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TECHNICAL REPORT
Protection against lightning
Risk assessment
selection of protection measures
Designer info:
Name: James
Address: Badoers
City: Kinsington
Postal code: 44200
Country: NZ
Professional register: Engineering
Professional register number: K121-NZ
VAT number: Tax code: -
Customer:
Customer: METALPHA Sa - industrial design
Structure description: Production site
Address: 32, Newport Rd
City: New Castle
District: NZ
INDEX
1. DOCUMENT CONTENTS
2. TECHNICAL STANDARDS
3. STRUCTURE TO BE PROTECTED
4. INPUT DATA
4.1 Lightning ground flash density.
4.2 Structure data.
4.3 Electrical lines data.
4.4 Definition and characteristics of zones
5. STRUCTURE AND ELECTRICAL LINES COLLECTION AREAS
6. RISK ASSESSMENT
6.1 Risk R1 loss of human life
6.1.1 Risk calculation R1
6.1.2 Risk assessment R1
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7. SELECTION OF PROTECTION MEASURES
7.1 Economic analysis
8. CONCLUSIONS
9. APPENDICES
10. ANNEXS
Structure layout
Collection area Ad
Collection area Am
SPD installation Am
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1. CONTENT OF DOCUMENT
This document contains:
- the lightning risk assessment;
- the draft design of required protection measures.
2. TECHNICAL STANDARDS
This document refers to the following standards:
- EN 62305-1: "Protection against lightning. Part 1: General principles"
March 2006;
- EN 62305-2: "Protection against lightning. Part 2: Risk assessment"
March 2006;
- EN 62305-3: "Protection against lightning. Part 3: Physical damage to structures and life hazards"
March 2006;
- EN 62305-4: "Protection against lightning. Part 4: Electrical and electronic systems within structures"
March 2006;
3. STRUCTURE TO BE PROTECTED
It is important to define the part of structure to be protected in order to define dimensions and
characteristics to be used for collection area calculation.
The structure to be protected:
- is a vertical part of a building;
- there are not internal systems in common with other part of the building,
- is separated from other parts of the building by menas of walls with resistance to fire of 120 min (REI
120).
Therefore the dimensions and characteristics of the structure to be considered are the same of the
structure (art. A.2.1.2 - standard EN 62305-2).
4.
INPUT DATA
4.1 Lightning ground flash density
The lightning flash density in the city of where the structure is located is:
Ng = 2,0 flashes/km² year
4.2 Structure data
The structure's layout is described in Annex Structure layout.
The prevalent type of structure is: industrial
The structure could be subject to:
- loss of human life
- loss of economic value
To evaluate the need of protection against lightning, according to standard EN 62305-2, should be
calculated:
- risk R1;
To evaluate the cost effectiveness of protection it is necessary to calculate risk 4.
The building has a metallic structure or continuos reinforced concrete framework.
4.3 Electrical lines data
The structure is served by the following electrical lines:
- Power line: Power aerial
- Power line: Power mixed
- Power line: Telecom
The electrical lines characteristics are described in Appendix Electrical lines charactersitics.
4.4 Zones definition and characteristis
With reference to::
- existing walls with resistence to fire of 120 min;
- rooms already protected or that should be opportune to protect against LEMP (lightning
electromagnetic pulse);
- type of soil outside the structure, type of surface inside the structure and the possible presence of
persons;
- others structure characteristics, as the layout of internal systems and existing protection measures;
are defined the following zones:
Z1: External
Z2: Office
Z3: Production
The zones characteristics, mean loss values, type of risks and related component are reported in
Appendix Zones characteristics.
5. STRUCTURE AND ELECTRICAL LINES COLLECTION AREAS
The collection area Ad due to direct flashes to the structure is calculated with graphic method
according to standard EN 62305-2, art.A.2 and it is reported in Annex Collection area Ad.
The collection area Am due to flashes near the structure, which could damage internal systems due to
induced overvoltages, is calculated with graphic method according to standard EN 62305-2, art.A.3 and
it is reported in Annex Collection area Am.
