AU700189B2 - Electromechanical switch unit and arrangement of a plurality of such switch units - Google Patents

Description

-2housing from which electrically conducting gas can exit in the case of short circuits, generating, for example, electrical leakage paths, and, on the other hand, increases the actuating force required for switching on the switch unit. Apart from that, In the additional switch elements of a switch with contacts for the usually encountered low currents and voltages of electronic signal processing, corrosive effects may cause spurious contact closure which prevents unambiguous identification of the switch state.

The older European Patent Application No. 94106336.4, which is not a prior publication, has taught a process for identifying switch states, using a capacitor applied from the outside to the switch housing to obtain capacitive coupling to the live parts within the switch unit. The signals detected via a capacitive voltage divider have waveforms indicative of the on/off state of the switch unit and can be analysed In regard to overcurrent and the like. US-A-4 706 073 describes a switch unit in which optical and magnetic sensors detect In non-contacting fashion the trigger position of the switch handle from the front of the unit or, In a translucent process, from both sides of the switch handle. There part of the sensor system is accommodated in the door of the switch cabinet so that the trigger function can be detected only if the door is closed. Switch states which cannot be Identified via the switch handle alone, cannot be detected, and therefore a differentiating identification of the switch state is not possible. Further, US-A-4 611 209 describes a switch unit in which the switch handle contalns a permanent magnet actuating a reed contact when In a specific position. There again only the *o S state "on/off", as well as "switch actuated", can be identified. With the o 1038z/jrb 3 exposed arrangement of the permanent magnet, there Is particularly the risk of soiling, which can lead to mislndicatlons In practice.

By contrast, the problem underlying the invention Is to modify an electromechanical switch unit In a simple way so that non-contacting Identification of the switch state is possible and that particularly misinterpretations are precluded.

According to the Invention, the problem Is solved in that the sensors are accommodated within a separate sensor housing at an appropriate point; that, for monitoring the switch states, the sensor housing is coupled to the side of the housing of the switch unit; and that neither an effective mechanical or optical coupling nor an electrical connection from the housing of the switch unit and/or the mains conductors connected to the same into the Interior of the sensor housing exist.

It turned out that static differential Hall effect sensors are suitable for sensing the on/off state of the switch unit, the triggering by overcurrent, arid the fusion of contacts. A reed contact' however, is more suitable for detecting triggering by a short circuit.

According to the invention, in order to detect the noise of switching, Sin the sensor housing there can be an acoustic sensor the signal of which, together with the signal for triggering by overcurrent, is used for identifying a short circuit. The acoustic sensor is preferably a capacitor microphone or a piezoelectric microphone.

In comparison with the detection of a short circuit through the magnetic field alone, the advantage of the additional detection of sound results from the fact that the place and the spacing of the source of sound from the acoustic sensor only slightly influence the acoustic signal and that there are no shielding effects which could be possible by ferromagnetic parts in the case of magnetic fields. In order to detect a short-circuit event in 3 8z/jrb 3a dependable and interference-insensitive fashion, the signal picked up by the acoustic sensor in an acoustic event and the signal generated particularly with a differential Hall effect sensor for triggering by overcurrent are advantageously processed via timer circuits and an AND gate and a short-circuit situation is indicated only if the two signals overlap in time or have a small spacing on the time scale.

Particularly, in the case of multi-pole switches, an additional acoustic sensor can effect positive detection of a short circuit in one line or a plurality of lines because the spacing of the acoustic sensor from the acoustic event at the switch terminal ranges from 3 to 10 cm. It is assumed that the acoustic event generated by the short circuit occurs approximately at the same time as the triggering of the respective line of the circuit breaker so that particularly interfering noise sources can be suppressed by means of a window on the time scale for logic AND coupling of the two events.

According to one aspect of the present invention there is provided an electromechanical switchgear with at least one movable contact and associated drive in a switchgear housing with magnetic field sensor means for non-contacting identification of the switching states and optionally additional sensors such as acoustic sensors or the like, the sensor signals of which indicate switching states defined by logic functions, wherein said sensor means are arranged inside a separate sensor housing at a suitable location, and wherein for the monitoring of switching states said sensor housing is laterally coupled to said switchgear housing, wherein neither a mechanical or optical active connection nor an electrical line connection exists from said switchgear housing and/or power conductors connected thereto into the interior of said sensor housing.

