# CHAPTER 2.14: LIGHTNING AND PROTECTION AGAINST OVERVOLTAGES DUE TO LIGHTNING¶

## Example 2.14.1, Page number 382¶

In :
#Variable declaration
RI_072 = 72000.0     #Charactersistic of lightning arrester
Z_c = 500.0          #Surge impedance(ohm)
V = 500.0            #Surge voltage(kV)

#Calculation
#Case(a)
V_a = 2.0*V            #Voltage at the end of line at open-circuit(kV)
ratio_a = V_a/V        #Ratio of voltage when line in open-circuited
#Case(b)
I = V*1000/Z_c         #Surge current(A)
R = RI_072/(I)**0.72   #Resistance of LA(ohm)
ratio_b = R/Z_c        #Ratio of voltage when line is terminated by arrester

#Result
print('Case(a): Ratio of voltages appearing at the end of a line when line is open-circuited = %.f' %ratio_a)
print('Case(b): Ratio of voltages appearing at the end of a line when line is terminated by arrester = %.f' %ratio_b)

Case(a): Ratio of voltages appearing at the end of a line when line is open-circuited = 2
Case(b): Ratio of voltages appearing at the end of a line when line is terminated by arrester = 1


## Example 2.14.2, Page number 384¶

In :
#Variable declaration
rating = 5000.0       #Rating of transformer(kVA)
V_hv = 66.0           #HV voltage(kV)
V_lv = 11.0           #LV voltage(kV)
V = 66.0              #System voltage(kV)
fluctuation = 0.1     #Voltage fluctuations
BIL = 350.0           #BIL for 66kV(kV)
dynamic_ov = 1.3      #Dynamic over-voltage = 1.3*system operating voltage
V_power_freq = 1.5    #Power frequency breakdown voltage of arrester = 1.5*arrester rating(kV)
lower_limit = 0.05    #Margin of lower limit of arrester rating

#Calculation & Result
V_rating = V*(1+fluctuation)*0.8*(1+lower_limit)          #Voltage rating of arrester(kV)
if(round(V_rating,1)==51):
V_rating_choosen = 50.0                               #Arrester rating choosen(kV)
V_discharge = 176.0                                   #Discharge voltage for 50kV arrester(kV)
protective_margin = BIL-V_discharge                   #Protective margin available(kV)
V_power_frequency_bd = V_rating_choosen*V_power_freq  #Power frequency breakdown voltage(kV)
Over_voltage_dynamic = dynamic_ov*V/3**0.5            #Dynamic overvoltage(kV)
if(V_power_frequency_bd>Over_voltage_dynamic):
print('First arrester with rating 50 kV (rms) & discharge voltage 176 kV chosen is suitable')
if(round(V_rating,1)==61):
V_rating_choosen = 60.0                               #Arrester rating choosen(kV)
V_discharge = 220.0                                   #Discharge voltage for 50kV arrester(kV)
protective_margin = BIL-V_discharge                   #Protective margin available(kV)
V_power_frequency_bd = V_rating_choosen*V_power_freq  #Power frequency breakdown voltage(kV)
Over_voltage_dynamic = dynamic_ov*V/3**0.5            #Dynamic overvoltage(kV)
if(V_power_frequency_bd>Over_voltage_dynamic):
print('Second arrester with rating 60 kV (rms) & discharge voltage 220 kV chosen is suitable')
if(round(V_rating,1)==74):
V_rating_choosen = 73.0                               #Arrester rating choosen(kV)
V_discharge = 264.0                                   #Discharge voltage for 50kV arrester(kV)
protective_margin = BIL-V_discharge                   #Protective margin available(kV)
V_power_frequency_bd = V_rating_choosen*V_power_freq  #Power frequency breakdown voltage(kV)
Over_voltage_dynamic = dynamic_ov*V/3**0.5            #Dynamic overvoltage(kV)
if(V_power_frequency_bd>Over_voltage_dynamic):
print('Third arrester with rating 73 kV (rms) & discharge voltage 264 kV chosen is suitable')

Second arrester with rating 60 kV (rms) & discharge voltage 220 kV chosen is suitable