GB2626976A

GB2626976A - Method, evaluation module and detection system for detecting electric series arcs or glowing contacts by use of a differentiated time course of a relevant...

Info

Publication number: GB2626976A
Application number: GB2301910.2A
Authority: GB
Inventors: Ragginger Philipp
Original assignee: Eaton Intelligent Power Ltd
Current assignee: Eaton Intelligent Power Ltd
Priority date: 2023-02-10
Filing date: 2023-02-10
Publication date: 2024-08-14
Also published as: GB202301910D0

Abstract

A method for detecting a fault event such as an arc or glowing contact at two electric conductors, e.g. a switch, uses an evaluation module 6a to measure and differentiate the current flowing in the conductors with respect to time. The event is classified as an electric series arc if the current has a rate of change above 100 A/s. Alternatively, the event is classified as a glowing contact if the time differential of the current is between 20 A/s to 100 A/s. In addition to the time derivative of current, the frequency of the current may also be used to further classify the fault (10b, 12c; figure 4). The charge of the current in a time span may also be used as a partial discharge equivalent to further classify the fault (12d, figure 4). The current may be measured using a transformer with a core, a winding and a Hall sensor (figure 5).

Description

METHOD, EVALUATION MODULE AND DETECTION SYSTEM FOR DETECTING ELECTRIC SERIES ARCS OR GLOWING CONTACTS BY USE OF A DIFFERENTIATED TIME COURSE OF A RELEVANT CURRENT

TECHNICAL FIELD

The invention relates to a method, an evaluation module and a detection system for detecting an event at two electric conductors, concretely for detecting electric series arcs or glowing contacts.

BACKGROUND ART

Methods and devices for detecting arcs in general are known in prior art and are used, for example, in electrical installations to protect people and/or the installation itself from the destructive effects of an arc caused by a short circuit, or at least to mitigate its effects. In many cases, monitoring of electrical systems is done by measuring the current flowing through the electrical conductors and detecting the extremely intense light emitted by an arc. If both criteria are met, then an alarm signal is issued, or a switching signal to close a switch between said conductors at different voltage potentials.

However, although numerous proposals have been made for detection there is still room for improvement in particular in view of more special phenomena. Concretely, the proposed method, evaluation module and detection system focus on detecting electric series arcs or glowing contacts.

An electric series arcs can occur when a current flows via a gap between electric conductors of the same phase. For example, a loosely connected screw terminal, a broken wire or also defective switching contacts may cause electric series arcs. The very same counts for a glowing contact, where in fact no arc is burning, but where a molten oxide bridge can get formed across a small gap after repeated on and off cycles. The molten oxide bridge can get very hot (up to and even over 1000°C) and can glow bright orange.

Both, an electric series arc and a glowing contact are undesired events, which can get very dangerous under certain circumstances. For example, if an electric series arc or a glowing contact occurs nearby flammable materials, fire and thus destruction and injury can be caused. However, even if the consequences are less dramatic, said events are at least undesired because waste of energy and malfunction can be caused.

As said, the above phenomena are hard to detect and even harder to distinguish. However, there is a big difference for the need of intervention in terms of what is to be done and when it is to be done depending on whether an electric series arc or a glowing contact occurs.

DISCLOSURE OF INVENTION

Accordingly, an object of the invention is the provision of an improved method, an improved evaluation module and an improved detection system for detecting an event at two electric conductors. In particular, an electric series arc and a glowing contact shall be reliably detected and distinguished.

The object of the invention is solved by a method of detecting an event at two electric conductors, comprising the steps of - measuring a time course of a current flowing over the two electric conductors, - generating a differentiated time course by differentiating said time course or a filtered course of said time course and a) classifying the event as an electric series arc if the differentiated time course has a current changing rate above 100 A/s or b) classifying the event as a glowing contact if the differentiated time course has a current changing rate in a range of 20 A/s to 100 A/s.