The collection areas Al e Ai for each electrical line is calculated with analytic method according to
standard EN 62305-2, art.A.4.
The values of collection areas (A) and related annual number of dangerous events (N) are reported in
Appendix Collection areas and annual number of dangerous events.
The values of probability of damage (P) used to calculate the selected risk components are reported in
Appendix Values of probability of damage for unprotected structure.
6. RISK ASSESSMENT
6.1 Risk R1: loss of human life
6.1.1 R1 calculation
The values of risk components and the value of risk R1 are listed below.
Z1: External
RA: 1,10E-07
Total: 1,10E-07
Z2: Office
RB: 1,10E-06
RC: 5,51E-06
RM: 4,30E-05
RU(Power office): 1,90E-12
RV(Power office): 3,79E-07
RW(Power office): 1,90E-06
RZ(Power office): 3,07E-05
RU(Telecom office): 5,37E-12
RV(Telecom office): 1,07E-06
RW(Telecom office): 5,37E-06
RZ(Telecom office): 1,12E-05
Total: 1,00E-04
Z3: Production
RB: 1,10E-06
RC: 1,65E-05
RM: 1,72E-04
RU(Power production): 3,57E-12
RV(Power production): 7,15E-08
RW(Power production): 1,07E-06
RZ(Power production): 9,51E-06
RU(Telecom production): 5,37E-11
RV(Telecom production): 1,07E-06
RW(Telecom production): 1,61E-05
RZ(Telecom production): 3,36E-05
Total: 2,51E-04
Value of total risk R1 for the structure: 3,51E-04
6.1.2 Analysis of risk R1
The total risk R1 = 3,51E-04 is greater than the tolerable risk RT = 1E-05, therefore it is necessary to
select protection measures to reduce it.
The risk components that constitute risk R1, reported in percentage of risk R1 for the structure, is listed
below.
Z1 - External
RD = 0,0314 %
RI = 0 %
Total = 0,0314 %
RS = 0,0314 %
RF = 0 %
RO = 0 %
Total = 0,0314 %
Z2 - Office
RD = 1,8826 %
RI = 26,6432 %
Total = 28,5258 %
RS = 0 %
RF = 0,7275 %
RO = 27,7982 %
Total = 28,5257 %
Z3 - Production
RD = 5,0201 %
RI = 66,4227 %
Total = 71,4428 %
RS = 0 %
RF = 0,64 %
RO = 70,8029 %
Total = 71,4429 %
where:
- RD = RA + RB + RC
- RI = RM + RU + RV+ RW + RZ
- RS = RA + RU
- RF = RB + RV
- RO = RM + RC + RW + RZ
and:
- RD is the risk due to flashes striking the structure
- RI is the risk due to flashes influencing it but not striking the structure
- RS is the risk due to injury to livings beings
- RF is the risk due to physical damage
- RO is the risk due to failure of internal systems.
The values listed above, show that risk R1 for the structure is essentially present in the following zones:
Z3 - Production (71,4428 %)
- essentially due to failure of internal systems
- mainly due to flashes striking the structure and flashes influencing it but not striking the
structure
- the mainly contribution to the value of risk R1 inside the zone is determineted by the
following
risk components:
RM = 68,4946 %
Internal systems failure due to flashes influencing it but not striking the structure
7. SELECTION OF PROTECTION MEASURES
To reduce the risk R1 below to the tolerable risk RT = 1E-05, it is necessary to act on the following
risk components:
- RC in the zones:
Z3 - Production
- RM in the zones:
Z2 - Office
Z3 - Production
- RW in the zones:
Z3 - Production
- RZ in the zones:
Z2 - Office
Z3 - Production
using at least one of the following possible protection measures:
- for risk component C:
1) Coordinated SPD protection
- for risk component M:
1) Coordinated SPD protection
2) Shielding the structure
3) Shielding the internal system or provide an adeguate routing
4) Increasing the impulse withstand voltage of equipments
- for risk component W:
1) Coordinated SPD protection
2) Increasing the impulse withstand voltage of equipments
- for risk component Z:
1) Coordinated SPD protection
2) Increasing the impulse withstand voltage of equipments
To protect the structure the following protection measures are selected:
- install LPS of class III (Pb = 0,1)
- In the zone Z2 - Office:
Internal system: Power office
- Coordinated SPD - level: II
Internal system: Telecom office
- Coordinated SPD - level: I
- In the zone Z3 - Production:
Internal system: Power production
- Coordinated SPD - level: I
Internal system: Telecom production
- Coordinated SPD - level: I
- For the line Line1 - Power aerial:
- SPD at line entrance - level: II
- For the line Line2 - Power mixed:
- SPD at line entrance - level: I
- For the line Line3 - Telecom:
- SPD at line entrance - level: I
The selected protection measures modify risk parameters and components.
