Protect switching power supplies against voltage surges

Transient overvoltages, or voltage surges of very short duration in the low-voltage mains network, occur every day. Causes include not only thunderstorms but also switching operations at the energy utility or in industrial facilities, or defective electrical equipment in an electrical installation. The disruptions last for only a very brief period: they can be small and go unnoticed, but can also involve very high energy levels, and consequences include partial and complete breakdown of systems and facilities. .

A switching power supply is often unable to discharge the high energy levels involved, or can do so only with difficulty, because the complexity of its construction limits its passive surge capability. Additional active surge protection devices offer a solution, whether or not a surge protection concept has already been considered in the electrical installation.

• To offer the best protection against any disturbances that occur, the SPD should be as close as possible to the terminal equipment.

• A good surge voltage protector offers a protection level as low as possible, ideally under 1500V (for 230/400 VAC system voltage), and high discharge capability.
• Selecting the right SPD depends on the magnitude of the maximum energy absorption. Key criteria are type, installation situation, and risk for the system and people.
• Active SPDs, because they are less complex than switching power supplies, are considerably better at handling higher impulse energy levels.

For optimal protection for sensitive, high-quality facilities and systems, limits should, as far as possible, be put on the protection level. With this in mind, installing an SPD of type 1 to 3 offers suitable protection, depending on the expected overvoltage level and/or the installation location.
• Type 1: Lightning current discharge
• Types 1+2+3: Combined lightning and SPDs for discharging lightning-induced currents and for protection against rapidly rising voltage surges
• Type 2 / Types 2+3: SPDs for protection against switching overvoltages and switching events
• Type 3: SPDs for equipment protection, offering minimum protection

LED lighting: In addition to the mains connection, overvoltage protection equipment for LED lighting should also take into account protection for dimming and/or bus cables. Even if the producers of LED power supplies sometimes exceed the requirements for 2kV dielectric strength in accordance with EN61547 for external applications, it is important to consider using an SPD. With longer cable distances to the lamps or if there is potential interference in the electrical installation, it is worth employing an SPD in the lamp itself or very close to it.

Building services engineering: Equipping the electrical installation with SPDs at the sub-distribution level provides the first line of defence. However, because of the length of cables and possible sources of interference, SPDs at this level are often not enough, and an additional SPD in the terminal equipment offers extra protection.

Industrial applications: If particular equipment, for example, has to have as long an operational life as possible, or if service costs for maintenance and upkeep are high, it is also worth considering an additional SPD inside or very close to the equipment. Especially with systems that operate outdoors or in industrial environments, the risk of failure due to a voltage surge is particularly high.