## COnsider a 345 kV ,50 Hz,25 000 MVA circuit breaker whjch is capable of interrupting 40 kA which might be accomplished by having two interrupters in series .

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Qi- COnsider a 345 kV ,50 Hz,25 000 MVA circuit breaker whjch is capable of interrupting 40 kA which might be accomplished by having two interrupters in series . Without damping it was shown that the transient recove voltage (TTR) could reach a peak of twice the System voltage.supp that it is desired to reduce the voltage to 70 % of this value.The capacitance C of the bus to which the

breaker is connected might be 25 nF .Find the value of the resistance R connected in parallel at each interrupter.

Q2- A 154 / 34.5 kV, 50, 100 MVA transformer is protected against oveoItages by metal oxide surge arresters The 811. of the transformer ¡s 550 kV .Find the % protection margin and the protection distance of the arrester for an incoming Surge with a front slope of 1,000 kV/ps and an arrester of 350 kV AI find the voltage across the transformer if the arrester is connected is m far from the transformer Make the interpretation of the result.

Q3- Assume a resistor R = 50 ohm Connected in series between two lines with a characteristic impedance of Z1 = 200 ohm and Z2 250 ohm respectively .An incident wave of 250 kV propaga tes toward A .Find the voltage at point A and the voltages across R and Z2 Also find the currents flowing

through R and Z2 .Draw the current and voltage diagrams.