Switching device with overvoltage protection and isolating properties and method for protecting a switching device against overvoltages

Abstract

Switching device (SD) with a mechanical first switch (K1) via which a load (Z) can be connected to an electrical voltage source (DC) which provides an operating voltage (UH) and supplies the load (Z) with a direct current (IL) when the first switch (K1) is closed, wherein the first switch (K1) is formed from a source-side contact element (KS) and a load-side contact element (KL), wherein the contact elements (KS, KL) are mechanically separated from each other when the first switch (K1) is open and are in contact with each other under force when the first switch (K1) is closed, and wherein the contact elements (KS, KL) go through two phases (BP, TP) when the first switch (K1) is opened: a) first a contact phase (BP) in which the contact elements (KS, KL) touch each other with decreasing force, and b) immediately afterwards a separation phase (TP) in which the contact elements (KS, KL) are no longer in contact.in the course of which the separation distance (D) of the contact elements (KS, KL) increases at least at the beginning of the separation phase (TP), with an energy storage circuit (B) which has an electrical energy storage element (S) which can be charged by the voltage source (DC) when the first switch (K1) is closed and in the contact phase (BP), wherein the energy storage circuit (B) at least partially takes over the DC supply of the load (Z) by discharging the energy storage element (S) at the beginning of the separation phase (TP) and thereby at least reduces the energy flow via the contact elements (KS, KL) when an arc occurs between the contact elements (KS, KL), wherein the energy storage circuit (B) can be switched on in parallel to the voltage source (DC) behind the load-side contact element (KL) in relation to the opening of the first switch (K1) from the voltage source (DC),that the switching on is limited in time and that the time limitation includes at least the beginning of the separation phase (TP), wherein the switching on is effected by closing a second switch (K2), wherein the correlation of the switching on with the opening of the first switch (K1) is effected by closing the second switch (K2) before opening the first switch (K1) by means of an actuating element (T), the actuation of which is connected with a closing of the second switch (K2), wherein the closed first switch (K1) is locked in each case, wherein the actuation of the actuating element (T) closes the second switch (K2) and unlocks the first switch (K1).

Description

The invention relates to a switching device with overvoltage protection and isolator properties according to claim 1 and to a method for protecting a switching device against overvoltage according to claim 4.Switching devices which connect a load to an electrical energy source in the form of a power supply of a power grid, which provides an operating voltage and supplies the load with electrical energy are known, for example, as load interrupters. Such switching devices have at least one switching contact which has two contact elements which, when the switching device is closed, bear against one another under the action of force and are mechanically separated from one another in order to open the switching device even when the load current flows. This is effected, for example, by means of a switching axle which is rotated about its longitudinal axis by means of a push-on rotating handle (handle) for switching on and off. The mechanical separation of the contact elements first passes through a contact phase in which the force-loaded contact elements still contact one another at at least one contact point. The contact phase is followed by a separation phase in which there is no more direct mechanical contact with the contact elements.A gas or vacuum is usually located in the interspace between the separate contact elements; this is therefore also referred to as a gas or vacuum section, air frequently being used as the gas.Many switching devices must have separator properties, inter alia, for the protection of persons, i.e. the gas and creep paths always present in a gas or vacuum path must have a voltage-dependent minimum path (minimum length), for which there is a corresponding specification (IEC60947) in Germany. In the case of air for a surge voltage resistance, this specification specifies the minimum air gap for an inhomogeneous and a homogeneous (ideal) electric field as a function of the degree of contamination. The surge voltage strength is the strength when a corresponding surge voltage is applied. Only when this minimum distance is present does the switching device have separator properties.When the contact elements are separated, an arc is often formed between the contact elements. Depending on the duration and strength, an arc can lead to considerable wear of the contact