400kV Switchyard Calculations

Ref.

(4)-G77700-S0019-L061-A

Project:

Gilgel Gibe – II PROJECT

ETHIOPIA

Description:

400 kV SWITCHYARD

DESIGN

REPORT’s & CALCULATION’s

Subject:

Report on Calculations for Determination of

Cantilever Strength of Bus Post Insulators

Note:

This report establishes the sizing of bus post insulators for 400kV switchyard

on the basis of cantilever strength.

BPI Selection Design Report : Cantilever Strength Calculation

Page: 3 of 7

Handling:

Unrestricted

Siemens Power Engineering Pvt. Ltd.

The reproduction, transmission or use of this document or its contents is not permitted without express written authority. Offenders will be liable for damages. All rights, including rights created by patent grant or registration of a utility model or design, are reserved.

(4)-G77700-S0019-L061-A

Contents

page

1.

Introduction ... 4

2.

System Data... 4

3.

Conductor Data ... 4

4.

Bus Post Insulator data ... 5

5.

Attachments ... 6

6.

Conclusion ... 6

BPI Selection Design Report : Cantilever Strength Calculation

Page: 4 of 7

Handling:

Unrestricted

Siemens Power Engineering Pvt. Ltd.

The reproduction, transmission or use of this document or its contents is not permitted without express written authority. Offenders will be liable for damages. All rights, including rights created by patent grant or registration of a utility model or design, are reserved.

(4)-G77700-S0019-L061-A

1 Introduction

The rigid bus in out-door substation is primarily supported on Bus Post Insulators. These bus

post insulators are hence subjected to sustain all types of stresses on bus conductor owing to

electrically and mechanically originated forces.

The principal forces on the bus post insulator are as follows –

a. Short circuit current force on the bus conductor.

b. Wind force on the bus conductor.

c. Wind force on the insulator stack.

d. Weight of the bus conductor span supported by the bus post insulator.

Since the forces on the bus-conductors are transmitted to the bus post insulators, the strength of

the insulator must be considered. With various bus configurations, insulators may be required to

withstand cantilever, compressive, tensile and torsional forces. However, only the cantilever

force, which is a function of the effective conductor span length supported by the bus post

insulator, have been regarded significant and considered for design.

2 System data

400kV AC Switchyard

Nominal System Voltage

400 kV

System Frequency

50 Hz

Short Circuit Fault Current

31.5 kA

Duration of Fault Current

1 sec

Maximum Wind Pressure

700 N/m

2

Altitude above sea level

>1500 m

3 Conductor Data

Rigid Conductor

i) 250/6mm Aluminum Tube (AlMgSi0.5F25)

Outer Diameter

250 mm

BPI Selection Design Report : Cantilever Strength Calculation

Page: 5 of 7

Handling:

Unrestricted

Siemens Power Engineering Pvt. Ltd.

The reproduction, transmission or use of this document or its contents is not permitted without express written authority. Offenders will be liable for damages. All rights, including rights created by patent grant or registration of a utility model or design, are reserved.

(4)-G77700-S0019-L061-A

Weight

12.4 Kg/m

Weight of Damping Material (Twin 954 MCM Cardinal ACSR)

1829.8 Kg/kM

ii) 120/8mm Aluminum Tube (AlMgSi0.5F25)

Outer Diameter

120 mm

Wall thickness

8 mm

Weight

7.6 Kg/m

Weight of Damping Material (Single 954 MCM Cardinal ACSR)

1829.8 Kg/kM

iii) 120/6mm Aluminum Tube (AlMgSi0.5F25)

Outer Diameter

120 mm

Wall thickness

6 mm

Weight

5.8 Kg/m

Weight of Damping Material (Single 954 MCM Cardinal ACSR)

1829.8 Kg/kM

Common for all tubes specified above

Young’s Modulus

70000 N/mm

2

4 Bus Post Insulator data

i) C8-1550

Height of Insulator Stack

3350 mm

Maximum Width

310 mm

Minimum Width

140 mm

Weight of Insulator

349 Kg

Cantilever Strength (designated by manufacturer)

800 daN

i) C6-1550

Height of Insulator Stack

3350 mm

Maximum Width

290 mm

BPI Selection Design Report : Cantilever Strength Calculation

Page: 6 of 7

Handling:

Unrestricted

Siemens Power Engineering Pvt. Ltd.

