Please change the values in red
1.0
Highest system voltage V 132 kV
1.2 Short circuit current Isc 31.5 KA
1.3 Duration of fault, t Tkr 1 Sec
1.4 System frequency f 50 Hz
1.5 Design ambient temperature T 30 O
C
2.0 Busbar data
2.1 Busbar used Rabbit
2.2 Outer diameter Do 10.05 mm
Inner diameter Di - mm
2.4 Area of Cross-section A 61.78 mm2
2.5 Moment of Inertia J -
2.6 Weight per unit length of conductor m' 0.2139 Kg/m
2.7 Section modulus Z -
2.8 Young's modulus E 68900 N/mm2
2.9 yield point Rρ0.2 - N/mm2
2.10 ultimate bending stress of Al. Alloy 0 -
2.11 Initial temperature of busbar before short circuTo 75 o
C
2.12 Final temperature of busbar before short circuiTm 200 o
C
2.13 Allowable temperature rise over an ambient of 500C 25
2.14 Pressure in atmosphere (P = 1.0 for atmospheric pressure) 1
2.15 Minimum Velocity of wind in feet per second 2
2.16 Generator Transformer capacity = 20
2.17 Number of generator transformers = 4
765 Mole
400 Squirrel
220 Gopher
132 Weasel
66 Fox
33 Farret
50 Mink
40 Skunk
31.5 Beaver
25 hors
Recoon
1 otter
3 cat
hare
dog
hyena
leopard
coyote
tiger
wolf
lynx
panther
lion
Boar
Goat
Sheep
Antelope
Bison
Deer
Zebra
Iik
Camel
Moose
ACSR Conductor Sizing Calculations for 132 kV Switchyard
ACSR conductor Design Calculation
1.0 System data
1.1 Highest system voltage V 132 kV
1.2 Short circuit current Isc 31.5 KA
1.3 Duration of fault, t Tkr 1 Sec
1.4 System frequency f 50 Hz
1.5 Design ambient temperature T 30 O
C
2.0 Busbar data
2.1 Busbar used Rabbit ACSR
2.2 Outer diameter Do 10.05 mm
2.3 Inner diameter Di - mm
2.4 Area of Cross-section A 61.78 mm2
2.5 Moment of Inertia J -
2.6 Weight per unit length of conductor m' 0.2139 Kg/m
2.7 Section modulus Z -
2.8 Young's modulus E 68900 N/mm2
2.9 yield point Rρ0.2 - N/mm2
2.10 ultimate bending stress of Al. Alloy - N/mm2
2.11 Initial temperature of busbar before short circuit, To 75 o
C
2.12 Final temperature of busbar before short circuit, Tm 200 o
C
3.0 Reference
a)
b) a) IEC 865 - Edition 3.0, 2011- Short circuit currents - calculation of effects
c) b) IEC 909 - short circuit current calculations in three phase AC system.
d) c) Electrical transmission & distribution reference book by station engineers of the
westinghouse Electric corporation, chapter-3, page No. 48
d) Indal Aluminium Busbar book
ACSR conductor sizing calculation for 132kV AIS substation
1 Check for maximum continuous current carrying capacity of single zebra ACSR conductor
Note:-
As per electrical transmission & Distribution reference book by central Station Engineers of the Westinghouse Electric Corporation, Chapter-3 Page 48
Input data:
75
Allowable temperature rise over an ambient of 50 C 0
25 o
C
AC resistance at 750 C 0.0007761 Ohms/m
Minimum wind velocity 0.61 2
The max. continuous current carryingcapacity is calculated from the formula:
I2 x R = (Wc + Wr) x A (watts)
To find convectional Loss (Wc)
0.0128 𝑋 √(𝑃 𝑥 𝑉 𝑋 ∆𝑡)
Wc = Watts/ sq. inch
𝑇𝑎0.123 𝑋 √𝑑
where,
P = Pressure in atmosphere (P = 1.0 for atmospheric pressure)
= 1
V = Minimum Velocity of wind in feet per second
= 2 ft/sec
Ta = Average of absolute temperature of conductor & air in (Degrees Kelvin)
= 273 + 75 = 348 K
= 274 + 50 = 323 K
Ta = (348 + 323)/2 = 335.5 K
d = outside diameter of conductor in inches.
= 0.396 inch
∆t = Temperature rise in degree C
= 25 0C
Therefore,
Wc = 0.3518 Watts/sq. inch
To find radiation loss (Wr)
Wr = 36.8 x E[(T/1000)4 - (To/1000)4] Watts/sq. inch
where,
E = Relative emissivity of conductor surface.