The values for risk parameters related to the protected structure are listed below.
Zone Z1: External
Pa = 1,00E+00
Pb = 0,1
Pc = 1,00E+00
Pm = 1,00E+00
ra = 0,01
rp = 1
rf = 0
h=1
Zone Z2: Office
Pa = 1,00E+00
Pb = 0,1
Pc (Power office) = 2,00E-02
Pc (Telecom office) = 1,00E-02
Pc = 2,98E-02
Pm (Power office) = 2,00E-02
Pm (Telecom office) = 1,00E-04
Pm = 2,01E-02
Pu (Power office) = 2,00E-02
Pv (Power office) = 2,00E-02
Pw (Power office) = 2,00E-02
Pz (Power office) = 2,00E-02
Pu (Telecom office) = 1,00E-02
Pv (Telecom office) = 1,00E-02
Pw (Telecom office) = 1,00E-02
Pz (Telecom office) = 1,00E-02
ra = 0,00001
rp = 0,5
rf = 0,01
h=2
Zone Z3: Production
Pa = 1,00E+00
Pb = 0,1
Pc (Power production) = 1,00E-02
Pc (Telecom production) = 1,00E-02
Pc = 1,99E-02
Pm (Power production) = 1,00E-02
Pm (Telecom production) = 1,00E-04
Pm = 1,01E-02
Pu (Power production) = *
Pv (Power production) = *
Pw (Power production) = *
Pz (Power production) = *
Pu (Telecom production) = 1,00E-02
Pv (Telecom production) = 1,00E-02
Pw (Telecom production) = 1,00E-02
Pz (Telecom production) = 1,00E-02
ra = 0,00001
rp = 0,2
rf = 0,01
h=5
(*) In case of lines with different sections, the probability refers to each section. See Appendix
Electrical lines characteristics.
Risk R1: loss of human life
The values of risk components for protected structure are listed below.
Z1: External
RA: 1,10E-07
Total: 1,10E-07
Z2: Office
RB: 1,10E-07
RC: 1,64E-07
RM: 1,15E-06
RU(Power office): 3,79E-14
RV(Power office): 7,58E-09
RW(Power office): 3,79E-08
RZ(Power office): 1,53E-06
RU(Telecom office): 5,37E-14
RV(Telecom office): 1,07E-08
RW(Telecom office): 5,37E-08
RZ(Telecom office): 7,46E-07
Total: 3,81E-06
Z3: Production
RB: 1,10E-07
RC: 3,29E-07
RM: 1,74E-06
RU(Power production): 4,89E-14
RV(Power production): 9,77E-10
RW(Power production): 1,47E-08
RZ(Power production): 4,68E-07
RU(Telecom production): 5,37E-13
RV(Telecom production): 1,07E-08
RW(Telecom production): 1,61E-07
RZ(Telecom production): 2,24E-06
Total: 5,08E-06
Value of total risk R1 for the structure: 9,00E-06
For SPD selection see Appendix SPD selection.
7.1 Economic analysis
The economic analysis between different cases of protecion measures is done according to standard EN
62305-2 in order to select the best case.
