how to estimate the breaker capacity of breaker,please give the one example( 6

how to estimate the breaker capacity of breaker,please give
the one example( 6.6 kv breaker,800a)?????

Question Posted / yanamadala ashok

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how to estimate the breaker capacity of breaker,please give the one example( 6.6 kv breaker,800a)?..

Answer / praveen

breaker capaciy taken by 132kv for example 133*1.55 times
capacity 145kv suitable for beaker

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how to estimate the breaker capacity of breaker,please give the one example( 6.6 kv breaker,800a)?..

Answer / raghavendran.r

Step1: Calculate the system MVA.I have calculated that as 1.732*6600*800 = 9.144MVA. I have taken it as 10 MVA for easy calculations further.From the system MVA find out the Fault MVA value using the per unit impedance.i.e

Fault MVA = System MVA /P.u.Impedance.I am taking iot as .1
Hence we arrive at the Fault MVA.From this condition we get to know the Short circuit current as Isc = Fault MVA/Sys Voltage(6.6kV).

Usually, for a 6.6 kV system, the short circuit withstand rating is 40kA for 1 second.The Momentary current or making current is 2.55 times the Max. short circuit current.hHence we arrive at 100kA(Peak)

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