Surge arrester and circuit arrangement with surge arrester

Abstract

A surge arrester comprising: - an electrically insulating base body (GK) enclosing a cavity, - a first and a second electrode (A,B) arranged at a distance ab from each other in the cavity, - a central electrode (M) having a distance am and bm to the first and second electrodes respectively, where am = bm < ab, - a trigger electrode (T) having a distance tm to the central electrode, where tm < am, bm, - a trigger circuit (TS) for generating a trigger voltage at the trigger electrode suitable for igniting a gas discharge, wherein the trigger electrode (T) has a rectangular or square area.

Description

The invention relates to a arrester for protecting against overvoltage, in particular a gas discharge overvoltage arrester, and to a circuit arrangement having a arrester.A surge arrester, or surge arrester for short, serves to limit dangerous or undesired overvoltage conditions in electrical lines and devices. This makes it possible to avoid damage to the lines and devices caused by overvoltage.Gas-filled arresters, which are also referred to as gas arresters, are arresters in which an applied overvoltage in the gas arrester is dissipated by the automatic ignition of a gas discharge. They operate according to the gas-physical principle of arc discharge, wherein after reaching an arrester response voltage, referred to for short as response voltage or as ignition voltage, an arc forms within nanoseconds in the gas-tight discharge space. Due to the high current carrying capacity of the arc, the overvoltage is effectively short-circuited.3-electrode arresters known from the prior art are ignited by the overvoltage between one of the two potential-carrying electrodes A or B and a center electrode M connected to ground.The ignition voltage can be adjusted in the arrester by composition of the gas mixture, gas pressure and the electrode spacings.The protection level is determined on the basis of the ignition voltage of the arrester.In a arrester, a distinction is fundamentally made between two ignition voltages:• DC spark-over voltage or DC voltage ignition value. This ignition voltage is decisive when the voltage rise lies in the range 100 V / s to 1 kV / s• Pulse spark-over voltage or impulse response voltage. This ignition voltage is decisive when the voltage rise is in the range of 100 V / μs to 10 kV / μsThe DC ignition value is lower than the response surge voltage. The factor may be about 1.5 or higher. For example, a 1 kV DC voltage firing value arrester may have a response surge voltage of 1.5 kV.The gas ignition in the diverter is in part a stochastic process. As a result, the measured values scatter up to + / -20%. The DC voltage ignition value in the arrester must be set to a correspondingly high level in order to avoid ignition at the nominal mains voltage during normal operation. This also increases the response surge voltage and thus the protection level of the arrester.A diverter should have a firing value well above the normal operating voltage. This must already apply to the DC voltage ignition value. Since the specification of an arrester is also determined according to the response surge voltage, a higher ignition value for the response surge voltage must be set or accepted, which can load a load hanging on the line to be protected strongly with a high voltage in an overvoltage event before the arrester ignites.The publications CN 1 04 377 551 A, DE 10 2017 218 584 A1, DE 10 2017 114 383 A1, CN 1 738 135 A, US 2010 / 0 141 166 A1 and DE 101 29 139 A1 describe arresters.It is therefore an object of the present invention to provide a arrester which ignites as exactly as possible at a desired voltage and with which the ignition voltage can then be set to a lower value than in the case of known arresters.This object is achieved with a diverter according to claim 1. Advantageous embodiments of the invention and a circuit arrangement with a arrester can be found in the further claims.The basic idea is to lower the protection level (substantially the impulse response voltage) of a known 3-electrode arrester by adding an additional trigger electrode. At the same time, a trigger electrode makes it possible to configure the arrester such that it ignites at a defined overvoltage, since the ignition can be triggered at an exact voltage.Like a known arrester, such a arrester has an electrically insulating base body which encloses a cavity. A first and a second electrode are arranged in the cavity at a distance from one another. A center electrode arranged offset between them or laterally has a distance at or bmfrom the first and second electrodes, wherein the following applies for the distances / distances: am=bm<ab.Furthermore, a trigger electrode is provided which is at a distance tm from the center electrode, where tm<am, bm. A trigger circuit for generating and applying a trigger voltage or a trigger pulse to the trigger electrode completes the arrester. The trigger voltage is set to be suitable for igniting a gas discharge between the trigger electrode and the center electrode. The overvoltage is then dissipated to ground via the center electrode and is thus rendered harmless. The trigger electrode further has a rectangular or square surface.With the aid of the trigger electrode, it is possible to trigger the ignition via the trigger voltage. The trigger voltage can be generated as a function of an overvoltage present between the first and second electrodes. It is decisive that the trigger circuit generates a trigger voltage or a trigger pulse only when the voltage in the line or the voltage between the first and second electrode exceeds a set value which corresponds to the desired protection level of the arrester.The arrester according to the invention extended by an additional trigger electrode has a lower (better) response surge voltage and thus also a lower protection level than a 3-electrode arrester corresponding to the standard.The trigger circuit can generate a trigger voltage or a trigger pulse, by means of which the gas ignition is started in the entire interior of the arrester.The main body of the arrester can comprise a ceramic and be filled with a gas. The composition of the gas can be used to adjust the ionization capacity of the gas.In an advantageous embodiment, the diverter can have the geometry described below. The first and second electrodes are disposed along a longitudinal axis of the cavity and are diametrically opposed to each other. The center electrode is arranged on a side wall in the interior of the base body between