Lightning Calculation

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LIGHTNING CALCULATION FOR METHANOL PLANT

PROJECT 525 MTPD METHANOL PROJECT

OWNER M/S GUJARAT STATE FERTILIZERS & CHEMICALS LIMITED VADODARA

INDIAN ENGINEERING CONSULTANT (IEC)

M/S PROJECTS & DEVELOPMENT INDIA LIMITED WESTERN REGIONAL OFFICE, VADODARA

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CONTENTS Sr. No.

DESCRPTION

PAGE No.

1.

SCOPE OF WORK

3

2.

REFERENCE DOCUMENTS FOR LIGHTNING CALCULATION

3

3.

SITE CONDITIONS

3

4.

ELECTRICAL SUPPLY SYSTEM

3

5.

LIGHTNING PROTECTION

3

6.

CALCULATIONS

5

7.

ANNEXURES

5

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SCOPE OF WORK This document details the Lightning protection calculations for Methanol Plant, Gujarat state fertilizers Co. LTD., Vadodara, Gujarat, India.

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REFERENCE DOCUMENTS FOR LIGHNING CALCULATION Code of practice for protection of buildings and

: IS-2309-1989 (Reaffirmed 2005)

allied structures against lightning

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SITE CONDITION Maximum temperature

: 46.7C

Atmosphere

: DUSTS – Industrial, polluted : VAPOUR - Natural gas, Methanol & air borne chemical contaminants & corrosive as found in industrial process plants.

Altitude 4.0

: Above sea level < 1000 M

ELECTRICAL SUPPLY SYSTEM Supply system voltage

: (i) HV: 11KV ± 10%, 3 phase, 3 wire 3.3KV ± 10%, 3 phase, 3 wire, resistance earthed (ii) LV: 415V ± 10%,3 phase 4 wire , Neutral solidly earthed, supply frequency: 50Hz +2, -6 %

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LIGHTNING PROTECTION

5.1

BASIS FOR LIGHTNING CALCULATIONS: Lightning protection shall be as per IS: 2309 The probability of a structure or building struck by lightning in any one year is the product of the lightning flash density (Ng) and the effective collection area of the structure (Ac). The lightning flash density (Ng) is the number of flashes to ground per sq. km. per year.

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The average number of thunderstorms day in a year at particular location in India is indicated in figure1 of IS-2309. Based on this average no. of thunderstorms day, lightning flashes per sq. km. per year (Ng) can be estimated using clause 8.1.2 of IS: 2309. Accordingly for GSFC-Vadodara location this value is estimated as below Lightning flash density Ng = 0.5 per sq. km. per year (Mean value) Since the value for the lightning flash density for Vadodara in figure-1 of IS:2309 is 8. The effective collection area of a structure is the area on the plan of the structure extended in all directions to take account of its height. The edge of the effective collection area is displaced from the edge of the structure by an amount equal to the height of the structure at that point. Hence for a simple rectangular building effective collection area shall be calculated using following equation. Collection area Ac = (L * W) + 2(L*H) + 2(W*H) + Π H

2

Where, L = Length of structure or building in m. W = Width of the structure or building in m. H = Height of the structure or building in m. The probable number of strikes (risk) to the structure per year is P = Ac *Ng * 10

-5

(Ref eq. 2 of IS: 2309) -5

The acceptable risk figure is indicated in IS: 2309 is 10 (i.e. 1 in 100000 per year) After calculating the value of P (Probable no. of strikes per year) using above equation, the next step is to apply “ weighing factors” in Tables 1 and 2 of IS: 2309. This is done by multiplying P by the -5 appropriate factors to see whether the result exceeds the acceptable risk of P= 10 per year. If the -5 result obtain is considerably less than 10 then, lightning protection does not appear necessary and if -5 the result is greater than 10 , then lightning protection shall be provided. 5.2

LIGHTNING PROTECTION SYSTEM DESIGN Please refer ANNEXURE-I for buildings to which lightning protection system shall be required to provide. As per IS: 2309, self conducting structure shall not be provided with aerial rod and down conductors, but shall be connected to earthing system at two or more points at the base. An independent earthing network shall be provided for lightning protection and this shall be bonded with the main earthing network below ground, minimum at two points. The individual earth pit resistance may vary between 5-

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SHEET 5 OF 8 10 ohms based on the soil resistivity. However the total grid resistance shall be maintained as required. As per IS: 2309, Table no. 4 component dimensions for lightning protection are considered as given below. TYPE OF EQUIPMENT Roof conductor/ Air termination Down conductors Below ground strip/ Fixed connections

5.3

STRIP SIZE 25 * 6 GI STRIP 25 * 6 GI STRIP 50 * 6 GI STRIP

CALCULATION FOR NUMBER OF DOWN CONDUCTOR As per IS:2309, cl. 12.2.3 and fig. 13 & 14, number of down conductor can be calculated as follows: a) A structure having a base area not exceeding 100 sq. m. needs only one down conductor, except when built on bare rock. b) For a structure having a base area exceeding 100 sq.mtr., the number of down conductors should be at least the smaller of the following (1) One plus an additional one for each 300 sq. mtr. or a part thereof, in excess of the first 100 sq.mtr. (2) One for each 30m of perimeter of the structure protected.

