Surge arresters
A surge arrester (ÜSP, Surge Protective Device SPD ) is a device or component for limiting dangerous surge voltages in electrical lines and devices. Efficient surge protection includes a combination of different surge arresters adapted to the purpose.
General
Overvoltages can be caused by direct or nearby lightning strikes, by magnetic storms caused by the sun , by an electromagnetic pulse ( EMP ), by electrostatic discharges ( ESD ) or switching processes in the power supply network and in devices and accordingly sometimes have considerable instantaneous power.
history
The German engineer Anton Kathrein senior invented the mast disconnector surge arrester with built-in fuse , which protects low-voltage networks from failures caused by lightning, and with which he started his own business in Rosenheim in 1919 .
Facilities
The following are used as surge arresters:
- Spark gaps (with insulators of overhead lines and insulators of self-radiating transmission masts): they are partially self-extinguishing with the appropriate geometry (horn arrester)
- Gas-filled surge arresters, so-called gas arresters . They are used as fine protection and for high energies. They are not self-extinguishing and trigger the upstream fuse.
- Varistors only limit the voltage and are de-energized again after the overvoltage pulse has subsided
- Suppressor diodes behave similarly to a Zener diode and are also de-energized at the end of the pulse
With suppressor diodes , the signal inputs of electrical devices in particular are protected against low voltages. They can only tolerate low energies, but offer a tightly tolerated protection level.
Varistors protect the mains voltage input of devices or endangered points in the power grid (e.g. building lightning protection, inputs and outputs of large transformers and traction power substations ).
Gas arresters are used to protect signal and, in some cases, network lines if very high discharge energies are expected.
Protection of overhead lines
Before the development of sufficiently good varistor material (low current at nominal voltage, long service life), the following were used to protect overhead lines from the consequences of a lightning strike:
- Cathode drop arrester
- They combine a spark gap and a varistor in series . The series connection of several varistors are dimensioned for the nominal voltage to be protected and, after the overvoltage event, limit the line follow current through the spark gap to such an extent that it extinguishes automatically due to the cathode drop. In normal operation, the varistors are de-energized due to the separating spark gap.
- Extinguishing pipe arrester
- A surge arrester that is no longer common: it extinguishes the discharge that ignites in the event of an overvoltage in that the arc releases gases from the pipe material, which blow the arc out of the pipe and thus extinguish it. Due to the jet of fire, it could only be used outdoors.
Overhead line insulators are protected with spark gaps from the direct effect of arcs induced by lightning strikes. They keep the arc away from the insulating material and, due to their shape, often contribute to extinguishing the arc (horn arrester). If the arc does not go out, the network section is switched off by means of a short interruption and then automatically switched on again after a short time.
The surge arrester shown on the right is a stack of varistor disks that become conductive in the event of a lightning strike , for example. B. protect a power transformer not visible in the picture from overvoltage.
Protection of small appliances
Gas-filled surge arresters insulate as long as the voltage remains below approx. 450 V and do not interfere because of their low capacitance of only approx. 2 pF. If the ignition voltage is exceeded, the resistance drops to very low values within microseconds, whereby current peaks of up to 20,000 A can be diverted. They are thermally overloaded during continuous operation.
Regulations
New DIN regulations have existed since October 2016. Surge protective devices must be installed in accordance with DIN VDE 0100-443 if there are effects on human life, in the event of people gathering in public facilities and cultural property, in commercial and industrial activities or if individuals could be affected in buildings with equipment in overvoltage category I or II (e.g. in residential buildings or small offices)
Footnotes
- ↑ Adalbert Varduhn, Walter Nell: Handbook of electrical engineering. Volume 2: Switchgear, measuring instruments, light and power installations, overhead lines and cables, lighting technology; Electric heat, other electrical appliances. Fachbuchverlag, Leipzig 1951.
- ↑ Protection against surges. In: GIT Sicherheit, issue 4/2017