elements, which correspondingly reduces the service life.WO2013098906 discloses a switching device in which the generation of an arc between the contact elements is prevented when a mechanical switch is opened. For this purpose, an electrical energy storage circuit is used which has a capacitor as an electrical energy storage element, which, in the event of interruption of a high direct current, in particular of a high-voltage direct current, takes over the direct current supply of the load by discharging the energy storage element and thus suppresses the occurrence of an arc. The interruption is performed without using a controller.DE 753 708 A describes a method for facilitating the disconnection of a load from a power source with the aid of a mechanical switch. This is characterized in that after opening the mechanical switch at the load, an auxiliary alternating voltage is switched on or brought into effect at the instant at which it is greater than the instantaneous value of the voltage of the power source to be switched off and thereby causes the arc at the main switch to break, and that after this arc has been broken, the auxiliary alternating voltage is interrupted by the usual means.DE 269 757 A describes a method for extinguishing the interruption arc occurring at switches with the aid of a capacitor. Shortly before the switch is opened, a surge is generated in a capacitor circuit connected in parallel with it, which surge reaches a sign opposite to the current to be interrupted at the instant of opening or as soon as possible thereafter.Electrical components of the energy storage circuit for arc suppression that are used permanently can be destroyed by the occurrence of an overvoltage, i.e., in particular in the event of a fault, so that their main function-the arc suppression-is no longer provided.In order to prevent this, electrical components can be used in the energy storage circuit, which have a correspondingly high voltage stability. Or surge arresters are used in parallel with the energy storage circuit. However, both solutions are not available for higher overvoltage conditions.The object of the invention is to specify a switching device having a mechanical switch and isolator properties, which switching device has an energy storage circuit which is protected against overvoltage which occurs during operation. In this sense, over-voltages are voltages that are greater than the voltage for which the energy storage circuit and its switching elements are designed. The object of the invention is furthermore a method for protecting an energy storage circuit of a switching device from overvoltage.The solution is given with respect to the switching device by the features of claim 1 and with respect to the method by the features of claim 4; the subclaims represent advantageous embodiments.The solution provides, with respect to the switching device, that the energy storage circuit can be connected in parallel to the voltage source behind the load-side contact element in a correlated manner with the opening of the first switch, that the connection is effected in each case in a time-limited manner, and that the time-limiting manner includes at least the beginning of the disconnection phase.In this case, the activation takes place by closing a second switch. In this case, the correlation of the activation with the opening of the first switch takes place by closing the second switch before the opening of the first switch by means of an actuating element, the actuation of which is connected to a closing of the second switch. In this case, the closed first switch is respectively locked, wherein the actuation of the actuating element closes the second switch and unlocks the first switch.Expediently, the time limitation includes at least the end of the contact phase.It is advantageous if the energy storage circuit is charged at the beginning of the disconnection phase in each case to a minimum voltage which differs from the operating voltage by at most a predefined voltage difference.A simple embodiment is obtained if the correlation of the connection with the opening of the first switch is effected by the opening of the first switch and the closing of the second switch being effected via a common switching means.It is technically simple if the opening of the first switch and the closing of the second switch take place in a positively controlled manner via the common switching means during the touch phase.A simple positive guidance is obtained by means of a common switching axle as common switching means.The solution provides, with respect to the method, that the energy storage circuit is connected in each case in a time-limited manner, in a correlated manner with the opening of the first switch, viewed from the voltage source, behind the load-side contact element parallel to the voltage source, wherein the time-limiting manner includes at least the beginning of the disconnection