DE10245144C5 - Overvoltage protection arrangement with a spark gap as coarse protection element - Google Patents

Abstract

Overvoltage protection arrangement with a spark gap as coarse protection element, wherein the spark gap two main electrodes (1, 2) and at least one auxiliary electrode (3) comprises and the auxiliary electrode (3) with an igniter acting as fine protection in connection, characterized in that the ignition device at least one non-linear temperature-dependent Resistor with positive temperature coefficient, namely one PTC thermistor (4) which under load its cold resistance without destruction increase by at least 5 times can and re the pulse currents up to several 100 A is stable, and the PTC thermistor (4) is connected in such a way that by the resistance increase same the response, the sensitivity as well as the ignition and delete behavior the spark gap is set specifically, which in addition to the self-protection or the protection of the ignition device also a load and / or temperature-dependent coordination of the operation of fine protection, d. H. the ignition device, and coarse protection, d. H. the spark gap, within the overvoltage protection arrangement achieved with minimal wear being, taking this the separation path (8) between the auxiliary electrode (3) and the main electrode ...

Description

The The invention relates to an overvoltage protection arrangement with a spark gap as coarse protection element, wherein the spark gap comprising two main electrodes and at least one auxiliary electrode and the Auxiliary electrode with an acting as a fine protection ignition device in connection, according to the generic term of claim 1

State of the art

Of the Protection level for electronic devices of the different kind and others, against transient overvoltages Sensitive equipment has become too prevalent in recent years smaller response values while increasing performance postponed.

The associated drastic reduction of the operating voltage causes however in undesirable Way a frequent Activate the arrester already at low-energy surges, thereby strengthening Wear the Arrester is created.

at for the use of triggerable surge arresters on the spark gap basis for optimized control of the response is assumed that by a pre-discharge by means of auxiliary electrode charge carriers within the rollover path be inserted between the main electrodes. This introduction of carriers causes the ignition a discharge between the main electrodes at a voltage which significantly below the operating voltage of the spark gap without ignition device or pre-discharge is.

at the known ignition devices the triggerable type exists a group that does not own any options has to limit the voltage and which when reaching a certain voltage value the ignition the spark gap enforces.

such Have arrangements, especially in the use of capacity, the Advantage of a so-called TOV (Temporary Overvoltage) strength, because of mains frequency overvoltages only equalizing currents into existing capacities flow, However, no long-lasting, continuous flow of current occurs. As a result of the comparatively small equalizing currents is too For impulse stresses, the energy used to ignite the pre-discharge to disposal stands, low, resulting in the design and application possibilities keep the spark gap within limits.

Of the Main disadvantage of the above-mentioned surge but above all in that the Spark gaps themselves are subject to high wear, as these too be ignited at very low energy pulse voltages and then one Burden of possible Line follow currents are exposed.

at another group of ignition devices The spark gaps are advantageously only at high energy Ignited pulse voltages, because with smaller pulses, the ignition device itself as overvoltage fine protection acts.

Also is the disadvantage of the limited energy of the ignition pulse in this type as well as the restriction not given in the spark gap design. However, it occurs but here's the problem that this Devices with mains frequency overvoltages, in which the Spark gap should not be detonated due to the function, overloaded become. In case of overvoltages is the probability of thermal overload of the used Components of such ignition devices even at comparatively low, but lasting, in particular mains frequency currents given. The cause of this is the design and optimization of surge arresters on impulse loads and not regarding long-lasting mains frequency loads.

At the Use of varistors as overvoltage fine protection elements for such ignition devices there is another disadvantage.

varistors are voltage dependent resistors, which become low at a certain voltage value and at which with increasing current the voltage drop increases only slightly. A voltage drop in ignition devices is thus determined essentially by the varistors themselves. In modern MOV type varistors, the voltage drop is included very large impulse currents in the kA range only two to three times as high as the varistor voltage at 1 mA. In common Suppressor diodes, this ratio is even even smaller.

There even with high-energy pulse currents, the voltage drop with varistors due to their characteristics, namely u behaves proportional to i, only slightly across from increases a load with small pulse currents, is in these ignition devices continue to be a disadvantage that the Delay Time until the ignition the mainline almost independent on the size of the pulse current is.

