EP0878015B1 - Method of establishing the residual useful life of contacts in switchgear and associated arrangement - Google Patents

Abstract

In order to establish the residual useful life of earth contacts, it has already been proposed to determine the so-called contact action at the breaker gap as a criterion for replacement in the event of contact erosion and to measure the change in contact action during the switching off stage in order to determine the erosion of the contact tips and convert it into the residual useful life. To that end, with a magnetic drive comprising a yoke, armature and magnet coil, the time taken for the armature to move from the beginning of its movement to the point when the contact starts to open has to be measured. According to the invention, the moment when the armature separates from the yoke of the protective magnetic drive is detected from the voltage at the magnet coil. In this respect, the increase in the magnetic resistance of the magnetic circuit when the armature lifts off is determined. The associated arrangement comprises an evaluation device for determining and displaying the residual useful life, said evaluation device (100) having means (110 - 150) for determining and detecting the voltage at the magnet coil (5).

Description

The invention relates to a method for determination the remaining life of contacts in switchgear, in particular of contactor contacts, whereby as a replacement criterion for the erosion of the so-called contact pressure on the switching path is detected and used to determine the erosion the contact pieces each the change in pressure during Switch-off process measured and converted as the remaining service life is what for the contactor drive from armature with solenoid and associated yoke and a time measurement of the anchor path from Beginning of the armature movement up to the beginning of the contact opening he follows. In addition, the invention also relates to the associated one Device with an evaluation device for determination and display of remaining life.

In the older, not previously published DE 44 27 006 A0 is the remaining life of a contactor when it is switched off from the time difference between the start of the anchor opening movement and the opening of the contact. From the A microprocessor determines the value of the time difference according to one Evaluation algorithm the current value of the so-called contact print, which by burning from its new value (= 100% remaining life) to its minimum value (= 0% remaining life) decreases.

The time signals required for this are on the one hand Interruption of an auxiliary current path via the anchor and yoke of the Magnet drive and via the contact voltage on the main contact pieces detected and in defined voltage pulses reshaped.

In order to simplify the measurement of the contact voltage, according to Parallel patent application proposed, opening the contact especially in the three-phase network by monitoring the voltage especially at an artificial star point. This allows the device to determine the remaining life as an independent additional device in the load circuit between the contactor and the electrical consumer too switch, which only with a communication line connected to the contactor to open the armature-yoke contact is.

In contrast, the object of the invention is a possibility with which the remaining service life detection of one Modification on the contactor, such as in particular an armature-yoke contact, made independently and used by any shooter can be.

The object of the invention is in a method of type mentioned solved in that from the tension the time at which the armature is separated from the magnet coil Yoke of the contactor magnet drive is detected. Advantageously will increase the magnetic resistance of the magnetic circuit when lifting the magnet armature. This is due to the change in flow over time Magnetic coil induced voltage signal used for time measurement.

In the associated arrangement, the evaluation device has means for detection and detection of the voltage on the solenoid. These means are preferably units for signal rectification, for signal limitation and shaping, as well as for Hiding and enabling signals.

The invention is based on the following physical behavior when a contactor magnet drive is switched off: To generate the necessary armature closing force, a current of a predetermined magnitude is built up in the iron circuit by the current of the magnet coil. When the control circuit is switched off, the magnet coil is de-energized and the magnetic flux decays in the closed iron circuit a few milliseconds later due to the remanence. The magnetic armature now begins to open at the moment when the magnetic closing force falls below the opening force, ie the sum of the spring forces of contacts and bridge girders. When the magnet armature is lifted, the magnetic resistance of the magnetic circuit increases suddenly, the remaining magnetic flux Φ (Kmagn ∼ Φ ² ) rapidly decaying and the change in flux over time induces a voltage signal on the magnet coil.

