Low-voltage AC Power Circuits Research Articles

Coordination of surge protective devices in low voltage AC power installations

The surges protection in low-voltage AC power circuits is commonly realized by Surge Protective Devices (SPDs). These devices divert a large amount of the surge energy to the ground and reduce the surge voltage to the level acceptable for protected device(s). Adequate protection performances are provided by applying multiple-stage protection assuming cascade deployment of SPDs starting from distribution board toward equipment in an installation. Therefore, SPDs coordination, (i.e. selection of SPDs parameters as well as determination of necessary distance between stages) becomes of great importance and the paper deals with this issue. The proper SPDs coordination is significant for both protected equipment and SPDs themselves (their survival during surges). The paper provides an analysis of the SPDs coordination for case of two-stage protection system. The influence of different lengths of cables between protection stages, as well as influence of type and parameters of load on SPDs protection characteristics have been analyzed and discussed with the purpose of determination of requirements for proper surge protection and coordination of applied SPDs.

Effects of Different Combination Wave Generator Design on Surge Protective Devices Characteristics in Cascade Protection Systems

Cascade application of surge protective devices (SPDs) in low-voltage ac power circuits is intended to ensure proper equipment protection against surges as well as to provide surge energy distribution between SPDs. In order to evaluate equipment response and SPDs performance, concept of representative surges, which can be used for surge testing purposes, is introduced by international standards. Combination wave surge is defined both by IEEE C62.41.2 standard and IEC 61000-4-5 standard as one of the representative surges. However, these standards specify different tolerances regarding short-circuit current waveform's undershoot delivered by combination wave generator (CWG). The aim of this paper is to investigate the influences of different CWGs regarding short-circuit current undershoot in cascade two-stage protection system. It will be shown that differences that appear during surge testing with application of different CWGs can lead to inappropriate selection of SPDs regarding energy absorption capability and/or protection level.

Estimation of transient surge energy transferred with associated time delays for individual components of surge protector circuits

Modern semiconductor technology is vulnerable to transient surges such as lightning. Transient voltage suppressor systems (TVSSs), which are installed to protect modern electronics, use non-linear components such as varistors and transient voltage suppressor diodes in their design. In the case of low-voltage (1000 V and less) AC power circuits, there is no clear approach to estimate the energy absorption and associated time delays in individual components in relation to the propagated transient surge. Numerical simulation techniques can be used to analyse the phenomenon of surge propagation within a TVSS and estimate the energy transferred to each component with associated time delays. Suitable mathematical models must be used for the non-linear components. This study presents the development of reasonably accurate models for the non-linear circuit elements and formulation of state equations for the TVSS, together with simulation results; results are experimentally validated using a lightning surge simulator. The method of analysing surge propagation presented here could be extended to analyse the phenomenon of surge propagation within power conversion stages which buffer the complex electronic circuits and the power source. The results discussed here indicate that the theoretical energy calculations are within 10% of the experimental results for the individual circuit elements.

Characteristics of Overvoltage Protection with Cascade Application of Surge Protective Devices in Low-Voltage AC Power Circuits

Surge Protective Devices (SPDs) are widely used for protection of the equipment in low-voltage AC power circuits against wide variety of surges. Cascade application of SPDs starting at ...

Frequency of flashovers of clearances in low‐voltage ac power circuits due to overvoltage waves

AbstractThe frequency distribution of the crest values of overvoltage waves in low voltage AC power circuits can be approximated by an exponential function. The flashover probability P of a clearance with an impulse withstand voltage Ǔst in an electrical equipment is given by P= exp (‐ α Ǔst). The annual number of flashovers of a single clearance in an unprotected house wiring system supplied by an unprotected overhead network depends upon the impulse withstand voltage, the latitude of the network, the annual number of thunderstorm days, the effective length and the height above ground of the overhead line. However, this does not mean, that every flashover triggers a dangerous power frequency follow current.

Bibliography on Surge Voltages in AC Power Circuits Rated 600 Volts and Less

Damage by transient overvoltages of equipment operating on low-voltage ac power circuits has received increasing attention. Before effective protection can be devised, it is necessary to understand the nature of the phenomenon. Relatively little information has been published. The Working Group on Surge Voltages in AC Power Circuits Rated 600 Volts and Less has compiled a bibliography on the subject. References are grouped in broad categories, and a short paragraph describing each paper follows the reference.