Page 13 - Surge-Protection-E_0.pdf

Terms and Definitions

SCI technology Total discharge current Itotal
Direct currents (d.c.) flow on the generator side of a PV system. The surge Current which flows through the PE, PEN or earth connection of a multi-
protective devices used on the generator side can be overloaded due to pole SPD during the total discharge current test. This test is used to de-
different scenarios (e.g. impulse load, insulation faults) and must not en- termine the total load if current simultaneously flows through several
danger the PV system. However, insufficient d.c. disconnection capability protective paths of a multipole SPD. This parameter is decisive for the
in a PV system may cause fire. Conventional surge arresters only feature total discharge capacity which is reliably handled by the sum of the indi-
a disconnector in the form of a simple break contact mechanism which is vidual paths of an SPD.
typically used for a.c. devices. Due to the lacking zero crossing of the d.c.
source, a d.c. arc may persist and cause fire. The SCI technology patented Voltage protection level UP
by DEHN with active arc extinction is an ideal solution. In case of over- The voltage protection level of a surge protective device is the maximum
load, a contact is opened and a short-circuit is generated (short circuit). instantaneous value of the voltage at the terminals of a surge protective
Thus, any switching arc which may arise is actively, quickly and safely device, determined from the standardised individual tests:
extinguished. The PV fuse integrated in the short-circuit path immediately – Lightning impulse sparkover voltage 1.2/50 μs (100%)
trips after the arc has been extinguished and ensures safe electrical isola- – Sparkover voltage with a rate of rise of 1 kV/μs
tion (interruption) (see also pages 32 / 84-92). Thus, all PV arresters from
DEHN combine surge protection, fire protection and personal protection – Measured limit voltage at a nominal discharge current In
in a single device. The voltage protection level characterises the capability of a surge pro-
tective device to limit surges to a residual level. The voltage protection
Series resistance level defines the installation location with regard to the overvoltage cat-
Resistance in the direction of the signal flow between the input and out- egory according to IEC 60664-1 in power supply systems. For surge pro-
put of an arrester. The series resistance is normally used to coordinate the tective devices to be used in information technology systems, the voltage
protection stages in a multi-stage SPD. protection level must be adapted to the immunity level of the equipment
to be protected (IEC 61000-4-5: 2015).
Shield attenuation
Relationship between the power fed into a coaxial cable and the power Wave breaker function
radiated from the cable through the phase conductor. Due to the technical design of type 1 SPDs, energy coordination of SPDs
varies considerably. Experience has shown that even small amplitudes of
Short-circuit withstand capability the 10/350 μs lightning impulse current can overload and even destroy
The short-circuit withstand capability is the value of the prospective pow- downstream SPDs if varistor-based type 1 lightning current arresters are
er-frequency short-circuit current handled by the surge protective device used. In case of spark-gap-based type 1 arresters, in contrast, virtually all
when the relevant maximum backup fuse is connected upstream. the current flows through the type 1 arrester. Similar to a wave breaker
the energy is reduced to an acceptable level. The advantage is that the
Short-circuit current rating I SCCR: time to half value of the 10/350 μs impulse current is reduced due to
Maximum prospective short-circuit current for which the SPD alone or in the reduction of the impulse time and the switching behaviour of type 1
conjunction with its disconnectors is rated (source: IEC 61643-11). SPDs. This considerably relieves downstream SPDs.
All devices of the DEHN Red / Line and Yellow / Line product families are
Short-circuit rating ISCPV of an SPD in a photovoltaic (PV) system energy-coordinated. Moreover, all type 1 arresters of the Red / Line family
Maximum uninfluenced short-circuit current which the SPD, alone or in are based on spark gaps and thus feature this WAVE BREAKER FUNC-
conjunction with its disconnection devices, is able to withstand. TION.

Temporary overvoltage (TOV) Yellow / Line SPD class
Temporary overvoltage may be present at the surge protective device for All DEHN arresters for use in information technology systems are catego-
a short period of time due to a fault in the high-voltage system. This must rised into a Yellow / Line SPD class and are marked with the corresponding
be clearly distinguished from a transient caused by a lightning strike or a symbol in the data sheet and on the rating plate (see page 133).
switching operation, which last no longer than about 1 ms. The amplitude
UT and the duration of this temporary overvoltage are specified in EN
61643-11 (200 ms, 5 s or 120 min.) and are individually tested for the
relevant SPDs according to the system configuration (TN, TT, etc.). The
SPD can either a) reliably fail (TOV safety) or b) be TOV-resistant (TOV
withstand), meaning that it is completely operational during and follow-
ing temporary overvoltages.

Thermal disconnector
Surge protective devices for use in power supply systems equipped with
voltage-controlled resistors (varistors) mostly feature an integrated ther-
mal disconnector that disconnects the surge protective device in case of
overload and indicates this operating state. The disconnector responds to
the “current heat“ generated by an overloaded varistor and disconnects
the surge protective device if a certain temperature is exceeded. The
disconnector is designed to disconnect the overloaded surge protective
device in time to prevent a fire. It is not intended to ensure protection
against indirect contact. The function of these thermal disconnectors can
be tested by means of a simulated overload / ageing of the arresters.

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