However, the magnitude of the voltage drop is, among other influencing variables, also decisive for the sparking behavior of the spark gap, since it determines the voltage difference between the main electrodes. By the described in varistors Given low voltage differences, it is very difficult to safely ignite the spark gap only at high-energy pulse currents. Rather, there is the need to ignite the spark gaps even at relatively low pulse currents here to protect the varistors from overloading. Thus, even such ignition devices are exposed to unnecessary sparking with respect to the spark gaps.

The specified groups or types of igniters can be in terms of its embodiment still differ in active or passive arrangements. At facilities with passive ignition a pre-discharge only takes place within the spark gap a voltage shift without voltage increase. For ignition devices with active ignition is a voltage increase, e.g. with the help of a transformer to ignite the Pre-discharge given.

In the case of passive ignition, the voltage is usually supplied to the auxiliary electrodes by means of impedances, for example capacitances, ohmic resistances or inductances, or else via a divider comprising impedances of the auxiliary electrode or via a voltage-dependent switching device, eg a gas arrester or suppressor diodes. As the DE 199 52 004 A1 shows, a combination of non-linear resistors, such as varistors is conceivable.

The EP 0 933 860 A1 discloses an ignition device for active ignition, which has a voltage divider parallel to the spark gap between the two main potentials of the basic structure. At the divider, a voltage is tapped in each case, and fed via a voltage-dependent switching device to a transformer, which generates a high voltage after the response of the switching device from the discharge pulse, which is supplied to the auxiliary electrode.

A such circuit has in common with the usual Sizes of the Arrester not insignificant disadvantages. So stays the duration and the height of Energy supply by the ignition discharge in the spark gap is limited. The necessary dimensioning of the components, especially when using capacities, is for effective overvoltage fine protection technically hardly feasible. In the case when the protection level of the arrester is to be kept low, this compulsorily leads to that the Spark gap must be ignited at the smallest pulse currents, which an unwanted one heavy wear the Spark gap is conditional.

at the ignition device with active ignition after JP 1-26-8427 a varistor is provided, which in addition to the function of the overvoltage fine protection simultaneously assumes the function of a voltage-dependent switch. Such a solution However, it is associated with a permanent leakage current and generated across from Gas discharge due to the so-called soft shadow lower di / dt values, which in turn generate lower ignition voltages, thereby the design options the spark gap are limited.

The prior art is still on the US-PS 4,760,486, the DE 19 47 349 A1 and the EP 0 186 939 A2 All of which disclose ignition devices in which a longitudinal decoupling by means of inductances or similar components is present between the spark gap and the ignition device.

The JP 10023661 A shows an ignition device in which a PTC thermistor is used for longitudinal decoupling. The above-mentioned ignition devices are very expensive and unacceptable in particular in the case of large nominal currents of the consumers to be protected in their design.

The there takes over the ignition device also the task of overvoltage fine protection. In addition to the disadvantage of longitudinal decoupling and the associated relatively large size have the known arrangements too low a strength against TOV load and overall high wear of the spark gap.

From the DE 199 14 313 A1 an overvoltage protection system is previously known, there being a monitoring device for the ignition device, which protects against thermal overload and the ignition device by switching off. As a monitoring circuit, a reversible thermal fuse can be provided in the ignition circuit, specifically, a temperature switch is used in the local teaching.

at the device for overvoltage protection in electrical low voltage networks according to G 93 14 632.9 is a Combination of coarse and fine protection previously known, with a spark gap as Coarse protection element provided and a PTC thermistor in Feinschutzzweig is arranged.

The Advantages of ceramic PTC thermistors for use as short-circuit and overload protection be in KAINZ G .: Ceramic PTC thermistors protect electronics. In: Electronics Information, 1990, N. 11, pp. 93-95 presented in detail.

For the use of PTC thermistors, which are arranged in the longitudinal branch of surge protective devices to prevent overload cases, is still on the DE 39 08 236 A1 and the JP 09084258 A made aware.

task

Out The above, it is therefore an object of the invention, an advanced surge protection device indicate with a spark gap as coarse protection element, wherein the Spark gap two main electrodes and at least one auxiliary electrode comprises and the auxiliary electrode in communication with an ignition device stands. The further developed arrangement should automatically with respect to the ignition device as overvoltage fine protection Act. Furthermore, loads caused by mains frequency overvoltages safely controlled and a quasi freely selectable ignition energy can be provided.

