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20-09-2010, 04:13 PM
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02-07-2012, 02:50 PM
Digital Testing of High4oltage Circuit Breakers
Digital Testing.pdf (Size: 523.36 KB / Downloads: 205) Circuit Breaker Switching and Arc Modeling The switching action, the basic function oi thc circuit breaker, refers to the change from conductor to insulator at a certain voltage. Be€ore interruption, the (shortcircuit) current flows through the arc channet of the circuit breaker. Bccause of the nonzero resistance of the arc channel, this short-circuit current caiises a voltage across the colitacts of the circuit breaker: the arc voltage. The arc behaves as a nonlinear resistance. Thus, both arc voltage and arc current cross the zero-value at the same time instant. If the arc is coded sufficiently at the time the current goes through zero, the circuit breaker interrupts the current, because thc electrical power input is zero. During current interruption, the arc resistance increases from practically zero to alinnst infinite in microseconds. Immediately aftcr current interruption, the transient recovery voltage builds up across the circuit breaker. As the gas mixture in the interelectrodc space does not change to a completely insulating state instantaneously, the arc resistance is finite at that time, and a sniall current can flow: thc post-arc current. Digital Testing The functionality of high-voltage circuit breakers is tcsted in high-power laboratories, Due to the ncccssary power and the physical size of the equipment, testing is rather expensive and timc consuming. In order to obtain as much information as possible about the degradation and operating limits of the circuit breaker from the costintensive tests, a project started with the following partners: KEMA High-Power Laboratory, The Netherlands; Delft University of Technology, The Nethcrlancls; Siemcris RG, Germany; RWE Encrgie, Germany; and Laborelec cv, Helgium. This project is sponsored by the Directoratc GeIieral XII of the ELiropcan Commission in Standards, Measurements, and Testing Prograiii under contract number SMt'4-CT96-212 1. Measurements and Data Analysis I-ligh-resolution ineasurcmcnts of current and voltage in the critical period around short-circuit current zero must supply the necessary parameters, characterizing the breakers' behavior. A tailor-macle high-frequency measuring system was realized for this purpose. This system consists of a number of battery-pciwcred, singlechaniicl, 40 MHz, 12 bit AD converters, each storing the data temporarily in on-board local RAM (2Stik samples each). The concept of on-site data storage is necessary for reaching a maximum overall sysLern bandwidth, Cables to the current and voltage S ~ I I S O ~caSn thus be kept very short, and thc system can operate 011 floating potential. The arc voltage is measured with standard brnad-band RCR-type voltage dividers; current is measurecl with a spccial Rogowski coil. Arc-Circuit Interaction Software At the final stage of the realization of digital testing, measured arc model parameters will be used as input for the arc model. Of course, this arc model behaves a a nonlinear element in the electrical circuit ancl must therefore be analyzed with a dedicated cnmputer program. The analysis of arc-circuit interaction iiivolving nonlinear clcments in relation to stiff differential equations makes it necessary to perform the calculations with a variable step size and adjustable accuracy of the computed currents, voltages, and canductaiices. Because they have fixed step-size solvers, EMTP ancl comparable programs are less suitable for this purpose and thercfore a new approach.
05-11-2012, 11:30 AM
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