Moreover, the object of the invention is solved by an evaluation module for detecting an event at two electric conductors, comprising - an input for a time course of a current flowing over the two electric conductors, - a time differential module, which is coupled to said input and which is designed to differentiate the time course, and - a decision making module, which is coupled to the time differential module and which a) is designed to classify the event as an electric series arc if the differentiated time course has a current changing rate above 100 A/s or b) to classify the event as a glowing contact if the differentiated time course has a current changing rate in a range of 20 A/s to 100 Ns.

Optionally, a filter can be provided between the input of the evaluation module and the time differential module.

Finally, the object of the invention is solved by a detection system, which comprises current measuring means and an evaluation module as disclosed above, the input of which is connected to the current measuring means.

It has turned out during intensive development that the above conditions a) and b) are particularly useful for reliably detecting distinguishing electric series arcs and glowing contacts in a gap between two electric conductors. In both cases, a current changing rate of a differentiated time course of the relevant current is used. The presented structure of the evaluation module in particular is related to its function and is no prejudice for a physical structure of a real evaluation module. Functions may be embodied in software and/or hardware. Finally one should note that numerical values in particular shall include a deviation of +/-10% from their base value throughout the disclosure.

Further advantageous embodiments are disclosed in the claims and in the description as well as in the figures.

In a beneficial embodiment, a frequency course of said current is generated by performing a fast Fourier transformation on said time course or on a filtered course of said time course and used as a further criterion to classify the event at two electric conductors, wherein: c1) the event is classified as an electric series arc if an absolute maximum of the frequency course additionally is located in one or more of the frequency ranges 3.6 to 3.8 MHz, 4.5 to 4.8 MHz and/or 6.1 to 6.7 MHz in case a) or c2) the event is classified as an electric series arc if a sum of the frequency course in one or more of the frequency ranges 3.6 to 3.8 MHz, 4.5 to 4.8 MHz and/or 6.1 to 6.7 MHz additionally exceeds a current threshold level of 5 RA as long as it stays above a sustain level of 1.6 RA after exceeding current threshold level of 5 RA in case a) or d) the event is classified as a glowing contact if a sum of the frequency course in a frequency range of 80 kHz to 1 MHz additionally exceeds a current threshold level of 5 u.A as long as it stays above a sustain level of 0.55 RA after exceeding current threshold level of 5 RA in case b).

Accordingly, the evaluation module beneficially can comprise - a fast Fourier transformation module, which is coupled to said input and which is designed to generate a frequency course of said current by performing a fast Fourier transformation on said time course and in a case C) - a maximum detection module, which is coupled to the fast Fourier transformation module and which is designed to detect an absolute maximum of the frequency course, - wherein the decision making module is further prepared c1) to classify the event as an electric series arc if an absolute maximum of the frequency course is located in one or more of the frequency ranges 3.6 to 3.8 MHz, 4.5 to 4.8 MHz and/or 6.1 to 6.7 MHz or in a case D) - a summation module, which is coupled to the fast Fourier transformation module and which is designed to sum the frequency course, - wherein the decision making module is further prepared c2) to classify the event as an electric series arc if a sum of the frequency course in one or more of the frequency ranges 3.6 to 3.8 MHz, 4.5 to 4.8 MHz and/or 6.1 to 6.7 MHz exceeds a current threshold level of 5 RA as long as it stays above a sustain level of 1.6 RA after exceeding current threshold level of 5 RA or d) to classify the event as a glowing contact if a sum of the frequency course in a frequency range of 80 kHz to 1 MHz exceeds a current threshold level of 5 RA as long as it stays above a sustain level of 0.55 RA after exceeding current threshold level of 5 RA.

In this embodiment, a further criterion is used to classify the event at two electric conductors. Concretely, the frequency course of the current flowing over the two electric conductors is used for that reason. In case c1) single maximums in the frequency course are used for detection, whereas in cases c2) and d) a sum or integral of the frequency course in particular frequency ranges is used. Cases or conditions c1) and c2) can also be used in combination. For example, an event can be classified as an electric series arc if both conditions cl) and c2) are true. Optionally, a filter can be provided between the input of the evaluation module and the fast Fourier transformation module.

