DE102020115169B4 - Surge arrester and circuit arrangement with surge arrester - Google Patents

Abstract

Surge arrester with
- an electrically insulating base body (GK) that encloses a cavity,
- a first and a second electrode (A,B) which are arranged at a distance ab from each other in the cavity,
- a central electrode (M) which has a distance am and bm to the first and second electrodes respectively, where am = bm < ab,
- a trigger electrode (T) which has a distance tm to the center 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 surge arrester for protection against overvoltages, in particular a gas discharge surge arrester, and a circuit arrangement with a surge arrester.

A surge arrester, or simply arrester, is used to limit dangerous or unwanted overvoltages in electrical lines and devices. This prevents damage to the lines and devices caused by overvoltages.

Gas-filled surge arresters, also known as gas discharge tubes, are devices in which an applied overvoltage within the gas discharge tube is dissipated by the automatic ignition of a gas discharge. They operate according to the gaseous physical principle of arc discharge, whereby, upon reaching a surge arrester response voltage, referred to simply as the trigger voltage or ignition voltage, an electric arc forms within nanoseconds in the gas-tight discharge chamber. Due to the high current-carrying capacity of the arc, the overvoltage is effectively short-circuited.

Three-electrode arresters known from the prior art are triggered by the overvoltage between one of the two potential-carrying electrodes A or B and a central electrode M connected to ground.

The ignition voltage in the discharge tube can be adjusted by the composition of the gas mixture, the gas pressure, and the electrode gaps.

The level of protection is determined based on the ignition voltage of the surge arrester.

• • DC spark-over voltage oder Gleichspannungszündwert. Diese Zündspannung ist maßgeblich, wenn der Spannungsanstieg im Bereich 100 V/s bis 1 kV/s liegt
• • Impulse spark-over voltage oder Ansprechstoßspannung. Diese Zündspannung ist maßgeblich, wenn der Spannungsanstieg im Bereich 100 V/µs bis 10 kV/µs liegt

A surge arrester is generally divided into two ignition voltages:

• • DC spark-over voltage. This ignition voltage is crucial when the voltage rise is in the range of 100 V/s to 1 kV/s.
• • Impulse spark-over voltage or trigger voltage. This ignition voltage is crucial when the voltage rise is in the range of 100 V/µs to 10 kV/µs.

The DC discharge voltage is lower than the impulse response voltage. This factor can be approximately 1.5 or higher. For example, a surge arrester with a 1 kV DC discharge voltage can have an impulse response voltage of 1.5 kV.

Gas ignition in the surge arrester is partly a stochastic process. This results in measured values varying by up to +/-20%. Accordingly, the DC ignition threshold in the arrester must be set high enough to prevent ignition during normal operation at nominal mains voltage. This also increases the impulse response voltage and thus the protection level of the arrester.

A surge arrester should have a firing threshold significantly higher than the normal operating voltage. This must apply even to the DC firing threshold. Since the specification of a surge arrester is also determined by the impulse response voltage, a higher firing threshold for the impulse response voltage must be set or accepted. This higher threshold can subject a load connected to the protected line to a high voltage during a surge event before the arrester fires.

The printed materials 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 the conductor.

The object of the present invention is therefore to provide a surge arrester that triggers as precisely as possible at a desired voltage and with which the trigger voltage can then be set to a lower value than with known surge arresters.

This problem is solved with a surge arrester according to claim 1. Advantageous embodiments of the invention and a circuit arrangement with a surge arrester can be found in the further claims.

The basic idea is to lower the protection level (essentially the impulse response voltage) of a known 3-electrode surge arrester by adding an additional trigger electrode. With a The trigger electrode simultaneously makes it possible to design the surge arrester in such a way that it ignites at a defined overvoltage, since the ignition can be triggered at an exact voltage.

Such a surge arrester, like a known surge arrester, has an electrically insulating base body that encloses a cavity. A first and a second electrode are arranged within the cavity at a distance ab from each other. A central electrode, positioned between or laterally offset from the first and second electrodes, has a distance am and bm, respectively, where the following applies to the distances: am = bm < ab.

Furthermore, a trigger electrode is provided, which has a distance tm from the center electrode, where tm < am, bm. A trigger circuit for generating and applying a trigger voltage or trigger pulse to the trigger electrode completes the surge arrester. The trigger voltage is set to ignite a gas discharge between the trigger electrode and the center electrode. The overvoltage is then dissipated to ground via the center electrode and thus rendered harmless. The trigger electrode also has a rectangular or square surface.

