DSLP dirct srole lightning protection

Ref. (4)-G77700-S0019-L063-A

Project:

Gilgel Gibe – II PROJECT ETHIOPIA Description:

400 kV SWITCHYARD DESIGN REPORT’s & CALCULATION’s

Subject:

Report on Direct Stroke Lightning Protection of Electrical Equipments in Outdoor Switchyard

Note:

This report gives the calculations in justification of the lightning protection system designed for protecting the switchyard equipments and conductors from direct strokes of lightning.

D.S.L.P. Calculation : 400kV Switchyard Handling:

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Contents page 1.

Introduction ....................................................................................................................... 4

2.

System Data...................................................................................................................... 5

3.

Conductor Data ................................................................................................................. 5

4.

Installation Data…………………………………………………………………………………..5

5.

Attachments ...................................................................................................................... 5

6.

Conclusion ........................................................................................................................ 6

7.

References........................................................................................................................ 6

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(4)-G77700-S0019-L063-A

D.S.L.P. Calculation : 400kV Switchyard Handling:

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Introduction The basic intent of this report is to provide design information to minimize direct lightning strokes on equipment and bus work within the substation. The method employed for design of the shielding system is Electrogeometric model – Rolling Sphere Method. The Electrogeometric Model (EGM) is a geometric representation of a facility, that, together with suitable analytical expressions correlating its dimensions to the current of the lightning stroke is capable of predicting whether the lightning stroke will terminate on the shielding system, the earth, or the element of the facility being protected. The Rolling Sphere method is a simple technique for applying the EGM theory for shielding of substations. The technique involves rolling an imaginary sphere of prescribed radius over the surface of the substation. The sphere rolls up and over (and is supported by) the lightning masts, shield wires and other grounded metal objects intended for lightning shielding. A piece of equipment is protected from a direct stroke of lightning if it remains below the curved surface of the sphere by virtue of the sphere being elevated by shield wires or other devices. Equipment that touches the sphere or penetrates its surface is not protected from direct stroke of lightning.

For the facility under consideration in this design report i.e. 400 kV Switchyard, shield wires at elevation of 27.75 metres is employed to protect the phase conductor at El+22M and bus work at EL+13.125M. The calculations as per Attachment – 1 justifies the design and the zone of protection is shown in the DSLP Layout.

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(4)-G77700-S0019-L063-A

D.S.L.P. Calculation : 400kV Switchyard Handling:

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System data 400kV AC Switchyard Nominal System Voltage

400 kV

System Frequency

50 Hz

Rated Lightning Impulse Withstand Voltage

1425 kV

Limiting Corona Gradient

1500 kV/m

3 Conductor Data Jack Bus Conductor at Coupling Bay Type of Conductor

Twin bundle of 954 MCM ACSR Cardinal

Diameter of Sub-conductor

30.42 mm

Sub-Conductor spacing in bundle

450 mm

Main Bus Conductor Type of Conductor

250/6 mm Tubular Bus of alloy ‘AlMgSi0.5F25’

Outer Diameter Thickness

250 mm 6 mm

4 Installation Data Jack Bus Conductor at Coupling Bay Height of installation above FGL

22.0 m

Main Bus Conductor Height of installation above FGL

13.125 m

5 Attachments Attachment-1: DSLP Calculation for 400kV Switchyard

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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-L063-A

D.S.L.P. Calculation : 400kV Switchyard Handling:

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6 Conclusion 1. The results as per Case – 1 of the attached calculation reveals that for protection of the phase conductors of the Jack Bus in the Coupling Bay at 22.0 m elevation by shield wires at elevation of 27.75 m, the maximum allowable horizontal separation of the shield wire is 37.73 m. As shown in the DSLP layout, the shield wires protecting the phase conductor at the Coupling Bay have a horizontal separation of 24.0 m. Thus the phase conductor is protected from direct strokes of lightning. 2. The results as per Case – 5 of the attached calculation reveals that for protection of the rigid conductors at the Main Buses at 13.125 m elevation by shield wires at elevation of 27.75 m, the maximum allowable horizontal separation of the shield wire is 58.12 m. As shown in the DSLP layout, the shield wires protecting the bus work have a horizontal separation of 48.0 m. Thus the Main Bus conductor is protected from direct strokes of lightning. All other equipments in the switchyard are at lower elevation than the Main Bus work and are hence protected by the shield wires.

