# A group of 4 identical synchro

A group of 4 identical synchronous motors is connected through a transformer to a 16-kV bus at a location remote from the generating plants of a power system The motors are rated 600V and operate at 89 5% efficiency when carrying a full load at unity power factor and rated voltage The sum of their output ratings is 4476 kW (6000 hp) The reactances In per unit of each motor based on its own input kilo-volt ampere rating are X”d = X1 = 0.20, X2 = 0.20, X0 = 0.04, and each is grounded through a reactance of 0.02 per unit The motors are connected to the 16-kV bus through a transformer bank composed of three Single-­phase units, each of which Is rated 2400/600 V, 2500 kVA The 600-V windings are connected in delta to the motors and the 2400-V windings are connected in star. The leakage reactance of each transformer is 10%
The power system which supplies the 16-kV bus is represented by a Thevenin equivalent generator rated 7500 kVA, 16 kV with reactances of X”d = X2 = 0.10 per unit, X0 = 0.05 per unit. and Xn from neutral to ground Equal to 0.05 per unit Each of the identical motors Is supplying an equal share of a total load of 3730 kW (5000 hp) and is operating at rated voltage, 85% power-factor lagging, and 88% efficiency when a single line-to-ground fault occurs on the low-voltage side of the transformer bank, Treat the group of motors as a single equivalent motor

4.1.1 Draw the sequence networks showing values of the impedances
4.1.2 Determine the sub-transient line currents In all parts of the system with pre-fault current neglected.