EP0694937B1 - Method and apparatus for determining the residual life of contacts in switching devices - Google Patents

Description

The invention relates to a method for determination the remaining life of contacts in switchgear, in particular of contactor contacts, in which the contact pieces with the Switch subject to a burn, being a replacement criterion is recorded and evaluated for the erosion.

In switchgear, there is a burn-up with every switching Contacts. This erosion leads depending on the stress through the current or the voltage ultimately to failure of the switching device, so that its lifespan is limited. Under certain operating conditions currently after a routinely determined number of operations Contacts or the entire switching device replaced, regardless of whether the contact pieces actually a extensive burning has occurred or not.

It is often required that the existing ones work to directly monitor electrical switching devices to a safe operation of electrical distributions and / or facilities to ensure. This is especially true for frequent actuated switching devices such as the contactors, because there especially in the Switching operation a progressive wear of the switch contacts is present. Here it is known that after a certain Number of switching cycles, which - as mentioned above - depend of the electrical load is the end of life the contact pieces is assumed.

For automated monitoring of electrical equipment it would be desirable, however, the remaining life the contacts, in particular contact pieces for contactors, also to be recorded directly during the operation of the contactor and the measurement data of a monitoring and reporting device feed.

Proposals are already known from the prior art at which more or less determine the remaining lifespan of shooters the operating time and / or derived from the number of switching cycles becomes. The electrical life is through Empirical values defined and by the device type, the electrical Load and e.g. depending on the contact material. In the event of a change One or more influencing variables must therefore be replaced by a new one Experience based on the electrical life of the switchgear be determined.

Generally used for determining the remaining life Replacement criteria selected for the erosion of contact pieces and evaluated. For example, DE-AS 23 05 149 a switching device is known in which by the contact erosion caused change in length of the switching stroke is detected. Around In this way, a reliable display of the contact erosion achieve, however, is a relatively complex mechanical Construction required. Furthermore, from DE-OS 37 14 802 an electrical switch known in which at least an optical fiber is assigned to one of the contact pieces, whose external transmission properties by means of suitable optical auxiliary devices can be measured. Appropriate arrangement of the light guide leads to an impermissible advanced contact erosion to destroy the Optical fiber and thus to change the optical transmission properties. Eventually, the older German Patent application P 43 07 177.6 proposed a switching device, in which the contact carrier is divided and the contact pieces slit on the back on the divided contact carrier are upset. With this switchgear it will Vibration behavior of the contact carrier as a replacement criterion and thus used as a measure of the erosion of the contact pieces.

In contrast, the object of the invention is a simplified one Specify methods and an associated arrangement with which a reliable determination of the remaining service life can be determined.

The object is achieved in that the so-called contact pressure of the switching bridge is selected as a replacement criterion in a method of the type mentioned above and that the pressure change during the switching-off process is determined and the remaining service life is calculated to determine the erosion of the contact pieces. The change in through-pressure is determined from the time measurement of the armature path from the beginning of the armature opening movement to the beginning of the contact opening. The conversion is done according to the relationship (1) Rld [%] = 100 * [((t i -t 0 ) / (t i, new -t 0 )) 2nd -c] / (1-c), where t _{0 is} the time of the armature movement and t _{i is} the time of the opening of the main contacts and c is a constructively determined constant.

In the context of the invention, the determination of the remaining service life done in software according to the given equation. In the same way can be derived from equations derived accordingly the remaining operating time and / or the remaining number of operations Switchgear can be calculated. This is advantageous an arrangement by a processor unit with memory and a controller and an associated display. If necessary, corresponding ones can be found on the switching device itself Display means are available.