The reproduction, transmission or use of this document or its contents is not permitted without express written authority. Offenders will be liable for damages. All rights, including rights created by patent grant or registration of a utility model or design, are reserved.

(4)-G77700-S0019-L061-A

Weight of Insulator

291 Kg

Cantilever Strength (designated by manufacturer)

600 daN

i) C12.5-1550

Height of Insulator Stack

3350 mm

Maximum Width

360 mm

Minimum Width

160 mm

Weight of Insulator

400 Kg

Cantilever Strength (designated by manufacturer)

1250 daN

Busbar Selection

The following types of tubular busbar has been considered in the design :

x 250/6 mm AlMgSi0.5F25 Tubular Bus bar to serve as Main Bus Conductor.

x 120/8 mm AlMgSi0.5F25 Tubular Bus bar to serve as Equipment Bus Conductor at the

Bus Coupling feeder.

x 120/6 mm AlMgSi0.5F25 Tubular Bus bar to serve as Equipment Bus Conductor at the

Transformer & Line feeders.

5 Attachments

Attachment-1: Calculation of Cantilever Strength of Bus Post Insulator supporting the Main Bus

Attachment-2: Calculation of Cantilever Strength of Bus Post Insulator supporting the Equipment

Bus at Coupling Bay

Attachment-3: Calculation of Cantilever Strength of Bus Post Insulator supporting the Equipment

Bus at Transformer & OHL Feeders.

6 Conclusion

1. The required Cantilever Strength of the C12.5-1550 for supporting the maximum bus span(24 m)

of the Main Bus is 995.67 daN, whereas the cantilever strength published by the manufacturer is

1250 daN. Thus the design is safe and Bus Post Insulators of C12.5-1550 type may be used for

supporting the Main Bus conductor.

2. The required Cantilever Strength of the C6-1550 for supporting the maximum bus span(12 m) of

the Equipment Bus at Coupling Bay is 281.23 daN, whereas the cantilever strength published by

BPI Selection Design Report : Cantilever Strength Calculation

Page: 7 of 7

Handling:

Unrestricted

Siemens Power Engineering Pvt. Ltd.

The reproduction, transmission or use of this document or its contents is not permitted without express written authority. Offenders will be liable for damages. All rights, including rights created by patent grant or registration of a utility model or design, are reserved.

(4)-G77700-S0019-L061-A

the manufacturer is 600 daN. Thus the design is safe and Bus Post Insulators of C6-1550 type

may be used for supporting the Equipment Bus conductor at the Coupling Bay.

3. The required Cantilever Strength of the C6-1550 for supporting the maximum bus span (12 m)

of the Equipment Bus at Transformer & OHL Feeders is 249.28 daN, whereas the cantilever

strength published by the manufacturer is 600 daN. Thus the design is safe and Bus Post

Insula-tors of C6-1550 type may be used for supporting the Equipment Bus conductor at Transformer &

OHL Feeders.

7 References

1. IEEE Std 605 : 1987 IEEE Guide for Design of Substation Rigid-Bus Structures.

2. Technical Data sheet for Aluminum Alloy Tubular Conductor: Manufacturer – Corus.

3. Technical Data sheet for Bus Post Insulator: Manufacturer – Porzellanfabrik Frauenthal

Insulators.

S

(4)-G77700-S0019-L062-A

ATTACHMENT-1

SYSTEM VOLTAGE ( IN KV. ): 400 FAULT LEVEL( IK3 ) ( IN KA.): 31.5

TUBULAR BUS CONDUCTOR :

a) Size : AlMgSi0.5F25 250 mm c) Thickness : 6 mm d) Weight 12.4 Kg/m e) conductor Young's Modulus 7.00E+10 N/m2 f) Conductor spacing 6 m g) Max Allowable stress 115 N/mm2

11.72 Kg/mm2 h) Max. Span 24 m

i) Weight of Damper Material 3.66 Kg/m (Twin 954 CARDINAL ACSR Conductor)

