BISHA CPS EXTENSION PROJECT

9

TCE CONSULTING ENGINEERS LIMITED

i

30421008-3CL-00016-P0A

DESIGN BASIS REPORT FOR LIGHTNING AND SHIELDING SYSTEM

SHEET OF iOF 4

SAUDI ELECTRICITY COMPANY

EASTERN OPERATING AREA

Dammam, Saudi Arabia

GENERATION EXPANSION OF RAFHA POWER PLANT

(CONTRACT NO : 30421008/00)

DESIGN BASIS REPORT FOR

LIGHTNING AND SHIELDING SYSTEM

DOCUMENT NO. : 30421008-3CL-00016-P0AOCTOBER, 2004

ENGINEERING CONSULTANT

TCE CONSULTING ENGINEERS LIMITED

73/1, ST. MARKS ROAD

BANGALORE 560 001

INDIA

CONTRACTOR:AL-TOUKHI COMPANY FOR INDUSTRY & TRADING

P.O. BOX 497, RIYADH 11411, KINGDOM OF SAUDI ARABIA

TEL. 00966-1-4633660 : FAX. 00966-1-4631150CONTENTS

CLAUSE No.

DESCRIPTION

PAGE No.

1.0

Introduction

2

2.0

Reference drawings / Documents

3

3.0

Design Basis

4

4.0

Considered buildings and Structures

6

5.0

Lightning Protection Conductor Details

6

6.0

Conclusion

7

ANNEXURES

7.0

Annexure-1-Lightning Protection System Calculations.

1.0 INTRODUCTION:

1.1 Al-Toukhi company for Industry & Trading has been awarded turnkey contract for Open Cycle Gas Turbine based CPS expansion project at Rafha of Saudi Electric Company-Eastern Operation Area (SEC-EOA), Saudi Arabia.

1.2 The project consists of design, engineering, procurement, installation, testing and commissioning of two (2) Nos. 29.92MW @ 50(C, Gas Turbine Generator unit of GE make along with associated Generator Transformer and other balance of plant electro-mechanical equipment

2.0 REFERENCE DRAWINGS/DOCUMENTS

2.1BS 6651: 1992

Protection of structures against lightning

2.2Scope of Work and Technical Specifications. PTS-1024.

2.3General site Layout. Dwg No:KA 666782, Rev-P0D

3.0DESIGN BASIS

3.1 The design of Lightning protection systems (LPS) for different structures present in the plant are based on overall risk factor as per the procedure indicated in the BS-6651 standard.

3.2 The number of thunderstorm days per year is 15 as per PTS-1024 of page 67 of 331.

3.3 Estimation of Overall Risk index.

The probability of Structure or building being struck by lightning in any one year is the product of Lightning Flash Density and Effective collection Area of the Structure to be protected

P = Ng x Ac x 10-6 -------- Equation as per Cl.No:9.2 of BS-6651.

Where,

P=Probable number of strikes/year (Risk)

Ng =Lightning Flash Density, i.e. the number of flashes to

Ground per Km2 per year.

Ac=Effective Collection Area of the Structure or building.

3.4 The established value of the probable number of strikes to the structure per year P, multiplied by weighing factors of A to E gives the Overall Risk factor.

3.5 BS-6651 recommends that the following weighing factors A to E vide Tables 8 to 12, page 16 & 17.

a)Weighing Factor A-Use of Structures (Table-8 )

b)Weighing Factor B-Type of construction (Table-9)

c)Weighing Factor C-Contents or Consequential

Effects (Table-10)

d)Weighing Factor D-Degree of Isolation (Table-11)

e)Weighing Factor E-Type of country (Table-12).

3.6 The Effective collection area of the structure or building shall be calculated as per Cl.No.9.2 of BS-6651.

Ac=LW + 2LH + 2WH + H2

Where,

L=Length of the building in meter.

W=Width of the building in meter.

H=Height of the building in meter.

3.7 Table-6 of BS 6651, page 14 gives the value of Ng lightning flashes per km2 per year corresponding to thunderstorm days per year.

3.8 The Suggested acceptable risk has been taken as 10-5 per year, i.e.1 in 100000 per year as per Cl.No 9.4 of BS 6651 page 16.

3.9 The value of overall Risk factor should be compared with the acceptable risk which is 10-5 .

3.10 If the Value of Overall risk factor is less than 10-5 , then Lightning protection for the structure is not required.

3.11 If the Value of Overall risk factor is greater than 10-4 , then Lightning protection is required.

3.12 Lightning protection for all the metallic steel structures have been followed as per Cl.No 6.19 b of PTS-1024 page 241 of 331.

4.0CONSIDERED BUILDINGS AND STRUCTURES.

4.1 The following buildings or structures of Arar Power Plant have been considered for the Lightning Protection System.

a) Control & Switchgear Building

b) GTG building

c) Attendant Room

d) Fuel Forwarding pump shed,

e) DFO unloading pump shed.

f) DFO storage tank

g) Exhaust stack.

h) Fin Fan cooler

i) Fuel filteration skid

j) Washing skid.

k) Air Compressor shed

4.2 The Lightning Protection System calculation along with recommendation for the above said buildings or structure have been compiled in ANNEXURE-1. Attached.

5.0 LIGHTNING PROTECTION CONDUCTOR DETAILS:

The following Lightning protection material/sizes are proposed to be used

In accordance with Cl.No:7.0 of BS-6651 Table-4.

5.1Control & Switchgear Building

- Horizontal mesh with bare stranded

Copper conductor of size 50 Sqmm

arranged in such a way that no part

of the roof is more than 5M from the

nearest horizontal conductor.

Down Conductors, one for every 20m

of perimeter with 50 Sqmm bare

stranded copper conductor, with each

down conductor terminated onto a

15mm dia, 2500mm long ground rod.

5.2Attendant Room- Horizontal mesh with bare stranded

Copper conductor of size 50 Sqmm

arranged in such a way that no part

of the roof is more than 5M from the

nearest horizontal conductor.

Down Conductors, one for every 20m

of perimeter with 50 Sqmm bare

stranded copper conductor, with each

down conductor terminated onto a

15mm dia, 2500mm long ground rod

5.3 GTG Building/Exhaust stack/DFO Storage Tank/Fuel Forwarding

Pump Shed/ Fuel unloading Pump shed / Fuel Filtration Skid /

Washing skid/Air compressor shed/Fin Fan cooling

No separate Lightning Protection grid with horizontal/vertical conductors

are required for the above structures, since the above are provided with

metallic frame structures.

All these metallic structures like steel columns, panel roof and metallic

enclosures would be effectively grounded at the base of the structures at

minimum two points to the grounding grid.

6.0 CONCLUSION.

6.1The structures that compose the Rafha Power Plant are mostly self protected since they are made of steel works except Control & Switchgear building and Attendant Room.

All the steel structures would be connected to the primary grounding system.

6.2 As indicated in Annexure-1, Lightning protection with horizontal roof conductor & Vertical Down conductor is recommended for Control & Switchgear Building and Attendant Room.

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P0A 25.10.2004

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