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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 10: PROTECTION OF TRANSMISSION LINE, SHUNT INDUCTORS AND CAPACITORS
// EXAMPLE : 10.1 :
// Page number 647-648
clear ; clc ; close ; // Clear the work space and console
// Given data
G2_per = 70.0 // G2 is fed at 70% distance from A in section AB(%)
X_T = 10.0 // Transformer reactance(%)
zone_1_per = 80.0 // Setting for first zone(%)
zone_2_per = 50.0 // Setting for second zone(%)
CT_ratio = 400.0/5 // CT ratio
PT_ratio = 166000.0/110 // PT ratio
Z_AB = complex(20.0,60.0) // Section AB impedance(ohm)
Z_BC = complex(10.0,25.0) // Section BC impedance(ohm)
MVA = 10.0 // Transformer rating(MVA)
kV_hv = 166.0 // HV side voltage(kV)
kV_lv = 33.0 // LV side voltage(kV)
// Calculations
// Case(i) Without infeed
Z_sec_1 = zone_1_per/100*Z_AB*CT_ratio/PT_ratio // First zone setting(ohm)
Z_BC_hv = Z_BC*(kV_hv/kV_lv)**2 // Z_BC on 166 kV base(ohm)
Z_T = %i*10*X_T*kV_hv**2/(MVA*1000) // Transformer impedance(ohm)
Z_sec_2 = (Z_AB+zone_2_per/100*Z_BC_hv+Z_T)*CT_ratio/PT_ratio // Second zone setting(ohm)
Z_sec_3 = (Z_AB+Z_BC_hv+Z_T)*CT_ratio/PT_ratio // Third zone setting(ohm)
// Case(ii) With infeed
I_AB = 2.0 // Current ratio
Z_zone_1 = (G2_per/100*Z_AB)+I_AB*(zone_1_per-G2_per)/100*Z_AB // First zone impedance(ohm)
Z_1 = Z_zone_1*CT_ratio/PT_ratio // First zone setting(ohm)
Z_zone_2 = (G2_per/100*Z_AB)+I_AB*(((zone_1_per-zone_2_per)/100*Z_AB)+(zone_2_per/100*Z_BC_hv)+Z_T) // Second zone impedance(ohm)
Z_2 = Z_zone_2*CT_ratio/PT_ratio // Second zone setting(ohm)
under_reach = Z_zone_2-(Z_AB+zone_2_per/100*Z_BC_hv+Z_T) // Under-reach due to infeed(ohm)
Z_zone_3 = (G2_per/100*Z_AB)+I_AB*(((zone_1_per-zone_2_per)/100*Z_AB)+Z_BC_hv+Z_T) // Third zone impedance(ohm)
Z_3 = Z_zone_3*CT_ratio/PT_ratio // Third zone setting(ohm)
// Results
disp("PART III - EXAMPLE : 10.1 : SOLUTION :-")
printf("\nCase(i) Without infeed:")
printf("\n First zone relay setting = (%.2f + %.2fj) ohm", real(Z_sec_1),imag(Z_sec_1))
printf("\n Second zone relay setting = (%.1f + %.1fj) ohm", real(Z_sec_2),imag(Z_sec_2))
printf("\n Third zone relay setting = (%.1f + %.1fj) ohm", real(Z_sec_3),imag(Z_sec_3))
printf("\nCase(ii) With infeed:")
printf("\n First zone relay setting = (%.3f + %.2fj) ohm", real(Z_1),imag(Z_1))
printf("\n Second zone relay setting = (%.1f + %.1fj) ohm", real(Z_2),imag(Z_2))
printf("\n Third zone relay setting = (%.1f + %.fj) ohm\n", real(Z_3),imag(Z_3))
printf("\nNOTE: ERROR: Calculation mistake in Z_BC. Hence, changes in the obtained answer from that of textbook")
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