The economic values related to the structure are listed below:
- Z1 - External
Structure (CB): € 20.000,00
Added value for the structure (CC): € 1.000,00
- Z2 - Office
Structure (CB): € 2.500.000,00
Added value for the structure (CC): € 800.000,00
Equipments value - internal system Power office (CS): € 150.000,00
Equipments value - internal system Telecom office (CS): € 300.000,00
- Z3 - Production
Structure (CB): € 4.000.000,00
Added value for the structure (CC): € 4.500.000,00
Equipments value - internal system Power production (CS): € 300.000,00
Equipments value - internal system Telecom production (CS): € 500.000,00
The cost of protection measures are listed below.
Cost of common protection measures (LPS + SPD at entrance line): € 28.700,00
Z2 - Office
- Internal system: Power office
Coordinated SPD - level: II- cost: € 7.000,00
- Internal system: Telecom office
Coordinated SPD - level: I- cost: € 8.500,00
Z3 - Production
- Internal system: Power production
Coordinated SPD - level: I- cost: € 6.450,00
- Internal system: Telecom production
Coordinated SPD - level: I- cost: € 4.500,00
The values for interest rate, amortisation and maintenance rate are listed below:
- Interest rate: 4 %
- Amortisation: 10 years
- Manteinance rate: 1 %
The values of risk components related to R4 for the unprotected structure are listed below:
Z2: Office
RB: 4,96E-05
RC(Power office): 2,20E-03
RM(Power office): 1,72E-02
RV(Power office): 1,71E-05
RW(Power office): 7,58E-04
RZ(Power office): 1,23E-02
RC(Telecom office): 2,20E-03
RM(Telecom office): 2,29E-06
RV(Telecom office): 4,83E-05
RW(Telecom office): 2,15E-03
RZ(Telecom office): 4,48E-03
Z3: Production
RB: 1,87E-05
RC(Power production): 1,10E-04
RM(Power production): 1,15E-03
RV(Power production): 1,22E-06
RW(Power production): 7,15E-06
RZ(Power production): 6,34E-05
RC(Telecom production): 1,10E-04
RM(Telecom production): 1,15E-07
RV(Telecom production): 1,83E-05
RW(Telecom production): 1,07E-04
RZ(Telecom production): 2,24E-04
Total value of risk R4 for the structure: 6,83E-05
The cost of residual loss (CRL) is calculated according to appendix G of EN 62305-2 standard using
the new values that risk R4 components have after the protection measures are applied in the selected
cases.
The cost of loss for unprotected structure (CL) and the total cost of residual loss in spite of protection
measures (CRL) for all the cases are listed below.
Zone Z1 - External
Cost without protection: € 0,00
Cost with protection: € 0,00
Cost of protection measures: € 0,00
Saving: € 0,00
Zone Z2 - Office
Cost without protection: € 7.945,00
Cost with protection: € 294,71
Cost of protection measures: € 2.325,00
Saving: € 5.325,29
Zone Z3 - Production
Cost without protection: € 974,14
Cost with protection: € 32,62
Cost of protection measures: € 1.642,50
Saving: € -700,98
Cost LPS and SPD at entrance line: € 4.305,00
Total cost without protection: € 8.919,14
Total cost with protection: € 327,33
Total cost of protection measures: € 8.272,50
Total saving: € 319,31
8. CONCLUSIONS
After protection measures (that must be correctly designed) are applied, risk assessment is:
Risk lower than tolerable risk: R1
ACCORDING TO STANDARD EN 62305-2 THE STRUCTURE IS PROTECTED AGAINST
LIGHTNING.
Date 24/10/2006
Rubber stamp and signature
9. APPENDICES
APPENDIX - Structure type
Dimensions: refer to Annex
Location factor: surrounded by smaller objects (Cd = 0,5)
Structure shield: No shield
Lightning flashes frequency (1/km² year) Ng = 2
APPENDIX - Electrical lines characteristics
Line characteristics: Power aerial
The whole line has uniform characteristics.
