• Hakel International
  • Hakelsoft
  • Catalogue
  • Isolguard
  • Definition

    Surge protection device (SPD)
    – a device that is intended to limit transient overvoltages and divert surge currents; it contains at least one nonlinear component.

    One – port SPD
    – an SPD connected in shunt with the circuit to be protected; a one-port device may have separate input and output terminals without a specific series impedance between these terminals.

    Two – port SPD
    – an SPD with two sets of terminals, input and output; a specific series impedance is inserted between these terminals.

    Voltage switching type
    – an SPD that has a high impedance when no surge is present, but can have a sudden change in impedance to a low value in response to a voltage surge; common examples of components used as voltage switching devices are spark gaps, gas tubes, thyristors (siliconcontrolled rectifiers) and triacs; these SPDs are sometimes called “crowbar types”.

    Voltage limiting type SPD
    – an SPD that has a high impedance when no surge is present, but will reduce it continuously with increased surge current and voltage; common examples of components used as nonlinear devices are varistors and suppressor diodes; these SPDs are sometimes called “clamping type”.

    Combination type SPD
    – an SPD that incorporates both voltage switching type components and voltage limiting type components may exhibit voltage switching, voltage limiting or both voltage switching and voltage limiting behaviour depending upon the characteristics of the applied voltage.

    Modes of protection
    – an SPDs protective component may be connected line-to-line or line-to-earth or line-to-neutral or neutral-to-earth and combination there of; these paths are referred to as modes of protection.

    Sparkover voltage of a voltage switching SPD
    – maximum voltage value before disruptive discharge between the electrodes of the gap of a SPD; it is used for classification of the SPD class I and II by testing impulse with waveshape 1,2/50μs.

    Nominal discharge current In (8/20)
    – the crest value of the current through the SPD having a current waveshape of 8/20; this is used for the classification of the SPD for class II test and also for preconditioning of the SPD for class I and II tests; arrester must discharge this current at least 15 times without any essential changes in its qualities.

    Maximum discharge current Imax for class II test
    – crest value of a current through the SPD having an 8/20 waveshape and magnitude according to the test sequence of the class II operating duty test; Imax is greater than In ; arrester must safely discharge this current without an obvious damage or aberration from the temperature stability; records of the voltage and current development musn´t show any marks of disruptive discharge or sparkover.

    Impulse current Iimp
    – it is defined by a current peak value Ipeak and the charge Q; tested according to the test sequence of the operating duty test; this is used for the classification of the SPD for class I test; arrester must safely discharge this current without any obvious damage or aberration from the temperature stability; records of the voltage and current development musn´t show any marks of disruptive discharge or sparkover.

    1,2/50μs voltage impulse
    – a voltage impulse with a virtual front time (time to rise from 10% to 90% of the peak value) of 1,2μs and a time to half-value of 50μs; it is used for classification of the SPD class I and II.
    Combination wave
    – the combination wave is delivered by a generator that applies a 1,2/50μs voltage impulse across an open circuit, and an 8/20 current impulse into a short circuit; the voltage, current amplitude and waveforms that are delivered to the SPD are determined by the generator and the impedance of the SPD to which the surge is applied. The ratio of peak open-circuit voltage to peak short-circuit current is 2Ω; this is defined as the fictive impedance Zf; the short-circuit current is symbolized by ISC ; the open-circuit voltage is symbolized by UOC.
    Note: In practice when it comes to the arresters (class III) there are data Imax (8/20) and In (8/20) often mentioned in place of UOC because of the commercial reasons. They are always mentioned in relation to the stated voltage protection level Up (the data concerned are always derived from the tests by the standardized combined impulse with the amplitude UOC; the test is carried out by use of a hybrid generator with inside resistance 2Ω).
    Specific energy W/R for class I test
    – the energy dissipated by the impulse current Iimp in a unit resistance of 1Ω; it is equal to the time integral of the square of the current; expressed in kJ/Ω or in kA2s.
    W/R=∫i2 . dt

    Charge Q
    – it equals the time integral of the current according to the time; expressed in As.
    Q=∫i . dt

    Charge Q
    – it equals the time integral of the current according to the time; expressed in As.
    Q=∫i . dt

    Thermal stability
    – an SPD is thermally stable if after the operating duty test causing temperature rise, the temperature of the SPD decreases with time when the SPD is energized at specified maximum continuous operating voltage and at specified ambient temperature conditions (it is monitored for 30 minutes, active power dissipation must show constant decline for the last 15 minutes).

