IDMT Relay

[lyledunn]

Is there an electronic replacement/alternative for the IDMT relay? It has been quite some time since I worked in the industry but I was told that the good-old IDMT has been virtually shelved on new or refurbed protection schemes.

Regards,

Lyledunn

 

[lyledunn]

I have just perused a number of web sites relating to this issue. Perhaps I should have done this first off! My question is thus answered. Thanks any way!

Regards,

Lyledunn

 

[RalphChristie]

Yes, there are a lot of manufacturers who manufacture IDMT-relays.

This new relays can do much more than the old elctromechanical relays - You can choose different curves, do metering, see fault data, have much lower burdens, do self testing, etc, etc. Some manufacturers are ABB, Reyrolle, SEL, Siemens, Strike, GE, just to name a few.

Some of the disadvantages of the modern relays are:
Can't see the disc turning
Must have some kind of power supply
Can't do series tripping (where you use the CTs to supply the tripcoil during a trip)

But, the advantages of the new relays are much more than the few disadvantages.

 

[EPPPL]

IDMT is a characteristic based on the fault current and operating time. All the latest Numerical and digital relays have the same charateristics in built. Well the new realys have the wide range of settings , so that it can be used for all over current applications. IDMT relays , in electromagnetic version has three different relays for different characteristics\viz normal, very inverse and extremely inverse.
The lateastrelayshave all these three modes inbuilt in one relay cabinet itself.

 

[samchoy97]

the characteristic of idmt "cdg 34"

 

[RalphChristie]

samchoy97

Please start a new thread when you are asking questions not relevant to the original question.

The CDG34 has an extremely inverse curve.

http://www.areva-td.com/static/largefiles/CDG14_UK.pdf

An approximate equation (IEC extremely inverse curve)

[blue]t = 80 x k / [((I-fault/I-set)^2)-1][/blue]

where:
t = time in seconds
k = time multiplier
I-fault = Fault current
I-set = Current setting



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

Make the best use of Eng-Tips.com
Read the Site Policies at FAQ731-376