phase before the connection is interrupted again.The energy storage circuit is advantageously in each case charged to a minimum voltage until the start of the disconnection phase, which minimum voltage differs from the operating voltage by at most a predefined voltage difference.The invention is described in more detail below with reference to an exemplary embodiment. The following are shown: FIG. 1 shows an electrical switching device from the prior art having a first switch which connects an energy source and a load, and having a second switch by means of which an energy storage circuit can be connected in a correlated manner with the opening of the first switch, FIG. 2 shows an enlarged detail of the switching device with the two switches according to FIG. 1, FIG. 3 schematically illustrates the contacting contact elements of the first switch according to FIGS. 1 and 2, FIG. 4 shows the contacting contact elements with already decreasing force application during the opening of the first switch, FIG. 5 shows the contact elements still in contact with each other with a further decreasing force application, FIG. 6 shows the contact elements still in contact with one another, FIG. 7 shows the contact elements which are mechanically separated from one another, FIG. 8 shows the contact elements according to FIG. 7 which are mechanically separated from one another, as shown in FIGS. 3, 5 and 6, FIG. 9 shows the electrical switching device according to FIG. 1 with a simple embodiment of the energy storage circuit, FIG. 10 shows a second embodiment of the switching device according to the invention, in which the energy storage circuit can be connected in a correlated manner with the opening of the first switch by means of a pushbutton, before the opening of the first switch, FIG. 11 shows the switching device according to FIG. 10 with the push button pressed in, FIG. 12 shows the switching device according to FIG. 11, wherein the pushbutton is held in the pressed-in position by a pivoting element of the first switch, and FIG. 13 shows the switching device according to FIG. 11 with the pushbutton released again by the pivoting element and correspondingly opened second switch.FIG. 1 shows an electrical circuit with a voltage source DC as energy source MS, which supplies a load Z (for example a load) with electrical energy, wherein the load Z is schematically illustrated in FIG. 1 as an electrical resistor. The voltage source DC generates a DC voltage UH, which brings about an electrical energy flow in the form of an electrical DC current ILthrough the load Z.The voltage source DC is connected to the load Z via a switching device SD, which has a first switch K 1, which is formed from a source-side contact element KS and a load-side contact element KL. In FIG. 1, the contact elements KS, KL bear against one another under the action of force (illustrated schematically as spring F) and the switch K 1 is closed. The voltage source DC, the switch K 1 and the load Z are connected in series. In FIG. 1, a current IL fließt via the closed switch K 1 and thus via the contact elements KS, KL anliegenden against one another and the load Z, which is thus supplied with electrical energy.An electrical energy storage circuit B can be connected to the load-side contact element KL, said electrical energy storage circuit having an electrical energy storage element S which is designed, for example, as an electrical capacitor C (illustrated schematically in FIG. 1 by the symbol for a capacitor C). Generally speaking, the energy storage circuit B comprises a rechargeable electrical energy store, in this case specifically a capacitive electrical energy store.The connection is effected by means of a second switch K2 which is open in FIG. 1. The energy storage circuit S can thus be connected in parallel with the voltage source DC downstream of the load-side contact element KL, as seen from the voltage source DC. The activation is effected in each case in a time-limited manner, wherein the closing of the second switch K 2 correlates in each case with the opening of the first switch K 1, which is schematically illustrated in FIG. 1 by the dashed connecting line L between the two switches K 1, K 2.In a first exemplary embodiment, the opening of the switch K 1 and the closing of the switch K 2 take place, for example, by rotating a common switching axis A. The two switches K 1, K 2 are therefore positively guided (fixedly coupled) here, i.e. the closing of the switch K 2 and thus the switching on each positively correlates with the opening of the switch K 1 via the common switching axis A, generally thus via the movement of a common switching means W. (of course, the switching means W can also be formed from two or more switching axes which are coupled to one another in terms of movement). FIG. 2 shows the two switches K 1, K 2 according to FIG. 1 in an enlarged illustration.FIG. 3 schematically illustrates the contact