In yet another beneficial embodiment, the partial discharge equivalents based on the time course of the current flowing over the two electric conductors or on a filtered course of said time course are used as a further criterion to classify the event at two electric conductors, wherein a partial discharge equivalent is the charge of said current during a first time span, wherein e) the event is classified as an electric series arc if at least 90% of the partial discharge equivalents or the sum of the partial discharge equivalents during a second longer time span additionally have a charge over 100 pC in cases a) or f) the event is classified as a glowing contact if at least 90% of the partial discharge equivalents or the sum of the partial discharge equivalents during a second longer time span additionally have a charge in a range of 1 pC to 100 pC in case b).

Accordingly the evaluation module beneficially can comprise - a maximum detection module, which is coupled to the input of the evaluation module and which is designed to detect an absolute maximum of the time course and - a summation module, which is coupled to the maximum detection module and which is designed to generate a partial discharge equivalent, which is a sum of the time course at the detected maximum during a first time span, wherein the decision making module is further prepared - e) to classify the event as an electric series arc if at least 90% of the partial discharge equivalents or the sum of the partial discharge equivalents during a second longer time span additionally have a charge over 100 pC or - f) to classify the event as a glowing contact if at least 90% of the partial discharge equivalents or the sum of the partial discharge equivalents during a second longer time span additionally have a charge in a range of 1 pC to 100 pC. In this embodiment, yet another further criterion is used to classify the event at two electric conductors. Concretely, the charge of the current flowing over the two electric conductors over a given time period, in particular at or after a maximum of said current is detected. This charge may also be referred as "partial discharge equivalent". For example, the partial discharge equivalent can be determined by summation or integration of the time course of the current flowing over the two electric conductors or of a filtered course of said time course around a detected maximum. The partial discharge equivalent can also be determined by quasi summation or integration, where the measured maximum is just multiplied by a factor. Doing so in particular is useful if the shape of a current pulse around its maximum is known. For example, the time course of the current around a maximum can have a Gaussian shape.

Beneficially the first time span can be in a range of 0.5 to 5.0 hrs and in particular can be 2.0 Rs. For example, the partial discharge equivalent can be determined by summation or integration of the time course of the current flowing over the two electric conductors or of a filtered course of said time course during +/-1 ps around a detected maximum. Further on, the second time span beneficially can be in a range of 100 to 500 is and in particular can be 200 Rs.

Beneficially, for obtaining the filtered time course, the time course of the current flowing over the two electric conductors can be band pass filtered with a band pass filter having a lower cut off frequency of 100 kHz and an upper cut off frequency of 1 MHz. These filter values are particularly useful if the partial discharge equivalent is determined by real summation or integration.

In an alternative embodiment, for obtaining the filtered time course, the time course of the current flowing over the two electric conductors can be band pass filtered with a band pass filter having a lower cut off frequency of 100 kHz and an upper cut off frequency in a range of 200 kHz to 1 MHz. These filter values are particularly useful if the partial discharge equivalent is determined by quasi summation or integration, where the measured maximum is just multiplied by a factor.

In another very advantageous embodiment, an event - is classified as an electric series arc if one or more of the conditions a), c1), c2) and e) including at least option a) are fulfilled or - is classified as a glowing contact if one or more of the conditions b), d) and f) including at least option b) are fulfilled.

Accordingly the evaluation module beneficially can comprise a decision making module, which is designed to - classify the event as an electric series arc if one or more of the conditions a), cl), c2) and e) including at least option a) are fulfilled or - is classified as a glowing contact if one or more of the conditions b), d) and f) including at least option b) are fulfilled.

In this way, more certainty can be obtained when an event is classified because the classification is based on more than one fulfilled condition. In detail, the sub results of the single conditions can be joined by a logical AND-function to obtain an overall result. For example two of four conditions, three of four conditions or all four conditions can be used.

In yet another very advantageous embodiment, an event - is classified as an electric series arc if a sum of weighted results of one or more of the conditions a), cl), c2) and e) including the weighted result of condition a) exceeds a first decision threshold or - is classified as a glowing contact if a sum of weighted results of one or more of the conditions b), d) and f) including the weighted result of condition b) exceeds a second decision threshold.