In an advantageous combination of the measures proposed in accordance with S2 the invention, there can be made up an arrangement an arrangement comprising a plurality of switchgears according to any one of the preceding claims, having the following features: the identification of said on/off switching state and of said tripping state, in particular overcurrent- or short-circuit tripping, of said switchgears is effected by sensors; said switchgears are connected via a data bus to a monitoring device and report the occurrence of a tripping state without delay to said monitoring device; said switchgears are installed as distributor switches in a common distributor cabinet; [n:\libppJO1087:1AD 3b detection of short-circuits in said distributor switches is effected by one or more acoustic sensors permanently installed at suitable measurement locations in said distributor cabinet; acoustic events, selected in accordance with acoustic level and a time characteristic, can be detected as possible short-circuit events and are reported without delay as electric signals via said data bus to said monitoring device; said monitoring device cancels an acoustic message unless a tripping message arrives within a preset time window; and said monitoring device establishes short-circuit tripping when an acoustic event signal and said tripping message arrive within said preset time window and assigns a short-circuit tripping to that distributor switch which has transmitted said tripping message.

Other details and advantages of the invention will become obvious from the following description of the figures of an embodiment by way of the drawing. There show: 4 •o [n:\libpplOl1087:IAD -4- Figure 1, Figure Figure Figure 4, Figure 5, Figure 6, the schematic block diagram of means for non-contacting identification of the switch state of a switch unit; a basic circuit diagram of the sensor circuit; as an alternative to Figure 2, a basic circuit diagram of a bus-independent sensor circuit; an electromechanical circuit breaker for mounting specific sensors on the sidewall of the housing and the required measures for actuating the sensors, and a basic drawing of the structure of the sensor for monitoring the position of the ferromagnetic elements of Figure 4; a schematic representation of the time dependence of acoustic signals upon switching off; a basic circuit for acoustic detection of a short circuit; an electronic circuit according to Figure 1, supplemented by acoustic recognition means of switch-off upon short circuit; the structure of a three-pole circuit breaker with monitoring means added on the side for non-contacting identification of the switch state; a distributor cabinet with a plurality of switches to be monitored; and a sequence of signals in a setup according to Figure first line of Figure 1 shows the particular identifying function.

Figure Figure Figure 9, Figure 10, Figure 11, The These are, in detail, the switch position, a possible short circuit and/or an overcurrent, and possible fused contacts. The associated sensors are listed underneath. There are provided a position sensor 1, a magnetic field sensor 2, and additional position sensors 3 and 4. Sensors 2 and 3 are connected via electronic memories 5 and 6 to outputs, with feedbacks provided for resetting the electronic memories and for a reset interlock.

In Figure 2, a static differential Hall effect sensor 10, 30, and 40 is provided as position sensor 1, 3, and 4 of Figure 1. A reed contact 20 serves as the magnetic field sensor.

Identification of the switch position (on/off) of the switch unit by sensors is effected by means of the static differential Hall effect sensor the output voltage of which is switched with the aid of the "high" and "low" positions of the ferromagnetic actuating member. This output voltage develops in unique fashion for example even after switching off and switching on again 1037z/jrb the electronics supply voltage because, by making use of appropriate design, the ferromagnetic actuating member does not leave the three-dimensional area analysed by sensor 10. The same holds for the fusion sensor 40 which monitors the position of the shaft by means of a small iron cylinder attached to the shaft. A static differential Hall effect sensor 30 is used to detect triggering by an overcurrent. The sensor 30 detects the change of the position of an iron rod which is attached to the latching end of the catch.

For example, such an iron rod can have a length of 4 mm and a diameter of 4 mm. In the unlatching process, the path of the iron rod exceeds the three-dimensional pickup range of the sensor so that the signal edge "high" to "low") at the output of the differential Hall effect sensor can be determined as a unique triggering signal. The signal edge sets an electronic memory which indicates triggering by overcurrent until it is reset.