FIG 1

ein Prinzipschaltbild zur Erfassung der Restlebensdauer bei Schützen beim Ausschaltvorgang,

FIG 2a bis d

in mehreren Oszillogrammen die Signalverläufe von Spulenspannung und Spulenstrom als Funktion der Zeit beim Ausschalten eines Schützes bei Wechsel- bzw. Gleichstrombetätigung,

FIG 3

ein Blockschaltbild zur Auswertung der Ausschaltspannung gemäß FIG 2,

FIG 4

die konkrete schaltungsmäßige Realisierung der FIG 3,

FIG 5a und b

zwei zugehörige Oszillogramme mit Signalspannungen zum Zeitpunkt des Ankeröffnens,

FIG 6

eine Variante der schaltungsmäßigen Ausführung von FIG 4 ,

FIG 7

ein zugehöriges Oszillogramm mit der beim Ausschalten der Schützspule auftretenden Signalspannung und

FIG 8

ein Oszillogramm mit Messung der Zeitdifferenz zwischen Ankeröffnungsbeginn und Kontaktöffnungsbeginn beim Ausschalten eines wechselstrombetätigten, serienmäßigen Schützes mit Mittelwertbildung.

Details and further advantages of the invention emerge from the following description of figures of exemplary embodiments with reference to the drawing in conjunction with the patent claims. Show it

FIG. 1

a basic circuit diagram for recording the remaining service life of contactors when switching off,

2a to d

in several oscillograms the signal curves of the coil voltage and coil current as a function of time when a contactor is switched off when AC or DC is actuated,

FIG 3

3 shows a block diagram for evaluating the switch-off voltage according to FIG. 2,

FIG 4

the specific circuit implementation of FIG 3,

5a and b

two associated oscillograms with signal voltages at the time the anchor is opened,

FIG 6

a variant of the circuit design of FIG 4,

FIG 7

an associated oscillogram with the signal voltage occurring when the contactor coil is switched off and

FIG 8

an oscillogram with measurement of the time difference between the beginning of the armature opening and the opening of the contact when switching off an AC-operated, standard contactor with averaging.

The figures have identical or equivalent parts same reference numerals. The figures are partly common described.

1 schematically shows the structure and arrangement of a device 100 for detecting the remaining service life of the main contacts of a contactor 1 in the three-phase network. This device is arranged on the load side between the protection 1 and a consumer 20, for example a three-phase motor. It contains a first evaluation module 101, preferably for detecting the contact opening time t _{k of} the first main contacts, or alternatively for detecting the contact opening times of each main contact. It also contains a second evaluation module 102 for detecting the start of the armature movement, which is also referred to as time t _{A of} the armature opening. From the time signals t _A and t _k , the contact pressure and therefrom the remaining service life are determined by an evaluation unit, for example a microprocessor 105, and this is shown on a display 106 and / or output via a data bus or further evaluation.

The second evaluation module 102 is connected with its two measuring inputs to the connections of the contactor magnet coil and determines the point in time at which the armature movement begins t _A from the signal curve of the coil voltage during the switch-off process.

The device 100 for detecting the remaining service life of the Main contacts is advantageously on the load side of the monitored switching device arranged to with little technical Effort to open the monitored switchgear to monitor how it is in a parallel application in individual is described. The device 100 can also arranged on the infeed side of the monitored switching device and in various facilities (e.g. overload relays) be integrated on the infeed or load side. The capture of contact opening can be done by measuring the contact voltages via measuring connections at the terminals of the individual switching poles.

2 shows measurement oscillograms of the coil voltage and the coil current when the armature opens a contactor in an arrangement modified for the measurement, in which the armature and yoke close an auxiliary circuit when they come into contact with one another or separate it when the armature is lifted. After the switch-off time t is obtained _from the time t _A of the armature opening a voltage pulse of 2 ms duration and 50 V amplitude, since the rapidly decaying residual magnetic flux induces a voltage surge.

As can be seen from the individual oscillograms according to FIG. 2a, 2b for alternating voltage and according to FIG. 2c or 2d for direct voltage, the occurrence of the characteristic voltage pulse is independent of whether an alternating current (for example 150 mA _eff ) or a direct current (for example 150 mA =) is present.

