In the system shown below, the generator was initially supplying power to the grid. A temporary LLLG bolted fault occurs at F very close to circuit breaker 1. The circuit breakers open to isolate the line. The fault self-clears. The circuit breakers reclose and restore the line. Which one of the following diagrams best indicates the rotor accelerating and decelerating areas?

A 30 kV, 50 Hz, 50 MVA generator has the positive, negative, and zero sequence reactances of 0.25 pu, 0.15 pu, and 0.05 pu, respectively. The neutral of the generator is grounded with a reactance so that the fault current for a bolted LG fault and that of a bolted three-phase fault at the generator terminal are equal. The value of grounding reactance in ohms (round off to two decimal place) is ________.

The positive, negative and zero sequence impedances of a 125 MVA, three-phase, 15.5 kV, star-grounded. 50 Hz generators are j0.1pu, j0.05pu and 10.01pu respectively on the machine rating base. The machine is unloaded and working at the rated terminal voltage. If the grounding impedance of the generator is j0.01pu, then the magnitude of fault current for a b-phase to ground fault (in kA) is _______ (up to 2 decimal places).

The positive, negative and zero sequence impedances of a three phase generator are  and  respectively. For a line-to-line fault with fault impedance, the fault current is, where is the fault current with zero fault impedance. The relation between  and k is

The positive, negative, and zero sequence reactances of a wye-connected synchronous generator are 0.2 pu, 0.2 pu and 0.1 pu, respectively. The generator is an open circuit with a terminal voltage of 1 pu. The minimum value of the inductive reactance, in pu, required to be connected between neutral and ground so that the fault current does not exceed 3.75 pu if a single line to ground fault occurs at the terminals is _________ (assume fault impedance to be zero). (Give the answer up to one decimal place.)

A 30MVA, 3-phase, 50Hz, 13.8kV star-connected synchronous generator has positive, negative and zero sequence reactance. 15%, 15% and 5% respectively. A reactance  is connected between the neutral of the generator and ground. A double line to ground fault takes place involving phase ‘b’ and ‘c’, with a fault impedance of j0.1 p.u. The value of  (in p.u.) that will limit the positive sequence generator current to 4270 A is______________.

Two identical unloaded generators are connected in parallel as shown in the figure. Both the generators are having positive, negative and zero sequence impedance of j0.4 p.u., j0.3 p.u. and j0.15 p.u. respectively. If the pre-fault voltage is 1 p.u. for a line-to-ground (L-G) fault at the terminals at the generators, the fault current, in p.u. is______________.

At a 220 kV substation of a power system, it is given that the three-phase fault level is 4000 MVA and single-line to ground fault level is 5000 MVA. Neglecting the resistance and the shunt susceptances of the system,         

(A) The positive sequence driving point reactance at the bus is:

(a) 2.5 Ω          (b) 4.033 Ω

(c) 5.5 Ω          (d) 12.1 Ω

(B) And the zero sequence driving point reactance at the bus is:                

(a) 2.2 Ω          (b) 4.84 Ω

(c) 18.18 Ω          (d) 22.72 Ω

A 20-MVA, 6.6-kV, 3-phase alternator is connected to a 3-phase transmission line. The per unit positive sequence, negative sequence and zero sequence impedances of the alternator are j0.1, and j0.04 respectively. The neutral of the alternator is connected to ground through an inductive reactor of j0.05 p.u. The per unit positive, negative and zero sequence impedances of the transmission line are j0.1 and j0.3 respectively. All per unit values are based on the machine ratings. A solid ground fault occurs at one phase of the far end of the transmission line. The voltage of the alternator neutral with respect to ground during the fault is

A single line-to-ground fault occurs on an unloaded generator in phase a positive, negative, and zero sequence impedances of the generator are j0.25p.u, j0.25p.u, and j0.15p.u. respectively. The generator neutral is grounded through a reactance of j0.05p.u.  The pre fault generator terminal voltage is 1.0p.u.

The severity of line-to-ground and three phase faults at the terminals of an unloaded synchronous generator is to be same. If the terminal voltage is 1.0 p.u. and ,  for the alternator, then the required inductive reactance for neutral grounding is:

For an unbalanced fault, with paths for zero sequence currents, at the point of fault

A three phase star-connected alternator is rated 30 MVA, 13.8 kV and has the following sequence reactance values:  

The neutral of the alternator is solidly grounded. Determine the alternator line currents when a double line-to-ground fault occurs on its terminals. Assume that the alternator is unloaded and is operating at rated voltage when the fault occurs.

A fault occurring at the terminals at the terminals of an unloaded synchronous generator operating at its rated voltage has resulted in the following values of current and voltage

The fault that has occurred is _________________.