The trigger electrode enables ignition via the trigger voltage. This trigger voltage can be generated based on an overvoltage present between the first and second electrodes. Crucially, the trigger circuit only generates a trigger voltage or pulse when the voltage in the line, or the voltage between the first and second electrodes, exceeds a preset value corresponding to the desired protection level of the surge arrester.

The surge arrester according to the invention, extended with an additional trigger electrode, has a lower (better) impulse response voltage and thus also a lower protection level than a standard 3-electrode surge arrester.

The trigger circuit can generate a trigger voltage or trigger pulse, which starts the gas ignition throughout the entire interior of the arrester.

The main body of the drain can be made of ceramic and filled with a gas. The ionizability of the gas can be adjusted by its composition.

In an advantageous embodiment, the current collector can have the geometry described below. The first and second electrodes are arranged along a longitudinal axis of the cavity and are diametrically opposed to each other. The middle electrode is located on a side wall inside the base body between the first and second electrodes. The trigger electrode is also located on a side wall of the base body between the middle electrode and the first and/or second electrode. The trigger electrode can be a point, a pin, or a flat surface. It is advantageous if the distance to the middle electrode can be adjusted as precisely as possible. This allows for more precise adjustment of the ignition voltage.

In another embodiment, the central electrode is designed as a closed ring and follows the entire circumference of the cavity along the side wall coaxially to the longitudinal axis, so that the same distance to the first and second electrodes is maintained everywhere.

The trigger electrode can also be ring-shaped and coaxial to the longitudinal axis, following the entire circumference of the cavity along the side wall. It runs adjacent to and at a constant distance from the central electrode.

In such a configuration, the base body is preferably cylindrical. The base body and all electrodes can then be rotationally symmetrical about the longitudinal axis.

According to another version, the trigger electrode projects radially from the side wall in the direction of the longitudinal axis, like a pin.

The surge arrester can be integrated into a circuit arrangement, such as a power supply circuit. There, it protects the circuit or a connected load from overvoltage occurring in the power supply, such as that caused by an event like lightning.

The circuit has a first and a second conductor at different potentials, typically at an operating or mains voltage. The first conductor is electrically connected to the first electrode and the second conductor to the second electrode of the surge arrester. At normal voltage, the surge arrester, connected in parallel to the two conductors, blocks the current flow. A conductor consisting of the first and second conductors is electrically connected to the trigger electrode via a trigger circuit. The middle electrode is connected to ground.

The trigger circuit comprises a series circuit consisting of a voltage-limiting element and a blocking capacitor.

The voltage-limiting element can be selected, for example, from a temperature distribution structure diode, a metal oxide varistor (MOV), or a multilayer varistor (MLV). All these elements are characterized by the fact that they become conductive at a breakdown voltage but are practically non-conductive at voltages below that voltage.

The voltage-limiting element is advantageously set to a voltage value that corresponds to the DC ignition voltage between the first or second electrode and the center electrode. This ensures that the spark gap between the trigger electrode and one of the three other electrodes of the current collector ignites independently of the impulse voltage that would occur between the three electrodes (without triggering).

The difference between DC ignition value and impulse response voltage no longer matters, since ignition now occurs completely when the trigger voltage is applied and not only when the impulse response voltage of the 3-electrode arrester is reached.

This allows for precise adjustment of the ignition voltage. Overvoltages can only build up to the trip voltage of the voltage-limiting element. If an overvoltage between the first and second conductors exceeds this trip voltage, a trigger voltage or trigger pulse is generated, which triggers the discharge current at the trigger electrode. By short-circuiting the first and/or second electrode with the center electrode, the overvoltage is immediately and reliably discharged to ground via the center electrode.

The invention will now be explained in more detail with reference to exemplary embodiments and the accompanying figures. The figures are schematic and not to scale.

Individual parts may be shown larger or smaller for clarity. Therefore, neither relative nor absolute dimensions can be derived from the figures.

• 1 einen konventionellen 3-Elektroden-Ableiter gemäß dem Stand der Technik im schematischen Querschnitt,
• 2 eine erste Ausführungsform eines 3-Elektroden-Ableiter mit zusätzlicher Triggerelektrode im schematischen Querschnitt,
• 3 verschiedene Spannungs/Zeitkurven bei verschiedenen Zündmechanismen im Ableiter,
• 4 eine zweite Ausführungsform eines 3-Elektroden-Ableiters mit zusätzlicher Triggerelektrode im schematischen Querschnitt,
• 5 eine Schaltungsanordnung mit einem ersten und einem zweiten Leiter und einem dazu parallel geschalteten Ableiter samt Triggerschaltung.

