Abstract
The object of research is an analytical expression for representing the switching current impulse of a surge arrester. Any current impulse (both lightning and switching) is characterized by such parameters as the virtual front time and the virtual time to half-value on the tail. According to the standard IEC 60099-4:2014, switching current impulse has a virtual time to half-value on the tail of roughly twice the virtual front time. This requirement is one of the most problematic places in this task. The existing approaches used to represent lightning current impulses are not suitable in this case, since these impulses have virtual time to half-value on the tail of two and a half times the virtual front time.This problem can be solved with a help of analytical piecewise continuous functions.It is shown how to describe switching current impulses of the surge arresters with a help of analytical piecewise continuous functions. In contrast to other expressions, the resulting expressions for the switching impulse have only one parameter (angular frequency). Instead of approximate calculation, the front time of the resulting impulse is calculated by an analytically exact formula. Hence, the tolerance of virtual front time is equal to zero. The time to half-value on the tail of the resulting impulses is determined with some error that can be reduced by some complication of the original expression.The proposed functions satisfy the requirements of the IEC 60099-4:2014 standard regarding switching current impulses of surge arresters. These functions allow representing current impulses having virtual time to half-value on the tail of roughly twice the virtual front time (30/60 or 45/90 microseconds). In such cases, minimal tolerance of time to half-value on the tail is +3.78 %. Additional study shows that one of proposed functions allows representing current impulses having virtual time to half-value on the tail of two and a half times the virtual front time (8/20 or 4/10 microseconds). Tolerance of time to half-value on the tail for such impulses is 0.55 %. The obtained functions are intended for study of various models of metal-oxide surge arresters on personal computers.
Highlights
Modeling of a metal-oxide surge arresters is necessary for calculating lightning and switching surges using personal computers
The surge arrester model should reproduce in the virtual experiment on the computer exactly these above-mentioned characteristics of a real arrester
Switching current impulse of an arrester has a virtual front time grea ter than 30 μs but less than 100 μs and a virtual time to half-value on the tail of roughly twice the virtual front time
Summary
Modeling of a metal-oxide surge arresters is necessary for calculating lightning and switching surges using personal computers. There are several similar dynamic (that is, frequency-dependent) models of a metaloxide surge arrester [1, 2]. As a rule, these models consist of two nonlinear resistances connected to each other by means of several linear elements: inductances, resistors and capacitance. There are residual voltages of the arrester for nominal discharge current (lightning current impulse), switching current im pulse and for steep current impulse. To draw a conclusion about how well this or that model reproduces the behavior of a real arrester, it is necessary to compare the simulation results with the corresponding values that manufacturers give in the catalogs of their products. In order to be able to test the model with as many control points as possible, it is necessary to consider problems related to the analytical representation of switching current impulses of arresters
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