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Mitigation measures for telecommunication installations
PART 2: CASE STUDIES
| Case study # |
2.1 |
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| Title |
Lightning surge troubles on transmission equipment, TCM, and MUX
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| Type of trouble |
Damage.
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| Source of trouble |
Lightning surge.
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| System affected |
Transmission equipment and MUX.
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| Location |
Telecommunication centre.
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| Keywords |
Damage, lightning surge.
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| Version date |
2004-01-01 |
| System configuration |
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The system configuration for a lightning surge trouble
case is shown in Figure 2.1-1. As depicted in the figure, a
transmission equipment, a TCM (transmission communication
module), was located in the telecommunication centre, and
there was a building with an antenna tower next to the
telecommunication centre. Coaxial cables were used between
the two buildings to connect the transmission equipment with
the radio equipment. The earthing of the telecommunication
centre and the earthing of the building were not connected to
each other. The main distribution frame (MDF) earthing was
not connected to the telecommunication centre earthing,
either.
Figure 2.1-1 – System configuration |
| Measurement/Searching techniques/Experiment
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As a result of the investigation, lightning surge strikes were detected at the radio antenna tower by visual inspection. Lightning surge current flowed through the tower, the earthing, power supply, MUX and TCM. It was considered that the surge current in the coaxial cables could damage the telecom equipment, TCM and MUX.
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| Mitigation method/Results/Conclusion |
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After investigations, it was confirmed
that the transmission equipment, and the MUX could be damaged
by surge current flowing from the building with the antenna
tower, due to the electric potential difference between the
building and telecommunication centre. For this
telecommunication installation, a bonding network reduced the
potential difference between the telecom centre and the other
building. MDF earthing was also connected to the earth, as
shown in Figure 2.1-2.
More detailed consideration should be given to connecting
earthing networks when dealing with power systems of IT
installations. The earthing resistance of IT systems is too
high to absorb power fault current. If the earthing networks
of several buildings are connected to each other, the total
earthing resistance is lower than the original individual
one. Therefore, national regulations or the relative
Recommendations should be referred to.
Figure 2.1-2 – Mitigation configuration |
| References |
Recs ITU-T K.27, ITU-T K.35, ITU-T K.40, ITU-T K.56; Annex C.
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