The solution The object of the invention is achieved with an article according to the features Claim 1, wherein the dependent claims comprise expedient refinements and developments.

According to the invention within the ignition device a PTC element, i. a PTC thermistor is used. PTC thermistors are non-linear, temperature-dependent resistors with a positive temperature coefficient.

One semiconducting resistor with positive temperature coefficient of, Resistance value may be, for example, sintered barium nitrate with additives made of metal compounds.

With the proposed solution the previous prejudice of the professional world was overcome, which the application of PTC thermistors in the ignition circuit therefore excluded, because at very high voltages or temperatures a PTC thermistor can assume negative temperature coefficients.

Performed experiments have revealed that specifically dimensioned PTC thermistors are suitable, the purpose sought here to fulfill, Such PTC thermistors under load their cold resistance without destruction can increase by at least 5 times and continue safety reserves of the ignition device until the safe Ignite ensure the spark gap of the arrester.

The inserted PTC thermistors are regarding the pulse currents in the range up to several 100 A stable.

A for controlling the characteristics of the surge protective device used resistance increase the PTC thermistor can in case of application by Joule heating at very high-energy pulse currents, but also for longer-lasting Stream small amplitude, e.g. occur at TOV loads.

Of the knowledge according to the invention the appropriate use of PTC thermistors these are such, an ignition device forming that interconnects resistance increase the PTC thermistor under load the spark gap the ignition and delete behavior the latter controls.

In In one embodiment of the invention, the PTC resistor can have an impedance, a varistor or a voltage-dependent switch are connected in series. As a voltage-dependent Switch can be found using a gas discharge tube, which has a setting of ignition the pre-discharge regardless of State of the actual spark gap allows.

Of the PTC thermistor is preferably connected to the junction of a voltage divider, this voltage divider being parallel between the input potential is arranged to the main electrodes. The voltage divider can have a varistor.

at an active embodiment has the ignition device an ignition voltage transformer, which primary side between the input potential and its secondary side to Auxiliary electrode leads.

On the secondary side Here, an impedance is provided by a varistor, a capacity or another PTC thermistor is formed.

at the embodiment an active ignition device is the primary winding of the ignition transformer the PTC thermistor connected in series. This PTC thermistor can complement a Impedance can be connected in series, this series connection additionally a switching device includes. The supplementary Series connection can over it have a varistor and / or a suppressor diode.

at a further embodiment the invention is for Carried that one specified from outside Thermal influence of the PTC thermistor is possible. This device can e.g. a heater, i. be a heating coil to thus the properties of the PTC thermistor and ultimately the ignition device pretend indirectly.

embodiment

The Invention will be described below with reference to exemplary embodiments and under With the help of figures closer explained become.

In the embodiments according to the 2 - 4 With the exception of the series connection, PTC thermistors and gas discharge tubes ( 2 ) not essential to the invention.

in this connection demonstrate:

1 a schematic representation of the ignition device with PTC thermistor;

2 an embodiment of the ignition device with a series circuit of PTC thermistor and other passive elements;

3 a representation of a voltage divider with provided at the node PTC thermistor to form the ignition device and

4 an embodiment for the active control of the ignition device by means of ignition voltage transformer.

In the passive embodiments according to the 1 to 3 serves the separation line 8th between the auxiliary electrode 3 and the main electrode 2 as a quasi voltage-dependent switch.

Reaches the voltage load via the surge arrester 7 between the input potentials 5 and 6 the response voltage of the separation line 8th between the main electrodes 1 and 2 , ignites a pre-discharge between the electrodes 2 and 3 and it will be the voltage across the surge arrester 7 significantly reduced.

This voltage drop is then essentially due to the cold resistance of the PTC thermistor 4 and the amount of current determined by this.

For pulse currents in the range of a few 10 A to some 100 A, the voltage drop can immediately after the ignition of the pre-discharge to a few 10 V to several 100 V, depending on the cold resistance of the PTC thermistor 4 to be limited. As a result of this small voltage drop across the arrester, it is possible to ignite the spark gap between the main electrodes, especially in the case of low-energy pulse currents 1 and 2 and thus to control their unnecessary burden.

An optionally occurring follow-up current is increased by increasing the resistance of the PTC thermistor 4 limited to values, which then through the separation distance 8th can be deleted.

