EP1002325B1 - Method for determining switchgear-related data in switchgear contacts and/or operation-related data in a connected network - Google Patents

Description

The invention relates to a method for determination of switchgear-specific data on contacts in switchgear, in particular contactor contacts, and / or for determination of company-specific data in the switched Network according to the preamble of claim 1. Besides The invention also relates to the associated device to carry out the procedure.

In the previously published DE 44 27 006 A1 and in the unpublished DE 196 03 310 A1 and DE 196 03 319 A1 describes methods for determining the remaining service life described by shooters in which from the time difference between the start of the anchor opening movement and the Start of contact opening in the course of the electrical life increasing contact wear is detected. With help a microprocessor and customized electronic Circuits for the acquisition of the required measured quantities the current value of the so-called contact print is determined, which by burning off its new value (= 100% Remaining life) to its minimum value (= 0% remaining life) decreases. That distance is the contact print denotes which of the magnet armature during the switch-off process between the beginning of the anchor opening and the beginning of the contact opening travels.

Proceeding from this, it is an object of the invention in the above Procedures to integrate additional functionalities and to create the associated device.

The task is inventively by the total of Features of method claim 1 solved. A related one Device results from the subordinate device claim 15. Developments of the method according to the invention and the associated device are in the subclaims specified.

In the context of the present invention, the existing Electronics on the one hand can be used to identify certain malfunctions to recognize during the remaining service life recording and to avoid a false evaluation, and on the other hand for a Switchgear monitoring to gain useful data such as certain states of the switchgear or of the switch electrical network. With this functional extension is achieved that the further measurement data with the smallest Additional effort gained and usually already with one existing microprocessor can be evaluated.

1. Erfassung 'Schützantrieb elektrisch Ein/Aus'

2. Anzahl der Schaltspiele

3. Erfassung 'Phasenausfall'

4. Erfassung `Netzspannungsausfall'

5. Erfassung 'Kontaktverschweißen'

6. Erfassung 'Kurzschluß'

With the invention, the detection of additional states on the switching device and / or on the electrical network is therefore possible with the aid of the existing 'remaining life electronics'. These states, which can be detected with little or no additional technical effort, are preferably when using a contactor as a switching device:

1. Detection 'contactor drive electrical on / off'

2. Number of switching cycles

3. Recording 'phase failure'

4.Capturing `mains voltage failure '

5. Detection of 'contact welding'

6. Detection 'short circuit'

Points 1, 2 and 5 relate to switching device-specific Data of the contactor used as switching device and the points 3, 4 and 6 company-specific data in the switched Network.

In the event of a phase failure, the voltage at the artificial star point is not at zero potential, but alternating voltage is present with the amplitude ½ U _strand with two intact phases or 1 U _strand with an intact phase. The electronic evaluation circuit for the contact opening therefore generates a periodic output signal despite the closed bridge contacts, which would normally result in an incorrect evaluation of the remaining service life due to an incorrectly determined time difference.

The latter problem is now solved in that the microprocessor advantageously the evaluation of the remaining service life locks if the two states 'contactor switched on' and 'Phase failure' exist at the same time. The evaluation lock is from the microprocessor in a predetermined time interval updated and unchanged in the following Interval continued. The interval length is the Maximum value of the contactor switch-off time on.

In the event of a power failure, on the other hand, all three outer conductors are L1, L2, L3 of the three-phase network interrupted. Ideally would be the star point voltage on the load side of the contactor Zero, regardless of whether the contactor is switched on or off. In fact, those separated from the network, i.e. floating current paths like antennas and there can be interference voltages can be coupled inductively and capacitively. The electronic Evaluation circuit for contact opening reacts then with output signals sporadically generated by the interference signals.

Here, too, the microprocessor evaluates the Remaining service life locked if the two states' contactor switched on 'and' mains voltage failure 'exist simultaneously. The evaluation lock is made in an analogous manner as above stated maintained.

While in the general case the neutral point voltage against one Reference potential is measured can be in your own finder Training in the implementation of the device the occurrence a switching voltage as voltage drop in one Current branch of the star point circuit can be detected.

