#Variable declaration
V_lv = 220.0 #LV side voltage of transformer(V)
V_hv = 11000.0 #HV side voltage of transformer(V)
ratio_CT = 600.0/(5/3**0.5) #CT ratio on LV side of transformer
#Calculation
CT_pri = 600.0 #Primary CT
CT_sec = 5.0/3**0.5 #Secondary CT
I_1 = V_lv/V_hv*CT_pri #Line current in secondary of transformer corresponding to primary winding(A)
I_2 = CT_sec*3**0.5 #Current in secondary of CT(A)
#Result
print('Ratio of CTs on 11000 V side = %.f : %.f ' %(I_1,I_2))
print('\nNOTE: ERROR: Mistake in representing the final answer in textbook solution')
#Variable declaration
V_lv = 11.0*10**3 #LV side voltage of transformer(V)
V_hv = 66.0*10**3 #HV side voltage of transformer(V)
ratio_CT = 250.0/5 #CT ratio on LV side of transformer
#Calculation
V_hv_phase = V_hv/3**0.5 #HV side phase voltage(V)
ratio_main_T = V_hv_phase/V_lv #Ratio of main transformer
I_2 = 250.0 #Primary CT
I_1 = I_2/(ratio_main_T*3**0.5) #Primary line current(A)
CT_sec = 5.0 #Secondary CT
secondary_side = CT_sec/3**0.5 #HV side CT secondary
#Result
print('Ratio of CTs on high voltage side = %.1f : %.1f = (%.f/%.2f√3) : (%.f/√3) ' %(I_1,secondary_side,I_2,ratio_main_T,CT_sec))
#Variable declaration
V_hv = 33.0 #HV side voltage of transformer(kV)
V_lv = 6.6 #LV side voltage of transformer(kV)
ratio_CT = 100.0/1 #CT ratio on LV side of transformer
#Calculation
CT_pri = 100.0 #Primary CT
CT_sec = 1.0 #Secondary CT
I_hv = V_lv/V_hv*CT_pri #Line current on HV side(A)
I_lv = CT_sec/3**0.5 #Line current on LV side(A)
#Result
print('Ratio of protective CTs on 33 kV side = %.f : %.f/√3 = %.f : %.f ' %(I_hv,CT_sec,3**0.5*I_hv,I_lv*3**0.5))
#Variable declaration
kVA = 200.0 #Transformer rating(kVA)
E_1 = 11000.0 #HV side voltage of transformer(kV)
E_2 = 400.0 #LV side voltage of transformer(kV)
ratio_CT = 500.0/5 #CT ratio on LV side of transformer
I_f = 750.0 #Fault current(A)
#Calculation
I_2 = 500.0 #Primary CT
I_1 = 5.0 #Secondary CT
I_1_T = E_2*I_2/(3**0.5*E_1) #Primary current in transformer(A)
I_hv_T = I_1_T*3**0.5 #Equivalent line current on HV side(A)
I_pilot_lv = I_1*3**0.5 #Pilot current on LV side(A)
#Result
print('CT ratios on high voltage side = %.2f : %.2f ' %(I_hv_T,I_pilot_lv))
print('\nNOTE: Circulating current is not calculated')
#Variable declaration
MVA = 50.0 #Transformer rating(MVA)
V_hv = 132.0 #HV side voltage of transformer(kV)
V_lv = 33.0 #LV side voltage of transformer(kV)
CT_sec = 1.0 #Secondary CT rating
#Calculation
I_FL = MVA*1000/(3**0.5*V_lv) #Full-load current(A)
CT_ratio_33kV = I_FL/CT_sec #CT ratio on 33 kV side
CT_ratio_132kV = (I_FL*V_lv/V_hv)/(CT_sec/3**0.5) #CT ratio on 132 kV side
#Result
print('CT ratio on 33 kV side = %.f : 1 ' %CT_ratio_33kV)
print('CT ratio on 132 kV side = %.f : 1 = %.f√3 : 1 ' %(CT_ratio_132kV,CT_ratio_132kV/3**0.5))