b Values relevant to the case of the strike to the last pole of the line close to the consumer and multiconductor (three phase + neutral) line.
° Values referred to overhead lines. For buried lines values can be halved.
d Loop inductance and resistance affect the shape of the induced current. Where the loop resistance is negligible, the shape 10/350 ps should be assumed. This is the case where a switching type SPD is installed in the induced circuit
.Table Е.З - Expected surge overcurrents due to lightning flashes
on telecommunication systems
|
LPL (class) |
Telecommunication systems3 |
|||
|
Direct and indirect flashes to the service |
Flash near the structure6 |
Flash to the structure6 |
||
|
Source of damage S3 (direct flash)c Current shape: 10/350 ps kA |
Source of damage S4 (indirect flash)6 Current shape: 8/20 Jis kA |
Source of damage S2 (induced current) Current shape 8/20 ps kA |
Source of damage S1 (induced current) Current shape: 8/20jis kA |
|
|
III - IV |
1 |
0,035 |
0,1 |
5 |
|
II |
1,5 |
0,085 |
0,15 |
7,5 |
|
I |
2 |
0,160 |
0,2 |
10 |
|
NOTE All values refer to each line conductor. |
||||
|
a Refer to ITU-T Recommendation K.67 [6] for more information. b Loop conductors routing and distance from inducing current affect the values of expected surge overcurrents. Values in Table E.3 refer to short-circuited, unshielded loop conductors with different routing in large buildings (loop area in the order of 50 m , width = 5 m), 1 m apart from the structure wall, inside an unshielded structure or building with LPS (kc = 0,5). For other loop and structure characteristics, values should be multiplied by factors KS1, KS2, KS3 (see Clause B.4 of IEC 62305-2:2010). c Values referred to unshielded lines with many pairs. For an unshielded drop wire, values could be 5 times higher. d Values referred to overhead unshielded lines. For buried lines values can be halved. |
||||
For shielded lines, the values of the overcurrents given in Table E.2 can be reduced by a factor of 0,5.
NOTE It is assumed that the resistance of the shield is approximately equal to the resistance of all line conductors in parallel.
E.3.2 Surges due to flashes near the lines (source of damage S4)
Surges from flashes near lines have energies much lower than those associated with flashes to lines (source of damage S3).
Expected overcurrents, associated with a specific lightning protection level (LPL) are given in Tables E.2 and E.3.
For shielded lines the values of overcurrents given in Tables E.2 and E.3 can be reduced by a factor 0,5.
E.4 Surges due to induction effects (source of damage S1 or S2)
E.4.1 General
Surges due to induction effects from magnetic fields, generated either from nearby lightning flashes (source S2) or from lightning current flowing in the external LPS or the spatial shield of LPZ 1 (source S1) have a typical current shape of 8/20 ps. Such surges are to be considered close to or at the terminal of apparatus inside LPZ 1 and at the boundary of LPZ 1/2.
Е.4.2 Surges inside an unshielded LPZ 1
Inside an unshielded LPZ 1 (e.g. protected only by an external LPS according to IEC 62305- 3 with mesh width greater than 5 m) relatively high surges are to be expected due to the induction effects from the undamped magnetic field.
Expected overcurrents, associated with a specific lightning protection level (LPL) are given in Tables E.2 and E.3.
E.4.3 Surges inside shielded LPZs
Inside LPZs with effective spatial shielding (requiring mesh width below 5 m according to Annex A of IEC 62305-4:2011), the generation of surges due to induction effects from magnetic fields is strongly reduced. In such cases the surges are much lower than those given in E.4.2.
Inside LPZ 1 the induction effects are lower due to the damping effect of its spatial shield.
Inside LPZ 2 the surges are further reduced due to the cascaded effect of both spatial shields of LPZ 1 and LPZ 2.
E.5 General information relating to SPDs
The use of SPDs depends on their withstand capability, classified in IEC 61643-1[71 for power and in IEC 61643-21181 for telecommunication systems.
SPDs to be used according to their installation position are as follows:
At the line entrance into the structure (at the boundary of LPZ 1, e.g. at the main distribution board MB):
SPD tested with /imp (typical current shape 10/350), e.g. SPD tested according to Class I;
SPD tested with /n (typical current shape 8/20), e.g. SPD tested according to Class II.
Close to the apparatus to be protected (at the boundary of LPZ 2 and higher, e.g. at a secondary distribution board SB, or at a socket outlet SA):
SPD tested with /imp (typical current shape 10/350), e.g. SPD tested according to Class I for power SPDs);
SPD tested with /n (typical current shape 8/20), e.g. SPD tested according to Class II);
SPD tested with a combination wave (typical current current shape 8/20), e.g. SPD tested according to Class III.
Bibliography
I EC 60664-1:2007, Insulation coordination for equipment within low-voltage systems -
Part 1: Principles, requirements and tests
IEC 61000-4-5, Electromagnetic compatibility (EMC) - Part 4-5: Testing and measurement techniques - Surge immunity test
BERGER K., ANDERSON R.B., KRONINGER H., Parameters of lightning flashes. CIGRE Electra No 41 (1975), p. 23 - 37
ANDERSON R.B., ERIKSSON A.J., Lightning parameters for engineering application. CIGRE Electra No 69 (1980), p. 65 - 102
IEEE working group report, Estimating lightning performance of transmission lines- Analytical models. IEEE Transactions on Power Delivery, Volume 8, n. 3, July 1993
ITU-T Recommendation K.67, Expected surges on telecommunications and signalling networks due to lightning
IEC 61643-1, Low-voltage surge protective devices - Part 1: Surge protective devices connected to low-voltage power distribution systems - Requirements and tests
IEC 61643-21 Low-voltage surge protective devices - Part 21: Surge protective devices connected to telecommunications and signalling networks - Performance requirements and testing methods