region of the contact elements KS, KL according to FIGS. 1 and 2, which here have, by way of example, contact pieces SS, SL, which, when the switch K 1 is closed, bear against one another in the contact region under the action of force. The contact elements KS, KL could also make direct contact, i.e. without contact pieces SS, SL; the contact elements KS, KL with contact pieces SS, SL are a customary advantageous configuration. The contact elements KS, KL, here with the contact pieces SS, SL, usually have an at least slightly rounded shape as shown schematically in FIG. 3 and are shown hemispherically in FIG. 3 for the sake of clarity. Due to the application of force (by means of the spring F), an elastic deformation occurs in the contact region of the contact elements KS, KL, forming a common contact surface KF, which is shown schematically greatly exaggerated in FIG. 3 for better understanding.FIG. 4 shows the contact elements KS, KL according to FIG. 3 with a decreasing force application during the opening of the switch K 1 (schematically as shown in FIG. 2 ), wherein the contact elements KS, KL still touch, while the switch K 2 is already closed here by way of example. In the two switches K 1, K 2 designed as mechanical switches, a contact element KS, KL is each designed to be movable, which contact element can be pivoted in accordance with the direction of the arrows F 1, F 2 and is pivoted accordingly during the opening.In FIG. 5, the contact elements KS, KL still contacting are shown as in FIG. 3. In FIG. 5, the contact elements KS, KL therefore still bear against one another under the action of force, even if the action of force is lower and therefore the contact area KF is smaller.FIG. 6 shows the contact elements KS, KL according to FIG. 5, as shown in FIGS. 3 and 5, while the contact elements KS, KL are just still touching, here only with a very small contact surface KF, which is shown schematically in FIG. 6 as a point (almost point-shaped surface). The contact elements KS, KL are placed against one another in FIG. 6 almost without application of force.FIG. 7 shows the contact elements KS, KL as shown in FIGS. 2 and 4, while these are already mechanically separated from one another, i.e. the switch K 1 is already open here and the contact elements KS, KL no longer touch one another.FIG. 8 shows the contact elements KS, KL according to FIG. 7 which are mechanically separated from one another, as in FIGS. 3, 5 and 6.When the switch K 1 is opened, the contact elements KS, KL thus pass through two phases: a) first of all a contact phase BP (see FIGS. 3, 5, and 6, and FIG. 4 ), in which the contact elements KS, KL touch with a decreasing force application, and b) immediately thereafter a disconnection phase TP (see FIGS. 7 and 8 ) with contact elements KS, KL that are no longer touching, in the course of which the disconnection distance D (see FIG. 8 ) of the contact elements KS, KL increases at the beginning of the disconnection phase TP. The separation phase TP is characterized in that air (and no molten and ionized metal) is respectively located between the contact elements KS, KL.The capacitor C is charged during the entire touch phase BP.FIG. 9 shows the electrical circuit according to FIG. 1 with a simple embodiment of the energy storage circuit B, in which the energy storage device has a capacitor C as energy storage element S, which capacitor is connected in series with a charging resistor RL. The charging resistor RL limits the charging current of the capacitor C. When the capacitor C is charged to the voltage UH, the voltage UH is present at the load-side contact element KL (and thus between the load-side contact element KL and the energy source MS).The charging resistor RL and the capacitor C can be individual separate components or they are to be understood in the sense of an equivalent circuit, i.e. these can also be distributed capacitances and resistors.A diode D1 is connected in parallel with the charging resistor RL, but all the charging current flows through the charging resistor RL because the diode D1 is reverse-biased upon charging the capacitor C.When the switch K 1 is opened (actuated), the switch K 2 is closed, wherein the closing of the switch K 2 still takes place in the touch phase in which a charging current flows through the capacitor C on account of the touch. The charging resistor RL is dimensioned in such a way, adapted to the time profile of the switching off of the switch K 1, that, during the time until the disconnection phase, the capacitor C is charged up to a minimum voltage which differs from the operating voltage UH by at most a predefined voltage difference.The voltage drop across the diode D 1 can usually be neglected, in particular if this voltage drop is smaller by a multiple than the DC voltage UH.In the case of a load Z with inductive components, on the other hand, voltage elevations can occur at the load-side contact element