The method according to the invention is advantageous exploited that the change in contact pressure in principle on measuring time differences from turning off the Magnet system, i.e. exactly from the beginning of the anchor opening until based on opening the bridge contacts, which is simple can be done. The measured variables that arise can therefore be used, also the switching status of the contactor clearly display. The switch-on state can be checked in detail the contact of the pole faces of the armature and yoke is clear mark. This touch can be an electrical contact be measured between anchor and yoke, including anchor and yoke connected to an auxiliary circuit via spring contacts are. The contactor is in the regular switch-off state the anchor in its open position and the electrical contact between the pole faces of anchor and Yoke is interrupted. Even in the case of contact welding, where bridge contacts one-sided or two-sided can be welded away in the off state the contactor of the anchor by at least a fraction of the Contact pressure from the yoke. The electrical contact between the pole faces of anchor and yoke is also here interrupted.

Figur 1

die wesentliche Anordnung eines Antriebes für ein Schütz und die daraus abgeleitete Messung des Ankerbewegungsbeginns,

Figur 2

die Kontaktanordnung des Schützes und die daraus abgeleitete Messung des Kontaktöffnungsbeginns,

Figur 3

ein alternatives Prinzip der Bestimmung der Kontaktöffnungszeitpunkte bei stromlosem Öffnen der Hauptkontakte,

Figur 4

eine blockschaltbildmäßig dargestellte Anordnung zur softwaremäßigen Bestimmung und Anzeige der Restlebensdauer eines Schützes und

Figur 5

ein zugehöriges Ablaufdiagramm.

Further details and advantages of the invention result from the following description of exemplary embodiments. Show it

Figure 1

the essential arrangement of a drive for a contactor and the derived measurement of the armature start of movement,

Figure 2

the contact arrangement of the contactor and the measurement of the opening of the contact derived from it,

Figure 3

an alternative principle of determining the contact opening times when the main contacts open without current,

Figure 4

a block diagram arrangement shown for software determination and display of the remaining life of a contactor and

Figure 5

an associated flow chart.

Figures 1 and 2 each show parts of a contactor with the associated measuring device. 1 shows the magnetic drive and FIG. 2 shows the contact arrangement of the associated contactor. 1 means a switching bridge with two contact pieces 2 arranged thereon at the ends and 3 U-shaped cranked contact carriers with mating contacts 4 arranged thereon for the contacts 2 of the switching bridge 1. The associated drive essentially consists of a magnetic yoke 10 with coils 11 attached to it and one Associated magnet armature 12. The magnet armature is connected to a receiving device, the bridge support, for receiving the switching bridges, which is not shown in FIG. 1 or FIG. 2. Furthermore there are resiliently arranged contacts 15. The times t ₀ and t _i can be determined using associated electrical switching elements.

In FIG. 1, the magnet armature 12 and the magnet yoke 11 are connected to the direct voltage U _{0 of} an auxiliary circuit via resilient contacts 15 and a measuring resistor 21 with resistor R _meas . Alternatively, the magnetic yoke 11 can also be connected to the auxiliary circuit via a flexible or rigid electrical line instead of via a resilient contact 15. If the armature 12 touches the yoke 10, the auxiliary circuit is closed and the voltage U ₀ drops across the measuring resistor 21. When the armature 12 is lifted from the yoke 10, the current path through the pole faces is interrupted and the voltage across the measuring resistor changes from U ₀ to zero. The voltage edge U ₀ → 0 is further processed in an evaluation device as time t ₀ .

The determination of the contact opening times t _i can be derived from FIG. It is assumed that the main contacts 2 and 4 of the contactor open under current load and arcing arises. To measure the contact opening times, the switching voltage which arises when a main contact is opened, that is to say the arc voltage of short arcs, is rectified in a rectifier circuit 22 and fed to the control input of an optocoupler 28 via a limiting circuit comprising resistors 23 and 24 and capacitor 25 and associated zener diode 26. The switching output of the optocoupler 28 switches on an auxiliary circuit which consists of a measuring resistor 29 and a direct voltage source U ₀ . The voltage across the measuring resistor changes from zero to U ₀ and the voltage edge 0 → U ₀ is further processed in an evaluation device as time t _i (i = 1, 2, 3).

