In mobile communications, high availability and reliability of equipment and system technology are critical in both the private and public sectors. When configuring network infrastructure and planning new sites, planners, installers and operators must take lightning and surge protection measures, which are also required from an insurance perspective.
Increasing demand for 5G technology means that we need higher transmission capacities and better network availability. New cell site locations are being developed constantly for this purpose, with existing infrastructure being modified and expanded. These cell sites must obviously be reliable, but the exposed location of mobile radio masts makes them vulnerable to direct lightning strikes, which could cause severe damage to the systems.
Why bother with lightning and surge protection?
The exposed location of mobile radio masts makes them vulnerable to direct lightning strikes which could paralyze the systems. Damage is often also caused by surges, e.g. in case of nearby lightning strikes.
Another important aspect is protecting the personnel working on the system during a thunderstorm.
A lightning protection system provides optimal protection by coordinating both the external and internal lightning protection segments:
- The external lightning protection system consists of an air termination system, down conductor and earth-termination system.
- The internal lightning protection system encompasses lightning equipotential bonding and surge protective devices.
Protection Components inside the Surge Protection Device
The surge protection device interfaces with the AC power line and is subject to transients inherent in the AC power line.
A surge suppression fuse on the input of the surge protection circuit is recommended. This type of fuse can withstand a lightning surge up to 200 kA based on transient surges defined in UL 1449 and IEC 61000-4-5. This fuse also acts to provide current limiting protection under short circuit conditions.
Following the surge suppression fuse, consider using a series combination of a metal oxide varistor (MOV) and a gas discharge tube (GDT) to absorb the lightning strike and other large transients arising from load changes that occur on the power line.
Place the MOV-GDT combination as close to the input as possible to minimize the transient propagation into the circuit.
Connect the MOV between Line and Neutral and connect the gas discharge device from neutral to ground.
Additionally, a high-power transient voltage suppressor (TVS) diode is an alternative to a MOV if the TVS diode’s maximum surge handling capacity is adequate for the AC power line feed. TVS diodes have faster response times and clamp transients at lower voltages.
Protecting the Tower-Mounted Amplifier
The tower-mounted amplifier is exposed to the outdoor environment and needs protection from lightning strikes and ESD.
This circuit should have a series fuse to protect against current overloads and a parallel TVS diode to absorb lightning or ESD transient strikes.
High-power TVS diodes can safely absorb current overloads as high as 10 kA. These components are available in surface-mount packages when space constraints are critical.
Power Input Circuit
The power input circuit provides the DC power for the other AAS circuits.
On the input stage, a fuse for overcurrent protection is recommended. For this DC circuit, a fast-acting fuse is a suitable choice. Surface mount fast-acting versions are available for space-saving applications.
Consider a MOV and a gas discharge tube in series to protect the front-end of the power input circuit from transients that have passed through the SPD and the power supply and backup battery circuit.
Since the power input feeds all the other circuits, consider protecting these circuits from transient and ESD protection with a TVS diode at the back-end of the power input circuit. A TVS diode has a lower clamping voltage than a MOV and enables the use of lower, voltage-rated (and lower cost) components in the downstream circuits.