Figur 1

die Erfassung der Restlebensdauer von Schützkontakten beim Ausschaltvorgang mit gleichzeitiger Ermittlung von betriebsrelevanten Daten bzw. Zuständen,

Figur 2

die Generierung des Öffnungszeitpunktes T_K für die erstöffnenden Schaltkontakte von Schützen beim Ausschaltvorgang in Drehstromnetzen und Überwachung der Netzspannung durch Spannungsmessung an einem künstlichen Sternpunkt,

Figur 3

ein Beispiel für die Restlebensdauererfassung mit integrierter Magnetosensorik,

Figur 4

die Erfassung des Kontaktöffnens am künstlichen Sternpunkt ohne Verwendung eines weiteren Bezugspotentials und

Figur 5

die Auswertung zur Erfassung der Strangspannungen an den Stromzweigen am künstlichen Sternpunkt gemäß Figur 4.

Further advantages and details of the invention result from the following description of the figures of exemplary embodiments with reference to the drawing. They each show as a circuit diagram

Figure 1

the recording of the remaining service life of contactor contacts during the switch-off process with simultaneous determination of operationally relevant data or states,

Figure 2

generation of the opening time T _K for the first-opening switching contacts of contactors when switching off in three-phase networks and monitoring of the mains voltage by measuring the voltage at an artificial star point,

Figure 3

an example of the remaining lifetime measurement with integrated magnetosensorics,

Figure 4

the detection of the contact opening at the artificial star point without the use of a further reference potential and

Figure 5

the evaluation for detecting the phase voltages on the current branches at the artificial star point according to FIG. 4.

The same or equivalent elements have in the individual Figures have the same reference numerals. The figures become partial described together.

Figure 1 shows the schematic representation of a device to identify the remaining service life and their assignment to a contactor 1. An evaluation device 100 is located on the Load side 10 between the contactor and an electrical consumer, for example an engine 20 and is about a first Monitoring module 101 for the detection of the contact opening contacted with the outer conductors L1, L2 and L3. The monitoring unit 101 controls a microprocessor 105 which the contact pressure and additional switching operating states determined. For this purpose, the microprocessor receives further signals Monitoring the armature opening of the contactor magnet drive from a unit 102. The microprocessor outputs the result data to an output unit 106, from which an output, if applicable all switchgear-specific data via a bus further evaluation takes place.

A contactor magnetic drive 5 is assigned to the contactor there is an anchor 3 with associated yoke 4. On the yoke contactor coils 6 and 6 'are attached. The coils are controlled via a control switch. The tension on the Contactor magnetic coils are used to monitor the unit 102 Anchor opening fed and the anchor opening signal to the Evaluation unit 100 transmitted.

With the circuit described, it is possible from the the time signals delivered to the monitoring modules via the Microprocessor 105 and the current contact print to determine the electrical life of the main contact pieces. In addition, additional switchgear-specific devices are now also available Data determined, already referred to at the beginning has been. In detail, these are:

1.) Contactor drive "electrical on / off"

The electronic circuit for recording the start of the anchor opening generated from the coil voltage at the zero crossings the sine AC voltage pulse. These voltage pulses can the microprocessor 105 via an optocoupler can be fed for direct evaluation, or it can e.g. a square-wave signal with a retriggerable time stage are generated, which with a predetermined delay Switching state from on to off with voltage change e.g. from `high 'to` low' follows. For the delay time can specify the duration of a network half-period his.

2.) Number of switching cycles

the microprocessor 105 includes e.g. the number of Signal change high ⇒ low of the rectangular pulses described in 1.).

3.) Phase loss

The phase failure is when contactor 1 is switched on periodic star point signal is detected and can be used in the evaluation circuit of the contact opening according to Figure 2 immediately as periodic (double mains frequency) output signal from Microprocessor can be recognized.

4.) Mains voltage failure

It is connected to a voltage divider of the artificial star point circuit, the one between the load-side measuring connection External conductor and the measuring earth is connected, one for Tension proportional voltage tapped and as digital signal processed.

No such voltage when the contactor is switched on the microprocessor does not measure or recognize any Phase failure, the result is a mains voltage failure displayed.

5.) contact welding

Contact welding can take place when the contactor is switched off be detected when mains voltage is present.

The extreme case of three-pole welding is based on the `` Contactor drive electrically off '' and `` No mains voltage failure '' states recognized.

The one- or two-pole welding is recognized as such, if the states `contactor drive electrically off 'and 'Phase failure' meet. The one-sided welding A switching bridge can be in the off state of the contactor cannot be measured since the affected switching distance is still electrically separates. It is very likely that it will Bridge contact, however, when the contactor is switched on on the Generate a phase failure on the load side. Therefore at the Fault message `phase failure 'the additional reference to the two possible causes `Interruption of an outer conductor - or - contactor switching pole open 'necessary.

