IEC 61000-4-5 is an international standard by the International Electrotechnical Commission on surge immunity. In an electrical installation, disruptive surges can appear on power and data lines. Their sources include abrupt load switching and faults in the power system, as well as induced lightning transients from an indirect lightning strike (direct lightning is out of scope in this standard). It necessitates the test of surge immunity in electrical or electronic equipment. IEC 61000-4-5 defines test set-up, procedures, and classification levels. In particular, it standardizes the required surge voltage and current waveforms for laboratory testing, with the "1.2/50-8/20 μs" impulse being the most frequently used surge waveform. Although this standard is designed for testing equipment as a whole at system level, not for individual protection devices, in practice this surge waveform is often also used for rating Transient Voltage Suppressors (TVS), Gas Discharge Tubes (GDT), Metal Oxide Varistors (MOV), and other surge protection devices. The current version is Third Edition (2014), amended in 2017.
Test Setup Two major components are defined in this standard: two types of Combination Wave Generators (CWG) and various Coupling/Decoupling Networks (CDN) depending on the test level and type. First, a Combination Wave Generator is a standardized impulse generator (sometimes also referred to as a lightning surge generator), it's used for producing simulated, standard voltage and current surges under laboratory conditions. Subsequently, the surge is transmitted into a port of the Device-Under-Test (DUT) via a coupling network. Finally, to prevent surges from reaching other devices via the power system during the test, a decoupling network is also inserted between the power line and the DUT.
Surge Waveforms The Combination Wave Generator is required to have an output floating from ground, and be capable of generating both positive and negative impulses. Its repetition rate should be at least one impulse per 60 seconds. The surge is defined by the Combination Wave Generator's open-circuit voltage and short-circuit current waveforms, characterized by front time, duration, and peak values. With an open circuit output, the surge voltage is a double exponential pulse in the form of k ( e − α t − e − β t ) {\displaystyle k(e^{-\alpha t}-e^{-\beta t})} . With a short circuit output, the surge current waveform is a damped sine wave. The ratio between the peak open-circuit voltage and the peak short-circuit current is 2, giving an effective output impedance of 2 Ω.
Usually, the voltage waveform has a 1.2 μs front time and a 50 μs duration, and the current waveform has a 8 μs front time and 20 μs duration. This is the most commonly used surge waveform for most applications, often referred to as a "1.2/50-8/20 μs" surge. Alternatively, for outdoor telecommunication networks that experience a higher surge level, the standard also defines a more energetic generator with a 10/700 μs voltage waveform and a 5/320 μs current waveform. Front time and duration are not measured directly, but as virtual parameters derived from measurements. For open-circuit voltage, front time is defined to be 1.67 times the 30%-90% rise time, duration is defined as the time interval between the 50% point of its rising edge and the 50% point of its falling edge. For short-circuit current, front time is defined to be 1.25 times the 10%-90% rise time, duration is defined as 1.18 times time interval between the 50% point of its rising edge and the 50% point of its falling edge. At the output of the generator, a 30% undershoot below zero is allowed. There's no overshoot or overshoot limit at the output of the Coupling Network.
Comparison with different standards
IEC 60060-1 It's worth noting that both "1.2/50 μs" voltage and "8/20 μs" current impulses are classic waveforms with a well-established history of use in high-voltage testing for electric power transmission. Thus, these waveforms are also defined by IEC 60060-1 "High-Voltage Test Techniques" and other standards in this context. In fact, the waveform definitions in IEC 61000-4-5 were originally based on IEC 60060-1. Nevertheless, there are important differences. In traditional high-voltage testing, voltage and current impulses are tested separately, not in combination. The "1.2/50 μs" generator is designed for insulation testing, and produces a high-voltage, low-current impulse into a high-impedance load. The output current of this generator is on the milliampere scale. The "8/20 μs" generator is designed for surge arrester testing, and produces a high-current surge into a low-impedance load. On the other hand, modern electronic devices can be high and low-impedance loads simultaneously due to non-linear devices, protection circuits, and arcing in a dielectric breakdown. As a result, it motivated the creation of the Combination Wave Generator with the ability to generate a high-voltage, high-current output during the same surge. In addition, both standards have different waveform tolerances and other technical requirements. Thus, IEC 61000-4-5 is not to be confused with IEC 60060-1 and other high-voltage tests that also use a "1.2/50 μs" or "8/20 μs" impulse.
… excerpt ends here. Continue reading the full article.