Type of line: power - aerial
Length (m) Lc = 780
Height above ground (m) Hc = 6
Location factor (Cd): surrounded by higher objects
Environmental factor (Ce): suburban (h < 10 m)
Adjacent structure dimensions:
A (m): 10
B (m): 15
Location factor for adjacent structure (Cd): isolated
H (m): 8
Line characteristics: Power mixed
Type of line: power
Structure's height where the incoming line gets inside (m): 12
The line has more than one section.
Section 1
Buried section
Length (m) Lc = 200
Resistivity (ohm x m)  = 400
Location factor (Cd): surrounded by higher objects
Environmental factor (Ce): suburban (h < 10 m)
Shielding (ohm/km ) connected to the same equipotential bar of equipment: R <= 1 ohm/km
Section 2
Transformer HV/LV
Section 3
Aerial section
Length (m) Lc = 400
Height above ground (m) Hc = 6
Location factor (Cd): surrounded by smaller objects
Environmental factor (Ce): suburban (h < 10 m)
Section 4
Adjacent structure
Adjacent structure dimensions:
A (m): 10
B (m): 15
H (m): 7
Location factor for adjacent structure (Cd): surrounded by smaller objects
Line characteristics: Telecom
The whole line has uniform characteristics.
Type of line: TLC - aerial
Length (m) Lc = 800
Height above ground (m) Hc = 6
Location factor (Cd): isolated
Environmental factor (Ce): suburban (h < 10 m)
Shielding (ohm/km ) connected to the same equipotential bar of equipment: 5 < R <= 20 ohm/km
APPENDIX - Zones characteristics
Zone characteristics: External
Zone type: outside
Type of surface: Grass (ra = 0,01)
Protection measures to reduce the touch and step voltages:
no protection measures
Zone characteristics: Office
Zone type: inside
Type of surface: Linoleum (ru = 0,00001)
Risk of fire: ordinary (rf = 0,01)
Special hazard: Low panic level (h = 2)
Fire protections: manually operated (rp = 0,5)
Zone shielding: No shield
Protection against touch voltage: no protection measures
Internal system: Power office
Connected to line Power aerial
Wiring: Loop area in the order of 10 m² (Ks3 = 0,2)
Withstand voltage: 2,5 kV
Coordinated SPD - level: none (Pspd =1)
Internal system: Telecom office
Connected to line Telecom
Wiring: shielded cable 1 < R <= 5 ohm/km (Ks3 = 0,0002)
Withstand voltage: 1,5 kV
Coordinated SPD - level: none (Pspd =1)
Mean loss value for the zone: Office
Loss due to touch and step voltage (related to R1) Lt = 0,00001
Loss due to physical damage (related to R1) Lf = 0,002
Loss due to failure of internal systems (related to R1) Lo = 0,0001
Loss due to physical damage (related to R4) Lf = 0,09
Loss due to failure of internal systems (related to R4) Lo = 0,04
Risk and risk components for the structure: Office
Risk 1: Rb Rc Rm Ru Rv Rw Rz
Risk 4: Rb Rc Rm Rv Rw Rz
Zone characteristics: Production
Zone type: inside
Type of surface: Linoleum (ru = 0,00001)
Risk of fire: ordinary (rf = 0,01)
Special hazard: Average panic level (h = 5)
Fire protections: automatically operated (rp = 0,2)
Zone shielding: No shield
Protection against touch voltage: no protection measures
Internal system: Power production
Connected to line Power mixed
Wiring: Loop area in the order of 50 m² (Ks3 = 1)
Withstand voltage: 2,5 kV
Coordinated SPD - level: none (Pspd =1)
Internal system: Telecom production
Connected to line Telecom
Wiring: shielded cable 1 < R <= 5 ohm/km (Ks3 = 0,0002)
Withstand voltage: 1,5 kV
Coordinated SPD - level: none (Pspd =1)
Mean loss value for the zone: Production
Loss due to touch and step voltage (related to R1) Lt = 0,0001
Loss due to physical damage (related to R1) Lf = 0,002
Loss due to failure of internal systems (related to R1) Lo = 0,0003
Loss due to physical damage (related to R4) Lf = 0,034
Loss due to failure of internal systems (related to R4) Lo = 0,002
Risk and risk components for the structure: Production
Risk 1: Rb Rc Rm Ru Rv Rw Rz
Risk 4: Rb Rc Rm Rv Rw Rz
APPENDIX - Collection areas and number of annual dangerous events.