7 References 1. IEEE Std.998 – 1996(R2002) – IEEE Guide for Direct Lightning Stroke Shielding of Substations 2. Technical Data sheet for ACSR Conductor: Manufacturer – HASCELIK. 3. Technical Data sheet for Aluminum Alloy Tubular Conductor: Manufacturer – Corus 4. 400kV Switchyard DSLP Layout – Drawing No. (1)-G77700-S0019-L069-A

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(4)-G77700-S0019-L063-A

S

(4)-G77700-S0019-L063-A

ATTACHMENT - 1 D.S.L.P CALCULATION FOR 400kV Switchyard By Rolling Sphere method, as per IEEE-std 998-1996 Conductor Data: Flexible conductor bundle Sub conductor Type Diameter Sub-conductor Spacing height of the conductor Rigid conductor Conductor Type Outer Diameter height of the conductor

= = = =

954 MCM ACSR Cardinal 0.03042 m 0.45 m 22 m

= = =

Tubular Aluminium Alloy 0.25 m 13.125 m

In case of a twin conductor bundle, the equivalent radius is given by ¥(r x l) R0 = where

r l

= =

( eqn. C.5, IEEE 998 - 1996)

= 0.082731 m radius of subconductors in m spacing between adjacent conductor in m

In case of a single conductor bundle, the equivalent radius is given by Rc x ln {(2xh)/Rc} - (Vc/E0) = 0 where

h Vc

=

= = E0 = = By solving the equation for R c, we have Rc

for 400kV Twin Bundle

=

( eqn. C.1, IEEE 998 - 1996)

average height of the conductor Rated Lightning Impulse withstand voltage 1425 kV Limiting corona gradient 1500 kV / m 0.171194 m

For Bundle Conductor , the radius of the bundle under corona is R'c = R0 + Rc = 0.253925 m For tubular conductor the equivalent radius is given by

for Twin Bundle Rc x ln {(2xh)/Rc} - (Vc/E0) = 0

By solving the equation for R c, we have Rc

=

0.193255 m

The surge impedence of conductors under corona is given as, 60 x ¥( ln ( 2xh / R'c ) x ln ( 2xh / R 0 ) Zs = where

( eqn. C.7, IEEE 998 - 1996)

h R'c

= =

Corona radius of the bundle conductor

R0

=

Equivalent radius of bundle conductor

ZS

hence

=

average height of the conductor

341.2832 ohms

for Twin Bundle

For Single conductor the expression to determine surge impedance is 60 x ¥( ln ( 2xh / R'c ) x ln ( 2xh / r ) Zs = where h = average height of the conductor R'c = Rc = Corona radius of the single conductor r = metallic radius of single conductor ZS = 307.4778 ohms

for Tubular Conductor

The allowable stroke current is obtained by the equation IS where

Gilgel Gibe II Hydroelectric Project

= BIL ZS

2.2 BIL / ZS = =

( eqn. 5-2A, IEEE 998 - 1996)

Rated Lightning Impulse withstand voltage Surge Impedence of the conductor carrying the surge

1

S

(4)-G77700-S0019-L063-A

ATTACHMENT - 1 IS

hence

=

9.185918 kA 10.19586 kA

for Twin Bundle for Tubular Conductor

The allowable stike Distance is obtained by the equation S

=

where

S k IS S s wire

hence

8 x k x I s0.65 = = = = =

( eqn. 5-1B, IEEE 998 - 1996)

Strike distance in m 1 for strikes on Shield Wire Allowable return stroke current in kA 33.8158 m 36.18807 m

(pg.25 IEEE 998 - 1996) for Twin Bundle for Tubular Conductor

Combined protection by two shield wires

here,` Case - 1 :-

'O' is the origin of the Rolling Sphere 'SW' denotes the location of the shield wire Object to be protected : Twin Conductor Bundle of Coupling Bus

Now, allowable strike distance (S) height of shield wire (H) height of object to be protected (A) elevation difference between Shield wire & Object to be protected D= H-A elevation difference between Origin of the Rolling Sphere & Shield Wire E= S-D horizantal distance between Origin of the Rolling Sphere & Shield wire 2 2 ¥S - E L=

= = =

33.8158 m 27.75 m 22 m

=

5.75 m

=

28.0658 m

=

18.863 m

Maximum allowable horizontal seperation of the shield wires ensuring protection of object at height (A) X= 2L = 37.73 m Case - 2 :-

Object to be protected : Tubur Rigid Bus Conductor of Main Bus

Now, allowable strike distance (S) height of shield wire (H) height of object to be protected (A) elevation difference between Shield wire & Object to be protected D= H-A elevation difference between Origin of the Rolling Sphere & Shield Wire E= S-D horizantal distance between Origin of the Rolling Sphere & Shield wire 2 2 ¥S - E L=

= = =

36.188073 m 27.75 m 13.125 m

=

14.625 m

=

21.563073 m

=

29.062 m

Maximum allowable horizontal seperation of the shield wires ensuring protection of object at height (A) X= 2L = 58.12 m

Gilgel Gibe II Hydroelectric Project

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