A 13.8 kV, three-phase bus is supplied from a solidly grounded system with an ef

Question

A 13.8 kV, three-phase bus is supplied from a solidly grounded system with an effective reactance of 0.4 Ohm. A 5.4 MVA capacitor bank is connected to a bus. During switching operation to disconnect the capacitor from the bus, the switch reignites, the reignite ion occurring when the voltage across the switch is 18 kV. What will be the peak value of the reignition current? What voltage will be left trapped on the capacitor if this reignition current is interrupted? At its first current zero? At its second current zero? If following (a), a second reignition occurs exactly half a cycle after the first, what would then be the peak transient voltage appearing on the capacitor?

Explanation / Answer

where again parameter b 3 is a breaker related black box model’s constant with a value of b 3 =100. With the mentioned values of k 2 , , and b 3 , the cooling power P 3 in equation (7) is obtained in [W]. All previous relations are established using a limited number of tests and respective data with two similar designs of circuit breakers. It is possible that the presented approach can be used in a more general way with other circuit breaker designs and similar switching conditions, but obviously additional testing and data are necessary. Comparing parameters determined using equations (2) to (7) with parameters evaluated using current zero measurement data following the conclusions can be made: - there are relatively good correlation between values of parameter P 1 . Both values, evaluated using current zero measurement and calculated using equations from equations (2) to (7), are generally close enough in almost all cases (tests). Pearson’s correlation coefficient is 0.866. - values of 1 and P 2 have no significant correlation and in some cases the values are different significantly. If evaluated parameters are used, arc-circuit interaction simulations by MatLAB using the composite black box model results in better curve fitting with the measured current and voltage traces. It is obvious that with evaluated parameters the level of accuracy reaches a practical maximum. But also it is demonstrated that it is possible to calculate another set of free parameters ( P 1 , P 2 and 1 ) of composite black box model which can be used with a satisfactory level of accuracy. The calculated set of parameters is based on real physical values.

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