Answer Posted / pradhyumn

Buchholz relay is installed between the pipe connecting the
main tank & conservator. It indicates about the incipient
(initial) faults like insulation failure, core heating, and
fall in oil level due to leakage joints.
During initial faults when oil in the main tank decompose,
hydrogen gas is produced as result whose volume is more
than 70%, so this gas as result of being lighter tries to
escape to the conservator which is at the top, but gets
caught in the buchholz relay, where when determined amt. of
gas is accumulated, it gives the alarm of gas surge.

During major faults when enormous amount of gas is
released, this causes the oil surge which enters the
buchholz relay & thus due to this oil surge the causes the
circuit to trip as this being the major fault.

* Used in oil and gas surge protection.(plz. forgive
spelling mistakes.)

My question is whether bellow formula is correct to find bus size for 46kA for 0.5 second & what is RT in bellow formula. formula to calculate the size of busbar to withstand the thermal stresses due to currents with duration of 0.2 sec to 5 sec. Sp = RT( I x I x t) / K Where Sp – is the cross sectional area of bus bar in millimeters. I -    is the value of AC fault current. t -    is the operating time of disconnecting device in seconds. K –  is the factor depending on the material of the conductor, insulation and initial and final temperature. Value of ‘k’ for copper is 143.

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