6.) Short circuit

For short-circuit detection, current transformers such as those in a Overload relays are used. As alternative if, for example, magnetosensors are used, with which the exceeding of a predetermined current threshold is detected. In addition to Hall effect sensors or magnetoresistive ones Sensors can also be inexpensive inductance sensors be used. The sensors are isolated immediately arranged on the main current paths so that the measured Magnetic field dominates and the magnetic field influence of neighboring short-circuit-bearing switching devices are neglected can.

The short-circuit detection is fundamentally by the microprocessor linked to the contactor switch-on state. In the case of one The microprocessor can register a registered short circuit Issue additional warning message, the contactor contacts open Check welding. In particular, could be a controlled one The contactor is switched off to carry out a welding test perform. The tax phase of the Contactor drive via a microprocessor controlled Normally open contact, or in the event of a persistent short circuit be switched off permanently.

FIG. 2 shows an example of a circuit for generating a time signal T _K at the start of contact opening of the most burned down main contacts. The essential property of this circuit is to measure the contact voltages (arc voltage) of a three-pole switching device in the three-phase network at the artificial star point 15. In addition to the circuits described above, there is now an extended evaluation unit 180 for detecting the mains voltage and for detecting the neutral point voltage. On the one hand, the time T _K for the first opening switching contacts during the switch-off process can be determined and, on the other hand, the mains voltage can be monitored.

In corresponding extensions to the previously described status the technology can, according to FIG. 3, determine the remaining service life With integrated magneto sensors for short-circuit detection respectively. Contactor 1 has an overload relay with an integrated one Residual life detection unit 200 before Motor 20 interposed, the units 201, 202 and 205 correspond to units 101, 102 and 105 from FIG. 1. Furthermore, a module 220 for monitoring of Short circuits exist. The monitoring module 220 is operated by magnetic sensors assigned to the individual lines 221 to 223 controlled.

From the table "Evaluation by logically linking the detected signals "results in a self-explanatory manner that by the logical combination of the figures 1 to 3 individually recorded signals each in addition to the detection of The contacts continue to burn due to the pressure monitoring the switchgear-specific states are also specified can be. It is essential that largely on the same structure of the evaluation circuits can be.

When detecting the beginning of the armature opening from the coil tension So far, the connection with R-C elements has been excluded, since this leads to a non-evaluable course of the Coil voltage leads. Alternatives are varistors or Called zener diodes.

It has been shown that varistors only limit overvoltages to approximately 1.75 times their nominal operating voltage. Suppressor diodes, whose current-voltage characteristic curve breaks sharply, have proven to be cheaper. It is advantageous that the suppressor diodes, like the varistors, do not consume any electrical power in normal operation. Another connection option is a capacitor connected to the plus and minus output via a bridge rectifier, to which a high-resistance resistor is connected in parallel for discharge. When the contactor coil is switched on, the capacitor charges up to the peak voltage of the control phase and briefly increases its voltage when an overvoltage is damped. When the contactor coil is switched off, the capacitor discharges through the parallel resistor (power loss = Û _mains ² / R).

In freewheeling circuits to prevent overvoltages when Switching DC-operated contactor drives can do that Anchor opening can be detected on the current profile. The evaluation the exact time of anchor opening hardly appears possible because the characteristic signal curve around the Factor 5 compared to an evaluable coil voltage signal is widened in time. When replacing the freewheeling diode in Freewheeling circuit through a microprocessor-controlled freewheeling transistor, a Zener diode to limit the switching voltage (anti) connected in parallel, the switch-off delay of the Contactor shortens and an evaluable coil voltage signal be generated.

The time signal necessary for this was shown in FIG Switching voltage on the first opening main contacts Measurement of the differential voltage between a fixed reference potential, like zero or earth potential, and the potential an artificial star point on the load side of the monitored Contactor generated. In certain applications However, neither a neutral conductor, nor a protective conductor must be available. The opportunity in this Case on the infeed side of the contactor with another artificial star point to form a fixed reference potential would require additional technical effort. As alternative can start the contact opening in Figures 4 or 5 can be detected without using a zero or earth potential.