They show

• 1 a conventional 3-electrode surge arrester according to the state of the art in schematic cross-section,
• 2 a first embodiment of a 3-electrode current collector with an additional trigger electrode in schematic cross-section,
• 3 different voltage/time curves for different ignition mechanisms in the discharge tube,
• 4 a second embodiment of a 3-electrode current collector with an additional trigger electrode in schematic cross-section,
• 5 a circuit arrangement with a first and a second conductor and a surge arrester connected in parallel to it, including a trigger circuit.

1 Figure 1 shows a schematic cross-section of a conventional three-electrode current collector according to the prior art. Within the cavity of an electrically insulating base body GK, a first electrode A and a second electrode B are arranged diametrically opposite each other along a longitudinal axis LA. They are separated by a distance ab. A ground-connected central electrode M is arranged between the first electrode A and the second electrode B. This central electrode M is separated by a distance am and bm from the first and second electrodes, respectively, where ab ≥ 2am and am = bm. The base body can be made of ceramic and is, for example, shaped as a hollow cylinder.

The ends of the base body can each be sealed with a cap K1, K2 to create a gas-tight seal around the cavity within the base body. The caps K1, K2 can also be made of ceramic and, for example, joined to the base body by brazing.

The electrodes can contain copper. FeNi or WCu are also suitable as electrode metals or as electrode coatings.

If the voltage applied to the first and second electrodes exceeds the surge arrester's protection level, the gas mixture inside the arrester is ignited. A spark gap is initially created along a discharge path at or bm. The gas discharge then spreads throughout the entire interior of the arrester. If the voltage rise at electrodes A and B, or along one of the paths at or bm, is not too steep and occurs within a few seconds, the arrester will ignite at the DC ignition threshold. However, if the rise is rapid, for example, in the microsecond range, ignition will only occur at the impulse voltage, which is considerably higher than the DC ignition threshold.

The 3 This shows a voltage curve for different voltage rise rates above one of the ignition thresholds. Curve 1 corresponds to the curve when the trigger impulse voltage is exceeded quickly (in the microsecond range). Curve 2 corresponds to the curve when the DC ignition threshold is exceeded more slowly (in the second range). After discharge, the voltage drops back to the value U _{_ARC} in both cases.

U _AM corresponds in curve 1 to the response impulse voltage between the first or second electrode and the center electrode.

In curve 2, U _AM corresponds to the DC ignition voltage between the first or second electrode and the center electrode. Normally, with a rapid voltage rise, the value of the impulse response voltage is also the effective ignition voltage of the surge arrester.

The following table gives an example of the electrical specifications of such a conventional 3-electrode current collector: Voltage increase proportion of measured values Ignition voltage DC ignition value 100V/s Typical value 230 V ± 20% Response voltage 100V/µs 99% of the measurements <600V Response voltage 100V/µs Typical value <550 V Response voltage 1kV/µs 99% of the measured values <700V Response voltage 1kV/µs Typical value <650V

2 Figure 1 shows a first embodiment of a 3-electrode arrester with an additional trigger electrode T in a schematic cross-section. Except for the trigger electrode T, the arrester can be compared to a known 3-electrode arrester, such as those shown in Figure 2. 1 The trigger electrode T is positioned on a side wall of the base body between the center electrode and the first or second electrode A or B, respectively, such that its distance tm to the center electrode M is smaller than the distance am, bm from the first or second electrode to the center electrode. The shorter the distance between two electrodes ab, am, bm, or tm in the current collector, the lower the required ignition voltage to establish a spark gap between these two electrodes.

The DC ignition value and the impulse response voltage of the "tm" section are therefore lower than those of the "am" or "bm" section.

The trigger electrode T can be, as shown, a wire-shaped conductor or a pin, e.g., made of copper, passing through the side wall of the base body. The tip of the trigger electrode can protrude a short distance into the cavity or just barely penetrate the side wall.

Furthermore, the side wall of the base body can be covered with a graphite stripe.

Using a simple semiconductor circuit (see also 5 The trigger voltage for the trigger pulse can be adjusted to approximately the DC ignition value of the "am" section. This ensures that the response impulse voltage of the "am" section, and therefore also the protection level, is equal to or slightly higher than the protection level of the "am" section at the DC ignition value.

The trigger electrode acts as a trigger for the entire probe. The first and second electrodes A and B are also ignited against the center electrode M after triggering.

In this case, the protection level of the surge arrester depends on the impulse response voltage of the path "tm" between the trigger and center electrodes. This can be set to a value that is reliably exceeded by the trigger voltage.