Accordingly the evaluation module beneficially can comprise a decision making module, which is designed to - classify the event as an electric series arc if a sum of weighted results of one or more of the conditions a), cl), c2) and e) including the weighted result of condition a) exceeds a first decision threshold or - is classified as a glowing contact if a sum of weighted results of one or more of the conditions b), d) and f) including the weighted result of condition b) exceeds a second decision threshold.

In this way, more certainty can be obtained when a event is classified, too, because the classification is based on more than one fulfilled condition again. However, there is not just a simple a logical AND-function for joining the sub results of the single conditions to obtain an overall result, but the weighting factors are used to prioritize some of the results. For example, the classification resulting from the condition a) may be multiplied by 0.5, the classification resulting from the condition cl) may be multiplied by 0.2, the classification resulting from the condition c2) may be multiplied by 0.2 and the classification resulting from the condition e) may be multiplied by 0.1. An event can be classified as an electric series arc if the sum of the four single classifications is above a first decision threshold of 0.3. Again two of four conditions, three of four conditions or all four conditions can be used. In one embodiment, there is only a common decision making module. which classifies the event, whereas in an alternative embodiment, for each condition a dedicated decision making sub module is provided, wherein the results of the decision making sub modules are fed to a common decision making module.

Beneficially, the current flowing over the two electric conductors is measured - by means of a transformer, wherein the current over the two electric conductors flows through a primary winding of the transformer and the current measurement takes places at the secondary winding of the transformer or - by means of an arrangement, comprising a magnetic core, a winding, which is wound around the magnetic core and through which the current over the two electric conductors flows, and a Hall sensor, which is arranged in an air gap of the magnetic core and which is prepared to measure the magnetic flux generated by the current through the winding.

In this way, the current pulses before and during an electric arc can be measured with high accuracy.

It should be noted at this point that embodiments related to the proposed method and their advantages similarly relate to embodiments related to the proposed evaluation module and detection system and their advantages and vice versa.

BRIEF DESCRIPTION OF DRAWINGS

The invention now is described in more detail hereinafter with reference to particular embodiments, which the invention however is not limited to.

Fig. 1 shows an exemplary electric circuit and a detection system for detecting electric series arcs or glowing contacts; Fig. 2 shows a schematically drawn functional block diagram of an example of a detection system based on a time differential of the relevant current; Fig. 3 shows a schematically drawn functional block diagram of a detection system using more than one condition for the event classification and Fig. 4 shows exemplary current measuring means with a magnetic core, a winding and a Hall sensor.

DETAILED DESCRIPTION

Generally, same parts or similar parts are denoted with the same/similar names and reference signs. The features disclosed in the description apply to parts with the same/similar names respectively same/similar reference signs. Indicating the orientation and relative position is related to the associated figure, and indication of the orientation and/or relative position has to be amended in different figures accordingly as the case may be.

Fig. 1 shows an arrangement of a simple electric circuit and a detection system 1 for detecting electric series arcs or glowing contacts. The electric circuit comprises a voltage source 2, a switch 3 and a load 4. Further on, the arrangement comprises current measuring means 5, which are part of the detection system 1 and which are provided to measure a current I flowing over the switch 3. Additionally, the detection system 1 comprises an evaluation module 6 which is connected to the current measuring means 5 and to an external control or display 7.

Fig. 2 shows a schematically drawn functional block diagram of an example of a detection system la to illustrate the disclosed method. The detection system la comprises current measuring means 5 and an example of an evaluation module 6a connected thereto. The evaluation module 6a comprises an optional filter 8a, which is embodied as a bandpass filter in this example, a time differential module 13a, an optional summation module 12a and a decision making module 11a.

As illustrated in Fig. 1, an electric series arc event may occur between the switching contacts of the switch 3 or between two electric conductors in general. Accordingly, the switching contacts are to be seen as a special case of two electric conductors in the following.

A method of detecting an event at two electric conductors by use of the detection system la can comprise the following steps: -10 - - measuring a time course of the current I flowing over the two electric conductors by use of the current measuring means 5, - differentiating the time course of said current, and - classifying the event by use of the decision making module 11a, wherein a) the event is classified as an electric series arc if the differentiated time course has a current changing rate above 100 A/s or b) the event is classified as a glowing contact if the differentiated time course has a current changing rate in a range of 20 A/s to 100 A/s.

