The two-bus power system shown in figure (i) has one alternator supplying a synchronous motor load through a  -  transformer. The positive, negative and zero-sequence diagrams of the system are shown in figures (ii), (iii) and (iv), respectively. All reactances in the sequence diagrams are in p.u. For a bolted line-to-line fault (fault impedance = zero) between phases '  ' and '  ' at bus 1 , neglecting all pre-fault currents, the magnitude of the fault current (from phase '  ' to '  ') in p.u. is _______ (Round off to 2 decimal places).

Fig. (i) : Single-line diagram of the power system

Fig. (iii) : Negative-sequence network Fig. (ii) : Positive-sequence network

Fig. (iv) : Zero-sequence network

A 2 – bus system and corresponding zero sequence network are shown in the figure.        

The two transformers  and  are connected as,

For a fully transposed transmission line

The zero-sequence circuit of the three phase transformers shown in the figure is

A 3-phase transmission line is shown in the figure:

Voltage drop across the transmission line is given by the following equation:

Shunt capacitance of the line can be neglected. If the line has positive sequence impedance of 15Ω and zero sequence impedance of 48Ω, then the values of , and will be

The parameters of a transposed overhead transmission line are given as:

Self reactance  / km and Mutual reactance

The positive sequence reactance and zero sequence reactance, respectively, in Ω/km are

A generator is connected to a transformer which feeds another transformer through a short feeder (see Figure). The zero sequence impedance values are expressed in pu on a common base and are indicated in Figure. The Thevenin’s equivalent zero sequence impedance at point B is

Two transposed 3 phase lines run parallel to each other, the equation describing the voltage drop in both lines is given below.

Compute the self and mutual zero sequence impedances of this system i.e. compute in the following equations

Where  are the zero sequence voltage drops and currents for the two lines respectively

For the network shown in fig, the zero sequence reactance’s in p.u. are indicated. The zero sequence driving point reactance of the node 3 is: