data/assets/smilies/wink.gif "[wink] [wink]")