According to FIG. 4, the occurrence of a switching voltage is detected as a voltage drop in a current branch of the star point circuit. The measured voltage is further processed with a high-pass filter and provides an output voltage proportional to the switching voltage. In a conventional manner, this can generate the desired control signal of the first start of contact opening when a predetermined threshold value is exceeded.

wobei U(_1,2,3) = Strangspannungen, U_STP = Sternpunktspannung, I(_1,2,3) = Strangströme, U_B(_1,2,3) = Bogenspannungen, R = ohmsche Last, L = induktive Last bedeuten.The following equations apply to the switching voltages (arc voltage): U 1 + U 2 + U 3 = 0.1 1 + I 2 + I 3 = 0

where U _(1,2,3) = phase voltages, U _STP = star point voltage, I _(1,2,3) = phase currents, U _{B (1,2,3)} = arc voltages, R = resistance load, inductive load L = mean ,

In the case of a switching pole opening for the first time, for example U _B2 and U _{B3 are} zero and one obtains U STP = - U B1 / 3rd

When used in the above equations, the two possible measured values for a current branch of the star point circuit are obtained for L = 0, U: = U _1,2,3 and I: = I _1,2,3 R * I = U - 2/3 U B R * I = U + 1/3 U B

In FIG. 4, 50 denotes a passive high-pass filter with capacitance C _X and ohmic resistance R _X , by means of which a unit 500 is controlled to determine the contact opening time. In this way, the time T _{K is} exactly determined without a reference potential, such as zero or earth potential, having to be present. To detect the arc voltage component, the disturbing 50 Hz mains voltage component is eliminated with a high-pass filter 50 (eg f (-3dB) = 5 ... 10 kHz).

Measurements for a structure according to FIG. 4 with passive High pass filter to a 16V voltage jump, which is the switching voltage immediately after the contact separation of a contactor bridge contact corresponds to a useful signal of approximately 1V Amplitude with a residual signal of the disturbing mains voltage (220 V∼) of also about 1V amplitude. Through an active High-pass filters, possibly of a higher order, can cause the disturbing mains voltage component reduced to a negligible value become.

For better suppression of the mains voltage component in the Measuring voltage can therefore instead of the passive high-pass filter 50 from Figure 4 an active high-pass filter of higher order or a series connection of passive and active high-pass filter be used.

With the series connection of the passive high-pass filter 50 can the amplitude of the input voltage at the active high-pass filter be limited to permissible values.

5, the circuit according to FIG. 4 is modified in such a way that that to one strand of the artificial star point circuit an evaluation unit 600 is switched directly which is both the contact opening and the mains voltage supervised. One of the two other strands is another Measuring line for monitoring their string voltage on the Evaluation unit connected. The evaluation unit contains 600 passive and / or active high-pass filters for detection the switching voltage of the first opening switching contact and in addition, an electronic circuit for recording the String voltages of the monitored circuits.

While essentially monitoring based on the figures of contactor contacts apply to the remaining service life recording The following considerations for circuit breakers:

During the operational switch-off process, mechanical energy is used of a spring energy store in kinetic energy of the moving Switch lock components and the moving contacts, as well converted into friction work.

With the conversion of mechanical into kinetic energy the Movement sequence and thus the time required from the start of the switch-off operation of the key switch until the start of contact opening certainly.

Contact erosion changes the position of the movable one Contact carrier to the fixed contact carrier both in Switch-on status, as well as at the moment of contact separation, and correspondingly the position of the movable one Contact carrier coupled switch lock components. To these switch components include e.g. the selector shaft which the moving contact carriers are mounted, or the lever mechanism for power transmission to the selector shaft and / or on the moving contacts.

1.) Beschleunigte Bewegung mit konstanter Beschleunigung b Laufzeiten t₁, t₂ Laufzeitunterschied Δt = t₁- t₂

t₁ = Öffnungszeit im Neuzustand der Kontakte

t₂ = Öffnungszeit der Kontakte mit Materialabbrand

Wege s₁, s₂ Wegunterschied Δs = s₁ - s₂

Δs =

Positionsänderung infolge des Abbrandes, z.B. Dickenänderung der Kontaktauflagen

v₁ =

konstruktiv vorgegebene Konstante, z.B. Geschwindigkeit der positionsüberwachten Schaltschloßkomponente im Kontaktöffnungszeitpunkt

s₁ = ½ b*t₁ ², s₂ = ½ b*t₂ ², Δs = ½ b*(t₁ ² - t₂ ²) = ½ b*(2t₁ - Δt)*Δt
Mit v₁ = b*t₁ folgt Δs = (v₁ - ½ b*Δt)*Δt

2.) Gleichförmige Bewegung mit konstanter Geschwindigkeit v₁ s₁ = v₁* t₁, s₂ = v₁*t₂, Δs = v₁*Δt

The movement (linear and / or rotational movement) of the switching mechanism components is generally a non-uniformly accelerated movement. As shown by the following simple examples, the contact erosion causes a time shift Δt of the contact opening time to shorter times:

