RELATED APPLICATIONS

This application claims priority to International Patent Application Serial No. PCT/EP2017/082131, titled “Switching Apparatus”, filed Dec. 11, 2017, which claims priority to Europe Application Serial No. 16204367.3, titled “Switching Apparatus”, filed Dec. 15, 2016, the contents of which are both incorporated herein by reference.

This invention relates to a switching apparatus, preferably for use in high voltage direct current (HVDC) applications.

It is known to use a switching apparatus that comprises a plurality of switches connected in parallel.

According to an aspect of the invention, there is provided a switching apparatus comprising a plurality of current-conductive branches connected in parallel between first and second terminals, each current-conductive branch including at least one respective electrical connection member in series connection with at least one respective gas tube switch between the first and second terminals, wherein the inductance value of each electrical connection member is configured to balance the inductance values of the current-conductive branches.

It will be understood that, in the switching apparatus of the invention, each current-conductive branch may include a single gas tube switch or a plurality of gas tube switches (e.g. a plurality of series-connected gas tube switches).

It will be also understood that, in the switching apparatus of the invention, each current-conductive branch may include a single electrical connection member or a plurality of electrical connection members (e.g. a plurality of series-connected electrical connection members).

It will be further understood that, in the switching apparatus of the invention, each electrical connection member may take the form of any type of electrically conductive component (e.g. an electrical lead or wiring) capable of connecting a gas tube switch to either of the first and second terminals.

Depending on the switching application, the current rating of a given gas tube switch may be too low to meet the current rating requirements of the switching application.

The parallel connection of the current-conductive branches in the switching apparatus of the invention provides a “gas tube switch”-based switching apparatus with a combined current rating that is higher than the current rating of the individual gas tube switch, and thereby enables the use of gas tube switches in switching applications with higher current rating requirements.

In order to provide a reliable switching apparatus, it is necessary to control the sharing of current between the parallel-connected current-conductive branches.

In a conventional switching apparatus based on parallel-connected power semiconductor switches, the positive slope resistances of the power semiconductor switches are such that current sharing between the parallel-connected power semiconductor switches occurs naturally to a degree, especially if the temperature coefficient is positive.FIG. 1illustrates the stable current sharing between parallel-connected power semiconductor switches (which are referred to as Device1and Device2respectively), where there is a stable crossover point between their voltage-current characteristics. In addition, for certain types of power semiconductor switches, gate control can be employed to control the states of the parallel-connected power semiconductor switches in order to rebalance the currents flowing through the parallel-connected power semiconductor switches.

On the other hand, in a switching apparatus based on parallel-connected gas tube switches, it is not possible to obtain stable sharing of current between the parallel-connected gas tube switches. This is because, as shown inFIG. 2which illustrates the unstable current sharing between parallel-connected gas tube switches, the stable operating points are when all of the current flows through one of the gas tube switches but zero current flows through the other gas tube switch. This is because the negative slope resistances of the gas tube switches are such that there is a tendency of the current to flow through only one or the other of the gas tube switches on either side of the unstable crossover point between their voltage-current characteristics. Moreover it would not be possible to rebalance the currents flowing through the parallel-connected gas tube switches through switching control due to the fact that gas tube switches only have fully-on and fully-off states.

Moreover the inventor has found that assembling the gas tube switches, e.g. side-by-side in a straight line, results in the presence of unequal stray inductance in the electrical connection members which adversely affects the sharing of current between the current-conductive branches.

Configuring the inductance values of the electrical connection members to balance the inductance values of the current-conductive branches advantageously improves the sharing of current between the current-conductive branches based on gas tube switches, thus beneficially improving the reliability of the “gas tube switch”-based switching apparatus.

The switching apparatus may vary in configuration in order to configure the inductance value of each electrical connection member so as to balance the inductance values of the current-conductive branches.

In embodiments of the invention, at least one of the electrical connection members may be or may include a reactor, wherein the inductance value of the or each reactor is configured to balance the inductance values of the current-conductive branches.

In such embodiments, the or each reactor may be arranged as a coil, and the number of coil turns in the or each reactor may be defined to configure the inductance value of the or each reactor so as to balance the inductance values of the current-conductive branches.

It will be appreciated that the number of coil turns in the or each reactor arranged as a coil may range from a single coil turn to a plurality of coil turns.

In further embodiments of the invention, the electrical connection members may be dimensioned to configure their respective inductance values so as to balance the inductance values of the current-conductive branches. For example, the lengths of the electrical connection members may be dimensioned to configure their respective stray inductance values.

The gas tube switches may be positioned relative to the terminals to simplify the configuration of the inductance value of each electrical connection member to balance the inductance values of the current-conductive branches. For example, the gas tube switches may be positioned relative to the terminals to simplify the configuration of the inductance value of the or each reactor and/or the dimensioning of the electrical connection members required to configure the inductance value of each electrical connection member so as to balance the inductance values of the current-conductive branches.

Such positioning of the gas tube switches may be carried out in a number of different ways, non-limiting examples of which are described as follows.

In a first non-limiting example, the gas tube switches may be positioned in a symmetrical arrangement about a reference axis extending through the terminals.

In a second non-limiting example, the gas tube switches may be positioned in a circular arrangement about a reference axis extending through the terminals.

In a third non-limiting example, the gas tube switches may be positioned in a radial arrangement about a reference axis extending through the terminals.

In a fourth non-limiting example, the gas tube switches may be arranged to be equidistant from a reference axis extending through the terminals.

In a fifth non-limiting example, the gas tube switches may be arranged to be equidistant from the first terminal, and the gas tube switches are arranged to be equidistant from the second terminal.

It will be appreciated that the switching apparatus of the invention may be used in a wide range of switching applications.

In a preferred embodiment of the invention, the switching apparatus may be configured for use in a HVDC application. In such an embodiment, the number of current-conductive branches of the switching apparatus may be configured so that the switching apparatus has a current rating suitable for a HVDC application.

The ability of the switching apparatus of the invention to control the distribution of current between the current-conductive branches improves the compatibility of gas tube switches with the high current rating requirements of HVDC applications.

It will be appreciated that the use of the terms “first” and “second”, and the like, in this patent specification is merely intended to help distinguish between similar features (e.g. the first and second terminals), and is not intended to indicate the relative importance of one feature over another feature, unless otherwise specified.

