# CHAPTER 2.15: INSULATION CO-ORDINATION¶

## Example 2.15.1, Page number 398-399¶

In [1]:
#Variable declaration
L = 30.0          #Height of arrester located(m)
BIL = 650.0       #BIL(kV)
de_dt = 1000.0    #Rate of rising surge wave front(kV/µ-sec)
V = 132.0         #Transformer voltage at HV side(kV)
E_a = 400.0       #Discharge voltage of arrester(kV)
v = 3.0*10**8     #Velocity of surge propagation(m/sec)

#Calculation
E_t = E_a+(2.0*de_dt*L/300)   #Highest voltage the transformer is subjected(kV)

#Result
print('Highest voltage to which the transformer is subjected, E_t = %.f kV' %E_t)

Highest voltage to which the transformer is subjected, E_t = 600 kV


## Example 2.15.2, Page number 399¶

In [1]:
#Variable declaration
V_hv = 132.0      #Voltage at the HV side of transformer(kV)
V_lv = 33.0       #Voltage at the LV side of transformer(kV)
V = 860.0         #Insulator allowable voltage(kV)
Z = 400.0         #Line surge impedance(ohm)
BIL = 550.0       #BIL(kV)

#Calculation
V_rating_LA = V_hv*1.1*0.8                 #Voltage rating of LA(kV)
E_a = 351.0                                #Discharge voltage at 5 kA(kV)
I_disc = (2*V-E_a)*1000/Z                  #Discharge current(A)
L_1 = 37.7                                 #Separation distance in current b/w arrester tap and power transformer tap(m)
dist = 11.0                                #Lead length from tap point to ground level(m)
de_dt = 500.0                              #Maximum rate of rise of surge(kV/µ-sec)
Inductance = 1.2                           #Inductance(µH/metre)
di_dt = 5000.0                             #di/dt(A/µ-sec)
V_tr_terminal = E_d+2*de_dt*L_1/300        #Voltage at transformer terminals(kV)
E_t = BIL/1.2                              #Highest voltage the transformer is subjected(kV)
L = (E_t-E_a)/(2*de_dt)*300                #Distance at which lightning arrester located from transformer(m)
L_lead = (E_t-E_a*1.1)/(2*de_dt)*300       #Distance at which lightning arrester located from transformer taken 10% lead drop(m)

#Result
print('Rating of L.A = %.1f kV' %V_rating_LA)
print('Location of L.A, L = %.f m' %L)
print('Location of L.A if 10 percent lead drop is considered, L = %.1f m' %L_lead)
print('Maximum distance at which a ligtning arrester is usually connected from transformer is %.f-%.f m' %(L-2,L+3))

Rating of L.A = 116.2 kV
Location of L.A, L = 32 m
Location of L.A if 10 percent lead drop is considered, L = 21.7 m
Maximum distance at which a ligtning arrester is usually connected from transformer is 30-35 m


## Example 2.15.3, Page number 400¶

In [1]:
#Variable declaration
V = 138.0           #Voltage(kV)
Z = 400.0           #Surge impedance(ohm)
L = 15.0            #Distance of surge diverter to transformer(m)
E = 960.0           #Maximum surge(kV)
L_line = 60.0       #Distance of surge diverter to line entrance(m)
margin_5 = 0.25     #Protective margin b/w BIL & protective level
margin_6 = 0.15     #Margin with surge diverter

#Calculation
V_rating_LA = V*1.1*0.8                                              #Voltage rating of LA(kV)
V_rated = 120.0                                                      #Chosen rated voltage(kV)
max_spark_over = V_rated*3.1                                         #Front of wave spark-over,max(kV)
max_full_spark_over = V_rated*2.8                                    #Full wave spark-over,max(kV)
max_switch_spark_over = 3.0*V_rated                                  #Switching surge spark over,max(kV)
E_d = max_switch_spark_over                                          #Maximum discharge voltage(kV)
I_disch = (2*E-E_d)/Z                                                #Discharge current(kA)
E_d1 = E_d+V_LA_lead                                                 #Effective discharge voltage(kV)
de_dt = 480.0                                                        #Maximum rate of rise of surge(kV/µ-sec)
V_tr_terminal = E_d1+2*de_dt*L/300                                   #Voltage at transformer terminals(kV)
BIL_calc = V_tr_terminal*(1+margin_5)                                #BIL calculated(kV)
BIL_1 = 550.0                                                        #Standard BIL(kV)
max_switch_spark_over_margin = max_switch_spark_over*(1+margin_6)    #Switching surge spark over,max(kV)
distance_effect = 2.0*de_dt*L_line/300                               #Distance effect for line entrance(kV)
V_peak_entrance = E_d1+distance_effect                               #Voltage at peak entrance(kV)

#Result
print('Appropriate BIL of transformer and switchgear = 650 kV')

Appropriate BIL of transformer and switchgear = 650 kV