Page 577 - Handbook of Electrical Engineering

570 HANDBOOK OF ELECTRICAL ENGINEERING

The parallel impedance of the running motor is Z mn :-

R ms = 3.8244 and X ms = j0.9875 pu

The series impedance of the running motor is Z msl :-

Z msl = R msl + jX msl = 0.2390 + j0.9257 pu

Now add the feeder cable impedance in series to obtain the total series impedance between
the MCC and the motor. Call this total impedance Z mlc .

Z mslc = R mslc + jX mslc = R mslc + R cm + j(X mslc + X cm )

= 0.00844 + 0.2390 + j(0.003175 + 0.9257)
= 0.2475 + j0.9289 pu

The total load on the MCC consists of the static load Z ol1 (series components) in parallel with
the cable and motor Z mnsc (series components). The total impedance Z ols is therefore:-

Z oll × Z mslc
Z ols = R ols + jX ols = = 0.3050 + j0.7874 pu
Z oll + Z mnsc
The impedance seen at the SWBD for the cable, motor and MCC load is Z cs :-

Z cs = Z ols + Z c = 0.3050 + j0.7874 + 0.00635 + j0.05446
= 0.3114 + j0.8418 pu

This impedance is in parallel with that of the local load Z og on the SWBD. The total equivalent
load on SWBD is Z ogs where:-

Z ogl × Z cs
Z ogs = R ogs + jX ogs = = 0.3631 + j0.6375 pu
Z ogl + Z cs

Hence the total impedance seen by the generator emf E o is Z gs :-

Z ogs = R g + R ogs + j(X g + X ogs )
= 0.02 + 0.3631 + j(0.25 + 0.6375)
= 0.3831 + j0.8875 pu

The current in the generator I gs is:-

1.0687 − j0.1068
E o
I gns = = = 0.5395 − j0.9713 pu
Z gs 0.5395 + j0.9713