According to the currently valid product standard IEC 61643-11, a distinction is made between ‘Type I, Type II and Type III’ arresters. These arresters differ in terms of their discharge capacity, the respective protection level and their test pulses.
An arrester is a protective component that contains a surge protection circuit in an enclosure that also takes electrical and mechanical installation conditions into account. At Weidmüller, the surge protection circuit for energy arresters consists of gas arresters, varistors or suppressor diodes.
In the event of surges, an arrester provides lightning protection potential equalisation in the micro- to nanosecond range, allowing the transient current to flow away and limiting the occurring surge to harmless values. This protects the electrical equipment and systems. In this case, a fuse usually does not even trip due to its inertia, which is why its use as surge protection is completely unsuitable.
The type I arrester (lightning arrester) is used for personal protection and the protection of electrical installations and systems in the event of direct or nearby lightning strikes.
According to the lightning protection standard DIN EN 62305, the use of a type I arrester is mandatory as soon as the building has an external lightning protection system. Type I arresters are installed at the interfaces of the lightning protection zones LPZ 0 and LPZ 1 in the building feed-in / main distribution board. They conduct the lightning current directly to earth and must have a protection level < 6 kV.
The test impulse of the type I arrester symbolises the lightning impulse of a direct lightning strike. It is characterised by a rise time of 10 µs and a back half-life of 350 µs, with the area under the curve describing the energy of the test pulse.
The type II arrester (surge arrester) protects the electrical equipment and systems from overvoltages caused by remote lightning strikes and switching operations.
It has a protection level < 4 kV and is installed at the interfaces of the LPZ 1 and LPZ 2 lightning protection zones, normally in the sub-distribution board.
The test impulse of a type II arrester is characterised by a rise time of 8 µs and a back half-value time of 20 µs and symbolises the overvoltage impulse caused by switching operations or indirect lightning strikes.
Type III arresters (end device surge protection) reduce the overvoltages to a voltage level that is safe for the electrical terminal device.
They are installed directly in front of the end device to be protected in lightning protection zones LPZ 1 or LPZ 2 and have a protection level < 2.5 kV.
Type III arresters with a 2-ohm hybrid impulse current generator and a voltage of 6 kV are tested. According to I = U / R, this results in a current of 3 kA. As the test is carried out both in open circuit and in short circuit, there are two test pulses.
In idle mode, the test pulse is characterised by a rise time of 1.2 µs and a back half-life of 50 µs. As with the type II arrester, the test pulse in the short circuit is the 8/20 µs pulse.
The figure compares the two test pulses 10/350 µs (1) and 8/20 µs (2). It can be seen here that the lightning impulse, in addition to having a significantly higher amplitude, is also more energetic and slower than the surge impulse.
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