GB2460254A

GB2460254A - Filtered polyphase voltage apparatus

Info

Publication number: GB2460254A
Application number: GB0809248A
Authority: GB
Inventors: Peter Lonsdale
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2008-05-22
Filing date: 2008-05-22
Publication date: 2009-11-25
Anticipated expiration: 2028-05-22
Also published as: GB0809248D0; GB2460254B

Abstract

A poly-phase apparatus includes a mains input 2, a set of lines U1, U2, U3 carrying one of a number of voltage phases from the input and an earth line PE, a filtering arrangement comprising an inductor L1 and a set of capacitances C1-3 connected between at least one of the set of lines and the earth line and a switch S for at least one of selectively breaking or applying an additional resistance R1 to the connection between the filtering arrangement and the earth line during phase balancing. In this way, tripping of an RCD may be prevented during the phase balancing.

Description

A Poly-phase Apparatus This invention relates to power supply apparatus for providing a filtered poy-phase output.

Power supp'y apparatus for providing a poly-phase supply is often provided with line filtering components comprising inductances and capacitors. Some of the capacitors are connected from the lines to earth. A phase balancing period causes a significant current flow via these capacitors to earth and this may erroneously cause a trip of a residual current device (ROD) which may be used with the apparatus.

A prior art poly-phase supply apparatus 1 is shown in Figure 1. It ncludes a mains supply 2 providing three phases U 1, U2 and U3 and an earth PE. This is coupled to an inductor LI which is arranged in series in the lines. Before the nductor is a set of capacitances Cl to C 3. A second set of capacitances 04 to 06 are connected as shown to the lines after the inductor Li. A further capacitor 07 is provide between 04 to 06 and the earth PE. The resulting filtered phase supplies UI', U2' and U3' are output to output 3. The filtering is provided by the inductor and capacitors interacting. The filtering also utilises the PE line as a return path for part of the noise.

During the phase balance phase, a current may pass via the capacitances C4 to 07 to the Protective Earth PE which will cause the tripping of an RCD device 4. The phase balancing phase starts at switching on of the mains input this is done by switches on each phase line which may not operate simultaneously. The phase balancing ends within mili-seconds. This then means the circuit stabilises and the voltage across C7 stabiUses.

The invention provides apparatus as recited in the main claim in a broadest aspect.

According to the invention n a more detailed aspect there is provided a poly-phase apparatus comprising a mains input, a set of lines carrying one of a number of voltage phases from the input and an earth me, a filtering arrangement comprising an inductor and a set of capacitances connected between at least one of the set of lines and the earth line and a switch for at least one of selectively breaking or applying an additional resistance to the connection between the filtering arrangement and the earth line during phase balancing.

In a first embodiment the switch shunts out a resistance during normal operation but during phase balancing will cause aU the current to flow through a resistance reducing the current to below a trip value for the ROD.

In a second embodiment the switch breaks the connection completely to the earth line from the filtering arrangement.

The switch may be a microprocessor which also detects the phase balancing period starting and finishing. It may be a relay or a timer circuit.

The preferred form of inductor is one comprising coils wound on a common core. This so called common core inductor is sometimes referred to a common mode choke and t enables higher inductance values for a given current value and hence may be more compact.

A specific embodiment of the invention will now be described with reference to the drawings in which:

Figure 1 is a prior art figure;

Figure 2 shows a first embodiment; and Figure 3 shows a second embodiment.

As is shown in figure 2, a poly-phase supply apparatus comprises a mains input 2 (any required voltage) providing a set of three phases Ui, U2 and U3 (it could be more or less than three in some embodiments). These are coupled via set of line inductances Li (in this case a coupled inductor which being an inductor comprising a set of coils wound on a common core although other types of inductor may be used) of a filtering arrangement to provide filtered outputs Ui', U2' and U3' at an output 3. The filtering arrangement also includes capacitors Cl, 02 and 03 coupled at first ends to respective lines and coupled to each other at their other ends. iO

The filtering arrangement further includes a set of capacitors C4, 05 and 06 similarly coupled to respective lines after the inductor Li and at their other ends they are co-joined and hence by a capacitance 07 and resistor Ri and switch S to earth line PE. is

The switch S is open and closed by a microprocessor (or by other means).

