2.3

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Damage of LD-SLT and DCS telecommunication equipment

Damage.

Lightning.

Transmission equipment.

Telecom centre.

Damage, lightning surge.

2004-01-01

A system configuration and an estimated current flow are shown in Figure 2.3-1. This telecommunication centre is a co-location building. Company A's telecommunication equipment and another company's equipment are sharing one same floor of the building. The radio equipment is connected to the antennas as shown in Figure 2.3-1. The power supply equipment located on the first floor is used to distribute DC power to both companies' telecommunication equipment. IBS in the figure is a DC power distribution module.

Company A's telecommunication equipment is powered through the IBS, while the other company's equipment is powered through the PDF, where PDF and IBS are power distribution frames. The PDF and IBS are also connected to the RF located on the first floor. DCS is a clock-supplying equipment that provides the clock signal to the radio equipment CR-822. CR-822 has a telecom interface and is connected to the switching equipment LD-SLT through a DF (a distribution frame). At this telecom centre, LD-SLT, SLM, DCS, and PSF were damaged by lightning.

Figure 2.3-1 – A system configuration and an estimated surge current

It was estimated that direct lightning hit the antenna tower, and the surge current entered the telecom centre through the coaxial cables and the building structures, flowing into the radio equipment. The current entered the LD-SLT through the radio equipment, the SLM through the building structure or floor, and the DCS through the radio equipment.

To prevent these damages from occurring again, it was required to do the following, as shown in Figure 2.3-2:

–    Bonding earthing networks.

–    Insert insulation transformer in CLK line.

–    Insert insulation bushing to isolate the equipment from building structures.

–    Change the cable panel with high insulation resistibility.

More detailed consideration should be given to connecting earthing networks when dealing with power systems of IT or other systems. 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 2.3-2 – Mitigation configuration

Recs ITU-T K.27, ITU-T K.35, ITU-T K.40, ITU-T K.56; Annex C.