Page 585 - Handbook of Electrical Engineering

578 HANDBOOK OF ELECTRICAL ENGINEERING

All the impedances are in their complex form R + jX.

The simplifications made in t) have been applied viz:-
• Cable impedances have been ignored.
• Transformer impedances have been ignored.
• All the standing loads are grouped at the generator terminals.
The initial conditions are easily calculated. The terminal voltage V o is known and assumed
to be 1.0 + j0.0 per unit. The motor starter is open. The initial circuit consists of Z l in series
with Z g and is fed by E o . The initial load current I l is I lo .

V o
I lo = and E o = V o + I lo
Z l
Therefore it consists of Z l in series with Z g and is fed by E o . The initial load current I l is I lo .

V o
E o = V o 1 +
Z l
The general case for the running conditions are also easily calculated. The motor starter
is closed. The motor and load impedance are then connected in parallel. The total of these
impedances is Z lm in series with Z g and is fed by E o . The initial load current I l where:-

Z l Z m
Z lm =
Z l + Z m
and

E o Z lm
V =
Z lm + Z g
V o (1 + Z g )Z lm
=
Z l (Z lm + Z g )
Let
a = (Z l + Z g )Z lm

and
b = (Z lm + Z g )Z l
Therefore

aV o
V =
b
V o − V

The Percentage volt-drop V = × 100%
V

aV o
V = V o − × 100%
b