Provided that the contactor is switched off when there is no current, for example when switching three-phase asynchronous motors without interruption or when starting three-phase asynchronous motors automatically via three-pole resistors with time relays, instead of an arrangement according to FIG. 2, an arrangement corresponding to FIG use. Here, the contact opening times when the main contacts to be monitored are opened without current can be determined by the inductance measurement, for example if the mains voltage is interrupted or if there are parallel current paths to the main contacts. For this purpose, Figure 3 has a motor as a load, which is electrically connected in series to a parallel connection of a main contact S1 of a contactor 31 with a main contact S2 of a contactor 32, the switching paths connected in parallel capacitively to capacitors 33 and 34 with capacitance C _o Auxiliary circuit with generator 35 and resistor 36 are connected. Parallel connections of this type are used in particular for a transition contactor.

According to FIG. 3, a damped resonant circuit is therefore connected to the main contact to be monitored, which is fed via the higher-frequency generator 35 at a frequency of, for example, 1 to 10 MHz. When the main contact S ₁ is closed, the generator frequency, the capacitance and the inductance of the resonant circuit are set approximately to resonance. For example, for the geometry relationships of the parallel circuits that are adapted to reality, an inductance of L ₁ = 0.3 μH is obtained for the monitored current path, L ₂ = 0.8 μH for the monitored parallel current path and L _res = 0.2 for the resulting inductance of both closed current paths µH. With values for the capacitors 33 and 34 and the measuring resistor 36 of, for example, C _o = 10 nF, R = 5 Ω and a generator frequency of 5 mHz, the measuring voltage across the resistor decreases approximately when the main contact S ₁ opens and the main contact S ₂ closes 1/2 to 1/3 of the initial value. Without the parallel current path, ie with the main contact S ₂ open, the measuring voltage at the measuring resistor R would drop to zero when the main contact S _{1 was opened} .

While the method of inductance measurement according to FIG. 3 clear results when the contacts are opened without current supplies, takes place when a live contact is opened Main contact no significant change in inductance. However, the sudden change in contact voltage creates from zero to, for example, 20 V when the contact is opened current-carrying main contact on measuring resistor 36 of FIG. 3 a very short voltage pulse with a pulse width less than one microsecond, which is used to determine the contact opening time could be used.

The determined times t ₀ and t _i are used to determine the remaining service life. The following considerations can be made to derive a suitable relationship:

In the switched-on state, the contact forces of the switching bridges add up with the spring force of the armature springs to the total opening force F _{A of} the magnet armature 10. During the initial movement of the armature 10, this force F _A delivers a practically constant armature acceleration until the opening process of the bridge contacts begins. If the switching load of the contactor main contacts 2 or 4 is different, for example in a 3-phase network, the main contacts 2, 4 of each phase burn to different extents and the contact opening in the three phases takes place in chronological order, starting with the most burned-out contacts. The time average of the armature acceleration for the later opening, ie less burned main contacts, is therefore somewhat less than for the main contact opening first.

The so-called pressure s _i = 1/2 b (t _i -t.) Is obtained from the time measurement of the beginning of the armature movement t ₀ and the beginning of the opening of the main contacts 2, 4 with the times ti (phase index i = 1, 2, 3) and the armature acceleration b ₀ ) ² . The simple relation s _i / s _{i, new} = ((t _i -t ₀ ) / (t _{i, new} -t ₀ )) ² results from the printing s when new. Is a secure power-a minimum pressure s _min is specified, the remaining lifetime can be from it by a constant C = S _min / s _redefine (1) Rld [%] = 100 * [((t i -t 0 ) / (t i, new -t 0 )) 2nd -c] / (1-c).

