Page 40 - Solutions Manual to accompany Electric Machinery Fundamentals

% Calculate the full-load current
i_fl = S / Vrms;

% Calculate the percentage of full-load current
percnt = irms / i_fl * 100;
disp(['The magnetization current is ' num2str(percnt) ...
'% of full-load current.']);

% Plot the magnetization current.
figure(1)
plot(time,im);
title ('\bfMagnetization Current at 120 V and 60 Hz');
xlabel ('\bfTime (s)');
ylabel ('\bf\itI_{m} \rm(A)');
axis([0 0.04 -0.5 0.5]);
grid on;

When this program is executed, the results are

» prob2_5a
The rms current at 120 V and 60 Hz is 0.31863
The magnetization current is 3.8236% of full-load current.
The rms magnetization current is 0.318 A. Since the full-load current is 1000 VA / 120 V = 8.33 A, the
magnetization current is 3.82% of the full-load current. The resulting plot is

(b) When this transformer is connected to a 240-V 50 Hz source, the flux in the core will be given by
the equation
V
 (t )   M cos  t
 N S

The magnetization current required for any given flux level can be found from Figure P2-2, or alternately
from the equivalent table in file p22_mag.dat. The MATLAB program shown below calculates the
flux level at each time, the corresponding magnetization current, and the rms value of the magnetization
current.

% M-file: prob2_5b.m
% M-file to calculate and plot the magnetization
% current of a 120/240 transformer operating at
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