KL. Therefore, a voltage limiter UL is connected in parallel with the energy storage circuit B. The voltage limiter UL ensures that no voltage elevations (with sign reversal) occur.The voltage limiter UL is here simply formed from two diodes D 1, D 2 connected in series; it limits the voltage at the load-side contact element KL. The diode D 1 thus has a dual function here.In generalization, diode D1 represents a specific type of polarity dependent electrical valve means and charging resistor RL represents a specific type of current limiting electrical charging means. Together, the diode D 1 and the charging resistor RL form a special embodiment of an electrical changeover device UE, which, when the first switch K 1 is opened, switches the capacitive electrical energy store S and thus the energy store circuit B automatically from the charging mode (during charging) to the discharging mode (during discharging).In addition, the activation is limited in time; the limiting in time includes at least the beginning of the disconnection phase, and the switch K 2 is then opened again.FIGS. 10-13 show a second exemplary embodiment for a correlation of the activation, namely before the opening of the first switch K1 by means of an actuating element T and a pivoting element E, which is arranged here in a rotationally fixed manner, for example, on the switching axis of the switch K1. The activation takes place here in particular immediately before the opening of the first switch K 1.The actuating element T is designed as a spring-loaded pushbutton T 1, which is pressed in upon actuation and closes the second switch K 2 (or triggers a closing of the second switch K 2). At the same time, the pressed-in pushbutton T 1 enables pivoting of the pivoting element E in order to open the first switch K 1 by rotating the switching axis (here in the clockwise direction). The pivoting element is designed, for example, as a pitch circle disk. The activation correlates with the opening of the first switch K 1, which is schematically illustrated in FIG. 1 by the dashed connecting line L 1 between the pushbutton T 1 and the switch K 2.The closing of the second switch K 2 for charging the energy storage element S takes place (in this way) in correlation with the opening of the first switch K 1 in each case before the opening of the first switch K 1, in that the actuation of the actuating element T is connected to the closing of the second switch K 2 and only thereby is an opening of the first switch K 1 enabled. The release can be connected-as here-to a release and thus to a release of the switching axle A. The actuating element T in the form of the pushbutton T 1 can also latch for a short time after the pressing in.FIG. 10 shows the pivoting element E in its starting position and closed first switch K 1 and open second switch K 2, that is to say in ongoing operation.In FIG. 11, the pushbutton T 1 is pressed in, the second switch K 2 is already closed by the pushbutton actuation, and the opening of the first switch K 1 is enabled by rotation of the switching axis A. (If the pushbutton T1 was not pressed in, the protruding pushbutton T1 would block a further rotation of the switching axis and thus the opening of the first switch K1.) FIG. 11 shows the current operation (shortly) before its interruption by (immediately following) opening of the first switch K 1.FIG. 12 shows the pushbutton T 1, which is held here by the pivoting element E in the pressed-in position, namely at the end of the time-limited activation, in which the second switch K 2 is still closed.In FIG. 13, the spring-loaded pushbutton T 1 is released again (i.e. no longer pressed in), and the second switch K 2 is opened again accordingly.The time limitation thus includes at least the end of the contact phase BP and at least the beginning of the separation phase TP. In particular, the time limitation can include the complete opening of the first switch K 1, i.e. it can last until the complete opening of the first switch K 1.The energy storage circuit B or the energy storage S is not connected to the source-side contact element KS when the first switch K 1 is open, which is why the switching device SD has the necessary prerequisite for isolator properties, since at least one galvanic isolation of the contact elements KS, KL is present. The minimum distance of the contact elements KS, KL (contact pieces SS, SL) required for separator properties when the first switch K 1 is open is given in a first switch K 1, which per se has separator properties (alone).The exemplary embodiment is not limited to the case of direct current or direct voltage. In this case, however, the instantaneous values of the auxiliary voltage UC and of the operating voltage UH must be taken into account in order to design and implement the energy storage circuit B.The switch K 2 can of course also be designed as an electronic switch, i.e. without mechanical contact elements.