Structure
Collection area due to direct flashes to the structure Ad = 5,51E-02 km²
Collection area due to flashes near the structure Am = 3,14E-01 km²
Annual number of dangerous events due to direct flashes to the structure Nd = 5,51E-02
Annual number of dangerous events due to flashes near the structure Nm = 5,73E-01
Electrical lines
Collection area due to direct flashes (Al) and to flashes near (Ai) to the lines:
Power aerial
Al = 0,025272 km²
Ai = 0,780000 km²
Power mixed
Al = 0,016924 km²
Ai = 0,500000 km²
Telecom
Al = 0,026856 km²
Ai = 0,800000 km²
Annual number of dangerous events due to direct flashes (Nl) and to flashes near (Ni) to the lines:
Power aerial
Nl = 0,012636
Ni = 0,780000
Power mixed
Nl = 0,004369
Ni = 0,180000
Telecom
Nl = 0,053712
Ni = 0,800000
APPENDIX - Values of probability of damage for unprotected structure
Zone Z1: External
Pa = 1,00E+00
Pb = 1,0
Pc = 1,00E+00
Pm = 1,00E+00
Zone Z2: Office
Pa = 1,00E+00
Pb = 1,0
Pc (Power office) = 1,00E+00
Pc (Telecom office) = 1,00E+00
Pc = 1,00E+00
Pm (Power office) = 7,50E-01
Pm (Telecom office) = 1,00E-04
Pm = 7,50E-01
Pu (Power office) = 1,00E+00
Pv (Power office) = 1,00E+00
Pw (Power office) = 1,00E+00
Pz (Power office) = 4,00E-01
Pu (Telecom office) = 1,00E+00
Pv (Telecom office) = 1,00E+00
Pw (Telecom office) = 1,00E+00
Pz (Telecom office) = 1,50E-01
Zone Z3: Production
Pa = 1,00E+00
Pb = 1,0
Pc (Power production) = 1,00E+00
Pc (Telecom production) = 1,00E+00
Pc = 1,00E+00
Pm (Power production) = 1,00E+00
Pm (Telecom production) = 1,00E-04
Pm = 1,00E+00
Pu (Power production) = *
Pv (Power production) = *
Pw (Power production) = *
Pz (Power production) = *
Pu (Telecom production) = 1,00E+00
Pv (Telecom production) = 1,00E+00
Pw (Telecom production) = 1,00E+00
Pz (Telecom production) = 1,50E-01
(*) In case of lines with different sections, the probability refers to each section. See Appendix
Electrical lines characteristics.
APPENDIX - SPD selection
It is assumed that a cascade of SPD (if present) is coordinated (installed as required by the
manufacturer's instructions).
In this case the selection of SPD is required for the following lines:
L1 - Power aerial
L2 - Power mixed
L3 - Telecom
LINE L1 - Power aerial
General data
The electrical installation is a TN system.
The line that supplies the main board is three phase + neutral and phase to neutral voltage is 230 V.
Overvoltages due to direct flashes to the structure are considered.
It is assumed a safety coefficient b = 0,9
Lightning current that flows in each line conductor is 5,68 kA (resistivity of soil : 500 ohm x m number of entering services : 5).
Installation structure
The structure of low voltage electrical installation, considered for selection of protection measures
against overvoltages, is reported in Annex Structure installation (**** provided by designer ****).
The main characteristics of installation are listed below.