INSULATOR DATA (Type:C12,5-1550):

a. Height 3.35 m b. Max. Width 0.36 m c. Min. Width 0.16 m d Bus Cen. Line

height above Insulator 0.215 m e. Weight 400 Kg

Max. Wind Pressure(Pmax) = 700 N/m 2

(as per technical specification) Ambient air density(d) = 0.613 Kg/m3

Wind Velocity(V) = (Pmax/d) 1/2

m/s = 33.79 m/s Now,

Coss sectional moment of inertia of the tube (J) = = (S/64 ).(Do 4

- Di 4

) where,

DO = Outer Diameter of Conductor = 250 mm

Di = Inner Diameter of Tube = 238 mm

Therefore, J = 34231262.64 mm4

= 82.24027953 in4 Sectional Modulus of the tube S = J/(DO/2) mm

3

= 273850.1011 mm3 = 16.71125822 in3

Conductor Wind Force (FW) = 2.132 x 10 -4

CDKZGFV 2

(DO+2r1) lbf/ft (Cl. 10. of IEEE:605)

Where

DO = Outer Diameter of Conductor 9.84 inch

r1 = Radial Ice thickness. = 0 inch

CD = Drag coefficient (Ref. Table 1 of IEEE:605) = 1

KZ = Height and exposure factor (Cl. 10.2 of IEEE:605) = 1

GF = Gust factor (Cl. 10.3 of IEEE:605) = 1.3

V =Wind speed at 30ft. above ground = 33.79 m/s = 75.59 mi/h Hence, FW = 15.59 lbf/ft

Short Circuit Current Unit Force (FSC) = 27.6* ISC2 /107(D) lbf/ft

CALCULATION OF CANTILEVER STRENGTH OF BUS POST INSULATOR SUPPORTING THE MAIN BUS

b) Outer dia.

Calculation for conductor Wind Force:

Calculation for Short Circuit Current Unit Force:

(For Round conductor)

Gilgel Gibe II Hydroelectric Project

Page 1 OF 3

S

(4)-G77700-S0019-L062-A

ATTACHMENT-1

ISC = Symmettrical short circuit current = 31500 A

D = Conductor spacing centre to centre = 236.22 inch * = Constant based on type of short circuit and = 0.866

conductor location (Ref. Table 2 of IEEE:605) Hence, FSC = 10.04 lbf/ft

Total bus unit weight (FG) = FC + FI+ FD lbf/ft

FC = Conductor unit weight = 8.33 lbf/ft

FD = Damping material unit weight = 2.46 lbf/ft

FI = Ice Unit weight = 0 lbf/ft

Hence, FG = 10.79 lbf/ft

Calculation for Insulator Strength

a. Calculation for Bus Short circuit Current Force: FSB = LE.FSC lbf

FSB = Bus Short Circuit Force transmitted to bus support fitting

LE = Effective Bus span length = 78.74 ft

FSC = Short Circuit Current Unit Force = 10.04 lbf/ft

Now, for a Rigid Bus Section of Equipment connection in a typical Line bay

across the Main Bus (as shown in the figure alongside) P P P LE = 1/2(L1+L2) (Refer Table 5 of IEEE-605)

= 78.74016 ft

Adjescent Bus Span (L1) = 24 m

= 78.74 ft Adjescent Bus Span (L2) = 24 m

= 78.74 ft 24m 24m Therefore FSB = 790.55 lbf

L1 L2

b. Calculation for Bus Wind Force : Fig 1

FWB = LE.FW lbf

Where,

FWB = Bus Wind force transmitted to bus support fitting

LE = Effective Bus span length = 78.74 ft

FW = Wind unit force on the bus = 15.59 lbf/ft

Therefore FWB = 1227.38 lbf

c. Calculation for Insulator wind force: FWI = 1.776 x 10 -5 CDKZGFV 2 (Di+2r1)Hi lbf Where,

FWI = Wind Force on Insulator

Hi = Insulator Height = 131.89 Inch

Di = Effective insulator diameter

= (D1+D2)/2 = 10.2362 inch

D1 = Max. Insulator Width = 14.1732 inch

D2 = Min. Insulator Width = 6.2992 inch

BPI BPI BPI

Calculation for Gravitational Force:

Gilgel Gibe II Hydroelectric Project

S

(4)-G77700-S0019-L062-A

ATTACHMENT-1

r1 = Radial Ice thickness = 0 inch

CD = Drag coefficient = 1 (For 'round conductor' as per Table 1 of IEEE:605)

