Page 475 - 35_DS702_E_2014_Lightning_Protection_Guide

C. Terms and definitions

actiVsense Degree of protection
The actiVsense technology is integrated in universal combined The IP degree of protection corresponds to the protection cat-
arresters for protecting information technology installations egories described in IEC 60529.
and devices. The arrester automatically detects the signal volt-
age applied and optimally adapts the voltage protection level Disconnecting time t a
to it. Thus, the arrester can be universally used for different The disconnecting time is the time passing until the automatic
interfaces and provides maximum protection for the devices disconnection from power supply in case of a failure of the
and system circuits connected to it in case of failure. circuit or equipment to be protected. The disconnecting time is
an application-specific value resulting from the intensity of the
Breaking capacity, follow current extinguishing fault current and the characteristics of the protective device.
capability I fi
The breaking capacity is the uninfluenced (prospective) r.m.s. Energy coordination of SPDs
value of the mains follow current which can automatically be Energy coordination is the selective and coordinated interac-
extinguished by the surge protective device when connecting tion of cascaded protection elements (= SPDs) of an overall
U C . It can be proven in an operating duty test according to lightning and surge protection concept. This means that the
EN 61643-11. total load of the lightning impulse current is split between the
SPDs according to their energy carrying capability. If energy co-
Categories according to IEC 61643-21:2009 ordination is not possible, downstream SPDs are insufficiently
A number of impulse voltages and impulse currents are de- relieved by the upstream SPDs since the upstream SPDs oper-
scribed in IEC 61643-21:2009 for testing the current carrying ate too late, insufficiently or not at all. Consequently, down-
capability and voltage limitation of impulse interference. Ta- stream SPDs as well as terminal equipment to be protected
ble 3 of this standard lists these into categories and provides may be destroyed. CLC/TS 61643-12:2010 describes how to
preferred values. In Table 2 of the IEC 61643-22 standard the verify energy coordination. Spark-gap-based type 1 SPDs offer
considerable advantages due to their voltage-switching char-
sources of transients are assigned to the different impulse acteristic (see WAVE BREAKER FUNCTION).
categories according to the decoupling mechanism. Category
C2 includes inductive coupling (surges), category D1 galvanic Frequency range
coupling (lightning currents). The relevant category is specified The frequency range represents the transmission range or cut-
in the technical data. DEHN + SÖHNE surge protective devices off frequency of an arrester depending on the described at-
surpass the values in the specified categories. Therefore, the tenuation characteristics.
exact value for the impulse current carrying capability is in-
dicated by the nominal discharge current (8/20 μs) and the Insertion loss
lightning impulse current (10/350 μs). With a given frequency, the insertion loss of a surge protec-
tive device is defined by the relation of the voltage value at
Combination wave the place of installation before and after installing the surge
A combination wave is generated by a hybrid generator protective device. Unless otherwise indicated, the value refers
(1.2/50 μs, 8/20 μs) with a fictitious impedance of 2 Ω. The to a 50 Ω system.
open-circuit voltage of this generator is referred to as U OC . U OC
is a preferred indicator for type 3 arresters since only these Integrated backup fuse
arresters may be tested with a combination wave (according According to the product standard for SPDs,
to EN 61643-11). overcurrent protective devices / backup
fuses must be used. This, however, requires
Cut-off frequency f G additional space in the distribution board,
The cut-off frequency defines the frequency-dependent behav- additional cable lengths, which should
iour of an arrester. The cut-off frequency is equivalent to the be as short as possible according to IEC 60364-5-53, ad-
frequency which induces an insertion loss (a E ) of 3 dB under ditional installation time (and costs) and dimensioning of
certain test conditions (see EN 61643-21:2010). Unless other- the fuse. A fuse integrated in the arrester ideally suited for
wise indicated, this value refers to a 50 Ω system. the impulse currents involved eliminates all these disadvan-

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