the first and second electrodes. The trigger electrode is likewise arranged on a side wall of the base body between the center electrode and the first and / or the second electrode. The trigger electrode can be formed in a punctiform manner, as a pin or in a planar manner. It is advantageous if the distance from the center electrode can be set as accurately as possible. Thereby, the ignition voltage can be more accurately adjusted.In a further embodiment, the center electrode is of annularly closed configuration and follows the entire circumference of the cavity along the side wall coaxially with respect to the longitudinal axis, with the result that the same distance from the first and second electrodes is maintained everywhere.In this case, the trigger electrode can also be configured annularly and coaxially with respect to the longitudinal axis and follow the entire circumference of the cavity along the side wall. It extends adjacent to and throughout the same distance from the center electrode.In such an embodiment, the base body is preferably cylindrical. The base body and all electrodes can then be configured rotationally symmetrically to the longitudinal axis.According to a further embodiment, the trigger electrode protrudes radially like a pin from the side wall in the direction of the longitudinal axis.The arrester can be connected in a circuit arrangement such as a power supply circuit. There, it protects the circuit or a load connected thereto from an overvoltage occurring in a power supply, as can be triggered, for example, by an event such as a flash.The circuit has a first and a second line, which are at different potentials, normally at an operating or mains voltage. The first line is electrically connected to the first electrode and the second line is connected to the second electrode of the arrester. In the case of normal voltage, the arrester connected in parallel with the two conductors bypasses the latter in a blocking manner. One of the first and second lines is electrically connected to the trigger electrode via a trigger circuit. The center electrode is connected to ground.The trigger circuit comprises a series circuit of a voltage limiting element and a blocking capacitor.The voltage limiting element may be selected from, for example, temperature distribution structure diode, metal oxide varistor (MOV), or multilayer varistor (MLV). All these elements are characterized in that they become conductive at a breakdown voltage, but are practically non-conductive at a voltage below it.The voltage-limiting element is advantageously set to a voltage value which is set to the DC voltage ignition value between the first or second electrode and the center electrode. Thus, the spark gap between the trigger electrode and one of the three other electrodes of the arrester ignites independently of the response surge voltage that would be established between the three electrodes (without triggering).The difference between the DC voltage firing value and the response impulse voltage no longer plays a role, since the firing now already takes place completely when the trigger voltage is applied and not only when the response impulse voltage of the 3-electrode arrester is reached.Thus, it is possible to accurately set the ignition voltage. Over-voltages can only build up up up to the triggering voltage of the voltage-limiting element. If an overvoltage between the first and second conductors exceeds this triggering voltage, a trigger voltage or a trigger pulse is generated which triggers the ignition of the arrester at the trigger electrode. By short-circuiting the first and / or second electrode to the center electrode, the overvoltage is immediately and reliably conducted away to ground via the center electrode.The invention is explained in more detail below with reference to exemplary embodiments and the associated figures. The figures are schematic and not true to scale.Individual parts may be shown larger or smaller for clarity. Therefore, neither relative nor absolute dimensions can be gathered from the figures.They show FIG. 1 shows a conventional 3-electrode arrester according to the prior art in schematic cross section, FIG. 2 shows a first embodiment of a 3-electrode arrester with an additional trigger electrode in schematic cross section, FIG. 3 shows different voltage / time curves for different ignition mechanisms in the arrester, FIG. 4 shows a second embodiment of a 3-electrode arrester with an additional trigger electrode in schematic cross section, FIG. 5 shows a circuit arrangement with a first and a second conductor and a shunt connected in parallel thereto together with a trigger circuit.FIG. 1 shows a conventional 3-electrode arrester according to the prior art in schematic cross section. In the cavity of an electrically insulating base body GK, a first electrode A and a second electrode B are arranged diametrically opposite one another along a longitudinal axis LA. They are spaced apart from one another. Between the first electrode A and the second electrode B, a center electrode M connected to ground is arranged, which center electrode is at a distance am and bm from the first and second electrodes, where am≥2 am and am=bm. The base body can comprise ceramic and is shaped, for example, as a hollow cylinder.The ends of the base body can be closed with a cap K 1, K 2 in each case in order to seal off the cavity in the base body in a gas-tight manner. The caps K 1, K 2 can likewise be made of ceramic and be connected to the base body, for example, by brazing.The electrodes may comprise Cu. FeNi or WCu are also suitable as electrode metals or as a coating of the electrodes.If a voltage applied to the first and second electrodes exceeds the protection level of the arrester, the gas mixture inside the arrester is ignited. First, a spark gap is produced along a discharge path at or bm. The gas discharge is then distributed throughout the interior of the arrester. If the voltage rise at the electrodes A and B or along one of the paths am and bm is not too steep and lies in the second range, the arrester ignites at the DC voltage ignition value. If, on the other hand, the increase takes place rapidly and, for example, in the μs range, the ignition takes place only at the response surge voltage which is somewhat higher than the DC voltage ignition value.FIG. 3 shows a voltage curve with voltage rises of different speeds over one of the ignition values. Curve 1 corresponds to the curve when the response surge voltage is rapidly exceeded (in the μs range). Curve 2 corresponds to the curve when the DC