Abstract
The number of devices either providing or demanding direct current is growing more and more. This led to the renascence of DC grids and revealed a need for research. One critical component is the DC circuit breaker. It has to handle nominal and fault currents to keep the grid stable and operable. Interrupting currents in DC grids can be challenging because of the absence of a natural current zero crossing. Therefore, complex arcing chambers are needed. Especially at low currents, the self-induced force may not be sufficient to force the arc into the arcing chamber. Hybrid circuit breakers (HCB) are one possible solution to meet theses sophisticated requirements. There are several different topologies. All have in common that mechanical switches and semiconductors are combined to create a switch with the advantages of both technologies. One simple solution consists of two mechanical switches and one bypassing semiconductor circuit. The arc is used to achieve commutation from the mechanical to the semiconductor branch. While it carries the current, the mechanical switch regains its dielectric strength. Since this recovery time is short, the semiconductor can be overloaded within the limits of its thermal capacity. Defining the recovery time can be challenging. In addition, the effect of contact distance, arcing time and current value are unknown. To research the recovery behavior a model-switching chamber with an adjustable contact gap is developed. This device under test (DUT) was implemented into a test circuit that reproduces part of the hybrid switching process. When the arc between the contacts of the DUT reaches its steady state, a parallel commutating path is activated. The residual conductance of the decaying arc was measured. The development and several iteration steps of the test circuit and DUT are laid out. Finally, some test runs and initial measurements are presented.
Highlights
The growing numbers of DC-applications result in a higher demand on DC-switchgear to ensure safe operation [1] [2]
Mechanical DC circuit breakers often use the self-induced Lorentz force to lead the arc in a quenching chamber
By enhancing a mechanical switch with power electronics (PE) the switch can be enabled to interrupt those currents. This so-called Hybrid-circuit-breaker (HCB) is able to achieve fast switching and minimizes contact erosion [5] [6]. This combination of mechanical circuit breaker and power electronic components might be the ideal switch in future DC grids [7]
Summary
The growing numbers of DC-applications result in a higher demand on DC-switchgear to ensure safe operation [1] [2]. The IGBT Q has to carry the load current for a certain amount of time to allow the plasma to cool down This ensures that the switch SM can reach a sufficient dielectric strength to prevent the arc from reigniting during phase 4. The resulting capacity of the bypass can be reduced if several diodes are connected in series This raises the activation voltage, which increases the stress on the shunt. Several diodes have to be connected in parallel This will increase the resulting capacity of the setup, which will falsify the measurement when recording transients. The composed diode forms a parasitic capacity allowing transient reverse currents to pass This current has to be subtracted from the measuring current IM in order to receive the current flowing through the DUT.
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