Main board
Short-circuit current : 10 kA
The Main board supplies the following boards :
Board (2° level)
- Distance : 45 m
- Wiring : loop area 0,5 m²
- Type : three phase + neutral
The Main board directly supplies (without intermediate boards) some terminal circuit.
All final circuits have the same withstand voltage (2500 V), therefore to select protection measures it is
considered the circuit with the worst characteristics :
Final circuit n° 1
- Distance from Main board : 22 m
- Wiring : loop area 0,5 m²
- Type of line : three phase + neutral
Board (2° level)
The Board (2° level) directly supplies (without intermediate boards) some terminal circuit.
All final circuits have the same withstand voltage (2500 V), therefore to select protection measures it is
considered the circuit with the worst characteristics :
Final circuit n° 1
- Distance from Board (2° level) : 2 m
- Wiring : shielded cable R <= 1 ohm/km
- Type of line : phase - neutral
Protection measures selection
The selected protection measures are described for each board.
Main board
On Main board, supplied by a line three phase + neutral, SPD are installed at the board entrance
(upstream of circuit breaker or residual current device), with the following characteristics :
level : I
class : I
type: varistor
protection level Up : 1000 V
length of connecting conductors : 0,2 m
effective protection level Up/f : 1200 V
max continuous operating voltage Uc : 253 V
impulse current Iimp : 10 kA
short-circuit current with or without fuse : 10 kA
The installed SPD protects this board.
The installed SPD protects final circuits / equipments according the following table:
Length (m) Uw (V) lpo (m)lpi (m) Protected
coeff.
Main board
- Final circuit n° 1
0,7
Board (2° level)
- Final circuit n° 1
-
22
2500
42 49,1
Si
47
2500
42 51,3
No
To select protection measures it is considered, for each withstand voltage, the circuit with the worst
characteristics. Because this circuit is protected, are protected also all the circuits supplied by Main
board.
Final circuits protected by SPD
SPD of class II (In >= 5 kA) or class III (Uoc >= 10 kV) are provided on the following circuits :
Board (2° level)
- Final circuit n° 1 - Up/f required for the SPD : 2250 V
SPD coordination
The installed SPD are coordinated.
The protection against overvoltages is completed.
The lengths of final circuits supplied by boards without SPD (for which the circuits with worst
Eff.
characteristics are protected directly by SPD), infact, have lengths lower than the one reported in
Annex B.
ANNEX B
It is necessary to verify that final circuits supplied by the following boards have length lower than the
one reported in table (distance in meters).
The table reports the lower length between the protection distance lpo (oscillation phenomenon) and
protection distance lpi (induction phenomenon).
Board (2° level)
Wiring
Loop area in the order of 50 m²"
Loop area in the order of 10 m²"
Loop area in the order of 0,5 m²"
Shielded cable R <= 1 ohm/km
Shielded cable 1 < R <= 5 ohm/km
Shielded cable 5 < R <= 20 ohm/km
Withstand voltage (V)
1500 2500 4000
0
0
0
0
0
0
0
0
0
6000
0
1,3
3
0
6,7
15,1
0
67,2
151,3
> 10000 > 10000
> 10000 > 10000
1343,8
3026,6
LINE L2 - Power mixed
General data
The electrical installation is a TN system.
The line that supplies the main board is three phase + neutral and phase to neutral voltage is 230 V.
Overvoltages due to direct flashes to the structure are considered.
The earth electrode of building and transformer HV/LV are not connected.
It is assumed a safety coefficient b = 0,9
Lightning current that flows in each line conductor is 3,37 kA (resistivity of soil : 500 ohm x m number of entering services : 5).
The connected line is shielded (S = 10 mm2 in copper) and the distance between the structure and the
closest earthing point of the screen is 60 m.
The minimum withstand voltage of installed equipment: 2500 (V).
The cross-section of connected line is 20 mm².
Installation structure
The structure of low voltage electrical installation, considered for selection of protection measures
against overvoltages, is reported in Annex Structure installation (**** provided by designer ****).
