Determine the momentary dc load

[Khalid1970]

Hi,


For sizing of DC system of 132/11 KV SS, how to compute the 1 minute DC load required for tripping (how many breakers to be assumed tripping simultaneously).

What is the criteria to be followed.

Also, should we add to this the closing coil load or choose the. Highest of the two.


Thanks.

 

[Khalid1970]

Hello Gents,

Nobody contributed, may be the question is not clear enough.

The situation is that we are having 11KV Switchgear (29 breakers) and 132 KV GIS ( 13 bays).

Tripping DC is a stand alone while we are having another DC for the control.

The continuous load is known and my problem is the temporary load ( for 1 min. As per IEEE).


Shall I sum all trip coils load ( GIS has two trip coils per each breaker), also what about the closing motors and charging motors should it be considered.

I believe few breakers to be considered as long as fault will not actuate the whole breakers .

I need a guideline To avoid overdosing knowing that I read a thread concerning this but it did not clear the issue ( answer of Mr. RCWilson).


Thanks.

 

[ScottyUK]

You need to assess the likely scenarios for simultaneous breaker tripping. If you have a breaker fail scheme or possibly a bus differential then these can typically require three or more breakers to operate simultaneously. Your specific scheme may have more, or less, breakers involved. If your protection scheme requires both the primary and secondary trip coils to energise simultaneously then yes, you must account for this in the loading calcs.

One reason responses are slow is that Saturday and Sunday is the weekend in much of the world, and many contributors aren't at work or are otherwise engaged. Wait a couple of days.

 

[DTR2011]

I would also consider what I call an avalanche situation - one where all he*l breaks loose, but getting the station up ASAP is desirable, including SCADA / communication / monitoring devices. Perhaps think of a very active storm, reclosing that is right at the edge of resetting and then going through the cycles again. I would also look at ScottyUK's scenarios as well.

How many battery banks do you have? Do you utilise a control power transformer from 33kV (which could be tripped off on a dead 33kV bus), do you have a separate Aux 33kV feed from another distribution line? Are the protection devices (control power) on the same tripping battery? How about emergency lighting?