KZ = Height and exposure factor = 1(as per Cl. 10.2 of IEEE:605)

GF = Gust factor = 1.3 (as per Cl. 10.3 of IEEE:605)

V =Wind speed at 30ft. above ground = 33.79 m/s = 75.59 mi/h Therefore FWI = 178.11 lbf

Calculation for Total Insulator Cantilever load

FIS = K1 [ FWI/2 + {(Hi+Hf)/Hi} FWB] + K2 [{(Hi+Hf)/Hi} FSB] lbf

FIS = Total Cantilever load acting at the end of Insulator

FWI = Wind force on the insulator in lbf = 178.11 lbf

FSB = Bus Short Circuit Force transmitted to bus support fitting = 790.55 lbf

FWB = Bus Wind force transmitted to bus support fitting = 1227.38 lbf

Hi = Insulator Height = 131.89 inch

Hf = Bus Cen. Height above Insulator = 8.46 inch

K1 = Overload Factor applied to wind force = 1

K2 = Overload Factor applied to short circuit force = 1

Therefore FIS = 2236.49 lbf

Now

Effective weight of bus transmitted to bus support fitting FGB = LE.FG lbf

where,

LE = Effective Bus span length = 78.74 ft

FG = Total Bus Unit Weight = 10.79 lbf/ft

Therefore FGB = 849.83 lbf

Natural Frequency of the Insulator with effective weight of the conductor span : fi = (1/2S) [Ki g / (0.226FGI + FGB)]

1/2

where,

Ki = Insulator cantilever Spring Constant = 1 lbf/inch

g = gravitional constant = 386 inch/s2 FGI = Weight of the insulator = 881.85 lbf

FGB = Effective weight of bus transmitted to bus support fitting = 849.83 lbf

Therefore fi = 0.10 Hz

As fi < 50Hz => K2 = 1 (Refer Cl. No. 13.2 of IEEE: 605)

Cantilever Load on the Support Insulator FIS (Eqp) = 1015.37 Kgf

(in the direction of the Equipment Connection)

=> Reqiured cantilever Strength of the Supporting Insulator = 995.67 daN

Gilgel Gibe II Hydroelectric Project

S

(4)-G77700-S0019-L061-A

ATTACHMENT-2

SYSTEM VOLTAGE ( IN KV. ): 400 FAULT LEVEL( IK3 ) ( IN KA.): 31.5

TUBULAR BUS CONDUCTOR :

a) Size : AlMgSi0.5F25 120 mm c) Thickness : 8 mm d) Weight 7.6 Kg/m e) conductor Young's Modulus 7.00E+10 N/m2 f) Conductor spacing 6.5 m g) Max Allowable stress 115 N/mm2

11.72 Kg/mm2 h) Max. Span 12 m

i) Weight of Damper Material 1.83 Kg/m (Single 954 CARDINAL ACSR Conductor)

INSULATOR DATA (Type:C6-1550):

a. Height 3.35 m b. Max. Width 0.29 m c. Min. Width 0.13 m d Bus Cen. Line

height above Insulator 0.15 m e. Weight 291 Kg

Max. Wind Pressure(Pmax) = 700 N/m 2

(as per technical specification) Ambient air density(d) = 0.613 Kg/m3

Wind Velocity(V) = (Pmax/d) 1/2

m/s = 33.79 m/s Now,

Coss sectional moment of inertia of the tube (J) = = (S/64 ).(Do4 - Di4)

where,

DO = Outer Diameter of Conductor = 120 mm

Di = Inner Diameter of Tube = 104 mm

Therefore, J = 4433981.44 mm4 = 10.6525978 in4 Sectional Modulus of the tube S = J/(DO/2) mm

3

= 73899.69067 mm3 = 4.509608754 in3

Conductor Wind Force (FW) = 2.132 x 10 -4

CDKZGFV 2

(DO+2r1) lbf/ft (Cl. 10. of IEEE:605)

Where

DO = Outer Diameter of Conductor 4.72 inch

r1 = Radial Ice thickness. = 0 inch

CD = Drag coefficient (Ref. Table 1 of IEEE:605) = 1

KZ = Height and exposure factor (Cl. 10.2 of IEEE:605) = 1

GF = Gust factor (Cl. 10.3 of IEEE:605) = 1.3

V =Wind speed at 30ft. above ground = 33.79 m/s = 75.59 mi/h Hence, FW = 7.48 lbf/ft

Short Circuit Current Unit Force (FSC) = 27.6* ISC2 /107(D) lbf/ft

CALCULATION OF CANTILEVER STRENGTH OF BUS POST INSULATOR SUPPORTING THE EQUIPMENT BUS

b) Outer dia.