In the equation (1), the constant c is given by design. The equation means that the time difference t _{i, new} -t ₀ must be determined for each main contact when new, after which only the time differences t _i -t _{0 have to be} determined during operation, which has been illustrated with reference to FIGS. 1 to 3. The latter can advantageously be carried out digitally, which is illustrated in FIGS. 4 and 5. In FIG. 4, 40 means a controller to which the time signals t ₀ and t _i , ie their voltage edges from FIGS. 1 and 2, are supplied. As further variables, the controller determines the number of operations N and, for example, the accumulated operating time T with an internal clock. To monitor the mechanical state of wear, the controller 40 can determine the number of operations N ₀ accumulated over several electrical life cycles. The controller 40 contains the geometry variable c as a constant input variable. The controller 40 determines the time difference t _i -t ₀ from the time signals t ₀ , t _i , wherein the reference variable t _{i, new} -t ₀ characterizing the new state can be defined as the mean value of the time difference t _i -t _{0 of} a given number of switching cycles . For example, the average of the first ten switching cycles of a service life cycle can be used. In order to rule out data loss due to the supply voltage or the like being switched off, the current measurement data and evaluation variables are stored in non-volatile data memory 41 and are thus saved. There are also input and output units 42 to 44 and a display for displaying the results.

To determine the remaining service life, controller 40 can now calculate Formula 1 using an evaluation program. In the same way, further quantities characterizing the state of wear of the contactor can be calculated, such as a remaining operating time or a remaining number of operations. From the accumulated operating time T follows for the remaining operating time (2) Rbd (days) = T (days) * RLD [%] / (100-RLD) [%].

In the same way, the remaining number of operations can be determined from the number of operations N accumulated (3) Rsz = N * Rld [%] / (100-Rld) [%]

The formulas (2) and (3) can be evaluated as soon as the a residual life determined according to formula (1) (Rld) <100% has assumed.

It is particularly favorable if those determined by controller 40 Remaining life data on one attached to the switchgear itself Display element to be displayed optically. Besides the digitized evaluation sizes can be obtained from the controller 40 via a data bus to a central, not shown Monitoring unit are transmitted.

Based on the flow chart according to FIG. 5, the program results Calculation process. In the flow chart with The usual, self-explanatory decision-making structure is that corresponding stations 100 to 110 each entered. According to equations (1) to (3), this can be used derive a statement as to whether a contact needs to be renewed or not.

The measuring and evaluation device for determining the remaining service life of contacts in switchgear and monitoring allow on contact welding, under certain circumstances if additional means are used, extended switchgear monitoring regarding serious malfunctions, such as breakage of contact carriers and / or spring clips, unsoldering of contact pieces, impermissible contact resistances, excessive Contact temperature and the like.

For example, if the spring clip breaks, the switching bridge would only give uncontrolled electrical contact when the contactor drive was switched on, so that a serious change in the time sequence of the measured variables t _o (start of armature movement) and t _i (start of contact opening) can be expected.

The same follows if the bridge contact carrier breaks or of the fixed contact carrier.

Other faults concern the poor contact with the Contact pieces under the influence of dirt, material precipitation and corrosion. This will make the contact resistance increased and the contact voltage drop or Contact temperature reaches impermissibly high values.

To check the contact overtemperature, the electrical power loss, by multiplying the measured Contact voltage with e.g. with a current transformer, measured switch current, power limits are given, to those when their amount and duration are exceeded an error message is issued.

Through electronic storage of operating and fault data A switching device diagnosis, e.g. via a display element on the switching device or via data bus a central evaluation device at any time and without gaps perform.

The statements derived from the examples can also take place if there are welds or partial welds of contacts is coming. To determine if bridge contacts are welded on both sides or on one side and therefore none regular off state is reached, it is possible to Check the armature opening via a second, springy contact. In the same way as in Figure 1, therefore Auxiliary circuit closed when both spring contacts the Touch anchor 10. Through a lead of the two resilient Leaves contacts from about half of the full anchor opening experience has shown that there are certain differences between the regular Switched off state, or whether due to contact welding only a small fraction of the full anchor opening is achieved.

The described method thus enables a clear one Statement about the welded condition or the burn-up of the Main contacts and a necessary exchange of the contact pieces.