The main characteristics of installation are listed below.
Main board
Short-circuit current : 12 kA
The Main board supplies the following boards :
Board (2° level)
- Distance : 23 m
- Wiring : shielded cable 1 < R <= 5 ohm/km
- Type : three phase + neutral
The Main board directly supplies (without intermediate boards) some terminal circuit.
All final circuits have the same withstand voltage (2500 V), therefore to select protection measures it is
considered the circuit with the worst characteristics :
Final circuit n° 1
- Distance from Main board : 22 m
- Wiring : shielded cable R <= 1 ohm/km
- Type of line : three phase + neutral
Board (2° level)
The Board (2° level) supplies the following boards :
Board (3° level)
- distance : 33 m
- Wiring : shielded cable R <= 1 ohm/km
- Type : three phase + neutral
Board (3° level)
The Board (3° level) supplies the following boards :
Board (4° level)
- distance : 22 m
- Wiring : shielded cable R <= 1 ohm/km
- Type : phase - neutral
The Board (3° level) directly supplies (without intermediate boards) some terminal circuit.
All final circuits does not have the same withstand voltage, therefore to select protection measures it is
considered, for each withstand voltage, the circuit with the worst characteristics :
Final circuit n° 1
- Impulse withstand voltage : 2500 (V).
- Distance from Board (3° level) : 12 m
- Wiring : shielded cable 1 < R <= 5 ohm/km
- Type of line : phase - neutral
Final circuit n° 2
- Impulse withstand voltage : 4000 (V).
- Distance from Board (3° level) : 27 m
- Wiring : shielded cable R <= 1 ohm/km
- Type of line : three phase + neutral
Board (4° level)
The Board (4° level) directly supplies (without intermediate boards) some terminal circuit.
All final circuits have the same withstand voltage (2500 V), therefore to select protection measures it is
considered the circuit with the worst characteristics :
Final circuit n° 1
- Distance from Board (4° level) : 22 m
- Wiring : shielded cable R <= 1 ohm/km
- Type of line : phase - neutral
Protection measures selection
The selected protection measures are described for each board.
Main board
On Main board, supplied by a line three phase + neutral, SPD are installed at the board entrance
(upstream of circuit breaker or residual current device), with the following characteristics :
level : I
class : I
type: varistor
protection level Up : 1000 V
length of connecting conductors : 0 m
effective protection level Up/f : 1000 V
max continuous operating voltage Uc : 253 V
impulse current Iimp : 5 kA
short-circuit current with or without fuse : 12 kA
The installed SPD protects this board.
The installed SPD protects final circuits / equipments according the following table:
Length (m) Uw (V) lpo (m) lpi (m)
Eff. coeff.
Main board
- Final circuit n° 1
Board (3° level)
- Final circuit n° 1
- Final circuit n° 2
Board (4° level)
- Final circuit n° 1
-
Protected
22
2500
***
---
Si
68
2500
***
---
Si
83
4000
***
---
Si
100
2500
***
---
Si
*** Up/f <= bUw / 2 and/or circuit length is lower than 10 m, therefore it is not ncessary to evaluate
the oscillation protection distance (lpo).
--- It is not necessary to evaluate the induction protection distance (lpi).
To select protection measures it is considered, for each withstand voltage, the circuit with the worst
characteristics. Because this circuit is protected, are protected also all the circuits supplied by Main
board.
Final circuits protected by SPD
SPD are not provided on the final circuits.
The protection against overvoltages is completed.
Cross-section of connecting conductors for SPD
The minimum cross-section of connecting conductors for SPD is:
 Class I : 6 mm2
 Class II : 4 mm2
 Class III : 1,5 mm2
In any case, for SPD class I, the cross-section of connecting conductors (S) should respect the
following relation:
S >= Iimp / 8 for PVC connecting conductors
S >= Iimp / 10 for EPR connecting conductors
The layout of SPD installation is reported in Annex "SPD installation".