International Telecommunication Union
Risk regarding safety
Phil Day
Protection Specialist, Telstra Corp, Australia
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
Introduction
ITU-T
o
This presentation will introduce:
1. Missing risk components
2. Risk mechanisms
3. The magnitudes of voltages and
currents relevant to electric shock;
4. Discussion on 62305-2
5. Future work
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
2
Lightning as source of damages
ITU-T
Direct to the
structure
Close to the
structure
RA Injury to
people
RB Physical
damage
RC Equipment
failure
RM Equipment
failure
R1: Risk
R2: Risk
R3: Risk
R4: Risk
Direct to the
tlc line
RU Injury to
people
RV Physical
damage
RW Equipment
failure
RZ Equipment
failure
of loss of human life = RA+RB+RU+RV+(RC+RW+RM+RZ)
of loss of service = RB+RC+RV+RW+RM+RZ
of loss of cultural heritage = RB+RV
of loss of economic value = RB+RC+RV+RW+RM+RZ
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
Close to the
tlc line
3
Missing Risk components
ITU-T
o
RA is the risk of electric shock
component due to a strike to the
structure
1. Does not calculate inside structure
• Note in 620305
2. Remote telecommunication earth is
a particular risk and not calculated
3. Following figures show mechanisms
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
4
Missing Risk components
ITU-T
o
RU is the risk of eclectic shock
component due to a strike to the
services
1. Remote telecommunication earth is
a particular risk and not calculated
2. Following figures show mechanisms
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
5
Risk mechanisms
ITU-T
RA1
Power
User environment
V
ra
Figure 3 - Direct strike to structure (touch potential with respect to the ground
outside the structure)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
6
Risk mechanisms (cont)
ITU-T
Not covered by 62305-2
Excluded by note in 62305-2
Power
User environment
V
ra
Figure 4 - Direct strike to structure (touch potential with respect to the floor of the
structure)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
7
Risk mechanisms (cont)
Not covered by 62305-2
ITU-T
If covered by 62305-2, r a= 1
Power
User environment
Telecommunications line
connected to remote earth
V
R
Figure 5 - Direct strike to structure (touch potential; earthed object to a
telecommunication line which is connected to a remote earth)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
8
Risk mechanisms (cont)
ITU-T
Not covered by 62305-2
If covered by 62305-2, r amay be 1 in some circumstances
Power
User environment
Telecommunications line
connected to remote earth
V
ra
R
Figure 6 - Direct strike to structure (touch potential; floor to a telecommunication line
which is connected to a remote earth)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
9
Risk mechanisms (cont)
ITU-T
R B1
Power
Figure 7 - Direct strike to structure (flashover to internal wiring or plumbing)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
10
Risk mechanisms (cont)
Not covered by 62305-2
ITU-T
Power
equip
Telecommication cable
Figure 8 - Direct strike to structure (flashover to telecommunication line due to EPR)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
11
Risk mechanisms (cont)
ITU-T
Covered by 62305-2 but needs modification
Source S1
Source S1
Strike to the structure
Strike to the structure
Equipment
a) current paths for a strike to the structure,
shielded telecommunication cable
Equipment
b) current paths for a strike to the structure,
unshielded telecommunication cable
Figure 9 - Direct strike to structure (Damage to telecommunication equipment)
(No SPDs)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
12
Risk mechanisms (cont)
ITU-T
Covered by 62305-2
Power
User environment
V
ra
Figure 10 - Direct strike to overhead power line (touch potential with respect to the floor
of the structure)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
13
Risk mechanisms (cont)
ITU-T
Not covered by 62305-2
Power
User environment
Telecommunications line
connected to remote earth
V
R
Figure 11 - Direct strike to a power line (touch potential earthed object to the
telecommunication line which is connected to a remote earth)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
14
Risk mechanisms (cont)
Not covered by 62305-2
ITU-T
Power
User environment
Telecommunications line
connected to remote earth
V
ra
R
Figure 12 - Direct strike to a power line (touch potential floor to the telecommunication
line which is connected to a remote earth)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
15
Risk mechanisms (cont)
Covered by 62305-2, but may require change
Power
ITU-T
User environment
Telecommunications
V
ra
Figure 13 - Direct strike to telecommunication line (touch potential with respect to the
floor of the structure)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
16
Risk mechanisms (cont)
Not covered by 62305-2
Power
ITU-T
User environment
V