It is common to wire contactor coils to avoid switching overvoltages to be avoided when the stream of arcs is interrupted (chopping). Examples of wiring elements are R-C elements, Varistors and in the DC case Zener diodes intended. A detection of the anchor opening time the coil voltage when using R-C suppressors not possible because when the coil current is switched off an excited one R-C-L resonant circuit is created and the coil voltage as decaying sine wave no significant waveform for assignment to the anchor opening time.

3 shows a block diagram of a device for determination the anchor opening time from the switch-off voltage on the solenoid 5 of a contactor 1. The control of the Contactor magnet system can expediently by an auxiliary contactor 2 take place, which the control supply voltage to the Contactor coil 5 turns on or off in two poles. The coil voltage is then at the potential at the time the anchor is opened the control supply voltage separately.

3 is the evaluation module 102 from the series connection of a unit 110 for signal rectification, a unit 120 for signal limitation and formation, a unit 130 for signal suppression and a Unit 140 for signal release. The output signals of the Units 120 and 140 are placed on an AND gate 150, that exactly outputs the desired anchor opening time. Especially because of the necessary exact determination of the small time intervals is a corresponding interpretation of the Units 110 to 140 thanks to problem-adapted components necessary.

With the signal processing of the now proposed Coil voltage - i.e. Rectification, limitation / shaping, Fade out, release - an output pulse is generated with the characteristic voltage pulse, for example pulse width ≈ 2 ms, pulse height ≈ 50 V, in FIG 2, which at the Separation of the anchor from the yoke occurs, coinciding in time. For further signal processing, the output pulse for example with an optocoupler not shown in FIG. 3 an output signal can be derived from the supply network of the contactor magnet drive galvanically isolated is.

4 shows a specific wiring example of an evaluation circuit to record the anchor opening time with Components 111 to 136, which are used to assemble the units 110, 120, 130, 140 are self-explanatory. The circuit connects to the Test leads for voltage monitoring of solenoid 6, 6 ' of the contactor drive 5 of FIG 1. Both measuring connections included the same series resistor 9 for voltage division of the Measurement signal to a free pin assignment on the contactor coil 5 to get. The measuring earth is connected to the protective earth and is practically at zero potential, so that during the The auxiliary contactor is only switched on by the outer conductor L a measuring current flows into the evaluation circuit.

By signal rectification and the limiter circuit a characteristic measurement signal is generated. This contains short voltage pulses when the contactor magnet drive is switched on of, for example, 300 µs width and at 50 Hz AC voltage 10 ms interval during the switch-off process two approximately 2 ms long voltage pulses with a few milliseconds Time interval arise, of which the first pulse is the Induction waste in the iron core marks during the second pulse by lifting the anchor from the yoke and the associated induction change is generated.

In the following part of the electronic circuit suppresses all voltage pulses except the latter, so that the evaluation circuit only a single output pulse delivers that timed with the beginning of the anchor opening falls together.

5 shows measurement oscillograms of the evaluation circuit according to FIG. 4. The armature-yoke auxiliary contact of the modified contactor was used to record the time at which the armature opening began electrically and mechanically and to be able to compare it with the output signal of the evaluation circuit. By signal averaging of the time signals t _A and t _k , time fluctuations, which are caused by mechanical tolerances influenced contact separation of the main contactor contacts and different magnetization state of the contactor magnetic drive, can be largely eliminated, so that the averaged time difference between the beginning of the The armature opening movement and the start of the contact opening are recorded with a measuring accuracy of +/- 100 ... 200 µs.

6 shows a further evaluation circuit for detecting the Anchor opening time. It differs from that Circuit in FIG. 4 only through the circuit part of the signal limitation and shaping, especially due to the high input resistance of comparators 128 and 129. The evaluation circuit therefore processes the measurement signal from the contactor coil in the same way, regardless of whether the ground connection of the Electronics supply voltage is at ground potential, or Not. Furthermore, the detection of the anchor opening time even with single-pole interruption of the coil voltage enables.

The circuit of FIG. 6 can therefore be used for earthed and ungrounded Networks with both AC and DC voltage be used. For signal processing, e.g. with an optocoupler galvanic isolation of the output signal to be provided by the supply network of the contactor magnet drive.