Calculation for conductor Wind Force:

Calculation for Short Circuit Current Unit Force:

(For Round conductor)

AT COUPLING BAY

Gilgel Gibe II Hydroelectric Project

S

(4)-G77700-S0019-L061-A

ATTACHMENT-2

ISC = Symmettrical short circuit current = 31500 A

D = Conductor spacing centre to centre = 255.91 inch * = Constant based on type of short circuit and = 0.866

conductor location (Ref. Table 2 of IEEE:605) Hence, FSC = 9.27 lbf/ft

Total bus unit weight (FG) = FC + FI+ FD lbf/ft

FC = Conductor unit weight = 5.11 lbf/ft

FD = Damping material unit weight = 1.23 lbf/ft

FI = Ice Unit weight = 0 lbf/ft

Hence, FG = 6.34 lbf/ft

Calculation for Insulator Strength

a. Calculation for Bus Short circuit Current Force: FSB = LE.FSC lbf

FSB = Bus Short Circuit Force transmitted to bus support fitting

LE = Effective Bus span length = 31.99 ft

FSC = Short Circuit Current Unit Force = 9.27 lbf/ft

Now, for a Rigid Bus Section of Equipment connection in a typical Line bay

across the Equipment Bus in Coupling bay(as shown in the figure alongside) F P P LE = 1/8(3L1+4L2) (Refer Table 5 of IEEE-605)

= 31.98819 ft

Adjescent Bus Span (L1) = 12 m

= 39.37 ft Adjescent Bus Span (L2) = 10.5 m

= 34.45 ft 12m 10.5m Therefore FSB = 296.45 lbf

L1 L2

b. Calculation for Bus Wind Force : Fig 1

FWB = LE.FW lbf

Where,

FWB = Bus Wind force transmitted to bus support fitting

LE = Effective Bus span length = 31.99 ft

FW = Wind unit force on the bus = 7.48 lbf/ft

Therefore FWB = 239.34 lbf

c. Calculation for Insulator wind force: FWI = 1.776 x 10 -5 CDKZGFV 2 (Di+2r1)Hi lbf Where,

FWI = Wind Force on Insulator

Hi = Insulator Height = 131.89 Inch

Di = Effective insulator diameter

= (D1+D2)/2 = 8.2677 inch

D1 = Max. Insulator Width = 11.4173 inch

D2 = Min. Insulator Width = 5.1181 inch

ISO(Panto) BPI CT

Calculation for Gravitational Force:

Gilgel Gibe II Hydroelectric Project

S

(4)-G77700-S0019-L061-A

ATTACHMENT-2

r1 = Radial Ice thickness = 0 inch

CD = Drag coefficient = 1 (For 'round conductor' as per Table 1 of IEEE:605)

KZ = Height and exposure factor = 1(as per Cl. 10.2 of IEEE:605)

GF = Gust factor = 1.3 (as per Cl. 10.3 of IEEE:605)

V =Wind speed at 30ft. above ground = 33.79 m/s = 75.59 mi/h Therefore FWI = 143.86 lbf

Calculation for Total Insulator Cantilever load

FIS = K1 [ FWI/2 + {(Hi+Hf)/Hi} FWB] + K2 [{(Hi+Hf)/Hi} FSB] lbf

FIS = Total Cantilever load acting at the end of Insulator

FWI = Wind force on the insulator in lbf = 143.86 lbf

FSB = Bus Short Circuit Force transmitted to bus support fitting = 296.45 lbf

FWB = Bus Wind force transmitted to bus support fitting = 239.34 lbf

Hi = Insulator Height = 131.89 inch

Hf = Bus Cen. Height above Insulator = 5.91 inch

K1 = Overload Factor applied to wind force = 1

K2 = Overload Factor applied to short circuit force = 1

Therefore FIS = 631.71 lbf

Now

Effective weight of bus transmitted to bus support fitting FGB = LE.FG lbf

where,

LE = Effective Bus span length = 31.99 ft

FG = Total Bus Unit Weight = 6.34 lbf/ft

Therefore FGB = 202.72 lbf

Natural Frequency of the Insulator with effective weight of the conductor span : fi = (1/2S) [Ki g / (0.226FGI + FGB)]

