The arrangement comprises an input side for connecting the arrangement to the power source (in particular with an input current rectifier for rectifying an alternating current from the power source); a direct current intermediate circuit, wherein the intermediate circuit comprises a first and a second direct current connection line, at least one of the first and the second direct current connection lines being connected to the input side; and a current converter for inverting a direct current and for delivering alternating current power to the power consumer. The current converter is connected to the first and to the second direct current connection line. At least one capacitor is provided in the intermediate circuit. The capacitor has two opposite poles, wherein a first pole is connected to the first direct current connection line and wherein the second pole is connected to the second direct current connection line.

The term"power source"covers any electric device or network that is adapted to deliver electric power. In particular, means for connecting the arrangement to a current network, for example to an alternating current network, may be provided. The means are connected to the input side of the arrangement, in particular to an alternating current side of the input current rectifier.

Especially when the power consumer is a high power consumer, such as a driving motor of a railroad vehicle, the electric energy stored in the capacitor is high. In case of a defect in the arrangement (or in the arrangement including any electrically connected parts), an immediate and fast discharge of the capacitor might occur and result in mechanical damages. The term"defect"includes internal short circuits in the arrangement and external short circuits at electrically connected parts. In particular, a pair of semiconductor elements of the current converter might become defective. The two semiconductors of the pair are connected in series to each other and form a link between the first and the second direct current connection line. Normally, only one of the two semiconductors is carrying a current from the power source to the power

consumer at a time. In case of a defect, both semiconductor elements are conductive at the same time and, therefore, the pair forms a short circuit. Although such a defect is rare, it is necessary to protect the arrangement from damages, since there is the potential of a substantial destruction.

It has been proposed to provide a device, which is adapted to limit the current in case of such an immediate discharge. However, the costs for such a device are high.

Further, the electrical resistance of such a device results in substantial electrical losses. Therefore, it is practice in railway traction vehicles to actively cool the device by forced circulation of cooling liquid. As a consequence, additional space is required and costs rise.

Further, it has been proposed to interrupt an electric line of the intermediate circuit, using an electronic valve when the defect occurs. But so far, practical attempts to realize a corresponding device have failed, due to insufficient switching properties of the electronic valve in the field of high power transfer arrangements.

It is an object of the present invention to provide an arrangement of the type indicated above which prevents mechanical damages in case of a defect. The costs for adapting the arrangement and/or the additional costs for providing any means that protect from damages shall be low. Preferably, the electric losses of the arrangement shall be small too.

It is proposed to provide at least one fuse that is connected in series to the capacitor or to at least one of the capacitors, so as to connect the first and second direct current connection lines via the capacitor.

It is preferred that the fuse is adapted and/or chosen to melt or burn through and thereby to interrupt the connection between the capacitor and at least one of the direct current connection lines, if the time-integral of the square of a current carried by at least a part of the connection exceeds a threshold value. Further, it is preferred that the threshold value corresponds to a current which may appear only in case of an immediate discharge of the capacitor due to an electric short circuit in the arrangement or in the arrangement including any electrically connected parts.

In particular, the arrangement is adapted to transferring electric power from a current network to a driving motor of a railroad vehicle, wherein means for connecting the

arrangement to the current network are provided and wherein the means are connected to the input side of the arrangement.

The described way of using the fuse (connecting the first and second direct current connection lines via the capacitor) has the advantage that the arrangement (including all other parts or elements in the intermediate circuit) and any means or device, which is electrically connected to the arrangement, are protected. Further, a fuse usually comprises a very small electric resistance. Thus, the electric losses during the operation of the arrangement are small. Furthermore, since the charging and discharging currents into and from the capacitor are usually much smaller than the current carried by the direct current connection lines, a threshold value of the fuse may be chosen which corresponds to currents well above the typical charging and discharging currents. Due to a smaller DC-resistance of the fuse, this reduces the electric losses even further.

Compared to the device described above, which limits the current to or from the capacitor, a cooling circuit can be avoided. Therefore, the required space is smaller and the arrangement becomes more easily accessible.

In case of a plurality of capacitors in the intermediate circuit, which are arranged in parallel to each other, it is preferred to provide at least two of the fuses, wherein each of these fuses carries the charging and discharging currents of only one of the capacitors. In this case, the electric losses caused by the fuses are even smaller.

Another advantage of this arrangement is that the other capacitor or capacitors is/are protected in case of an internal defect of one of the capacitors.

In the following, preferred embodiments of the present invention are described by way of example and by reference to the accompanied drawing. The only figure of the drawing, Fig. 1, schematically shows an arrangement having four capacitors which are connected in parallel to each other within the intermediate circuit.

The arrangement 1 of Fig. 1 comprises an AC/DC rectifier 7, an AC side of which is connected to means 3 for connecting the arrangement 1 to a single-phase alternating current railroad power network. The means 3 may comprise a pantograph. Further, the arrangement 1 comprises an intermediate circuit 9 having two direct current connection

lines 13,15. These lines 13,15 connect a DC side of the rectifier 7 with a DC/AC current converter 11.