(E=1.0 for "black body", or 0.5 for average oxidized copper)
= 0.5
T = Absolute temperature of conductor in degree Kelvin.
= 273 + 75
= 348 K
To = Absolute temperature of surroundings in degree Kelvin.
= 273 + 50
= 323 K
Wr = 0.0696 Watts/sq. inch
To find AC resisitance "R" at 75 oC:
R = AC resistance at 75oC
0.0007761 Ohm/m
0.0002366 Ohm/Ft
To find continuous current rating of the ZEBRA ACSR Conductor :-
I2 x R = (Wc + Wr) x A (watts)
where,
I = Conductor current in amperes
A = Conductor surface area in sq. inch per ft length
A = ∏*d*l
= 14.91 Sq. inch
Therefore,
I = √{(𝑊𝑐 + Wr ).A}
√𝑅
= 163.00 Amps
Current Rating
For 132 kV jack bus :
Conductor used = Single"ZEBRA" ACSR
Step-1 :
Continuous Current carrying of on 25 oC temp. rise over 50oC amb. As per calculations
= 162.997 Amps
Hence, Continuous current carrying of on 25 oC temp. rise over 50oC amb
= 162.997 Amps
Step-2 :
To find maximum Continuous current:-
Full load current for 20 MVA GT transformer derived by the formula,
IL = MVA
√3xkV
System Nominal Voltage, Vs = 132 kV
Lowest system voltage (-10%) = 118.8 kV
Generator Transformer capacity = 20 MVA
Hence, IL = 1x20x106
√3x118.8x103
= 97.31 Amps
For 20% Overload consideration = 116.77 Amps
162.997 > 116.77
b) For 132 kV Main Bus :
Conductor used = SINGLE "ZEBRA" ACSR
Step-1:
Continuous current carrying of on 25 oC temp rise over 50oC amb. As per calculation.
= 163.000 X 1
= 162.997 Amps
Hence, continuous current carrying of on 25 oC temp rise over 50oC amb.
= 162.997 Amps
Step-2:
C) To find Maximum Continuous Current :-
Full oad current for 4x20 MVA GT transformer derived by the formula,
IL = MVA
√3 x kV
System Nominal Voltage, Vs = 132 kV
Lowest system voltage (-10%) = 118.8 kV
Generator Transformer capacity = 20 MVA
Number of generator transformers = 4
Hence, IL = 4X20x10^6
√3x119x10^3
= 389.25 Amps
For 20% Overload consideration = 467.10 Amps
162.997 > 467.10
Increase the condcutor Size
Hence, the selected single ZEBRA ACSR conductor's carrying capacity is greater than the required. Hence, safe.
4.0 Check for Short circuit withstand rating of "Zebra" ACSR conductor
For Zebra ACSR Conductor:
a) Conductor Temperature at the beginning of a short Circuit, T o = 75 oC
b) Conductor Temperature at the end of a short circuit, T m = 200 oC
(As per IEC 865-1:2011, table6, page. No:43- Recommended highest temperatures for mechanically stressed conductors during a short-circuit)
The rated short -circuit withstand current density for 1 sec. S thr is given by
1/√𝑇𝐾𝑟 √( 〖 (𝐾20𝑐 𝜌)/𝛼20 ln 〗〖 (1+𝛼20(𝜗𝑒
= −20 𝐶))/(1+𝛼20(𝜗𝑏 −20 𝐶)) 〗 )
𝑜 𝑜
Sthr As per IEC 865-1: 2011, page no. 50
with the following data of material
Specific conductivity at 20oC, K20 = 34800000 1/(Ωm)
Specific thermal heat capacity ACSR conductor, C = 910 J/(Kg K)
Specific mass (Density) of ACSR conductor, ρ = 2700 Kg/m3
Tempareture Coefficient, α20 = 0.004 O
C
Tkr = 1
√((𝐾20𝑐 𝜌)/𝛼20 ) = 2.13759E+016
ln(1+𝛼20(𝜗𝑒 −20𝑜𝐶))/(1+𝛼20(𝜗𝑏 −20𝑜𝐶)))
= 0.343473432080197
Ksc = 85685784.9167706 Amp/m2
= 85.69 Amp/mm2
Sthr = Ksc/√Tkr
= 85.686 Amp/mm2
Rated short-circuit withstand current density of single "ZEBRA" ACSR conductor for 1 sec. Sth is given by
= 85.000 Amp/mm2 Refer Annexure-3
Thermal equivalent short-circuit withstand of single"ZEBRA" ACSR conductor for 1 sec. Sth is given by
= 5251.3 A
= 5.25 KA
Since, 5 > 32 Hence Safe
3.2786885
Refer Annexure-3