1/2

where,

Ki = Insulator cantilever Spring Constant = 1 lbf/inch

g = gravitional constant = 386 inch/s2 FGI = Weight of the insulator = 641.54 lbf

FGB = Effective weight of bus transmitted to bus support fitting = 202.72 lbf

Therefore fi = 0.17 Hz

As fi < 50Hz => K2 = 1 (Refer Cl. No. 13.2 of IEEE: 605)

Cantilever Load on the Support Insulator FIS (Eqp) = 286.80 Kgf

(in the direction of the Equipment Connection)

=> Reqiured cantilever Strength of the Supporting Insulator = 281.23 daN

Gilgel Gibe II Hydroelectric Project

S

(4)-G77700-S0019-L061-A

ATTACHMENT-3

SYSTEM VOLTAGE ( IN KV. ): 400 FAULT LEVEL( IK3 ) ( IN KA.): 31.5

TUBULAR BUS CONDUCTOR :

a) Size : AlMgSi0.5F25 120 mm c) Thickness : 6 mm d) Weight 5.8 Kg/m e) conductor Young's Modulus 7.00E+10 N/m2 f) Conductor spacing 6.5 m g) Max Allowable stress 115 N/mm2

11.72 Kg/mm2 h) Max. Span 12 m

i) Weight of Damper Material 1.83 Kg/m (Single 954 CARDINAL ACSR Conductor)

INSULATOR DATA (Type:C6-1550):

a. Height 3.35 m b. Max. Width 0.29 m c. Min. Width 0.13 m d Bus Cen. Line

height above Insulator 0.15 m e. Weight 291 Kg

Max. Wind Pressure(Pmax) = 700 N/m 2

(as per technical specification) Ambient air density(d) = 0.613 Kg/m3

Wind Velocity(V) = (Pmax/d) 1/2

m/s = 33.79 m/s Now,

Coss sectional moment of inertia of the tube (J) = = (S/64 ).(Do4 - Di4)

where,

DO = Outer Diameter of Conductor = 120 mm

Di = Inner Diameter of Tube = 108 mm

Therefore, J = 3498701.04 mm4 = 8.405595626 in4 Sectional Modulus of the tube S = J/(DO/2) mm

3

= 58311.684 mm3 = 3.558375932 in3

Conductor Wind Force (FW) = 2.132 x 10 -4

CDKZGFV 2

(DO+2r1) lbf/ft (Cl. 10. of IEEE:605)

Where

DO = Outer Diameter of Conductor 4.72 inch

r1 = Radial Ice thickness. = 0 inch

CD = Drag coefficient (Ref. Table 1 of IEEE:605) = 1

KZ = Height and exposure factor (Cl. 10.2 of IEEE:605) = 1

GF = Gust factor (Cl. 10.3 of IEEE:605) = 1.3

V =Wind speed at 30ft. above ground = 33.79 m/s = 75.59 mi/h Hence, FW = 7.48 lbf/ft

Short Circuit Current Unit Force (FSC) = 27.6* ISC2 /107(D) lbf/ft

CALCULATION OF CANTILEVER STRENGTH OF BUS POST INSULATOR SUPPORTING THE EQUIPMENT BUS

b) Outer dia.

Calculation for conductor Wind Force:

Calculation for Short Circuit Current Unit Force:

(For Round conductor)

