Coordination between hi-set unit and IDMT-relay 4

[redox]

What is the time interval between a high-set (instantaneous) unit and IDMT-relay? I know time between relay-relay is 0.3 - 0.4 seconds, is it the same between high-set and relay or not?

Thanks

 

[DanDel]

Since an Inst relay will pickup with no intended time delay, it is not realistic to consider separation by a time interval. Obviously, the only separation possible is by current settings.
In general terms, the main point to remember is that you should try to avoid two devices tripping for the same fault by their Inst trips. This is done by limiting Main device Inst settings to the maximum fault value seen at the bus upon which they are located, or by not having Inst trips on the Main device at all.

 

[SMB1]

Yes the time between any two relay should not be less than 0.3 sec. Also this apply when using Inst. relay.

But you need to chick three point in the courve:
First:At low fault current the time diff bet the two relay >0.3sec

Second: At operation of Ins time >0.3 sec

Third: At max fult- extend the courve and chick the 0.3 sec.

This will be clear if you deal with curves.

 

[RalphChristie]

Just remember:

Electronic relays - 0.3 seconds
Electromecanical relays - 0.4 seconds

RCC

 

[DanDel]

The time delay separation should be at the end of the inverse current curves(high current, low time), not at the Inst curves, which should be separated by current pickup values.

 

[jbartos]

Suggestion: Visit

http://www.pbeng.co.uk/products/transformer/files/mspi.pdf

for:
7.5.4 Low set stage time multiplier/time delay
This is normally selected to give sufficient time delay between upstream and downstream operating
times to allow for breaker clearance and measurement errors etc. This is usually taken as 0.3 - 0.4
seconds

http://www.ee.polyu.edu.hk/staff/eekkli/BEngOpt/Lect/Ch3_OC2003.pdf

for: differences between time and time/current discriminations
etc. for more info

 

[RalphChristie]

jbaros: Red star for a good site! (last one)

see also:

http://www.usace.army.mil/inet/usace-docs/armytm/tm5-81-14/chap4.pdf

http://www.usbr.gov/power/data/fist/fist3~9/3~9_8.htm