    Short-circuit withstand capability IP
    – the SPD shall be able to carry the power short-circuit current until it is interrupted either by the SPD itself, by an internal or external overcurrent disconnector or by the backup overcurrent protection; expressed in kArms (tested according to short-circuit withstand capability test in conjunction with backup overcurrent protection).

    Nominal voltage UN
    – an effective value of the alternating voltage or value of the direct voltage, which is set for the SPD by manufacturer.

    Maximum continuous operating voltage UC
    – the maximum r.m.s. or d.c. voltage which may continuously applied to the SPDs mode of protection; this is equal to the rated voltage.

    Nominal current IN of load.
    – the maximal effective value of the alternating current or value of the direct current, which can be constantly taken away by the load connected to the SPD output.

    Continuous operating current IC
    – the current flowing through each mode of protection of the SPD when energized at the maximum continuous operating voltage UC for each mode.
    Note: IC corresponds to the sum of currents flowing in the protective component of the SPD and in all internal circuits connected in parallel with the protective components of the SPD.

    Follow current If
    – current supplied by the electrical power system and flowing through the SPD after a discharge current impulse; the folow current is significantly different from the continuous operating current Ic ; expressed in kArms.

    Follow current interrupting rating Ifi
    – the prospective short-circuit follow current that is SPD able to self-extinquish after its previous activation (without a back-up fuse); this current is indicated in some company’s materials as “Follow current extinguishing capability at Uc“ or “ Eliminates short circuit current without back-up fuse at Uc “, alternatively “Quenching short circuit current without back-up fuse“.

    Voltage protection level UP
    – a parameter that characterizes the performance of the SPD in limiting the voltage across the terminals, which is selected from a list of preferred values; this value shall be greater than the highest value of the measured limiting voltages.

    Operating temperature ϑ
    – an extent of the allowed surrounding temperatures, where manufacturer guarantees the right operating SPD.

    Response time tA
    – the response time defines the reaction speed of protective elements built-in the SPD; the response time can vary in different limits, which are dependent on the rate of rise du/dt of the impulse voltage or on the di/dt of the impulse current.

    Insertion loss
    – at a given frequency, the insertion loss of an SPD connected into a given power system is defined as the ratio of voltages appearing across the mains immediately beyond the point of insertion before and after the insertion of the SPD under test; this result is expressed in decibels (dB).

    SPD disconnector
    – a device for disconnecting an SPD from the system in the event of SPD failure; it is to prevent a persistent fault on the system and to give visible indication of the SPD failure; some kinds of the SPD are extra fitted with so-called non-potential signall contact for needs of remote failure signalling.

    Backup overcurrent protection
    – an overcurrent device (e.g. fuse or circuit breaker), which is a part of the electrical installation located externally upstreamof the SPD, to avoid overheating and destruction in case the SPD is unable to interrupt the power frequency short-circuit current.

    Residual current device (RCD)
    – an electromechanical switching device or association of devices intended to cause the opening of the contacts when the residual or unbalanced current attains a given value under specified conditions.

    Degrees of protection provided by enclosure (IP code)
    – the extent of protection provided by an enclosure against access to hazardous parts, against ingress of solid foreign objects and/or against ingress of water (see IEC 60 529).

     

    Contact form

    Your message was sent successfully! We will be in touch with you soon. Thank you.
    Sending

    Don't hesitate to contact us with everything
    you want to know!

    Hakel facebook Hakel google+ Hakel youtube Hakel linkedin
    HAKEL LTD. 2019