According to Figure 2, triggering by a short circuit is conveniently detected with the aid of the reed contact 20. If the magnetic field is sufficiently strong, the same switches regardless of polarity. Measurements which were made on a reed contact of robust design have shown that switching occurs at a magnetic induction of 3 to 4 mT. Magnetic fields of this amplitude are generated, for example, as stray fields of the actuating coil of a circuit breaker having 1200 ampere turns. At large short-circuit currents the reed contact examined had a switchover delay time of about 0.2 msec. After the decay of the short-circuit current, the reed contact 20 switches off again.

The switching signal provided by the reed contact 20 is used to set an electronic memory which stores the short-circuit induced triggering until resetting.

As an alternative to the reed contact 20, a possible short circuit can be monitored by other sensors which are sensitive to a magnetic field, e.g., Hall effect ICs, such as the "Hall effect switch", and can be processed with analysing logic circuits.

In the case of making contact upon occurrence of a short circuit, setting and resetting of the electronic memory must be controlled in a specific manner.

For example, when the circuit breaker is actuated by hand, braking contact upon a short circuit can occur though the actuating handle was transferred into the switch-on position; this is termed the so-called free triggering. By logic AND 1037z/jrb -6correlation of the switch-on signal with the signals "no triggering at overcurrent" and "no making contact at short circuit", resetting of the electronic memories is directly disabled during the triggering by overcurrent and by short circuit.

For the latter purpose in Figure 2 there are monostable flipflops 12, and 51 for adjusting the pulse length, with the noninverting output Q and the inverting outputs Q connected to the inputs of an AND gate 52 the output of which controls the reset inputs of flipflops 22 and 32. Resetting and the reset interlock are achieved in this way.

As to details, the basic circuit diagram for identifying the switch state in Figure 2 is built up of sensors 10, 20, 30, and 40 for detecting the various states, of pulse-shaping circuits 11, 31, and 41 in the form of a series circuit of a Zener diode correcting the offset voltage and an RC low-pass filter, a load resistor 21 for the reed contact 20, and of a memory circuit for the transient signals of the short-circuit sensor 20 and the overcurrent sensor 30; the memory circuit comprises two flipflops 22 and 32 the stored signal states of which are resetted in time-controlled fashion by the resetting circuit formed by the monostable flipflops 12, 50, 51, the AND gate 52, and the interference-suppressing circuit 55. The drivers 13, 23, 33, and 43 serve to adapt the amplitude of the switch state signal to the further signal processing such as a visual display, coupling to the bus, and the like.

The basic circuit diagram of Figure 3 shows an embodiment of a bus-independent sensor circuit for identifying switch states. By distinction from the circuit of Figure 2, the circuit of Figure 3 proper analyses and indicates the switch states. The basic circuit diagram of Figure 3 therefore includes additional logic correlations for analysing and Indicating the switch states, such as the switch position on/off, short circuit, overcurrent, and fused contacts. The output signals of flipflops 22 and 32 are coupled via the AND gate 54 to shut off the overcurrent display in the case of a short circuit and to activate only the display of the short circuit. The resetting circuit is formed by the two monostable flipflops 12 and 50, the AND gate 52, the NAND gate 53, and the interference-suppressing circuit 55. Fused contacts per se are recognised if the shaft remains in the switch-on position while the switch unit is in the "off" position. To this end, the two sensor signals "switch position" and "contact shaft" are correlated in time-controlled fashion by the 1037z/jrb -7monostable flipflops 12 and 60, the NAND gate 61, and the AND gates 62 and 63.

The visual display is carried out by display elements 12, 24, 34, and 44, e.g., LEDs.

In Figure 4, a conventional switch unit, a circuit breaker, is denoted by 100. In such a switch 100, the stationary contact 102 and the movable contact 104 arranged on a movable contact support 103 are essential.

Mechanical coupling of the movable contact support to the latch is effected by a ferromagnetic actuating member 105.