The voltage profile during a voltage increase in the arrester according to the invention is shown by curve 3. 3 The diagram illustrates this. Here, ignition is triggered at a voltage _UTM that is just above the DC ignition threshold of a conventional 3-electrode arrester (without a trigger electrode). A further voltage increase, as seen in curve 1 of the conventional arrester, is reliably prevented.

Since the DC trigger voltage can also be exceeded during a slow voltage increase, as shown in curve 2, this discharge process can also be triggered. However, in contrast to the conventional 3-electrode arrester, this DC trigger voltage is only slightly above the impulse response voltage for the discharge path tm.

The protection level is therefore approximately the same for different speeds or steep voltage increases and can be set to a lower value overall than with a conventional 3-electrode arrester.

4 Figure 1 shows a second embodiment of a 3-electrode current collector with an additional trigger electrode in a schematic cross-section. Here, the trigger electrode differs from the point-like design shown in Figure 2. 2 The trigger electrode is ring-shaped or hollow cylindrical and mounted coaxially to the longitudinal axis on the side wall. It can also be designed as a metallic plate filling the cross-section of the interior, with only a passage left open for possible discharge paths at or bm.

5 Figure 1 shows a circuit arrangement with a first conductor L+ and a second conductor L-, between which a voltage is applied, usually a mains voltage or a supply voltage. The surge arrester AL is positioned between the two conductors. The first and second electrodes are each electrically connected to one of the two conductors L. Since the first and second electrodes are galvanically isolated, the surge arrester is non-conductive below its trigger voltage along one of its discharge paths. The center electrode of the surge 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 surge arrester according to the invention, lies between the DC trigger voltage and the impulse response voltage along the discharge paths am and bm.

The voltage-limiting element SE can be selected from, for example, a temperature distribution structure diode, a metal oxide varistor (MOV), or a multilayer varistor (MLV).

The invention is not limited to the illustrated embodiments and also includes surge arrester designs with differently shaped base bodies and optionally additional electrodes. The materials may also differ from those used as examples. The ignition voltage, which corresponds to the tripping voltage of the voltage-limiting element, can be set almost arbitrarily, provided suitable voltage-limiting elements are available.

Reference symbol list

A

First electrode

away

Distance between A and B

AL

drain

at

Discharge distance and distance between A and M

B

Second electrode

bm

Discharge distance and distance between B and M

GK

basic body

GS

Graphite line

K1

First cap

K2

Second cap

L

Second line

L+

First line

LA

Longitudinal axis of the base body

M

center electrode

SE

voltage-limiting element

SK

Blocking capacitor

T

Trigger electrode

tm

Discharge distance and distance between T and M

TS

Trigger circuit

Claims (8)

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 within 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. A draft tube according to the preceding claim, wherein the base body (GK) comprises a ceramic and is filled with a gas. A current collector according to one of the preceding claims, in which the first and second electrodes (A,B) are arranged along a longitudinal axis (LA) of the cavity and are diametrically opposed to each other, in which the central electrode (M) is arranged on a side wall inside the base body (GK) between the first and second electrodes (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). A current collector according to one of the preceding claims, wherein the central electrode (M) is formed along the side wall following the entire circumference of the cavity and is closed there in a ring shape. Circuit arrangement with a surge arrester and a trigger circuit (TS), wherein the surge arrester comprises: 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 respectively to the first and second electrodes, where am = bm < ab - a trigger electrode (T) having a distance tm to the center electrode, where tm < am, bm, wherein the trigger circuit (TS) is provided for generating a trigger voltage at the trigger electrode suitable for igniting a gas discharge, - a first and a second conductor (L+,L-) having different potentials, wherein - the first conductor (L+) is connected to the first electrode (A) and the second conductor (L-) is connected to the second electrode (B) of the arrester (AL), - a circuit consisting of the first and second conductors (L+,L-) is electrically connected to the trigger electrode (T) via the trigger circuit (TS), - the trigger circuit (TS) comprises a series connection of a voltage-limiting element (SE) and a blocking capacitor (SK), - the center electrode (M) is connected to ground. Circuit arrangement comprising - a surge arrester after one of the Claims 1 until 4 , - a first and a second conductor (L+,L-) which have different potentials, wherein - the first conductor (L+) is connected to the first electrode (A) and the second conductor (L-) is connected to the second electrode (B) of the arrester (AL), - a first and second conductor (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 center electrode (M) is 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 the Claims 5 until 7 , in which the voltage limiting element (SE) is set to a voltage value corresponding to the DC ignition value between the first or second electrode (A,B) and the center electrode (M).