Abstract
This paper shows that successful switching of extremely high short-circuit currents I> 50 kA can be achieved by joint operation of a liquid-metal self-resetting current limiter and a circuit breaker connected in series. The type NFU-225 device from Mitsubishi was taken as an example. The time-current characteristic of joint operation of a liquid-metal self-resetting current-limiting device and a circuit breaker was compiled. However, further in the article physical processes occurring in a liquid-metal self-resetting current limiter with a complete transformation of fusible unit are considered. The result of work is modelling of operation of liquid-metal fuses when overcurrents are switched off based on the pilot studies obtained by the Japanese scientists. It is proposed to simulate the break process not at every time moment, but at specific time moments (reference points). At other time moments, current and voltage should be considered as approximately linearly changing characteristics. The work of current limiter can be represented by three stages: the pre-arc, the main arc and the final arc. If the current density is less than 1000 A/mm2, then the pre-arc operation stage of the current limiter includes the following sections for heating the fusible unit: primary heating to the melting temperature; melting and its transition to liquid state; secondary heating to evaporation temperature; evaporation of fusible unit.
Highlights
Implementation of new electrical equipment and promising circuit solutions, for example, by means of:− Increasing the unit capacity of power transformers to Sn = 4 MVA;− Switching of two or three power transformers to parallel operation;− Using powerful autonomous energy systems;− Advancement of powerful converters that provide conversion of alternating current to direct current, depends on the presence of high current and currentlimiting electrical devices which enable switching high short circuit (SC) currents.Successful switching of extremely high short-circuit currents I> 50 kA can be achieved by joint operation of liquid-metal self-resetting current limiter and a circuit breaker connected in series
A current limiter can be a structural part of a single electrical device, and in some cases it can be used separately, operating not with one circuit breaker, but with a group of linear circuit breakers
The combination current limiter - circuit breaker opens up the possibility of using conventional circuit breakers with a relatively low switching capacity
Summary
Implementation of new electrical equipment and promising circuit solutions, for example, by means of:. Limitation of shortcircuit current is provided by a current limiter, and the circuit breaker completes the shutdown process, opening the circuit using its contact-arc damping system. On the first subsection 3-4, the response time enables to reignite the arc at the location of fusible unit of the current limiter, since the possibility of "picking up" the short circuit current by a circuit breaker is limited by its relatively long operation. On the second subsection 4-5, the response time of current limiter is less than 10 ms, and the current passed through it is quite sufficient for reliable operation of the circuit breaker and completion of breaking after the first passing of current through zero. The analysis of the listed information sources shows that the work of current limiter can be represented in three stages: pre-arc, main arc and final arc
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