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CALCULATIONS Lightning Protection calculation is attached as per ANNEXURE.

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ANNEXURES ANNEXURE- I

Lightning protection need

ANNEXURE- II Lightning calculation for methanol substation & existing old compressor house ANNEXURE-III Lightning calculation for methanol control room

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ANNEXURE-I A LIGHTNING PROTECTION NEED Sr. no.

Equipment no.

Service

Dimensions

Length Width (L) (Wi)

Height (H)

Collection area Ac , for building (in Sq. mtr.) =

Overall risk factor

Need of lightning protection -6

P= Ac * Ng *W * 10 -5

1

Methanol Sub station

52

17

5

1652.5

6.36 *10

2

Methanol Control Room

25

10

8.6

1084.23

4.1 * 10

3

Old existing compressor house

52

18

12

1700.16

6.546*10

YES/ NO YES YES

-5

-5

YES

Collection area for Sr. no. (1) & (2) Ac (in sq. mtr.) = (L*Wi) + 2(L*H) + 2(Wi * H) +Π H2 Collection area for Sr. no. (3) Ac (in sq. mtr.)= Π H2 +2 (L*H) Lightning flash density Ng = 0.5 per sq. km. per year (Mean value) Applying weighting factors: A = 1 (Factory/ workshop) B = 0.8 (Steel frame encased or reinforced concrete with metal roof) C = 0.8 (industrial building) D = 0.4 (Structure located in a large area of structures or trees) E = 0.3 (Flat country) W = A*B*C*D*E = 0.077 Acceptable Risk per year = 1 * 10

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If the result obtain is considerably less than 10 then, lightning protection does not appear necessary and if the -5 result is greater than 10 then, lightning protection shall be provided.

ANNEXURE- II

A LIGHTNING CALCULATION FOR METHANOL SUBSTATION & EXISTING OLD COMPRESSOR HOUSE Calculation of down conductors for Methanol Sub-station & existing old compressor house (i) Calculation based on total base area Length of sub-station area & Existing old compressor house (L) = 52 mtr. Width of sub-station area (W1) = 17 mtrs. Width of existing old compressor house (W2) = 18 mtrs. Total width of base area W = W1 + W2 W = 35 mtrs. Total base area of sub-station & existing old compressor house = L*W = 1820 mtr

2

As per clause no. 12.2.3 (b)-1 of IS-2309 Total no. of Down conductors = {(Area-100)/300} + 1 = 6.7

----------------------- Equ. (1)

(ii) Calculation based on Perimeter Perimeter of methanol substation & existing old compressor house area = 2 * (L+W) = 174 As per clause no. 12.2.3 (b)-2 of IS: 2309 Total no. of down conductors = Perimeter/30 = 5.8

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-------------------------- Equ. (2)

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SHEET 8 OF 8 Hence, concluding from result of Equ. (1) & (2) is that number of down conductors and electrodes shall be equal 6. (Considering the smaller value of result from Equ. (1) & (2) as per clause no. 12.2.3 of IS:2309)

ANNEXURE- III

A

LIGHTNING CALCULATION FOR METHANOL CONTROL ROOM Calculation of down conductors for Methanol Control room (i) Calculation based on total base area Length of sub-station area (L) = 25 mtr. Width of sub-station area (W) = 10 mtrs. Total base area of sub-station = L*W = 250 mtr

2

As per clause no. 12.2.3 (b)-1 of IS-2309 Total no. of Down conductors = {(Area-100)/300} + 1 = 1.5

------------------------- Equ (1)

(ii) Calculation based on Perimeter Perimeter of methanol control room = 2 * (L+W) = 70 As per clause no. 12.2.3 (b)-2 of IS: 2309 Total no. of down conductors = Perimeter/30 = 2.3

---------------------------- Equ (2)

Hence, concluding from result of Equ (1) & (2) is that number of down conductors and electrodes shall be equal 2. (Considering the smaller value of result from Equ (1) & (2) as per clause no. 12.2.3 of IS:2309)

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