Four capacitors 17 to 20 are arranged in parallel to each other. Each capacitor is connected in series to a fuse 21 to 24, so that each series connects the direct current connection lines 13,15.

The current converter 11 may be constructed as known from the prior art. For example, it comprises six electronic switches (one of which is denoted with the reference numeral 32). A diode 30 is connected anti-parallel to each of the six electronic switches 32. combinations. Each two of the electronic switches 32 are connected in series and the series connection is connected at both sides to one of the direct current connection lines 13,15. Further, each of the three series connections is connected to one phase of a three-phase driving motor 5 of a railroad vehicle. The electronic switches 32 are controlled by an additional device (not shown in Fig. 1).

In a preferred embodiment, the fuses 21 to 24 are semiconductor fuses, i. e. fuses that are designed to protect a power semiconductor element from damage due to electric overload. Semiconductor fuses (sometimes referred to as"rectifier fuses"or"ultra fast fuses") comprise a very short clearing time in case of an overload. Thus, the electric connection is interrupted before the current can reach its maximum. Further, semiconductor fuses that are designed for high power applications can reliably protect circuit elements at high surrounding temperatures (e. g. 50° C and more) which usually occur due to dissipation of electric energy.

However, in the arrangement of the present invention the fuses are not used to protect semiconductor elements in the first instance. Rather, they protect the arrangement, if (for example) semiconductor elements are defect already and cause a short circuit.

For example, the fuses 21 to 24 comprise a 12t (clearing time-integral of the square of the current carried by the fuse) value in the range of 40 to 80 kA2s, in particular of 50 to 70 kA2s at an average intermediate circuit voltage in the range of 2.7 to 3.3 kV, in particular of 2.9 to 3.1 kV. Such a fuse is extremely fast acting, if a short circuit situation occurs in which a capacitor may be charged at a voltage of typically up to 2.8 kV.

It is preferred to use a type of fuses 21 to 24, which is designed to clear at a short circuit voltage in the range of 1.8 kV to 2.2 kV. Although a higher capacitor voltage

might occur (see example of the preceding paragraph with intermediate circuit voltages higher than 2.7 kV) this is sufficient, since the normal charging and discharging currents as well as the voltage at the fuse are substantially lower in normal operation compared to the short circuit situation. This allows for smaller and cheaper fuses and, therefore, saves space and investment costs.

The capacitance of each capacitor is for example in the range of 2 to 2.4 mF, in particular 2. 1 to 2. 3 mF.

The fuses 21 to 24 might be arranged below the capacitors in order to provide good accessibility to the capacitors, wherein the other components of the intermediate circuit are also arranged below the capacitors. Therefore, electric connection links between each of the fuses 21 to 24 and the respective capacitor are needed. In a preferred embodiment, the total inductance of each of the fuses 21 to 24 including the respective electric connection link between the fuse 21 to 24 and the capacitor is lower than 100 nH, in particular lower than 85 nH, in order to limit the adverse effects of the parasitic inductance.

In a further preferred embodiment, the fuses 21 to 24 are provided with at least two heat dissipators for natural air convection dissipation of heat to the ambient air. The dissipators are located at opposite ends of the fuse 21 to 24, in particular ends that comprise the electrical contacts of the fuse. Even in high power applications like in railroad traction vehicles the dissipation power of such dissipators (in the region of 40 to 90 W) is sufficient. There is no need for liquid cooling. The dissipators may comprise a plurality of fins and may be formed of a metal block. The DC-resistance of each of the fuses is preferably lower than 1.1 mQ, in particular lower than 0. 6 mQ.

The arrangement 1, in particular the intermediate circuit 9, may comprise more elements and/or parts as shown in Fig. 1, e. g. an inductor in one of the direct current connection lines 13,15.

According to an alternative arrangement the intermediate circuit 9 is connected to a direct current (DC) electric power network. In this case, the rectifier 7 is not necessary and is omitted. For example, the direct current connection line 13 is connected to the to means 3, in particular via an inductor. The direct current connection line 15 may be connected to ground potential.

Some of the railroad power networks are operated with alternating currents having the small frequency of 16 2/3 Hz. Thus, the ratio of the energy stored in the capacitors 17 to 20 to the nominal power of the current rectifier 9 and of the current converter 11 is particularly high. In case of a defect, particularly high discharging currents from the capacitors 17 to 20 can be expected. The concept of the fuse 21 to 24, which is arranged directly in series to the capacitor 17 to 20, plays an important role in protection against failure. Otherwise, severe damages in the intermediate circuit 9 might occur.

Compared to the prior-art device, which is adapted to limit the current in case of an immediate discharge of a capacitor, the electrical losses due to the DC-resistance of the device can be reduced to about 5 %, i. e. by a factor of 20.