Voltage escalation in vacuum switching operations

Abstract

The ability of vacuum switching devices to interrupt high frequency currents can lead to repeated prestrikes and clearings when such switches are being closed and repeated reignitions and clearings when the switches are opening. This paper focuses on the interruption of a motor inrush current (aborted starts) where the successive trapping of magnetic stored energy in the motor winding and its subsequent release to the motor and cable capacitance, can result in the development of a sequence of escalating voltage surges. Of particular concern is the sudden collapse of voltage when sequential reignitions occur and the impact of this on the interturn insulation of the motor winding. The study reports on many simulated tests with circuit breakers of different manufacturers and attempts through analysis to identify cause and effect with respect to the magnitudes of the voltages developed and the characteristics of the switch, paying particular attention to the rate of dielectric recovery of the contact gap and the dI/dt interrupting capability of the switch.

Time domain severity factor (TDSF)

“…For this, different performing properties of the breaker are considered to control the state of the breaker during its operation simulation (Glinkowski et al, 1997;Greenwood and Glinkowski, 1988; COMPEL 31,2 Helmer and Lindmayer, 1996;Kondala and Gajjar, 2006;Popov and Archa, 1999;Popov et al, 2001). The mean chopping current of the VCB is calculated by (Kondala and Gajjar, 2006;Popov et al, 2001):…”

Induced Transient Voltage Performance Between Transformers and VCB. Severity Factors and Case Studies

“…Substituting (4) in (3), the coefficient TDSF can be expressed in terms of the dielectric strength along the dielectric th paths as (5) In order to carry out the TDSF calculation, it is necessary to build a detailed internal transformer model from its geometry and material data. The detailed internal model (white box model) permits: first, to build the terminal model (black box model), which can be implemented into a power system model in an Electromagnetic Transients Program (EMTP) environment to obtain the waveform at transformer terminals during VCB switching operations; and second, to compute the internal transient voltage distribution along transformer windings, considering the switching waveform obtained previously at transformer terminals as input data.…”

Vacuum Switching of High Current and High Voltage at Power Frequencies

“…144 ] [45] Range of Products Vacuum interrupters to be incorporated in the switchgear applications described in the last section, and in the many other places where vacuum is used, range in size from something that would comfortably fit in the palm of one's hand, to units perhaps 50 cm long and 20 cm in diameter. High frequency currents are sometimes interrupted inadvertently.…”