# Chapter 11: Dynamics of Electric Machines¶

## Example 11.7, Page 646¶

In [1]:
import math

#Variable declaration
KVA=71500;#Kilo Volt-Ampere
V_r=13800;#in Volts
X_af=0.57;#in per unit
X_la=0.125;#in per unit
X_lf=0.239;#in per unit
X_ld=0.172;#in per unit

#Calculations&Results
X_ds=X_la+((X_af*X_lf*X_ld)/(X_lf*X_ld+X_af*X_ld+X_af*X_lf));#subtransient reactance(in per unit)
E_phy=1.;#generated voltage (in per unit)
I_ds=E_phy/X_ds;#short circuit current (in per unit)
X_d=X_la+((X_af*X_lf)/(X_af+X_lf));#transient reactance (in per unit)
I_d=E_phy/X_d;#transient current (in per unit)
I_rated=KVA*1000/(math.sqrt(3)*V_r);#in Amperes
I_dsa=I_ds*I_rated;#sub transient current (in Amperes)
print 'sub-transient current (in Amperes)=%.2f'%I_dsa
I_da=I_d*I_rated;#transient current (in Amperes)
print 'transient current (in Amperes)=%.2f'%I_da
#Answer varies due to rounding-off errors

sub-transient current (in Amperes)=14238.48
transient current (in Amperes)=10195.69


## Example 11.8, Page 652¶

In [2]:
import math

#Variable declaration
f=60.;#in Hertzs
P=4.;#no. of poles
P_m=0.9;
H=10;#in Joule/Volt-Amperee

#Calculations&Results
N_s=f*120/P;#synchronous speed in (rpm)
P_dm=P_m/math.sin(18*math.pi/180);
t_c=P/f;#fault clearing time (in sec)

(a) power generated (in per unit)=0.95