voltage ignition value exceeds (in the second range) more slowly. After discharge, the voltage drops back to the value U ARC in both cases.U AM in curve 1 corresponds to the response surge voltage between the first and second electrodes and the center electrode.In curve 2, U AM corresponds to the DC voltage ignition value between the first and second electrodes and the center electrode. In the normal case, in which a rapid voltage rise occurs, the value of the response surge voltage is at the same time also the effective ignition voltage of the arrester.The following table gives an example of the electrical specification of such a conventional 3-electrode arrester:DC ignition value100V / sTypical Value230 V±20%Transient Response Voltage100V / μs99% the measured values of the measured values<600VTransient Response Voltage100V / μsTypical Value<550 VTransient Response Voltage1 kV / μs99% the measured values of the measured values<700VTransient Response Voltage1 kV / μsTypical Value<650VFIG. 2 shows a first embodiment of a 3-electrode arrester with an additional trigger electrode T in schematic cross section. Except for the trigger electrode T, the arrester can correspond to a known 3-electrode arrester, as described for example with reference to FIG. 1. Trigger electrode T is arranged on a side wall of the base body between the center electrode and the first or second electrode A or B such that its distance tm from center electrode M is smaller than distance am, bm from the first or second electrode to the center electrode. The shorter a distance between two electrodes ab, am, bm or tm in the arrester, the lower the ignition voltage required for establishing a spark gap between these two electrodes.The DC ignition value and the response surge voltage of the "tm" path are thereby lower than those of the "am" and "bm" paths, respectively.As illustrated, the trigger electrode T can be a wire-shaped conductor, for example, which is guided through the side wall of the base body or a pin, for example made of Cu. The tip of the trigger electrode can protrude a certain distance into the cavity or can only break through the side wall just as flat.Furthermore, the side wall of the base body can be covered with a graphite coatingWith a simple semiconductor circuit (see also FIG. 5 ), the trigger voltage for the trigger pulse can be adjusted approximately to the DC voltage ignition value of the "on" path. This ensures that the response surge voltage of the "on" path and thus also the protection level is equal to or somewhat higher than the protection level of the "on" path at the DC voltage ignition value.The trigger electrode performs a trigger function for the entire arrester. First and second electrodes A, B are also ignited against the center electrode M after triggering.The protection level of the arrester in this case depends on the response surge voltage of the distance "tm" between the trigger and center electrodes. This can be set to a value which is reliably exceeded by the trigger voltage.The voltage curve in the event of a voltage rise in the arrester according to the invention is illustrated by the curve 3 of FIG. 3. Here, the ignition is triggered at a voltage U TM which is just above the DC voltage ignition value of the conventional 3-electrode arrester (without trigger electrode). A further voltage rise as in curve 1 of the conventional arrester is reliably avoided.Since, in the event of a slow voltage rise corresponding to curve 2, the DC voltage ignition value can also be exceeded, this diversion process can also be triggered. In contrast to the conventional 3-electrode arrester, this DC voltage ignition value is however only just above the response surge voltage for the discharge path tm.The protection level is therefore approximately the same for voltage rises of different speeds or steep voltages and can be set overall to a lower value than in the case of the conventional 3-electrode arrester.FIG. 4 shows a second embodiment of a 3-electrode arrester with an additional trigger electrode in schematic cross section. In contrast to the punctiform embodiment according to FIG. 2, the trigger electrode is here applied to the side wall in the shape of a ring or hollow cylinder and coaxially to the longitudinal axis. The trigger electrode can also be designed as a metallic plate filling the cross section of the interior space, in which plate only a passage for possible discharge paths on or bm is left open.FIG. 5 shows a circuit arrangement with a first line L+ and a second line L- between which a voltage is present, usually a mains voltage or a supply voltage. The arrester AL is arranged between the two lines. The first and second electrodes are electrically connected to each of the two lines L. Since the first and second electrodes are galvanically separated, the arrester is non-conductive below its ignition voltage along one of its discharge paths. The center electrode of the arrester Al is connected to ground.A trigger circuit TS connects one of the two conductors L to the trigger electrode. The trigger circuit comprises at least one series circuit consisting of a voltage-limiting element SE and a blocking capacitor SK. The voltage-limiting element SE has a trigger voltage above which it becomes electrically conductive. The trigger voltage can be set to a desired value and, in the case of the arrester according to the invention, lies between the DC voltage starting value and the response surge voltage along the discharge paths am and bm.The voltage limiting element SE may be selected from, for example, temperature distribution structure diode, metal oxide varistor (MOV), or multilayer varistor (MLV).The invention is not limited to the exemplary embodiments shown and also comprises arrester configurations with base bodies of different design and optionally further electrodes. The materials can also deviate from those used by way of example. The ignition voltage, which corresponds to the trigger voltage of the voltage-limiting element, can be set almost arbitrarily, provided that suitable voltage-limiting elements are available.List of reference charactersA First electrode starting from the distance between A and B AL Arrester on the discharge gap and the distance between A and M B Second electrode bm Entladungs gap and the distance between B and M GK Base body GS Graphite rod K1 First cap K2 Second cap L Second line L+ First line LA Longitudinal axis of the base body M Central electrode SE Voltage-limiting element SK Blocking capacitor T Trigger electrode tm Gap and the distance between T and M TS Trigger circuit

