You are part of the protection section at Luano transmission substation and you are in charge of a busbar which is bolted and rated at 132 kV with two incomers and four outgoing lines. The protection switchgear has the capacity of 3500 MVA at the rated voltage. The power network has the parameters and constants given in the table below. egin{tabular}{|l|l|} hline Maximum full load current for each line & 500A \ hline Relay load & ( 1 Omega ) \ hline CT secondary resistance & ( 0.7 Omega ) \ hline Resistance of the connecting leads & ( 2 Omega ) \ hline CT saturation knee voltage & ( >120 mathrm{~V} ) \ hline CT magnetizing current up to 120 V assumed linear & ( 0.28 mathrm{~mA} / mathrm{V} ) \ hline end{tabular} If the overcurrent relay in the spill path is set to 1 A with the voltage setting of 100 V . (a) Calculate the maximum through fault current for which the protection scheme will just remain stable. (b) The minimum internal fault current which can be detected by the protection scheme. (c) The setting that can be able to detect minimum internal fault current of 500 A . (d) The value of the stabilizing resistor required in the protection scheme.
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- Total resistance \( R_t = \text{Relay load} + \text{CT secondary resistance} + \text{Resistance of connecting leads} \) - \( R_t = 1 \, \Omega + 0.7 \, \Omega + 2 \, \Omega = 3.7 \, \Omega \) Show more…
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