The mechanism and the drive means of such a known switch are not described in detail. The mechanical drive elements are summarily denoted by 110 and the magnetic drive means, by 120.

For the present application it is important that the actuating member is made from ferromagnetic material. The thickness of parts of the actuating member can be increased to, for example, 2.5 mm to increase its effect upon the magnetic field distribution. In addition, ferromagnetic rods 115 and 116 for monitoring the position are mounted on the latch lever and the contact shaft. The position of the elements 105, 115, 116 of ferromagnetic material is detected by the Hall effect sensors 10, 30, and 40. Furthermore, in addition to the magnetic drive means 120, the reed contact 20 is arranged for registering current-related magnetic fields.

In the embodiment of Figure 4, the sensors 10, 20, 30, and 40 are mounted outside the housing of the switch. The projection of the sensor positions upon the plane of the drawing is indicated by crosses or by a stylised symbol of a reed contact. If necessary, the sensors may be mounted partly within the housing or on the wall of the housing.

Figure 5 shows a schematic measuring setup for the non-contacting determination of the position at one of the ferromagnetic rods of Figure 4.

For this purpose, the differential Hall effect sensor 202 is situated at a given distance (which is characterised as air gap 203) from a ferromagnetic element 204. On the sensor's 202 side far from the air gap, there is a permanent magnet 200 the magnetic field of which passes about vertically through the sensor and enters into the air gap. When the ferromagnetic element moves in the direction 205, the magnetic field lines entering the element are moved too. The resulting field distortion at the point of the two 1037z/jrb

ML

-8- Hall segments generates a differential outpout signal of the differential Hall effect sensor 202.

As an alternative to determining the position of ferromagnetic elements, the differential Hall effect sensor can determine directly the position of a small element of a magnetic material which is hard to demagnetise. In this case, the permanent magnet 200 on the rear of the sensor 202 of Figure 5 is redundant.

The sensor arrangement shown in Figures 4 and 5 monitoring with sensors the four switch states on/off, triggering upon overcurrent, triggering upon short circuit, and fused contacts are dependable and not affected by interference. For that, the following points can be cited: the on/off signal and the fusion signal are indicated all the time; the trigger signal upon overcurrent is obtained at a moderate current amplitude and is stored, i 5 5*I N; the trigger signal of the reed contact 20 In the case of a short circuit persists until the current has decreased to small amplitudes so that positive identification and storage can be expected. For example, the reed contact 20 closes in the stray field of the solenoid if the electric current flowing through the switch unit with the trigger characteristic B16 exceeds 130 A and opens when the electric current drops below 40 A.

In order to avoid an influence of external magnetic fields, fields of adjacent switch units, upon the reed contact 20, the reed contact may be provided with a magnetic shield on the side far from the switch unit monitored.

Above there have been described in detail means for the non-contacting identification of the switch state by way of specific circuit breakers. The switch states "ON/OFF," "triggering upon overcurrent," and "fused contacts" are identified by differential Hall effect sensors at ferromagnetic pick-up elements, whereas short circuit is registered with a reed contact via the magnetic stray field of the magnetic trigger element. Such a unit can be designed as a compact identification module which is accommodated in a separate housing, for example, with modular spacing 1, and attached to the side of the circuit breaker to be monitored.

1037zljrb 9 Since magnetic fields decrease with increasing distance from their point of generation, specifically like l/r, it is not possible to identify directly with a single identifying module the switch states of single- and multi-pole circuit breakers. Owing to the mechanical coupling of the switch terminals of a multi-pole circuit breaker via the switch handle and the shaft, the latter does not hold for the switch states "ON/OFF" and "triggering upon overcurrent" but only for the two other switch states "triggering upon short circuit" and "fused contacts." More particularly, when short circuits are identified, it must be possible to determine unambiguously the respective switch unit in the case of multi-pole switches, regardless of the phase conductor in which the short circuit occurs.

In conventional circuit breakers, the minimum current required for triggering upon a short circuit depends upon the specific release [triggering] characteristic of the switch and on its rated current. For example, in a 16 A circuit breaker having the standardised release characteristic B, the fivefold trigger current, this minimum current amounts to about I 100 A.