Claims

Arrester having - an electrically insulating base body (GK) which encloses a cavity, - a first and a second electrode (A, B) which are arranged at a distance from one another in the cavity, - a central electrode (M) which has a distance am and bm, respectively, with am = bm < ab, - a trigger electrode (T) which has a distance tm from the central electrode, with a tm < am, bm, - a trigger circuit (TS) for generating a trigger voltage at the trigger electrode which is suitable for igniting a gas discharge, with the trigger electrode (T) having a rectangular or square area.Arrester according to the preceding claim, in which the base body (GK) comprises a ceramic and is filled with a gas.Arrester according to one of the preceding claims, - in which the first and the second electrode (A, B) are arranged along a longitudinal axis (LA) of the cavity and are diametrically opposite one another, - in which the central electrode (M) is arranged on a side wall in the interior of the base body (GK) between the first and second electrode (A, B), - in which the trigger electrode (T) is arranged on a side wall of the base body (GK) between the central electrode (M) and the first and / or the second electrode (A, B).Arrester according to one of the preceding claims, in which the central electrode (M) is formed along the side wall following the entire circumference of the cavity and is closed there in an annular manner.Circuit arrangement having - an arrester and a trigger circuit (TS), the arrester having: - an electrically insulating base body (GK) which encloses a cavity, - a first and a second electrode (A, B) which are arranged at a distance from one another in the cavity, - a central electrode (M) which is at a distance from the first and second electrode at a distance from the or bm, where am = bm < ab, - a trigger electrode (T) which is at a distance from the central electrode tm, where tm < am, bm, wherein the trigger circuit (TS) is provided for generating a trigger voltage at the trigger electrode which is suitable for igniting a gas discharge, - a first and a second line (L+, L-) which are at different potentials, wherein - the first line (L+) is connected to the first electrode (A) and the second line (L-) is connected to the second electrode (B) of the arrester (AL), - one of the first and second lines (L+,L-) is electrically connected to the trigger electrode (T) via the trigger circuit (TS), - the trigger circuit (TS) comprises a series circuit of a voltage-limiting element (SE) and a blocking capacitor (SK), - the central electrode (M) is connected to ground.Circuit arrangement, comprising - an arrester according to one of Claims 1 to 4, - a first and a second line (L+, L-) which have different potentials, - the first line (L+) being connected to the first electrode (A) and the second line (L-) being connected to the second electrode (B) of the arrester (AL), - one of the first and second lines (L+, L-) being electrically connected to the trigger electrode (T) via the trigger circuit (TS), - the trigger circuit (TS) comprising a series circuit composed of a voltage-limiting element (SE) and a blocking capacitor (SK), - the central electrode (M) being connected to ground.Circuit arrangement according to Claim 5 or 6, in which the voltage-limiting element (SE) is selected from TVS diode, metal oxide varistor MOV or multilayer varistor MLV.Circuit arrangement according to one of Claims 5 to 7, in which the voltage-limiting element (SE) is set to a voltage value which corresponds to the DC voltage ignition value between the first or second electrode (A, B) and the central electrode (M).

Images