Telecommunications
Figure 14 - Direct strike to telecommunication line (touch potential with respect to
earthed object)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
17
Risk mechanisms (cont)
Covered by 62305-2 but requires modification
ITU-T
Power
equip
Telecommication cable
Figure 15 - Direct strike to power line (flashover to telecommunication line due to EPR)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
18
Risk mechanisms (cont)
Covered by 62305-2 but requires modification
Power
ITU-T
equip
Telecommication cable
Figure 16 - Direct strike to telecommunication line (flashover to structure)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
19
Risk mechanisms (cont)
S3
ITU-T Source
Strike to the power line
Source S3
Strike to the power line
Covered by 62305-2 but requires change
Equipment
a) current paths for a strike to the power line,
shielded telecommunication cable
Equipment
b) current paths for a strike to the power line,
unshielded telecommunication cable
Figure 17 - Direct strike to power line/cable (Damage to telecommunication equipment)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
20
Risk mechanisms (cont)
ITU-T
Source S3
Strike to the telecommunication line
Source S3
Strike to the telecommunication line
Covered by 62305-2 but requires change
Equipment
a) current paths for a strike to the telecommunications line,
shielded telecommunication cable
Equipment
b) current paths for a strike to the telecommunications
line, unshielded telecommunication cable
Figure 18 - Direct strike to telecommunication line/cable (Damage to
telecommunication equipment)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
21
Magnitudes
Resistance at strike point
ITU-T
300
250
Resistance in ohm
200
R for 100 ohm-m
R for 1000 ohm-m
150
100
50
0
0
20
40
60
80
100
120
140
160
180
200
Strike current in kA
Figure 1 - Resistance to ground at strike point
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
22
Magnitudes (cont)
EPR versus current and resistivity
4500
ITU-T
4000
3500
3000
EPRV for 100 ohm-m
EPR in kV
EPR for 1000 ohm-m
2500
100 kV line
2000
1500
1000
500
0
0
20
40
60
80
100
120
140
160
180
200
Current in kA
Figure 2 - EPR at strike point versus current
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
23
Magnitudes (cont)
ITU-T
Table 1 – Limiting voltage of
different cable types
Cable type
Limiting voltage
Cellular (blown)
CPFUT MB
Solid PEIFLI MBHJ
b/d voltage to screen 5 10 kV
b/d voltage to screen up
to 75 kV
b/d voltage to ground up
to 150 kV
Unshielded PE cable
Cable limits the voltage
(MB = PE sheathed with Moisture Barrier screen; HJ = nylon jacket; PEIFLI = solid PE
insulated conductors, grease filled lead-in cable; CPFUT = cellular insulated unit twin
conductors;)
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
24
Magnitudes (cont)
Table 2 – Values of ra
ITU-T
Type of soil or floor
Contact resistance
(kΩ)*
ra and ru
Agricultural, Concrete
≤ 1
10-2
Marble, Ceramic
1-10
10-3
Gravel, Moquette,
Carpets
10-100
10-4
Asphalt, Linoleum,
Wood
≥ 100
10-5
(*) Values measured between a 400 cm² electrode compressed with a
force of 500 N and a point of infinity.
Low voltages only?
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
25
Discussion on 62305-2
ITU-T
o
As described by Roberto the Risk of
loss = NX * PX * LX
1. Nx for services uses Lc for the line
length. Need to validate values for
Lc
• Maybe different for direct strikes
versus induction
• What determines the value of Lc
• Need consistency for single section
versus multiple sections
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
26
Discussion on 62305-2 (cont)
ITU-T
1. Px is the probability of damage.
This includes:
• Whether SPDs are installed
• Shielding factors
• Screen resistance
o
Some rationale has been provided by
Roberto
• IEC have assumed both an LPS and
coordinated SPDs (software)
o
My approach is add one at a time. The most
common protection is an MSPD and possibly
a GDT on the telecommunication line
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
27
Discussion on 62305-2 (cont)
ITU-T
1. Lx is the consequence of loss. The
factors include:
• np, nt and t
I have difficulty considering these as
loss. They relate more to probability
• In particular ra, ru, rp, rf and hz relate
directly to probability of injury or
damage
• There is no loss factor for domestic
equipment
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
28
Discussion on 62305-2 (cont)
ITU-T
• Therefore I think SG 5 needs to review
the use of loss versus probability
• If loss is retained the values should be
carefully selected and rationale
provided
• Loss factors for domestic equipment
need to be developed
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
29
Future work
ITU-T
o
Consider
1. the use of 62305-2
2. The factor Lc
3. The factor ra
4. Loss factors
ITU-T SG 5 Technical Session “Lightning protection”
12 December 2005, ITU Headquarters, Geneva
dates
30