Abstract
The object of research is the magnitude and shape of the residual voltage that arises between the terminals of the surge arrester models when they are subjected to current and voltage pulses of a piecewise linear waveform. One of the most problematic places in this problem is the approximation of current switching pulses with a short duration and also steep front current pulses. With the help of the well-known double-exponential pulse, it is impossible to describe a pulse whose time-to-half duration is twice bigger the time-to-crest duration . At the same time, current pulses in the manufacturer catalogs of the surge arresters have exactly this ratio (1/2, 30/60 or 45/90 ). With the help of piecewise linear approximation, it is possible, bypassing complex calculations, to describe pulses of almost any shape, including switching current pulses and steep front current pulses. By means of evaluation version of Micro-Cap 11 circuit simulator the residual voltage on the surge arrester terminals is computed during a passage of the current pulses with different amplitude and wave shape. Current sources used in this research represent sources of simplified triangular (piecewise linear) current pulses. It is considered that the current wave rises linearly to its maximum value, and then also decays linearly to half its amplitude value. Comparison of the results suggests that proposed simplification of discharge current waveform has no significant effect on relative calculation error of residual voltage on surge arrester. If it is necessary to estimate only maximum value of residual voltage on surge arrester, it is possible to use piecewise linear approximation of switching and lightning currents with any amplitude and shape without loss of accuracy.
Highlights
When solving lightning protection problems, various analytic expressions are used to approximate the current in the lightning channel
It is assumed that the current in the lightning channel can be approximated by a triangular pulse, since the duration of the front is shorter than the tail duration
In the catalogs of their prod ucts, surge arrester manufacturers indicate several values of the residual voltage on the surge arrester at switching and lightning current pulses of different wave shapes and amplitudes. In one or another circuit simulation program, it is possible to determine the residual voltage on the surge arrester at the switching and lightning current pulses of a piecewise linear waveform
Summary
When solving lightning protection problems, various analytic expressions are used to approximate the current in the lightning channel. Approximations of the lightning current waveform, which do not always accurately describe the actual current in the lightning channel, can give quite acceptable results As such example can be mentioned a well-known double-exponential pulse, which has been used for many years to approximate both current and voltage waveforms. The use of a double-exponential pulse gives acceptable results It was shown in [1] that regardless of whether the current wave has a zero time derivative at the initial instant of time or not, this doesn’t affect the residual voltage of the surge arrester. It is considered that the current wave rises linearly to its maximum value, and decays linearly to half its amplitude value This is undoubtedly a simplification, since it becomes possible to specify pulses with any ratio of time-to-crest and time-to-half duration without complex calculations. It is important to study the feasibility of applying piecewise linear current and voltage pulses to estimate the possible values of lightning and switching overvoltage
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