Technical information

Terms and Definitions

Surge Protective Devices (SPDs)

Surge protective devices are devices consisting mainly of voltage-controlled resistors (varistors, suppressor diodes) and/or spark gaps (discharge paths). Surge protective devices are used to protect other electrical equipment and installations against impermissibly high surges and/or to establish equipotential bonding.

Surge protective devices are classified:

a) according to their use into:

  • Surge protective devices for power supply systems and equipment (OTOWA Power line SPDs)

    for nominal voltage ranges up to 1000 V -according to

    EN 61643-11:2012 in type 1 / 2 / 3 SPDs -according to

    IEC 61643-11:2011 in class Ⅰ/ Ⅱ / Ⅲ SPDss

  • Surge protective devices for IT systems and equipment(OTOWA Signal line SPDs)

    for protecting modern electronic systems in telecommunications and signal-processing networks with nominal voltages up to 1000 V a.c. [root-mean-square value (rms)] and 1500 V d.c against the indirect and direct effects of lightning strikes and other transients, -according to IEC 61643-21:2012, EN 61643-21:2013 and DIN VDE 0845-3-1.

  • Isolating spark gaps for earth-termination systems or equipotential bonding (OTOWA Power line SPDs)
  • Surge protective devices for use in photovoltaic installations(OTOWA Power line SPDs)

    for nominal voltage ranges up to 1500 V –

    according to EN 50539-11:2014 as type 1 / 2 SPDs

b) according to their impulse current discharge capacity and protective effect into:

  • Lightning current arresters “OTOWA Class Ⅰ SPDs”

    for interference resulting from direct or nearby lightning strikes for protecting installations and equipment [for use at the boundaries between lightning protection zones (LPZ) 0A and 1].

  • Surge arresters “OTOWA Class Ⅱ SPDs”

    for remote lightning strikes, switching overvoltages as well as electrostatic discharges for protecting installations, equipment and terminal devices {for use at the boundaries downstream of LPZ 0B).

Technical data

The technical data of surge protective devices comprise information defining their conditions of use according to:

  • use (e.g. installation, power supply conditions, temperature)
  • performance in case of interference (e.g. impulse current discharge capacity, follow current extinguishing capability, voltage protection level, response time)
  • performance during operation (e.g. nominal current, attenuation, insulationresistance)

Categories according to IEC 61643-21:2012

A number of impulse voltages and impulse currents are described in IEC 61643-21:2012 for testing the current carrying capability and voltage limitation of impulse interference. Table 3 of this standard lists these into categories and provides preferred values. In Table 2 of the IEC 61643-22 standard the sources of transients are assigned to the different impulse categories according to the decoupling mechanism. Category C2 includes inductive coupling (surges), category D1 galvanic coupling (lightningcurrents “OTOWA Class Ⅰ SPDs”). The relevant category is specified in the technical data.
OTOWA surge protective devices surpass the values in the specified categories. Therefore, the exact value for the impulse current carrying capability is indicated by the nominal discharge current (8/20 μs) and the lightning impulse current (10/350μs).

Combination wave UQC

A combination wave is generated by a hybrid generator (1.2/50 ps, 8/20 [is) with a fictitious impedance of 2 Q, The open-circuit voltage of this generator is referred to as Uoc. Uoc is a preferred indicator for Class Ⅲarresters since only these arresters may be tested with a combination wave (according to IEC/EN 61643-11).

Cut-off frequency fc

The cut-off frequency defines the frequency-dependent behavior of an arrester. The cut-off frequency is equivalent to the frequency which induces an insertion loss (at) of 3 dB under certain test conditions (see EN 61643-21:2013). Unless otherwise indicated, this value refers to a 50 Q system.

Degree of protection

The IP degree of protection corresponds to the protection categories described in IEC/EN 60529.

Direct Current Disconnection

When using an SPD in d.c. applications, disconnection must be reliably ensured even if there are no zero crossings. The specifically developed DC Disconnection (DCD) acts as a wedge similar to a blocking valve and interrupts the direct current. Consequently, the devices of the “OTOWA Class Ⅱ SPDs” DC series are capable of safely interrupting direct currents, thus preventing fire damage caused by d.c switching arcs.

Disconnecting time ta

The disconnecting time is the time passing until the automatic disconnection from power supply in case of a failure of the circuit or equipment to be protected. The disconnecting time is an application-specific value resulting from the intensity of the fault current and the characteristics of the protective device.

Energy coordination of SPDs

Energy coordination is the selective and coordinated interaction of cascaded protection elements (= SPDs) of an overall lightning and surge protection concept. This means that the total load of the lightning impulse current is split between the SPDs according to their energy carrying capability. If energy coordination is not possible, downstream SPDs are insufficiently relieved by the upstream SPDs since the upstream SPDs operate too late, insufficiently or not at all. Consequently, downstream SPDs as well as terminal equipment to be protected may be destroyed. DIN CLC/TS 61643-12:2010 describes how to verify energy coordination. “OTOWA Class Ⅰ SPDs” offer considerable advantages due to their voltage-switching characteristic (see WAVE BREAKER FUNCTION).

Frequency range

The frequency range represents the transmission range or cut-off frequency of an arrester depending on the described attenuation characteristics.

Insertion loss

With a given frequency, the insertion loss of a surge protective device is defined by the relation of the voltage value at the place of installation before and after installing the surge protective device. Unless otherwise indicated, the value refers to a 50 Q system.

Lightning impulse current ljmp

The lightning impulse current is a standardised impulse current curve with a 10/350 μswave form. Its parameters (peak value, charge, specific energy) simulate the load caused by natural lightning currents. Lightning current and combined arresters must be capable of discharging such lightning impulse currents several times without being destroyed.

