I am a trainee engineer in power plant. I am now days reading about HV circuit breakers nameplate data. 145 KV circuit breakers have following data in their nameplate
Short circuit making current
Short circuit breaking current
Line charging breaking current
Out of Phase breaking current
First pole to clear factor
Lighting impulse withstanding voltage
Among he following i have many queries related to first pole to clear factor and line charging breaking current.
The line charging breaking current is the maximum capacitive current that a breaker can break. For 145 KV it is 50A . When line is unloaded or very lightly loaded the charging current flows due to capacitive behavior of lines. If the trip command is given to breaker then there is a chance of arc re strike at current = 0 because at current zero the voltage is max for perfect capacitive load. Now what i am thinking in my mind why only capacitive line charging current is mentioned in nameplate the same thing can happens in inductive load because in inductor there is also a phase difference of 90 degrees between voltage and current. Secondly why this line charging breaking current capacity is too small it means only few amperes flow for line charging.
Then comes first pole to clear factor which says the recovery voltage across first pole is higher than the other two poles. It is due to fact that that three phase voltages have phase difference of 120 degrees so when trip command is given to breaker the arc current at 1 pole clears first as the current crosses zero but meanwhile the other two poles takes time due to 120 degree phase difference BUT............
why TRV transient recovery voltage gets high in first pole. What i am thinking that it is due to fact that as soon as the first pole opens the three phase supply get unbalance so that causes over voltages or there ma e some other reason.
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