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// A Texbook on POWER SYSTEM ENGINEERING
// A.Chakrabarti, M.L.Soni, P.V.Gupta, U.S.Bhatnagar
// DHANPAT RAI & Co.
// SECOND EDITION
// PART III : SWITCHGEAR AND PROTECTION
// CHAPTER 1: SYMMETRICAL SHORT CIRCUIT CAPACITY CALCULATIONS
// EXAMPLE : 1.3 :
// Page number 468-469
clear ; clc ; close ; // Clear the work space and console
// Given data
kVA_a = 40000.0 // Capacity of transmission line(kVA)
x_a = 10.0 // Reactance of transmission line(%)
kVA_b = 20000.0 // Capacity of transmission line(kVA)
x_b = 5.0 // Reactance of transmission line(%)
kVA_c = 50000.0 // Capacity of transmission line(kVA)
x_c = 20.0 // Reactance of transmission line(%)
kVA_d = 30000.0 // Capacity of transmission line(kVA)
x_d = 15.0 // Reactance of transmission line(%)
kVA_e = 10000.0 // Capacity of transmission line(kVA)
x_e = 6.0 // Reactance of transmission line(%)
kVA_T1 = 150000.0 // Capacity of transformer(kVA)
x_T1 = 10.0 // Reactance of transformer(%)
kVA_T2 = 50000.0 // Capacity of transformer(kVA)
x_T2 = 8.0 // Reactance of transformer(%)
kVA_T3 = 20000.0 // Capacity of transformer(kVA)
x_T3 = 5.0 // Reactance of transformer(%)
kVA_GA = 150000.0 // Capacity of generator(kVA)
x_sA = 90.0 // Synchronous reactance of generator(%)
x_tA = 30.0 // Transient reactance of generator(%)
kVA_GB = 50000.0 // Capacity of generator(kVA)
x_sB = 50.0 // Synchronous reactance of generator(%)
x_tB = 17.5 // Transient reactance of generator(%)
V = 33.0 // Feeder voltage(kV)
// Calculations
kVA_base = 200000.0 // Base rating(kVA)
X_a = kVA_base/kVA_a*x_a // Reactance(%)
X_b = kVA_base/kVA_b*x_b // Reactance(%)
X_c = kVA_base/kVA_c*x_c // Reactance(%)
X_d = kVA_base/kVA_d*x_d // Reactance(%)
X_e = kVA_base/kVA_e*x_e // Reactance(%)
X_T1 = kVA_base/kVA_T1*x_T1 // Reactance(%)
X_T2 = kVA_base/kVA_T2*x_T2 // Reactance(%)
X_T3 = kVA_base/kVA_T3*x_T3 // Reactance(%)
X_sA = kVA_base/kVA_GA*x_sA // Synchronous reactance(%)
X_tA = kVA_base/kVA_GA*x_tA // Transient reactance(%)
X_sB = kVA_base/kVA_GB*x_sB // Synchronous reactance(%)
X_tB = kVA_base/kVA_GB*x_tB // Transient reactance(%)
X_eq_ab = X_a+X_b // Equivalent reactance of transmission lines a & b(%)
X_eq_abc = X_eq_ab*X_c/(X_eq_ab+X_c) // Equivalent reactance of transmission line c with series combination of a & b(%)
X_CF = (X_eq_abc+X_sA)*X_d/(X_eq_abc+X_sA+X_d) // Total reactance b/w sub-station C & F(%)
// Case(i)
X_tr_genA = kVA_base/kVA_GA*x_tA // Reactance in transient state of generator A(%)
X_T1_tr = kVA_base/kVA_T1*x_T1 // Reactance in transient state of transformer T1(%)
X_CF_tr = X_CF // Total reactance in transient state b/w sub-station C & F(%)
X_eq_tAF = X_tr_genA+X_T1_tr+X_CF_tr // Equivalent transient reactance from generator A to substation F(%)
X_tr_genB = kVA_base/kVA_GB*x_tB // Reactance in transient state of generator B(%)
X_T2_tr = kVA_base/kVA_T2*x_T2 // Reactance in transient state of transformer T2(%)
X_eq_tBF = X_tr_genB+X_T2_tr // Equivalent transient reactance from generator B to substation F(%)
X_eq_tF = X_eq_tAF*X_eq_tBF/(X_eq_tAF+X_eq_tBF) // Equivalent transient reactance upto substation F(%)
X_eq_tfault = X_eq_tF+X_T3 // Equivalent transient reactance upto fault point(%)
kVA_t_sc = kVA_base/X_eq_tfault*100 // Transient short circuit kVA(kVA)
I_t_sc = kVA_t_sc/(3**0.5*V) // Transient short circuit rms current(A)
I_t_sc_peak = 2**0.5*I_t_sc // Peak value of transient short circuit current(A)
// Case(ii)
X_S_genA = kVA_base/kVA_GA*x_sA // Reactance in steady state of generator A(%)
X_eq_SAF = X_S_genA+X_T1+X_CF // Equivalent steady state reactance from generator A to substation F(%)
X_eq_SBF = X_sB+X_T2 // Equivalent steady state reactance from generator B to substation F(%)
X_eq_SF = X_eq_SAF*X_eq_SBF/(X_eq_SAF+X_eq_SBF) // Equivalent steady state reactance upto substation F(%)
X_eq_Sfault = X_eq_SF+X_T3 // Equivalent steady state reactance upto fault point(%)
kVA_S_sc = kVA_base/X_eq_Sfault*100 // Steady state short circuit kVA(kVA)
I_S_sc = kVA_S_sc/(3**0.5*V) // Sustained short circuit rms current(A)
I_S_sc_peak = 2**0.5*I_S_sc // Peak value of sustained short circuit current(A)
// Results
disp("PART III - EXAMPLE : 1.3 : SOLUTION :-")
printf("\nCase(i) : Transient short circuit current at X = %.f A (peak value)", I_t_sc_peak)
printf("\nCase(ii): Sustained short circuit current at X = %.f A (peak value) \n", I_S_sc_peak)
printf("\nNOTE: Changes in the obtained answer from that of textbook is due to more precision here")
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