AT TRANSFORMER & OHL BAY

Gilgel Gibe II Hydroelectric Project

S

(4)-G77700-S0019-L061-A

ATTACHMENT-3

ISC = Symmettrical short circuit current = 31500 A

D = Conductor spacing centre to centre = 255.91 inch * = Constant based on type of short circuit and = 0.866

conductor location (Ref. Table 2 of IEEE:605) Hence, FSC = 9.27 lbf/ft

Total bus unit weight (FG) = FC + FI+ FD lbf/ft

FC = Conductor unit weight = 3.90 lbf/ft

FD = Damping material unit weight = 1.23 lbf/ft

FI = Ice Unit weight = 0 lbf/ft

Hence, FG = 5.13 lbf/ft

Calculation for Insulator Strength

a. Calculation for Bus Short circuit Current Force: FSB = LE.FSC lbf

FSB = Bus Short Circuit Force transmitted to bus support fitting

LE = Effective Bus span length = 27.89 ft

FSC = Short Circuit Current Unit Force = 9.27 lbf/ft

Now, for a Rigid Bus Section of Equipment connection in a typical Line bay across

the Equipment Bus in Transformer & OHL bay(as shown in the figure alongside) F P P P LE = 1/8(3L1+4L2) (Refer Table 5 of IEEE-605)

= 27.88714 ft 8m Adjescent Bus Span (L1) = 12 m

= 39.37 ft Adjescent Bus Span (L2) = 8 m

= 26.25 ft 12m 10.5m Therefore FSB = 258.45 lbf

L1 L2

b. Calculation for Bus Wind Force : Fig 1

FWB = LE.FW lbf

Where,

FWB = Bus Wind force transmitted to bus support fitting

LE = Effective Bus span length = 27.89 ft

FW = Wind unit force on the bus = 7.48 lbf/ft

Therefore FWB = 208.65 lbf

c. Calculation for Insulator wind force: FWI = 1.776 x 10 -5 CDKZGFV 2 (Di+2r1)Hi lbf Where,

FWI = Wind Force on Insulator

Hi = Insulator Height = 131.89 Inch

Di = Effective insulator diameter

= (D1+D2)/2 = 8.2677 inch

D1 = Max. Insulator Width = 11.4173 inch

D2 = Min. Insulator Width = 5.1181 inch

ISO(Panto) BPI CB

Calculation for Gravitational Force:

Gilgel Gibe II Hydroelectric Project

S

(4)-G77700-S0019-L061-A

ATTACHMENT-3

r1 = Radial Ice thickness = 0 inch

CD = Drag coefficient = 1 (For 'round conductor' as per Table 1 of IEEE:605)

KZ = Height and exposure factor = 1(As per Cl. 10.2 of IEEE:605)

GF = Gust factor = 1.3 (As per Cl. 10.3 of IEEE:605)

V =Wind speed at 30ft. above ground = 33.79 m/s = 75.59 mi/h Therefore FWI = 143.86 lbf

Calculation for Total Insulator Cantilever load

FIS = K1 [ FWI/2 + {(Hi+Hf)/Hi} FWB] + K2 [{(Hi+Hf)/Hi} FSB] lbf

FIS = Total Cantilever load acting at the end of Insulator

FWI = Wind force on the insulator in lbf = 143.86 lbf

FSB = Bus Short Circuit Force transmitted to bus support fitting = 258.45 lbf

FWB = Bus Wind force transmitted to bus support fitting = 208.65 lbf

Hi = Insulator Height = 131.89 inch

Hf = Bus Cen. Height above Insulator = 5.91 inch

K1 = Overload Factor applied to wind force = 1

K2 = Overload Factor applied to short circuit force = 1

Therefore FIS = 559.95 lbf

Now

Effective weight of bus transmitted to bus support fitting FGB = LE.FG lbf

where,

LE = Effective Bus span length = 27.89 ft

FG = Total Bus Unit Weight = 5.13 lbf/ft

Therefore FGB = 142.99 lbf

Natural Frequency of the Insulator with effective weight of the conductor span : fi = (1/2S) [Ki g / (0.226FGI + FGB)]

1/2

where,

Ki = Insulator cantilever Spring Constant = 1 lbf/inch

g = gravitional constant = 386 inch/s2 FGI = Weight of the insulator = 641.54 lbf

FGB = Effective weight of bus transmitted to bus support fitting = 142.99 lbf

Therefore fi = 0.18 Hz

As fi < 50Hz => K2 = 1 (Refer Cl. No. 13.2 of IEEE: 605)

Cantilever Load on the Support Insulator FIS (Eqp) = 254.22 Kgf

(in the direction of the Equipment Connection)

=> Reqiured cantilever Strength of the Supporting Insulator = 249.28 daN

Gilgel Gibe II Hydroelectric Project