# Chapter 12: Special-Purpose Electric Machines¶

## Example 12.1, Page 662¶

In :
import math

#Variable declaration
flux=0.004;#(in Weber)
R_a=0.8;#armature resistance (in ohm)
V_s=40;#applied voltage (in Volts)
T_d=1.2;#in Newton-meter
K_a=95;#motor constant

#Calculations&Results
w_m=(V_s/(K_a*flux))-((R_a*T_d)/(K_a*flux)**2);
N_m=w_m*60/(2*math.pi);
print 'speed of motor (in rpm)=%.f'%(math.ceil(N_m))
w_mb=0;#for blocked rotor condition
T_db=(V_s*K_a*flux)/R_a;
print 'torque developed under blocked rotor condition (in Newton-meter)=%.f'%T_db

speed of motor (in rpm)=942
torque developed under blocked rotor condition (in Newton-meter)=19


## Example 12.2, Page 662¶

In :
import math

#Variable declaration
N_m=1500;#speed of motor (in rpm)
R_a=2;#armature resistance (in ohms)
V_s=100;
P_o=200;#rated power
K_a=85;#machine constant
P_rot=15;#rotational loss

#Calculations
w_m=(2*math.pi*N_m)/60;
P_d=P_o+P_rot;#power developed
T_d=P_d/w_m;#torque developed
def root(a,b,c):
return ((-b)+math.sqrt((b**2)-(4*a*c)))/(2*a);

#Result
print 'magnetic flux (in mWb)=%.2f'%(root(1,-0.0075,(2.41*10**-6))*1000)

magnetic flux (in mWb)=7.16


## Example 12.3, Page 682¶

In :
#Variable declaration
f=60;#frequency (in Hertzs)
P_pi=0.5;#pole pitch
F_d=100000;#developed thrust (in Newton)

#Calculations&Results
V_m=200000./3600;#speed of motor (in meter/sec)
P_d=F_d*V_m;
print 'developed power (in Kilo-Watts)=%.f'%(int(P_d/1000))
V_s=2*P_pi*f;#synchronous speed of the motor (in meter/sec)
s=(V_s-V_m)/V_s;#slip
P_cu=F_d*s*V_s;
print 'Copper loss (in Kilo-Watts)=%.f'%(int(P_cu/1000))

developed power (in Kilo-Watts)=5555
Copper loss (in Kilo-Watts)=444