ITE breakers

[buzzp]

We have several older breakers type KC 1000 and KC 600, ITE breakers. We are upgrading our protective relaying for this facility. I am having difficulty finding 'make' requirements of the 'tripping coil' and 'pick-up coil' of these breakers. I do have the original mfg data and apparently, back in the day, 'make' requirements of inductive loads was not specified. The data sheets only state 'heavy contacts' should be used. I know the resistance of these coils but do not have any other information. I would like to get rid of the MG-6 relays which are carrying the load now and let the protective relay handle the load of the trip and pick-up coils. I am a little hesitant to do this due to the over designing which occurred with these older relays. The MG-6 will make 30A@575VAC with 12A continuous. Notice this is not a DC make rating. The new protective relay makes 30A per IEEE C37.90. My question is if anyone has any make requirements of these breakers? I know I could measure it with a scope but don't really want to take units down to run the test. Without this information I will be keeping the MG-6 relays. My experience with DC coils (hydraulics and pneumatics) says that these coils could be pulling up to 30 times there continuous rating when they are first energized. Any info or hindsight would be appreciated. Thanks.

 

[busbar]

Extra-Long Shot —

http://www.selinc.com/sel-9502.htm

[The developer of these told me that for testing he made a 2-Henry choke from a 2,500-ft spool of 14AWG SIS with a galvanized water-pipe “core.”]

 

[buzzp]

Busbar,
The link does not work. Would you please relink it? Thanks.

 

[davidbeach]

http://www.selinc.com/sel-9502.htm

The forum software grabbed too much to include in the URL, you can also type it in.

 

[ScottyUK]

Hi buzzp.

A DC coil has a lot of inductance, so the current in the coil should rise slowly according to the L/R time constant from an initial value of zero to a final value of V/R. I see no way of getting a high inrush on a relay coil with a DC supply.

The DC breaking capability is a different issue as the voltage across the opening contacts can be quite high unless an antiparallel freewheel diode is fitted, but I fell that I'm teaching my granny to suck eggs at this point so...







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

 

[buzzp]

ScottyUK,
I am with you on 'disconnecting' the inductive load. I understand the rise in voltage due to the sudden change in current (inductor properties).
I remember hearing the 30X current on energization from Eaton. I tried looking on their site for this number again to no avail. However, I did not see this concern raised by the manufacturer's pages I visited. Some physics expert (supposedly) says their is an inrush current associated with DC coils with DC voltage applied (I really don't know what differences there would be with the winding on an AC coil and DC coil). The consensus seems to be there is no inrush current associated with DC coils. However, read this link for what it is worth

http://www.newton.dep.anl.gov/askasci/phy00/phy00701.htm

I guess I am going to have to review some things to understand what is going on. On the surface, I am in agreement with you but need to do some reviewing of my electromagnetic properties book (ughh). Seems the impedance will change the time constant as the core material will affect the impedance (not simply the resistance of the wire in the time constant).
Does IEEE C37.90 only address AC make ratings(I dont have a copy)? If it does not mention DC then I would have to believe there is no inrush associated with a standard DC coil.

 

[buzzp]

Strike "impedance" in my last post for reluctance.

 

[ScottyUK]

Hi Buzz,

Thanks for the link.

Some ideas in the link are at odds with everything I learned in class, but that doesn't always mean it is wrong. I remember being told that it was impossible to have a square root of a negative number, and then they sprang 'j'-notation on me a few years later!

I think you may be right that the presence of a saturable core will cause slight deviation from the 'perfect' inductance, but the general behaviour will still conform to the classical theory.




----------------------------------

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

 

[buzzp]

After sitting down and thinking about this, I agree with you that there would be no in rush current for DC. If it were AC there would be an inrush current, assuming both have some type of core (not just an inductor).

I think this is worthy of another post (perhaps in the circuit engineering forum or electrical engineering) to get some others opinions. Thanks again.