Claims

Switching device (SD), having a mechanical first switch (K1), via which a load (Z) can be connected to an electrical voltage source (DC), which provides an operating voltage (UH) and supplies the load (Z) with an electrical direct current (IL) when the first switch (K1) is closed, wherein the first switch (K1) is formed from a source-side contact element (KS) and a load-side contact element (KL), wherein the contact elements (KS, KL) are mechanically separated from one another when the first switch (K1) is open and bear against one another under the action of force when the first switch (K1) is closed, and wherein the contact elements (KS, KL) temporarily have two phases (BP) when the first switch (K1) is open, tp) pass through: a) first a contact phase (BP) in which the contact elements (KS, KL) touch with a decreasing application of force, and b) immediately thereafter a disconnection phase (TP) with contact elements (KS, KL) that are no longer touching, in the course of which the disconnection distance (D) of the contact elements (KS, KL) increases at least at the beginning of the disconnection phase (TP), with an energy storage circuit (B) which has an electrical energy storage element (S) which can be charged by the voltage source (DC) when the first switch (K1) is closed and in the contact phase (BP), wherein the energy storage circuit (B) at the beginning of the disconnection phase (TP) at least partially accepts the direct current supply of the load (Z) by discharging the energy storage element (S) and thereby at least reduces the energy flow via the contact elements (KS, KL) when an arc occurs between the contact elements (KS, KL), wherein the energy storage circuit (B) can be connected in parallel to the voltage source (DC) in each case correlated with the opening of the first switch (K1) behind the load-side contact element (KL), as seen from the voltage source (DC), that the connection is in each case effected in a time-limited manner and that the time limitation includes at least the beginning of the disconnection phase (TP), wherein the connection is effected by the closing of a second switch (K2), wherein, wherein the correlation of the connection with the opening of the first switch (K1) takes place by the closing of the second switch (K2) before the opening of the first switch (K1) by means of an actuating element (T), the actuation of which is connected to a closing of the second switch (K2), wherein the closed first switch (K1) is respectively locked, wherein the actuation of the actuating element (T) closes the second switch (K2) and unlocks the first switch (K1).Switching device (SD) according to Claim 1, characterized in that the time limitation includes at least the end of the contact phase (BP).Switching device (SD) according to Claim 1 or 2, characterized in that the energy storage circuit (B) is in each case charged at the beginning of the disconnection phase (TP) to a minimum voltage which differs from the operating voltage (UH) at most by a predefined voltage difference.Method for protecting a switching device (SD) against overvoltage, wherein the switching device (SD) has a mechanical first switch (K1), via which a load (Z) is connected to an electrical voltage source (DC), which provides an operating voltage (UH) and supplies the load (Z) with an electrical direct current (IL) when the first switch (K1) is closed, wherein the first switch (K1) is formed from a source-side contact element (KS) and a load-side contact element (KL), wherein the contact elements (KS, KL) are mechanically separated from one another when the first switch (K1) is open and bear against one another under the action of force when the first switch (K1) is closed, and wherein the contact elements (KS, kl) pass through two phases (BP, TP) in time when the first switch (K1) is opened: a) first a contact phase (BP) in which the contact elements (KS, KL) contact one another with a decreasing force application, and b) immediately thereafter a disconnection phase (TP) with contact elements (KS, KL) no longer contacting, in the course of which the disconnection distance (D) of the contact elements (KS, KL) increases at least at the beginning of the disconnection phase (TP), wherein an energy storage circuit (B) is present which has an electrical energy storage element (S) which can be charged by the voltage source (DC) when the first switch (K1) is closed and in the contact phase (BP), wherein the energy storage circuit (B) at the beginning of the disconnection phase (TP) at least partially accepts the direct current supply of the load (Z) by discharging the energy storage element (S), as a result of which the energy flow via the contact elements (KS, KL) is at least reduced when an arc occurs between the contact elements (KS, KL), wherein the energy storage circuit (B) is connected in each case in a time-limited manner, in a correlated manner with the opening of the first switch (K1) behind the load-side contact element (KL), as viewed from the voltage source (DC), parallel to the voltage source (DC), wherein the time-limiting manner includes at least the beginning of the disconnection phase (TP) before the connection is interrupted again, wherein the connection is effected by the closing of a second switch (K2), wherein the correlation of the connection with the opening of the first switch (K1) takes place by the closing of the second switch (K2) before the opening of the first switch (K1) by means of an actuating element (T), the actuation of which is connected to a closing of the second switch (K2), wherein the closed first switch (K1) is respectively locked, wherein the actuation of the actuating element (T) closes the second switch (K2) and unlocks the first switch (K1).Method according to Claim 4, characterized in that the energy storage circuit (B) is in each case charged to a minimum voltage which differs from the operating voltage (UH) at most by a predefined voltage difference until the start of the disconnection phase (TP).

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