After a phase to earth fault in a transmission line, opening of the circuit breaker poles at line extremities interrupts the fault current in the faulted phase. However, due to coupling between phases there is still a residual current through the electric arc, which is then denominated secondary arc. Interruption of the secondary arc defines if single pole reclosing operation will succeed. Nowadays, studies evaluate the likelihood of secondary arc interruption to define application of single phase reclosing. By several reasons, the secondary arc interruption may not occur leading the single pole reclosing operation to a failure. In this case, the circuit breaker pole has to open again and that depletes the energy stored in the operating mechanism. As the rated operating cycle of a fast reclosing circuit breaker is O – 0,3 s – CO – 15 s CO, a failure in the first reclosing shot makes necessary an interval longer than 15 s to perform a second reclosing shot. The methodology presented herein establishes a verification beforehand if a single pole reclosing will be successful. With the secondary arc still active, the single pole reclosing is blocked and the system proceeds to a three pole reclosing. Blocking of the first reclosing shot keeps the energy stored in the operating mechanism and the three pole reclosing shot may proceed with an interval of 300 ms.
This article presents a model to simulate disconnecting switches in transient studies. The distance between contacts of a disconnecting switch does not change instantaneously; it takes several seconds to complete the full movement from closed to open, or vice-versa. The disconnecting switches are able to operate with lower current amplitudes, so a disconnecting switch is operated only when the circuit breaker is in open position. However, even with the circuit breaker open, there is a current flowing through the grading capacitors. The grading capacitors in conjunction with the busbar capacitance form a capacitive divider, and there is a floating voltage in the busbar. When the contacts of the disconnecting switch move, the withstand voltage varies and an electric arc appears. This arc is unstable and is interrupted and reignited several times. Each arc reignition causes a sudden voltage change that propagates through the busbar and impacts any connected equipment. The developed model, with the withstand voltage variation and the electric arc behaviour taken into account, calculates the fast transient overvoltages originated during a disconnecting switch operation. The amplitude and waveform of these overvoltages may then be used to evaluate the impact on insulation ageing.
This article presents a model of Sparking Gap to be used in the Alternative Transients Program (ATP). The model includes the simulation of breakdown and a representation of the electric arc. The arc will be non-constrained and burn in air at atmospheric pressure, thus a discussion of the model and parameters to be used is presented. The effect of the arc on the interruption of current will be studied. Examples of power arc interruption following an impulse impact on a 230 kV transmission line are presented. The effects of interphase capacitive coupling and line length are discussed, in order to establish guidelines to allow successful reclosing operations.
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