High-resolution measurements on the postarc current in vacuum circuit breakers (VCBs) reveal a period, immediately following current-zero, in which the voltage remains practically zero. The most widely used model for simulating the interaction between the postarc current with the electrical circuit lacks a proper explanation for this event, and hence, it needs to be complemented. We demonstrate that the breaker's electrical behavior during this zero-voltage period can be explained by using the theory of a Langmuir probe. Such probes are used to investigate plasma properties such as the ion density and the electron temperature, and we extrapolate its theory to the VCB. After the voltage-zero period, when the transient recovery voltage starts to rise, the breaker's electrical behavior is mainly determined by the expansion of an ionic space-charge sheath in front of the cathode. In addition to the current from the Langmuir probe model, the time change of the electric field inside the sheath gives a displacement current. Instead of solving the complicated plasma equations to find the displacement current, we use an approximation by simulating it with the aid of a voltage-dependent sheath capacitance. We programmed the model as a function block in Matlab's SimPowerSystems to facilitate its application in different electrical circuits.
In many cases, single-break vacuum circuit breakers are used as circuit breakers, and so the characteristics of doublebreak vacuum circuit breakers have not received sufficient attention. This report describes our investigations of the interruption characteristics of double-break vacuum circuit breakers. We have investigated and clarified the relationship between the voltage distribution ratio and the post arc current in double-break vacuum circuit breakers by measuring the post arc current in the single-break vacuum circuit breaker, the voltage distribution ratio, and the post arc current in double-break vacuum circuit breakers. Our investigation has shown that the post arc current scatter of the spiral contact is much larger than that of the axial magnetic field contact. This result shows that the bias of the voltage distribution ratio was caused by the imbalanced post arc current in each vacuum interrupter in the double-break vacuum circuit breaker. Therefore, we conclude that axial magnetic field contacts are suitable for double-break vacuum circuit breakers.Index Terms-Double-break vacuum circuit breakers, grading capacitors, post arc current, vacuum interrupters.
The voltage signals measured in short sample qualification tests for the ITER conductors often show a linear relationship with the current starting from zero. This behavior is most likely caused by non-uniform current distribution in the joints. To counteract this, two samples have been equipped with extra sets of six voltage tap pairs, connected with regular spacing, as a star configuration around the conductor. The linear relationship still showed up in the average of the extra voltage signals, and were sometimes even seen to be inverse. In some occasions, it was negative for all individual signals.A fair judgment of the approval criterion requires a proper understanding of this behavior. This paper describes the analyses with the aid of the numerical model 'JackPot'. It demonstrates that the described observation is the result of the chosen cabling pattern in combination with the position of the voltage taps. The model also shows that this problem cannot be solved by changing the positions of the voltage taps, but that completely filling the joints with solder can greatly improve the situation.
The poloidal field (PF) magnet system of the International Thermonuclear Experimental Reactor (ITER) consists of six pulsed coils. Each coil comprises independent modules connected to each other through "shaking hands" joints. In the paper the results of the analysis of the electro-magnetic and thermal performance of the joints during the ITER 15 MA plasma scenario are presented. Of special concern is the radial magnetic field component that is particularly high close to the upper and lower edges of the coils. Moreover, the orientation of the joints in the PF coils is such as to give scope to large current loops between the two cables, which could potentially reduce the temperature and current margins to critical levels. The study has been carried out with the code JackPot-AC, which has been recently upgraded to allow a strand-level detailed analysis of lap-type joints.
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