1.) Accelerated movement with constant acceleration b running times t ₁ , t ₂ running time difference Δt = t ₁ - t ₂

t ₁ = opening time when the contacts are new

t ₂ = opening time of contacts with material erosion

Paths s ₁ , s ₂ path difference Δs = s ₁ - s ₂

Δs =

Change in position due to the erosion, eg change in thickness of the contact pads

v ₁ =

constructive predetermined constant, eg speed of the position-monitored switch lock component at the contact opening time

s ₁ = ½ b * t ₁ ² , s ₂ = ½ b * t ₂ ² , Δs = ½ b * (t ₁ ² - t ₂ ² ) = ½ b * (2t ₁ - Δt) * Δt
With v ₁ = b * t ₁ follows Δs = (v ₁ - ½ b * Δt) * Δt

2.) Uniform movement with constant speed v ₁ s ₁ = v ₁ * t ₁ , s ₂ = v ₁ * t ₂ , Δs = v ₁ * Δt

At values Δt << t ₁ , t ₂ , one can therefore approximately assume Δs ~ Δt or Δs = v ₁ * Δt for the non-uniformly accelerated movement in the real switch-off process, with the constructively predetermined constant v ₁ .

In the following the contact pressure is denoted by s, with the new state being assigned the structurally predetermined value S _new and the end of the service life the minimum pressure S _min .

In a time of flight measurement result to the values of the contact pressure s _new, s, s _min, the associated transit times t _new, t and t _', by means of which it is a fictitious velocity v ₁ can insert, comprising: s New - s = Δs = v 1 * .DELTA.t (s) respectively. s New - see min = Δs Max = v 1 * .DELTA.t Max

The maximum permissible contact erosion Δs _max thus corresponds to a maximum displacement Δt _{max of} the contact opening time for shorter running times.

By the time shift Δt of the contact opening time to get, run times are measured, their end time equated with the contact opening time is. The time is selected as the start time at a selected component of the key switch predetermined position reached during the switch-off process. This also ensures that short-circuit shutdowns, where the contact opening due to Current forces before reaching the predetermined Switch lock position is done, not to evaluate the Contact erosion can be used. This will make one incorrect evaluation of the contact erosion in the event of short-circuit shutdowns avoided.

Determine the design properties of the key switch in detail the method for generating the start time for the runtime measurement. To electromechanical Circuit breakers have a stable opening and closing position the key switch is usually implemented in the How a rocker arm mechanism works, at the lever mechanism a dead center position when changing position has to overcome. As a predetermined switch position to record a starting time of the runtime measurement a switch lock position is therefore specified at which is the lever mechanism between the dead center position and the end position is in the off position.

To ensure sufficient accuracy in determining the Contact erosion or the remaining service life is to be achieved it is necessary to characterize the starting time Detect key switch position with an accuracy of at least 1/10 mm. Because the speed of the position-monitored switching lock component at the start of the runtime measurement will be less than at the end time, is due to a position inaccuracy of 1/10 mm an inaccuracy of the burn detection expected of> 1/10 mm.

The required exact position detection can be done without contact working, field-dependent position sensors, like inductive or capacitive displacement sensors. Optical sensors are dealing with the problem of pollution, e.g. by the burn, exposed and therefore for the Position detection in the switchgear is not particularly suitable. As a simple, robust device for position detection an electromechanical auxiliary contact is proposed, which of the switch component to be monitored is opened. The fixed contact of this auxiliary contact device determines the beat position of the monitored Switch lock component on the associated moving contact. This should be a reproducible position detection be at least 1/10 mm possible without great effort.

In the new state of the switching device or at new switch contacts the running time t will now be _newly detected and stored in a suitable non-volatile data memory in the switch-off operation. With increasing contact erosion, the running time t is reduced to a value t _min , which corresponds to the maximum permissible erosion Δs _max . With the constructively specified variable Δt _max (= t _new - t _min ), as the maximum permissible reduction in runtime, the remaining service life (eg in percent) is determined with a microprocessor Rld [%] = (1 - (runtime (t New ) - transit time (t)) / Δt Max ) * 100th

In the above equation, a linear relationship between the change in position as a result of the contact erosion and the change in transit time is assumed for simplicity. If the course of the change in through-pressure differs significantly from the course of the change in transit time for design reasons, the fictitious speed v _{1 changes} with the size of the contact erosion. This can be taken into account approximately by forming v ₁ by linear interpolation from the design values v ₁ 'when new and v ₁ ''at the end of the service life: v 1 = v 1 '* (At Max - Δt) / Δt Max + v 1 '' * .DELTA.t / .DELTA.t Max . with Δt = transit time (t _new ) - transit time (t)

This gives the equation for determining the remaining life in percent: Rld [%] = (1 - Δt * v 1 / .DELTA.s Max ) * 100 The latter equation can be evaluated with the existing microprocessor so that the values can be displayed online.