The result can be sent to the external control or display 7 for further processing either by wire or wireless.

Optionally, the time course may be filtered by the optional filter 8a before it is passed over to the time differential module 13a, and optionally, the time differential may be summed up over a defined time period by means of the summation module 12a. Alternatively, also an averaging module may be used for calculating the average of the time differential over a defined time period.

Fig. 4 shows a schematically drawn functional block diagram of an example of a combined detection system 1 b, which comprises current measuring means 5, four different branches for signal preparation and a common decision making module 11b. In a first branch, there is an optional filter 8a, which is embodied as a bandpass filter in this example, a time differential module 13a and an optional summation module 12c like it is the case in Fig. 2. In a second branch, there is an optional filter 8b, which again is embodied as a bandpass filter in this example, a fast Fourier transformation module 9b ("FFT module" for short) and a maximum detection module 10b. The third branch comprises an optional filter 8c, which is embodied as a bandpass filter in this example, too, a FFT module 9c and a summation module 12c. Finally, the fourth branch comprises an optional filter 8d, which again is embodied as a bandpass filter in this example, a maximum detection module 10d and a summation module 12d.

The first branch up to the summation module 12a works like the detection system la of Fig. 2. However, the second to the fourth branches work differently.

A method of detecting an event at two electric conductors by use of the second branch can comprise the following steps: - measuring a time course of the current I flowing over the two electric conductors by use of the current measuring means 5, - generating a frequency course of said current I by performing a fast Fourier transformation on said time course by use of the FFT module 9b and - detecting an absolute maximum of the frequency course by use of the maximum detection module 10b.

Optionally, the time course may be filtered by the optional filter 8b before it is passed over to the FFT module 9b. A lower cutoff frequency may be set below 3.6 MHz and an upper cutoff frequency may be set above 6.7 MHz.

A method of detecting an event at two electric conductors by use of the third branch can comprise the following steps: - measuring a time course of the current I flowing over the two electric conductors by use of the current measuring means 5, - generating a frequency course of said current I by performing a fast Fourier transformation on said time course by use of the FFT module 9c and - summing the frequency course in one or more of the frequency ranges 80 kHz to 1 MHz, 3.6 to 3.8 MHz, 4.5 to 4.8 MHz and/or 6.1 to 6.7 MHz by use of the summation module 12c.

Again, the time course may be filtered by the optional filter 8c before it is passed over to the FFT module 9c, wherein a lower cutoff frequency may be set below 3.6 MHz and an upper cutoff frequency may be set above 6.7 MHz if electric series arcs shall be detected or wherein a lower cutoff frequency may be set below 80 kHz and an upper cutoff frequency may be set above 1 MHz if a glowing contact shall be detected.

In a method of detecting events at two electric conductors by use of the fourth branch, partial discharge equivalents can be used as a further criterion to classify an event at two electric conductors. In particular, partial discharge equivalents can be used, which are the charges of the current I flowing over the two electric conductors during a first time span.

-12 -A method of detecting an event at two electric conductors by use of the fourth branch can comprise the following steps: - measuring a time course of the current I flowing over the two electric conductors by use of the current measuring means 5, - detecting a maximum in the time course by use of the maximum detection module 10d and - summing the time course over a first time span at a detected maximum to obtain a partial discharge equivalent by use of the summation module 12d. Beneficially the first time span can be in a range of 0.5 to 5.0 ps and in particular can be 2.0 ',Ls. For example, the partial discharge equivalent can be determined by summation or integration of the time course of the current I flowing over the two electric conductors or of a filtered course of said time course over +/-1µs around a detected maximum. "Summation" in the given context may also be a multiplication of the maximum value with a multiplicator. Doing so in particular is useful if the shape of a current pulse around its maximum is known. For example, the time course of the current I around a maximum can have a Gaussian shape.