Mains-side overcurrent protection I arrester backup fuse

Over-current protective device (e.g. fuse or circuit breaker) located outside of the arrester on the infeed side to interrupt the power frequency following the current as soon as the breaking capacity of the surge protective device is exceeded. No additional backup fuse is required since the backup fuse is already integrated in the SPD (see relevant section)

Maximum continuous operating voltage Uc

The maximum continuous operating voltage (maximum permissible operating voltage) is the r.m.s. value of the maximum voltage which may be connected to the corresponding terminals of the surge protective device during operation. This is the maximum voltage on the arrester in the defined non-conducting state, which reverts the arrester back to this state after it has tripped and discharged. The value of Uc depends on the nominal voltage of the system to be protected and the installer’s specifications. (IEC 60364-5-53)

Maximum continuous operating voltage UCPV for a photovoltaic (PV) system

Value of the maximum d.c. voltage that may be permanently applied to the terminals of the SPD. To ensure that Ucpv is higher than the maximum open-circuit voltage of the PV system in case of all external influences (e.g. ambient temperature, solar radiation intensity), Ucpv must be higher than this maximum open-circuit voltage by a factor of 1,2 (according to CLGTS 50539-12). This factor of 1.2 ensures that the SPDs are not incorrectly dimensioned.

Maximum discharge current Imax

The maximum discharge current is the maximum peak value of the 8/20ps impulse current which the device can safely discharge.

Maximum transmission capacity

The maximum transmission capacity defines the maximum high-frequency power which can be transmitted via a coaxial surge protective device without interfering with the protection component.

Nominal discharge current ln

The nominal discharge current is the peak value of a 8/20μs impulse current for which the surge protective device is rated in a certain test program and which the surge protective device can discharge several times.

Nominal load current (nominal current) IL

The nominal load current is the maximum permissible operating current which may permanently flow through the corresponding terminals.

Nominal voltage UN

The nominal voltage stands for the nominal voltage of the system to be protected. The value of the nominal voltage often serves as a type of designation for surge protective devices for information technology systems. It is indicated as an r.m.s. value for a.c. systems.

N-PE arrester

Surge protective devices exclusively designed for installation between the N and PE conductor.

Operating temperature range Tu

The operating temperature range indicates the range in which the devices can be used. For non-self-heating devices, it is equal to the ambient temperature range. The temperature rise for self-heating devices must not exceed the maximum value indicated

Protective circuit

Protective circuits are multi-stage, cascaded protective devices. The individual protection stages may consist of spark gaps, varistors, semiconductor elements and gas discharge tubes (see Energy coordination)

Protective conductor current IPE

The protective conductor current is the current which flows through the PE connection when the surge protective device is connected to the maximum continuous operating voltage Uc, according to the installation instructions and without load-side consumers.

Remote signalling contact

A remote signalling contact allows easy remote monitoring and indication of the operating state of the device. It features a three-pole terminal in the form of a floating change-over contact. This contact can be used as a break and/or make contact and can thus be easily integrated in the building control system, controller of the switch gear cabinet, etc.

Response time tA

Response times mainly characterise the response performance of individual protection elements used in arresters. Depending on the rate of rise du/dt of the impulse voltage or di/dt of the impulse current, the response times may vary within certain limits.

Return loss

In high-frequency applications, the return loss refers to how many parts of the “leading” wave are reflected at the protective device (surge point). This is a direct measure of how well a protective device is attuned to the characteristic impedance of the system.

Series resistance

Resistance in the direction of the signal flow between the input and output of an arrester.

Shield attenuation

Relation of the power fed into a coaxial cable to the power radiated by the cable through the phase conductor.

Short-circuit withstand capability

The short-circuit withstand capability is the value of the prospective power-frequency short-circuit current handled by the surge protective device when the relevant maximum backup fuse is connected upstream.

Short-circuit rating Ucpv of an SPD in a photovoltaic (PV) system

Maximum uninfluenced short-circuit current which the SPD, alone or in conjunction with its disconnection devices, is able to withstand.

Temporary overvoltage (TOV)

Temporary overvoltage may be present at the surge protective device for a short period of time due to a fault in the high-voltage system. This must be clearly distinguished from a transient caused by a lightning strike or a switching operation, which lasts 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 (TNfTT, 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 following temporary overvoltages.

Thermal disconnector

Surge protective devices for use in power supply systems equipped with voltage-controlled resistors (varistors) mostly feature an integrated thermal 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 asimulated overload / aging of the arresters.

Total discharge current Itotal

The current which flows through the PE, PEN or earth connection of a multipofe SPD during the total discharge current test. This test is used to determine the total load if the current simultaneously flows through several protective paths of a multipole SPD. This parameter is decisive for the total discharge capacity which is reliably handled by the sum of the individual paths of an SPD.

Voltage protection level UP

The voltage protection level of a surge protective device is the maximum instantaneous value of the voltage at the terminals of a surge protective device,determined from the standardised individual tests:

  • 一Lightning impulse sparkover voltage 1,2/50μs (100%)
  • 一Sparkover voltage with a rate of rise of 1 kV/μs
  • 一Measured limit voltage at a nominal discharge current In

The voltage protection level characterises the capability of a surge protective device to limit surges to a residual level. The voltage protection level defines the installation location with regard to the overvoltage category according to IEC 60664-1 in power supply systems. For surge protective devices to be used in information technology systems, the voltage protection level must be adapted to the immunity level of the equipment to be protected (IEC 61000-4-5:2017).