A generator operating at 50 Hz delivers 1 pu power to an infinite bus through a transmission circuit in which resistance is ignored. A fault takes place reducing the maximum power transferable to 0.5 pu whereas before the fault, this power was 2.0 pu and after the clearance of the fault, it is 1.5 pu. By the use of equal area criterion, determine the critical clearing angle.

A synchronous generator is feeding its rated power of 250 MW to a large 60 Hz network over a double circuit transmission The maximum steady state power that can be transmitted over the line with both circuits in service is 500 MW and is 350 MW with any one out of service. A solid three-phase fault occurring at the network-end of one of the lines causes it to trip. If inertia constant is H = 3.5 s, calculate the critical clearing angle and critical clearing time in which the circuit breakers must trip so that synchronism is preserved.

7. Two 440V, 60Hz, 6 pole, 30 AC generators are running in parallel. The first supplies the busbars with 525kW of power at a power factor of 0.79 lagging. The second provides the busbars with 415kW at a power factor of 0.96 lagging. An additional load that requires 275kW at a power factor of 0.89 leading is added to the busbars. The two generators have their governor and magnetization controls adjusted so they provide 440V, 60Hz and share the active and reactive powers equally. What is the active and reactive power produced by each and their line currents and speeds?

A 15,000 KVA, 6.9 KV generator, star connected has positive, negative and zero sequence reactances of 0.25, 0.25 and 0.08 p.u. respectively. A reactor of 0.06 p.u. reactance on the generator rating is placed in the line from neutral to ground: A double line to ground fault occurs at the terminals of the generator when it is operating at its rated voltage and unloaded. Find the unitial r.m.s. line and ground wire current for a solidly grounded fault, and also the voltage to ground of the unfaulted line. (UPSC-1975) Ans: 1-1,-4970 A; I, 5480 A; V. 69.7 KV

A 3.3 kV/110 V, 50 Hz, single-phase trans- former is to have an approximate e.m.f. per turn of 22 V and operate with a maximum flux of 1.25 T. Calculate (a) the number of primary and secondary turns, and (b) the cross- sectional area of the core

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32. The incremental cost characteristics of two generators delivering a load of 200 MW are as follows: dF = 2.0 + 0.01 P, dP, dP dF, -= 1.6 + 0.02 P, For economic operation the generators P, and P, should be (a) 120 MW and 80 MW (b) 81 MW and 120 MW (c) 120 MW and 120 MW (d) 80 MW and 80 MW

Q3/ For the system shown in figure. The generator is supplying 1.0 pu MW power under prefault condition. When three-phase fault occur at point F. What should the value of fault reactance must be to make the critical clearing angle equal to 58.9. Sc j0.1 j0.1 10.21 BE j0.38 38 j0.21 IEgl-12 pu 10.19 F 10.19 IVI-1.00 pu j0.1 j0.1 Q4/ Figure below shows the one-line diagram

A power transmission line of 33kV (maximum) carries a maximum current of 1200A is connecting the two areas. A PMMC voltmeter of (0-600V) range and a PMMC ammeter of (0-25A) range are to be used for measurement of voltage and currents of the transmission line. 1.Design and draw a circuit with suitable instrument transformers for the measurement.  Use sample values for winding turns. 2.On a particular day, the readings shown by the meters were 17.5A and 440V.  Calculate the actual voltage and current in the transmission line.