Substation Bay Jumpers 1

[Engineer1916]

Eng Tip Family,
I know I have asked a similar question before. But I still have some concerns, I am sizing the bay jumpers and I have questions about the behavior of jumpers under fault conditions.
I calculated the jumper size based on steady state current and limited the temp to 160 deg F. But for the same conductor the temp rise under fault condition for 3 cycles is 1400 deg F. Which is more than the melting point of aluminum. So my question is, what is the industry standard? Do you normally look at the temp rise under fault condition for bay jumpers while sizing them?

 

[davidbeach]

1400 deg F after 3 cycles? Are you sure?

 

[cuky2000]

I do not see a lot of concerns sizing the substation jumpers.

The usual practice selecting jumpers is using the same conductor of the substation busses based on the maximum continuous current often driven by the standard circuit breaker ampacity ranging from 1200A to 4000A RMS continuous.

ACSR or AL conductor are usually used. The ACSR max temp = 640oC (1,093oF) and AL conductors are 340oC (644oF). At this temperature, the conductor remains with their mechanical strength usually good for conductors at significant mechanical tension.

Jumpers usually are lighted loaded and therefore the curve below is conservative in the safe size for most short circuit ranges in substation application.

If a smaller conductor is selected, corona losses could be a limiting factor.

Hope this helps.

 

[stevenal]

Seems odd to be using F. We generally use C for electrical work even in the US. 1400 F is 760 C, above the 640 C for ACSR Cuky mentioned (Aluminum Association says 645 C). Yes, if your fault duty is that high, it should be considered. I agree that jumpers are not under tension, but the same high short circuit current that melts the aluminum is also causing short circuit force on the conductors.