Optionally, the time course may be filtered by the optional filter 8d before it is passed over to the maximum detection module 10d, wherein a lower cutoff frequency may be set below 100 kHz and an upper cutoff frequency may be set above 200 kHz or above 1 MHz dependent on whether the partial discharge equivalents are determined by real integration or quasi integration. In the first case, the upper cutoff frequency in particular can be set above 1 MHz, in the second case in a range of 200 kHz to 1 MHz.

The common decision making module llb can classify an event as an electric series arc if one ore more of the following conditions are fulfilled: - the differentiated time course has a current changing rate above 100 A/s, - an absolute maximum of the frequency course is located in one or more of the frequency ranges 3.6 to 3.8 MHz, 4.5 to 4.8 MHz and/or 6.1 to 6.7 MHz, - a sum of the frequency course in one or more of the frequency ranges 3.6 to 3.8 MHz, 4.5 to 4.8 MHz and/or 6.1 to 6.7 MHz exceeds a current threshold level of 5 RA and it stays above a sustain level of 1.6 RA after exceeding current threshold level of 5 RA or -13 - - at least 90% of the partial discharge equivalents or the sum of the partial discharge equivalents during a second time span have a charge over 100 pC.

The common decision making module 11 b can classify an event as a glowing contact if one ore more of the following conditions are fulfilled: - the differentiated time course has a current changing rate in a range of 20 A/s to 100 A/s, - a sum of the frequency course in a frequency range of 80 kHz to 1 MHz exceeds a current threshold level of 5 RA and it stays above a sustain level of 0.55 RA after exceeding current threshold level of 5 RA, - at least 90% of the partial discharge equivalents or the sum of the partial discharge equivalents during a second time span have a charge in a range of 1 pC to 100 pC.

For example, the second time span can be in a range of 100 to 500 i_ts and in particular can be 200 Rs. Again, the result can be sent to the external control or display 7 either by wire or wireless.

In particular, weighting factors may be used in the above context to classify events as electric series arcs or glowing contacts. For example, the classification resulting from the first branch may be multiplied by 0.5, the classification resulting from the second branch may be multiplied by 0.2, the classification resulting from the third branch may be multiplied by 0.2 and the classification resulting from the fourth branch may be multiplied by 0.1. An event can be classified as an electric series arc if the sum of the four single classifications is above a first decision threshold of 0.3.

In Fig. 4, there is only the common decision making module 11 b. However, in an alternative embodiment each branch may have its own decision making sub module (see decision making module 11a in Fig. 2 for example), the results of which are fed to the common decision making module 11 b.

The filters 8a..8d may be different in terms of their design and their function.

However, filters 8a..8d may also be commonly used in the four branches as the case may be.

-14 -It should be noted that any combination of branches may be used in a combined detection system lb as long as the first branch is part of. For example two of four branches, three of four branches or all four branches can be used.

The current flowing over the two electric conductors can be measured by any current measuring means 5. However, Fig. 5 shows an advantageous embodiment of current measuring means 5a, which comprise a magnetic core 14, a winding 15 and a Hall sensor 16. In this example, the current I over the two electric conductors flows through the winding 15 and the current measurement is done by means of the Hall sensor 16, which measures the magnetic flux generated by the current I through the winding 15. Alternatively, a transformer can be used, wherein the current I over the two electric conductors flows through a primary winding of the transformer and the current measurement takes places at the secondary winding of the transformer. Basically, the Hall sensor 16 is replaced by the secondary winding then. In both cases, current pulses before and during an electric arc can be measured with high accuracy.

It should be noted that the schematically drawn functional block diagrams depicted in Figs. 2 to 4 shall no be used to construe the scope of the patent claims, and its functional structure is no prejudice for a physical structure of a real evaluation module 6, 6a..6c or detection system 1, la, lb. Instead, functions may be embodied in software and/or hardware in any desired grouping.

As has been noted before, numerical values in particular shall include a deviation of 4-10% from their base value.

Finally, it is noted that in reality, the evaluation module 6, 6a, 6b and the detection system 1, la may have more or less parts than shown in the figures. Moreover, the description may comprise subject matter of further independent inventions.