Claims (21)

1. Method for the determination of switchgear-specific data at contacts in switchgear, in particular of earthing contacts, and/or for the determination of operation-specific data in the network switched by this switchgear, where the so-called contact resilience at the contact-break distance is sensed as a substitute criterion for the erosion and the change in the contact resilience during the switch-off process is measured in each case in order to determine the erosion of the contact facings of the contact points, and is converted as residual service life, to which end a time measurement of the armature path takes place in the case of the switchgear drive comprising armature, solenoid coil and associated yoke from the beginning of the armature movement up to the beginning of contact opening, in which case the armature path and, from it, the contact resilience are determined from the measured time, with sensing of measuring data for contact opening on the load side of the monitored switchgear and with signalling of the start of armature movement from the voltage of the solenoid coil, characterised in that not only the resilience is determined from the resilience sensing signals produced by voltage measurement at the solenoid coil of the switchgear drive and at switching poles of the switchgear, in particular at an artificial star point, but that in addition the switching states, operational states and fault states on the switchgear and in the electrical network are sensed.
2. Method in accordance with Claim 1, characterised in that the operational state of the contactor drive is sensed as "Electrical On/Off".
3. Method in accordance with Claim 1, characterised in that the number of switching operations is sensed.
4. Method in accordance with Claim 1, characterised in that a phase failure is sensed.
5. Method in accordance with Claim 1, characterised in that a mains failure is sensed.
6. Method in accordance with Claim 1, characterised in that a welding of contacts is sensed.
7. Method in accordance with Claim 1, characterised in that a short-circuit which may be present in the network is additionally derived from the resilience sensing signals.
8. Method in accordance with Claims 1, 4 and 5, characterised in that incorrect evaluations are avoided during the determination of the residual service life of the switching contacts on account of the sensing of the phase failure and/or the mains failure.
9. Method in accordance with Claims 1 and 2, characterised in that the "Electrical On/Off" signals for the contactor drive are fed to a microprocessor by way of an optical coupler for further evaluation.
10. Method in accordance with Claims 1 and 3, characterised in that the number of "Electrical On/Off" signal changes is totalled in a microprocessor.
11. Method in accordance with Claims 1 and 4, characterised in that a phase failure is detected by the microprocessor when the contactor is switched on.
12. Method in accordance with Claims 1 and 5, characterised in that a mains failure is detected by the microprocessor by way of a voltage divider at the artificial star point.
13. Method in accordance with Claims 1 and 6, characterised in that a welding of contacts is detected when the contactor is switched off and mains voltage is applied.
14. Method in accordance with Claims 1 and 7, characterised in that a short-circuit is detected by the sensing of the magnetic field using a magnetic sensor system.
15. Device for implementation of the method in accordance with Claim 1 or one of Claims 2 to 14, with an evaluation circuit and a microprocessor (105, 205) for determination of the contact resilience from time signals, in which case the microprocessor (105, 205) equally processes signals relating to the network status, to which end the microprocessor (105, 205) is controlled by units (180, 190, 500, 600) for the evaluation of the mains voltage and/or of the phase-to-neutral voltage, which units contain means for sensing arc-drop voltages, in particular at an artificial star point (Figure 4).
16. Device in accordance with Claim 15, characterised in that the means for sensing the arc-drop voltages operate without a reference potential.
17. Device in accordance with Claim 15, characterised in that a high-pass filter (50) is assigned to one of the cable systems (L1, L2, L3) at the artificial star point (S).
18. Device in accordance with Claim 17, characterised in that the filter (50) is a passive high-pass filter.
19. Device in accordance with Claim 17, characterised in that the filter (50) is an active high-pass filter.
20. Device in accordance with Claim 17, characterised in that the filter (50) is a series connection of a passive high-pass filter and an active high-pass filter.
21. Device in accordance with one of Claims 18 to 20, characterised in that the evaluation circuit for determination of the arc-drop voltage without a reference potential has measuring leads for each cable system at the artificial star point (S) to perform the additional sensing of the phase-to-neutral voltages.

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