When the switch S is open, as it is during the phase balancing period, any transient current flow passes from the filter through 07 it then flows through the resistor Ri to the earth line PE. This reduces the current value to below that which would cause an RCD4 to trip. When the phase balancing period ends the switch S is closed shorting out the resistor Ri and providing a low resistance path to earth line PE to increase the filtering. The range of values of Ri may be from ten kilo ohms to a mega ohm. With the lower value determined with regard to the trip current and the upper value determined by a need to stabilises the circuit in a desired time.

In the second embodiment shown in figure 3, two switches SI and S2 are provided with the other parts of the apparatus as described with reference to the first embodiment.

In this case, the two swftches Si and 32 are operated by the microprocessor to break the connection to earth during phase balancing to prevent tripping of the RCD4. At the start of the balancing period both switches are open. After a delay to allow some level of balancing to occur, the switch S2 is closed.

This connects resistor Ri and current flows though it to the earth PE. Then after a further delay to allow stabilisation to occur the second switch Si is closed to provide a low resistance path to PE. The delays used will depend on the components and exterior operating conditions for example the required level of filtering that is desired. The advantage of this embodiment over the first is that the resistor Ri may have a lower value. A lower value means that the circuit will stabilise faster. This is possible without causing the ROD to trip because of the attendant current evel because of the first delay which achieves some partial stabilisation.

It will be appreciated that the invention will be applicabe to break the path to earth for filtering arrangements other than those shown in the embodiments.

For example, in some arrangements 01 to C3 will not be present and also 07 may be dispensed in favour of a direct connection to the earth line. The inductor may also not be present. Accordingly the invention is in its broadest aspect concerned with multiphase apparatus with fitering with a switch for isolating the lines from earth during phase balancing.

It will be appreciated that the switch may take many different forms for example contactors and reays. It may also involve microprocessor or logic control.

Claims

Claims 1. Poly-phase voltage apparatus for providing a number of voltage phases on voltage supply lines derived from a mains supply comprising: ffltering to provide filtering on the supply lines and means to isolate the filtering from an earth line during at least a phase balancing period upon initlaUsation of a supply to the apparatus.
2. Apparatus as claimed in claim 1 wherein the filtering comprises at least one of the group comprising an inductor and capacitor.
3. Apparatus as claimed in claim 2 wherein the inductor is a common mode choke.
4. Apparatus as claimed in claim 3 wherein the filtering comprises capacitances connected from the voltage phase carrying lines at positions at least prior and or after the inductances by respective first ends and at their other ends to each other.
5. Apparatus as claimed in any preceding claim wherein the filtering is selectively connected to the earth line via at least a resistor by means to isolate the filtering.
6. Apparatus as claimed in any preceding claim wherein the means to isolate the filtering is a switch.
7. Apparatus as claimed in claim 6 wherein the switch is responsive to a microprocessor.Amendments to the claims have been filed as follows: 1. Poly-phase voltage apparatus for providing a number of voltage phases on voltage supply lines derived from a mains supply comprising: filtering to provide filtering on the supply lines and means to isolate the filtering from an *and earth linea switch responsive to the means such that during a phase balancing period upon initialisation of a supply to the apparatus the switch is open to isolate the filtering and after a phase balancing period the switch is closed to connect the filtering.2. Apparatus as claimed in claim 1 wherein the filtering comprises at least one of the group comprising an inductor and capacitor.3. Apparatus as claimed in claim 2 wherein the inductor is a common mode CO 15 chokeC4. Apparatus as claimed in claim 3 wherein the filtering comprises capacitances connected from the voltage phase carrying lines at positions at least prior and or after the inductances by respective first ends and at their other ends to each other.5. Apparatus as claimed in any preceding claim wherein the filtering is selectively connected to the earth line via at least a resistor by means to isolate the filtering.6. Apparatus as claimed in claim 6 wherein the switch is responsive to a microprocessor.