It should also be noted that the term "comprising" does not exclude other elements and the use of articles "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

-15 -

LIST OF REFERENCE NUMERALS

1, 1 a, 1 b detection system 2 voltage source 3 switch 4 load 5, 5a current measuring means 6, 6a, 6b evaluation module 7 external control or display 8a..8d filter 9b, 9c fast Fourier transformation module 10b, 10d maximum detection module 11a, 11 b decision making module 13a time differential module 12a, 12c, 12d summation module 14 magnetic core primary winding 16 Hall sensor current

Claims

-16 -CLAIMS1. Method of detecting an event at two electric conductors, comprising the steps of - measuring a time course of a current (I) flowing over the two electric conductors, - generating a differentiated time course by differentiating said time course or a filtered course of said time course, characterized in that, a) the event is classified as an electric series arc if the differentiated time course has a current changing rate above 100 A/s or b) the event is classified as a glowing contact if the differentiated time course has a current changing rate in a range of 20 A/s to 100 A/s.
2. Method as claimed in claim 1, characterized in that a frequency course of said current is generated by performing a fast Fourier transformation on said time course or on a filtered course of said time course and used as a further criterion to classify the event at two electric conductors, wherein, c1) the event is classified as an electric series arc if an absolute maximum of the frequency course additionally is located in one or more of the frequency ranges 3.6 to 3.8 MHz, 4.5 to 4.8 MHz and/or 6.1 to 6.7 MHz in case a) or c2) the event is classified as an electric series arc if a sum of the frequency course in one or more of the frequency ranges 3.6 to 3.8 MHz, 4.5 to 4.8 MHz and/or 6.1 to 6.7 MHz additionally exceeds a current threshold level of 5 RA as long as it stays above a sustain level of 1.6 RA after exceeding current threshold level of 5 RA in case a) or d) the event is classified as a glowing contact if a sum of the frequency course in a frequency range of 80 kHz to 1 MHz additionally exceeds a current threshold level of 5 RA as long as it stays above a sustain level of 0.55 RA after exceeding current threshold level of 5 RA in case b).
-17 - 3. Method as claimed in claim 1 or 2, characterized in that partial discharge equivalents based on the time course of the current flowing over the two electric conductors or on a filtered course of said time course are used as a further criterion to classify the event at two electric conductors, wherein a partial discharge equivalent is the charge of said current during a first time span, wherein e) the event is classified as an electric series arc if at least 90% of the partial discharge equivalents or the sum of the partial discharge equivalents during a second longer time span additionally have a charge over 100 pC in case a) or f) the event is classified as a glowing contact if at least 90% of the partial discharge equivalents or the sum of the partial discharge equivalents during a second longer time span additionally have a charge in a range of 1 pC to 100 pC in case b).
4. Method as claimed in claim 3, characterized in that the first time span is in a range of 0.5 to 5.0!is and/or the second time span is in a range of 100 to 500 hts.
5. Method as claimed in claim 3 or 4, characterized in that for obtaining the filtered time course the time course of the current flowing over the two electric conductors is band pass filtered with a band pass filter having a lower cut off frequency of 100 kHz and an upper cut off frequency of 1 MHz.
6. Method as claimed in claim 3 or 4, characterized in that for obtaining the filtered time course the time course of the current flowing over the two electric conductors is band pass filtered with a band pass filter having a lower cut off frequency of 100 kHz and an upper cut off frequency in a range of 200 kHz to 1 MHz.
7. Method as claimed in any one of claims 3 to 6, characterized in that an event - is classified as an electric series arc if one or more of the conditions a), c1), c2) and e) including at least option a) are fulfilled or - is classified as a glowing contact if one or more of the conditions b), d) and f) including at least option b) are fulfilled.
-18 - 8. Method as claimed in any one of claims 3 to 6, characterized in that an event - is classified as an electric series arc if a sum of weighted results of one or more of the conditions a), cl), c2) and e) including the weighted result of condition a) exceeds a first decision threshold or - is classified as a glowing contact if a sum of weighted results of one or more of the conditions b), d) and f) including the weighted result of condition b) exceeds a second decision threshold.