7 shows measurement oscillograms of the evaluation circuit FIG. 6, the electronics ground potential here being at ground potential was laid. Comparable output signals are obtained with the same measuring accuracy as with the circuit according to FIG. 4th

The exact time assignment of the armature opening time t _A to the 'armature opening pulse' of the evaluation circuit according to FIG. 4 and 5 can be done by taking into account a contactor and circuit-specific time offset, calculated from the rising edge of the 'armature opening pulse', for example 0.7 ms for the above type of contactor. Depending on the size of the contactor and the voltage level of the control supply voltage, it may be necessary to adapt the circuit section for signal limitation.

FIG. 8 shows the signal curve of the armature opening time t _{A of} the evaluation circuit according to FIG. 6 and the contact opening time of a standard contactor, again using the averaging.

The signal averaging over 64 circuits, in which the positive edge of the armature opening pulse is the trigger time in each case, shows a weak scatter in the width of the armature opening pulse and a time scatter of the contact opening time of ≈ 0.5 ms. The mean time interval from the beginning of the armature opening t _A to the beginning of the contact opening t _k can be specified in the measured example as 4.6 ms ± 0.2 ms.

The evaluation circuit described for detecting the armature opening time can be part of an evaluation device for determining the remaining service life of contactor main contacts. The evaluation device is located on the load side between the contactor and the electrical consumer and is contacted with the outer conductors L1, L2, L3 via a first monitoring module to detect the opening of the contact from the change in voltage at an artificial star point. An in particular two-wire signal line connects the contacts of the contactor coil to a second monitoring module for the detection of the armature opening. From the time signals of the armature opening t _A and the contact opening t _K supplied by the monitoring modules, the microprocessor determines the current contact pressure and from this the electrical remaining service life of the main contact pieces.

Claims (12)

1. Method for determining the remaining lifetime of contacts in switchgear, in particular contactor contacts, the so-called contact spring action at the gap being determined as a substitute criterion for erosion, and the change in spring action, in each case, being measured during the shutdown cycle to determine the erosion of the contacts and being converted to give the remaining lifetime, for which purpose in the case of the contactor solenoid actuator comprising a yoke and an armature with a solenoid the armature travel from the start of the armature movement to the start of the contact opening is measured over time,
   characterised in that the time at which the armature separates from the yoke of the contactor solenoid actuator is detected from the voltage at the solenoid.
2. Method according to claim 1, characterised in that the increase in magnetic resistance of the magnetic circuit when the magnet armature is disengaged is detected.
3. Method according to claim 2, characterised in that the voltage signal induced at the solenoid by the change in flux over time is used for the time measurement.
4. Arrangement for carrying out the method according to claim 1 or one of claims 2 and 3, having an analyzing unit for the determination and display of the remaining lifetime, characterised in that the analyzing unit (100) has means (110-150) for measuring and detecting the voltage at the solenoid (5).
5. Arrangement according to claim 4,
   characterised in that the means for detecting the signal voltage include a unit for signal rectification (110), a unit for signal contraction and shaping (120), a unit for signal suppression (130) and a unit for signal release (140).
6. Arrangement according to claim 5, characterised in that the units (110, 120, 130, 140) comprise discrete circuits for generating a time signal for the time at which the armature opens.
7. Arrangement according to claim 5, characterised in that the unit (130) for suppression of the signal for the time at which the armature opens contains a plurality of timers (131, 132, 133).
8. Arrangement according to claim 7, characterised in that the timers (131, 132, 133) are connected to one another by way of at least one AND stage (135).
9. Arrangement according to one of claims 4 to 8, characterised in that the analyzing unit (100) is integrated as a supplementary component into the contactor (1) that is to be monitored.
10. Arrangement according to one of claims 4 to 8, characterised in that the analyzing unit (100) is connected to the contactor (1) that is to be monitored.
11. Arrangement according to one of claims 4 to 8, characterised in that the analyzing unit (100) is arranged in an overload relay on the load side of the contactor (1) that is to be monitored.
12. Arrangement according to one of claims 4 to 8, characterised in that the analyzing unit (100) is arranged as an independent supplementary unit on the load side of the contactor (1) that is to be monitored.

Images