Claims (17)

1. Method for determining the residual life of contacts (2, 4) in switching devices, in particular of earthing contacts, in which the contacts (2, 4) are, with the switching, subject to an erosion, wherein equivalent criteria for the erosion are evaluated, characterised in that there is chosen as an equivalent criterion the so-called contact spring action at the contact gap, and in that in order to determine the erosion of the contacts (2, 4), the change in spring action during the breaking operation is determined in each case and converted as residual life of the switching device.
2. Method according to claim 1, characterised in that the change in spring action is established by a time measurement of the armature travel from the start of the armature movement to the start of the contact opening.
3. Method according to one of the preceding claims, characterised in that the determining of the residual life takes place in accordance with equation (1)   Rld[%]= 100 * [((ti-t0)/(ti,neu-t0))2-c]/(1-c) where t₀ is the time of the start of the armature movement and t_i is the time of the start of opening of the main contacts and c is a structurally determined constant.
4. Method according to claim 3, characterised in that from the residual life (Rld), the residual running time of the switching device is calculated in accordance with equation (2)   Rbd (days) = T (days) * Rld[%]/(100-Rld) [%].
5. Method according to claim 3, characterised in that from the residual life (Rld), the residual number of operations of the switching device with respect to its number of operations N is calculated in accordance with equation (3)   Rsz = N*Rld[%]/(100-Rld) [%].
6. Method according to one of claims 3 to 5, characterised in that in accordance with the given equations (1, 2, 3), the residual life (Rld), residual running time (Rbd) and/or residual number of operations (Rsz) are software-calculated.
7. Method according to claim 2, characterised in that in order to determine the start of movement of the armature (12), the two states "pole faces of armature (12) and yoke (10) are touching" and "pole faces of armature (12) and yoke (10) are separated", the armature (12), by means of a spring-mounted first auxiliary contact (15), is connected to a first auxiliary circuit by way of one terminal, and the yoke is connected to said first auxiliary circuit by way of the other terminal.
8. Method according to claim 7 characterised in that in order to check for contact welding, the armature (12), by means of a spring-mounted first and second auxiliary contact (15), is connected to a second auxiliary circuit if the armature air gap falls below a predetermined value.
9. Method according to claim 8, characterised in that the pre-travel of the first and second auxiliary contact (15) is greater than the contact spring action in the new state, and in that the pre-travel preferably corresponds to half the complete armature opening.
10. Method according to claim 2, characterised in that the start of the contact opening is determined from the step-by-step change in the contact potential.
11. Method according to claim 2, characterised in that the start of the contact opening is determined from the change in inductance of an auxiliary circuit, which is connected to the main circuit in parallel with the main contact to be monitored.
12. Method according to claim 2, characterised in that if predetermined limits of the change in the residual life between two successive circuits, or between two successive mean values from a plurality of circuits, are exceeded, malfunctions are detected and displayed, such as breakage of contact carrier, spring clip, un-soldering of contacts and suchlike.
13. Method according to claim 12, characterised in that from the contact potential before the start of the contact opening, a disturbance of the contact closure is derived and displayed if the contact potential exceeds a predetermined limiting value during a predetermined duration.
14. Method according to claim 13, characterised in that in order to monitor the contact excess temperature, the power loss is determined by multiplying the values of the contact potential and the switch current, which can be measured by a current transformer, for example, and in the event of the exceeding of a predetermined limiting value during a predetermined duration, a disturbance of the contact closure is displayed.
15. Arrangement having means for determining the residual life of contacts (2, 4) in switching devices, in particular of earthing contacts, in which the contacts (2, 4) are, with the switching, subject to an erosion, wherein equivalent criteria for the erosion are evaluated, characterised in that the equivalent criterion is the so-called contact spring action at the contact gap, and in that the means for determining the residual life determine the erosion of the contacts (2, 4) by detecting the change in spring action during the breaking operation and comprise a processor unit, a controller (40) and memory (41) and an associated display (45) for display of at least the residual life (Rld).
16. Arrangement according to claim 15,
    characterised in that there are present on the switching device display means for the residual life (Rld), residual running time (Rbd) and/or residual number of operations (Rsz) and possibly further display variables.
17. Arrangement according to claim 15 for carrying out the method according to claim 11,
    characterised in that the auxiliary circuit is a damped oscillating circuit which is supplied by a generator, the frequency of which corresponds by approximation to the resonant frequency of the auxiliary circuit in the case of a closed main contact to be monitored.

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