9. Method as claimed in any one of claims 1 to 8, characterized in that the current (I) flowing over the two electric conductors is measured - by means of a transformer, wherein the current (I) over the two electric conductors flows through a primary winding of the transformer and the current measurement takes places at the secondary winding of the transformer or - by means of an arrangement, comprising a magnetic core (14), a winding (15), which is wound around the magnetic core (14) and through which the current (I) over the two electric conductors flows, and a Hall sensor (16), which is arranged in an air gap of the magnetic core (14) and which is prepared to measure the magnetic flux generated by the current (I) through the winding.
10. Evaluation module (6, 6a, 6b) for detecting an event at two electric conductors, comprising - an input for a time course of a current (I) flowing over the two electric conductors, - a time differential module (13a), which is coupled to said input and which is designed to differentiate the time course, and - a decision making module (11a, 11 b), which is coupled to the time differential module (13a) and which a) is designed to classify the event as an electric series arc if the differentiated time course has a current changing rate above 100 A/s or b) to classify the event as a glowing contact if the differentiated time course has a current changing rate in a range of 20 A/s to 100 A/s.
11. Evaluation module (6, 6a, 6b) as claimed in claim 10, characterized in - a fast Fourier transformation module (9b, 9c), which is coupled to said input -19 -and which is designed to generate a frequency course of said current (I) by performing a fast Fourier transformation on said time course and in a case C) - a maximum detection module (10b), which is coupled to the fast Fourier transformation module (9b) and which is designed to detect an absolute maximum of the frequency course, - wherein the decision making module (11b) is further prepared cl) to classify the event as an electric series arc if an absolute maximum of the frequency course additionally is located in one or more of the frequency ranges 3.6 to 3.8 MHz, 4.5 to 4.8 MHz and/or 6.1 to 6.7 MHz or in a case D) - a summation module (12c), which is coupled to the fast Fourier transformation module (9c) and which is designed to sum the frequency course, - wherein the decision making module (11 b) is further prepared c2) to classify the event as an electric series arc if a sum of the frequency course in one or more of the frequency ranges 3.6 to 3.8 MHz, 4.5 to 4.8 MHz and/or 6.1 to 6.7 MHz additionally exceeds a current threshold level of 5 pA as long as it stays above a sustain level of 1.6 pA after exceeding current threshold level of 5 IA or d) to classify the event as a glowing contact if a sum of the frequency course in a frequency range of 80 kHz to 1 MHz additionally exceeds a current threshold level of 5 RA as long as it stays above a sustain level of 0.55 pA after exceeding current threshold level of 5 kA.
12. Evaluation module (6, 6a, 6b) as claimed in claim 11, characterized in a filter (8b, 8c) between the input of the evaluation module (6, 6a, 6b) and the fast Fourier transformation module (9b, 9c).
13. Evaluation module (6, 6a, 6b) as claimed in any one of claims 10 to 12, characterized in - a maximum detection module (10d), which is coupled to the input of the evaluation module (6, 6a, 6b) and which is designed to detect an absolute maximum of the time course and - a summation module (12d), which is coupled to the maximum detection -20 -module (10d) and which is designed to generate a partial discharge equivalent, which is a sum of the time course at the detected maximum during a first time span, wherein the decision making module (11b) is further prepared - e) to classify the event as an electric series arc if at least 90% of the partial discharge equivalents or the sum of the partial discharge equivalents during a second longer time span additionally have a charge over 100 pC or - f) to classify the event as a glowing contact if at least 90% of the partial discharge equivalents or the sum of the partial discharge equivalents during a second longer time span additionally have a charge in a range of 1 pC to 100 pC.
14. Evaluation module (6, 6a, 6b) as claimed in claim 13, characterized in a decision making module (11b), which is designed to - classify the event as an electric series arc if a sum of weighted results of one or more of the conditions a), c1), c2) and e) including the weighted result of condition a) exceeds a first decision threshold or - is classified as a glowing contact if a sum of weighted results of one or more of the conditions b), d) and f) including the weighted result of condition b) exceeds a second decision threshold.
15. Detection system (1, 1a..1c), comprising current measuring means (5, 5a) and an evaluation module (6, 6a, 6b) as claimed in any one of the claims 10 to 14, the input of which is connected to the current measuring means (5, 5a).