Excercises Electric Machinery Fundamentals

Chapter 2 Problem 2-17



In [1]:

    
%pylab inline









    



Populating the interactive namespace from numpy and matplotlib

Description

A 10-kVA 480/120-V conventional transformer is to be used to supply power from a 600-V source to a 120-V load. Consider the transformer to be ideal, and assume that all insulation can handle 600 V.



In [2]:

    
Vp = 600  # [V]
Vl = 120  # [V] which is also the load voltage
Vh = 480  # [V] 
Sw = 10e3 # [VA]

(a)

Sketch the transformer connection that will do the required job.

(b)

Find the kilovoltampere rating of the transformer in the configuration.

(c)

Find the maximum primary and secondary currents under these conditions.

SOLUTION

(a)

For this configuration, the common winding must be the smaller of the two windings. The transformer connection is shown below:

(b)

The kVA rating of the autotransformer can be found from the equation:

$$S_{IO} = \frac{N_{SE} + N_C}{N_{SE}}S_W = \frac{4N_C + N_C}{4N_C}S_W$$



In [3]:

    
n = Vh/Vl  # = Nse/Nc
Sio = (n + 1)/n * Sw

print('''
Sio = {:.1f} kVA
==============
'''.format(Sio/1000))









    



Sio = 12.5 kVA
==============

(c)

The maximum primary current for this configuration will be:

$$I_P = \frac{S}{V_P}$$



In [4]:

    
Ip = Sio/Vp
print('''
Ip = {:.2f} A
============
'''.format(Ip))









    



Ip = 20.83 A
============

and the maximum secondary current is:

$$I_S = \frac{S}{V_S}$$



In [5]:

    
Is = Sio/Vl
print('''
s = {:.0f} A
=========
'''.format(Is))









    



s = 104 A
=========