Transformer Exercise (Part 2)

A particular transformer is governed by the following equations:

E 1 = Z S I 1 + Z M I 2 E 2 = Z M I 1 + Z S I 2 E_1 = Z_S I_1 + Z_M I_2 \\ E_2 = Z_M I_1 + Z_S I_2

In the equations, E 1 E_1 and E 2 E_2 are the terminal voltages and I 1 I_1 and I 2 I_2 are the terminal currents (note the polarity conventions in the diagram). Z S Z_S and Z M Z_M are the transformer self and mutual impedances.

An AC voltage source with internal voltage E S E_S and internal impedance Z 1 Z_1 is connected across the first set of terminals, and an impedance Z 2 Z_2 is connected across the second set of terminals.

What is the magnitude of E 2 E_2 ?

Details and Assumptions:
1) E S = 0 + j 10 E_S = 0 + j 10
2) Z 1 = 2 + j 5 Z_1 = 2 + j 5
3) Z 2 = 5 + j 5 Z_2 = 5 + j 5
4) Z S = 0 + j 10 Z_S = 0 + j 10
5) Z M = 0 + j 5 Z_M = 0 + j 5
6) Consider all quantities to be complex numbers. The quantity j j is the imaginary unit


The answer is 1.629.

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3 solutions

Steven Chase
Jul 11, 2020

@Neeraj Anand Badgujar has shown how the solution works. I will post some Python code which uses the linear system solver to calculate the currents. I will re-iterate the equations for the sake of completeness.

Basic equations

E 1 = Z S I 1 + Z M I 2 E 2 = Z M I 1 + Z S I 2 E_1 = Z_S I_1 + Z_M I_2 \\ E_2 = Z_M I_1 + Z_S I_2

Substituting in for E 1 E_1 and E 2 E_2 :

E S Z 1 I 1 = Z S I 1 + Z M I 2 Z 2 I 2 = Z M I 1 + Z S I 2 E_S - Z_1 I_1= Z_S I_1 + Z_M I_2 \\ -Z_2 I_2 = Z_M I_1 + Z_S I_2

Consolidating terms:

E S = ( Z S + Z 1 ) I 1 + Z M I 2 0 = Z M I 1 + ( Z S + Z 2 ) I 2 E_S = (Z_S + Z_1) I_1 + Z_M I_2 \\ 0 = Z_M I_1 + (Z_S + Z_2) I_2

Solve the linear system for the currents. Then calculate the terminal voltages.

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import math
import numpy as np

#############################################################

# System parameters

ES = complex(0.0,10.0)

Z1 = complex(2.0,5.0)
Z2 = complex(5.0,5.0)

ZS = complex(0.0,10.0)
ZM = complex(0.0,5.0)

#############################################################

# Set up linear system
# Solve for currents

M11 = ZS + Z1
M12 = ZM

M21 = ZM
M22 = ZS + Z2

M =  np.array([[M11,M12],[M21,M22]])
vec = np.array([ES,0.0])

Sol = np.linalg.solve(M, vec)

I1 = Sol[0]
I2 = Sol[1]

#############################################################

# Calculate terminal voltages 
# Check basic equations

E1 = ES - Z1*I1
E2 = -I2*Z2

c1 = E1 - ZS*I1 - ZM*I2
c2 = E2 - ZM*I1 - ZS*I2

print abs(c1)
print abs(c2)
print ""

#9.155133597044475e-16
#4.440892098500626e-16

#############################################################

# Print E2 magnitude

print abs(E2)

#1.6286558549611407

@Steven Chase I am enjoying this series very much. Please continue it for part 3
Thanks in advance

@Steven Chase sir I have uploaded a new problem.

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Nice one. I have solved it

Steven Chase - 11 months ago

@Steven Chase Sir why didn't you give a reply that you have seen the new problem or not??

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That's a pretty interesting problem. I have attempted it, but my answer was not accepted

Steven Chase - 11 months ago

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@Steven Chase sir whenever I dedicate a problem I try to make hard as possible as I can. Maybe the solution which I have solved, there would be some error, it take me whole 1 day to do that calculations.
Can you share what answer you are getting,
I will check my solution later.

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@A Former Brilliant Member Let me also check my work again, and when I am sure that it is the best I can do, I will share it. Thanks

Steven Chase - 11 months ago
Karan Chatrath
Jul 12, 2020

Referring to the system of equations derived by @Steven Chase , the final equation to compute the absolute value of E 2 E_2 can be re-arranged in a matrix form to be:

E 2 = m o d ( [ Z M Z S ] [ Z 1 + Z S Z M Z M Z 2 + Z S ] 1 [ E S 0 ] ) \lvert E_2 \rvert = \mathrm{mod}\left(\left[\begin{matrix}Z_M&Z_S\end{matrix}\right]\left[\begin{matrix}Z_1+Z_S&Z_M\\Z_M&Z_2+Z_S\end{matrix}\right]^{-1}\left[\begin{matrix}E_S\\0\end{matrix}\right] \right)

This is effectively only one line of MATLAB code, excluding initialisations.

1
E2_abs = abs([Zm ZS]*inv([Z1+ZS Zm;Zm ZS+Z2])*[ES;0])

@Karan Chatrath
It concludes that MATLAB is very strong
Right??
BTW sir i have studied Laplace very well.
Now I am able to solve 2nd order differential equation.
Please can you upload a problem ??
I will upload solution using Laplace.
Thanks in advance.

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Okay, I will think of one and post after sometime

Karan Chatrath - 11 months ago

Nice problem.
The basic equations are E 1 = Z s I 1 + Z M I 2 E_{1}=Z_{s}I_{1}+Z_{M}I_{2} E 1 = j ( 10 I 1 + 5 I 2 ) E_{1}=j(10I_{1}+5I_{2}) E 2 = Z M I 1 + Z s I 2 E_{2}=Z_{M}I_{1}+Z_{s}I_{2} E 2 = j ( 5 I 1 + 10 I 2 ) E_{2}=j(5I_{1}+10I_{2})
Using Kirchoff's voltage rule E s I 1 Z 1 = E 1 E_{s}-I_{1}Z_{1}=E_{1} E 2 = I 2 Z 2 E_{2}=-I_{2}Z_{2}
Solving the above 2 2 equation for I 1 I_{1} and I 2 I_{2} gives I 2 = 76 377 + 42 377 j I_{2}=\frac{76}{377}+\frac{42}{377}j
E 2 = I 2 Z 2 E_{2}=-I_{2}Z_{2}
Substituting the values of Z 2 Z_{2} and I 2 I_{2} in the above equation, and taking it's modulus gives E 2 1.628 \boxed{|E_{2}| \approx\textcolor{#20A900}{ 1.628}}

Sir please post more problems like this one and upgrade them also.
Thanks for this

I am expecting a MATLAB solution from @Karan Chatrath Sir.
Thanks in advance.

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I solved it the same way as @Steven Chase did, by using linear algebra.

Karan Chatrath - 11 months ago

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