In the case of high-energy pulse currents, on the other hand, the voltage drop at the PTC thermistor decreases 4 after reaching the Nennansprechtemperatur due to the Joule heating disproportionate to the current, resulting in the possibility of a rapid increase in voltage up to the safe ignition of the spark gap between the main electrodes 1 and 2 results.

at the small momentum currents on the other hand, the tension only increases proportionally according to the cold resistance to or because of the cold resistance at low currents and only minimal warming of the PTC in general decreases, not even a proportional increase in tension at appropriate Current increase achieved. In this work area, the voltage drop is above the entire spark gap too low to ignite it.

critical for the Dimensioning of the PTC's is the necessary energy input until the spark gap is safely ignited. These Energy should be significantly higher in all load cases before reaching the temperature are introduced into the spark gap, in which the resistance of the PTC again sinks. In the application, however, the ignition of the spark gap takes place often even before reaching the nominal response temperature or at a only minimal overshoot this temperature. After the ignition the spark gap relieves the PTC and cools down. The PTC should however, the upcoming mains voltage as a single device or in combination with a gas arrester or similar safe dominate.

The targeted overheating (for example, by heaters) takes place only in the reversible working area of PTC's, that is above the nominal response temperature and well below the temperature, from which the resistance of the PTC drops again. Since the nominal response temperature the PTC's about a certain Range is variable the required temperatures chosen almost arbitrarily become.

Basically by the described behavior of the PTC thermistor the ignition of Spark gap accelerates with the increase in the size of the pulse currents.

At power frequency overvoltages, the current flow leads to a Joule heating of the PTC thermistor 4 and thus to increase the resistance value according to the given characteristic curve. The current is thereby automatically limited to a non-critical value and the PTC thermistor 4 thus protected against overloading.

Out the above results when using PTC thermistors in addition the extremely positive self-protection effect at mains frequency overvoltages also a much improved possibility in the sense of a targeted load-dependent control of the response the actual spark gap.

Consequently becomes a burden-dependent Tuning the operation of the fine protection, i. the ignition device, and coarse protection, i. the spark gap, inside the arrester achieved with minimal wear.

As in the 2 and 3 shown in a passive ignition of the PTC thermistor 4 also be used in combination with an impedance, a varistor or a voltage-dependent switch use.

3 shows an embodiment with a voltage divider Z1 / Z2, where Z1 can be replaced by a varistor.

According to the disclosed basic circuit arrangement and their variants, there are simple possibilities, the interaction between the ignition device and to tune and set a given spark gap arrangement, whereby a wider control range is usable.

With the series connection of a gas arrester, for example, the ignition voltage the pre-discharge almost independent from the separation path of the spark gap even with aging of this be set.

With the extension by additional Impedances, such as resistances, inductors or capacities, it is possible, the response of the spark gap for certain load cases, e.g. certain slopes of the pulse currents or for certain To adapt energies of the momentum currents. A series connection with varistors can for better control the response voltage and the leakage currents at an expected aging serve the spark gap.

The in the 3 shown combination with a voltage divider or another varistor is also used to better adjust the operating voltage of the spark gap. Also in this way the adjustment of the performance of the fine protection function of the ignition device is improved.

The block diagram after the 4 shows ways of using PTC thermistors in an active ignition device with a transformer to increase the ignition voltage. As a result, the design options of the spark gap geometry are extended and it can be made useful by the influence on the response of the switching device used, other criteria except the voltage for triggering the spark gap. This can be, for example, currents, voltage changes or the like in the longitudinal path, transverse path or even in the devices to be protected.

at an active ignition device an arrangement without current or energy-limiting divider is preferred. When using such a circuit is after the response of the Switching element, which can be activated passively but also actively, the total voltage drop of the arrester almost exclusively by the cold resistance and the transformer winding certainly.

smaller pulse currents are thus directly over the ignition device and derived without any stress or involvement of the spark gap. The Energy and the height the streams, which do not lead to the response of the spark gap, in a simple manner by the response voltage of the partial spark gap, the capacity of the transformer, by a limiting element, e.g. Varistor and ignition circuit, or parallel to the transformer and be adjusted by the design of the spark gap itself.

