TRANSFORMER EXCITATION
CHARACTERISTICS
This
simulation is designed to illustrate the current inrush phenomenon in a
transformer when it is switched to an ac supply. The transformer is modeled by
a series resistance and leakage inductance and by a nonlinear magnetizing
inductance; the nonlinearity is expressed by a relationship relating the
magnetizing current Im and the flux λ of
the form
Im
= aλ +
bλ9
The flux λ
is obtained by integrating the voltage Vm
since
Vm
= 1/ωο*dλ/dt
Core loss is represented by a shunt resistive
Suggested studies:
1. Obtain plots of Vin, λ,
and Iin versus time for various levels of
the applied voltage (Vs=0.5,
1.0, 1.5).
2.
Perform a Fourier decomposition of the input current when Vs=1.0 and
phase=0o.
3. Plot the magnetizing curve, i.e. λ
versus Im; also plot λ
versus Iin (Vs=0 and phase=0o).
4. Examine and compare the effects of :
a) the
time of switching by adjusting the phase angle (90o and 0o)
b) the residual flux by adjusting the IC on the
integrator
c) the presence of a dc component by including a dc offset in
the sinusoidal input excitation
d) a
load represented by an RL-LL series circuit