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'''The wound-rotor induction motor of Fig.43.5 is rated at 30-kW,975 rpm,440-V,50 Hz.The open-circuit line voltage is 400V and the load
resistance is 0.5 ohm.If chopper frequency is 200 Hz,calculate Ton so that the motor develops a gross torque of 200 N-m at 750 rpm.Also,
calculate the magnitude of the current pulses drawn from the capacitor.'''
import math as m
Ns = 1000.0 #rpm (Synchronus speed)
N1 = 750.0 #rpm (rotating speed)
E2 = 400.0 #V (OC line voltage)
Tg = 200.0 #N-m (gross torque)
R0 = 0.5 #ohm (load resistance)
f = 200.0 #Hz (chopper frequency)
s = (Ns-N1)/Ns # slip
Vrl = s*E2 #V (rotor line voltage)
Vdc = 135.0 #V (DC voltage of 3-phase bridge rectifier)
#Now, Tg = P^2/(2*3.14*Ns).Therefore,
P2 = Tg*2*3.14*Ns/60 #W
#Power dissipated as heat
sP2 = s*P2 #W
#Power is actually dissipated in R and is equal to rectifier output Vdc*Idc.Therefore,
Idc = sP2/Vdc #A
#The apparent resistance at the input of chopper is
Ra = Vdc/Idc #ohm
#Now, Ra = Ro/(f*Ton)^2 .Therefore,
Ton = m.sqrt(R0/(f*f*Ra))*1000 #ms
#Current in R0 can be found from relation,I0^2*R0 = sP2
I0 = m.sqrt(sP2/R0) #A
print "Ton = ",round(Ton,2),"ms."
print "magnitude of the current pulse I0 =",round(I0,2),"A."
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