Additionally results through the voltage drop over the PTC thermistor, which by the cold resistance and the characteristic the PTC thermistor is determined at different currents, the possibility the control of the response of the spark gap, as at one low voltage drop even at the ignition of the pre-discharge the Spark gap not ignited can be.

at optimized tuning of the spark gap and the ignition device can with an active ignition device even the load on the spark gap due to the pre-discharges a minimum be limited.

at higher pulse currents is due to the higher Energy input and higher Voltage drop the spark gap ignited faster, so that the voltage drop across the PTC thermistor remains limited to values below the protection level.

at TOV loads and possibly existing downstream currents the current in the ignition device through the thermistor independent of Activation of the spark gap automatically limited. For some of these Examples can, as explained, also the combination of a PTC thermistor with a resistor, a inductance or even a varistor to increase the control range of advantage be.

In particular, with an active ignition of the spark gap, as in 4 shown, it should be noted that the secondary winding of the transformer and the impedance Z3 or the varistor and a possibly existing switching device, such as a gas arrester, by a partial stream after the ignition of the Pre-discharge between one of the main electrodes and the auxiliary electrode can be heavily loaded. This load increases especially with long delay times until the ignition of the spark gap between the main electrodes 1 and 2 at. However, particularly critical for these components are those loads in which, although the preliminary discharge is ignited, but does not ignite the main spark gap. In such cases, especially at elevated voltages, the current can not be controlled by existing varistors or switching devices and the components of the ignition device used would be overloaded. In addition to the inclusion of a further PTC thermistor, the use of a capacitance, for example as Z3, offers itself here as a protection option. The capacity limits the possible current flow through the secondary side of the transformer. However, the inclusion of such a capacity is not limiting in view of the energies required to ignite the spark gap.

At the Use of a PTC thermistor within ignition devices results another advantageous option the control of the behavior of the surge protective device.

The increase in the resistance of a PTC thermistor can be effected by an externally applied heating. By a targeted heating of the PTC thermistor, for example by use at higher ambient temperatures or by a heating coil or the like, the sensitivity of the ignition device can also be adjusted independently of overvoltages. By a further, drastic artificial overheating, moreover, there is the possibility of quasi passivating the ignition device, whereby the response voltage of the arrester except for the natural response voltage of the spark gaps between the two main electrodes 1 and 2 elevated.

Claims (3)

Overvoltage protection arrangement with a spark gap as coarse protection element, the spark gap comprising two main electrodes ( 1 . 2 ) and at least one auxiliary electrode ( 3 ) and the auxiliary electrode ( 3 ) is in connection with an ignition device acting as a fine protection, characterized in that the ignition device at least one non-linear temperature-dependent resistor having a positive temperature coefficient, namely a PTC thermistor ( 4 ) which can increase its cold resistance without destruction by at least 5-fold under load and with respect to the pulse currents up to several 100 A is stable, and the PTC thermistor ( 4 ) Is connected in such a way that the response, the sensitivity and the ignition and extinguishing behavior of the spark gap is set by the increase in resistance, which in addition to the self-protection or the protection of the ignition and a load and / or temperature-dependent tuning of the operation of the fine protection , ie the ignition device, and the coarse protection, ie the spark gap, within the overvoltage protection arrangement is achieved with minimal wear, for this purpose, the separation distance ( 8th ) between the auxiliary electrode ( 3 ) and the main electrode ( 2 ) serves as a voltage-dependent switch and the PTC thermistor ( 4 ) exclusively directly or in series with a gas discharge tube on the auxiliary electrode ( 3 ) and directly on the main electrode ( 1 ) is connected, so that when the voltage load of the protective device ( 7 ) between their input potentials ( 5 ; 6 ) the claim voltage of the separation distance between the main electrodes ( 1 ; 2 ), a pre-discharge between the main electrode ( 2 ) and the auxiliary electrode ( 3 ) ignites with the result of a significant reduction in the voltage across the protective device ( 7 ), this voltage drop being due to the cold resistance of the PTC thermistor ( 4 ) and the amount of current through it is determined. Surge protection order according to claim 1, characterized by a device for external, from the outside predeterminable thermal influence of the PTC thermistor. Overvoltage protection arrangement according to Claim 2, characterized in that a heating winding is provided in order to reduce the properties of the PTC thermistor ( 4 ) and thus indirectly control the ignition device.