Chapter9 - Instrument Transformers

Exa 9.1 page 203

In [20]:
from cmath import polar, sin
from __future__ import division
n=300/1 
Z2=1.5+1J 
I2=5 
E2=I2*Z2
E1=E2/n 
from math import atan, degrees, sin, cos
alpha=(atan(1/1.5))
Io=(100+40*1J)
delta=(atan(40/100) )
sigma=-(Io*sin(alpha+delta))*100/(n*I2) 
print "Ratio error=%.2f percent"%abs(sigma)
bet=(Io*cos(alpha+delta))/(n*I2) 
print "Phase angle=%.2f degree"%abs(bet)

Ratio error=5.92 percent
Phase angle=0.04 degree

Exa 9.2 page 203

In [21]:
I_ratio=500/5 
n=1/100 
I2=300/100 
print "Secondary current=%.2f A"%(I2)
V2=I2*1.5 
print "Secondary voltage=%.2f V"%(V2)

Secondary current=3.00 A
Secondary voltage=4.50 V

Exa 9.3 page 204

In [22]:
V_line=200*33000/220 
print "Voltage on line=%.0f "%V_line
I_line=4*100/5 
print "Current in line=%.0f A"%(I_line)

Voltage on line=30000 
Current in line=80 A

Exa 9.4 page 205

In [23]:
n=1000/5 
Ie=0.7*1000/100 
Tp=1 
n=200 
Ts=200 
R_actual=Ts+(7/5) 
Error_ratio=(200-R_actual)*100/R_actual 
print "Ratio error=%.2f percent"%(Error_ratio)
Ts=200-(0.5*200/100) 
n=199/1 
R_actual=Ts+(7/5) 
Error_ratio=(200-R_actual)*100/R_actual 
print "Ratio error=%.2f percent"%(Error_ratio)

Ratio error=-0.70 percent
Ratio error=-0.20 percent

Exa 9.5 page 206

In [24]:
Vp=1000 
Vs=100 
n=Vp/Vs 
pf_no_load=0.4 
sina=0.4 
cosa= (1-sina**2)**0.5 
tana=sina/cosa 
Im=0.02 
Ie=Im*tana 
xp=66.2 
rp=94.5 
#At no load Is=0 so
theta=((Ie*xp)-(Im*rp))/(n*Vs) 
print "Phase angle error at no load=%.4f"%(theta)

Phase angle error at no load=-0.0013

Exa 9.6 page 207

In [25]:
E2=((1.8+5*0.16)**2+(2.4+5*0.195)**2)**0.5 
pf2=2.6/E2 
AT_sec=600 
sina=3.375/E2 
AT_pri=600+10.1*pf2+13.4*sina 
I1=AT_pri/40 
Ratio_error=(15-I1)*100/I1 
print "Ratio error=%.2f percent"%(Ratio_error)

Ratio error=-2.72 percent