With such a current, switch noise generated by the switch-off arc is clearly recognisable and therefore can be detected with a microphone. With increasing amplitude of the short-circuit current, the switch noise becomes so loud that positive detection of such a short circuit event can be expected. To this end, a microphone is built into the housing of the switch-state identification means, with the distance of the acoustic event of the switch terminal amounting to about 3 to 10 cm, depending upon the distance of the switch terminal in a laterally mounted multi-pole circuit breaker. The latter is illustrated in Figure 6.

Figure 6a shows the microphone voltage U plotted versus the time t. In addition to the usual noise, a distinct acoustic event occurs in the switchoff operation, as illustrated by the waveform 121. For example, such an acoustic event has a width of 5 to 10 msec on the time scale.

Figure 6b illustrates that, if the acoustic event occurs at the time t

I

there begins a short circuit which terminates at the time t 3 In this example, the switch latch is transferred into the switch-off position at the time t 2 by the undelayed release member.

1037z/jrb 10 In Figure 7, a microphone is denoted by 130; the associated threshold switch, by 131; and a differential Hall effect sensor, by 132. The timer circuits 141 and 142 follow these elements, with the timer circuit 141 actuated at the time t, and the timer circuit 142, at the time t 2 by the associated sensor signals. Thus, two timer pulses t 1 and t 2 which are shifted relative to each other, can be generated in the output lines, as illustrated in Figure 3. The two output signals are applied to an AND gate 150 which is followed by a flipflop 160. This circuitry effects the displaying of a shortcircuit event if the two sensor signals overlap on the time scale.

In a basic arrangement as per Figure 7, a short circuit via the circuit breaker monitored is derived from the coincidence of an acoustic event with the release operation.

In Figure 8, the circuit of Figure 1 is modified by having instead of the sensor 20 for short circuit an arrangement according to the basic representation according to Figure 3 with an acoustic sensor 130, 131 and two monostable multivibrators 141 and 142 the output signals of which control the flipflop 22 via the AND gate 150 as per Figure 1.

The means for identifying the switch state, which were described with reference to Figure 8, are equally suitable for monitoring single- and/or multi-pole circuit breakers.

From Figure 9 there follows the three-dimensional association of a three-pole circuit breaker with means for non-contacting identification of the switch state. There is shown the common housing 300 which is composed of parallel partial housings 301, 302, 303 for the various lines Li, L2, L3, with a ganged handle 310 being provided- The identification module which works according to Figure 2 and 3 is flange-mounted on the side as a separate housing 400 and has three diodes 401 to 403 as visual indicators of the switch state in the extension of the handle 110.

The respective switch states of the three switch terminals, namely "ON/OFF" and "triggering upon overcurrent," are mechanically coupled through the ganged handle and the shaft and are monitored by magnetic field sensors, whereas "triggering by short circuit" in one or several of the lines is detected by the acoustic sensor 130 and the ensuing If amplifier 135 even at differences in the spacing of the acoustic event from the sensor.

1037z/jrb 11 The means described with reference to Figures 6 to 9 make it possible to safely discern short circuits in regard to the switch involved.

In a distributor having a plurality of circuit breakers which are mounted as distributor switches in a distributor box, it may be advantageous to detect the short circuit by one or several acoustic sensors and to reduce in this way the expenditures for sensors. It is a prerequisite for that that each of the switch units monitored outputs an undelayed message to a central monitoring unit. This is the case especially if the switch units communicate with a monitoring system via a data bus.

Figure 10 shows schematically the design of a distributor cabinet 500 in which the various inserted switch units 100, 100', indicate their switch state, specifically on/off and/or triggering, via a data bus 1000 with associated bus-coupling means 1010 to a controller 600 as the monitoring system, and the same receives, in addition, messages, for example, from two acoustic sensors 130 and 130', as soon as characteristic acoustic signals develop in the distributor cabinet 500.

Selecting the acoustic signals in dependence upon the sound level and time dependence of the acoustic signal by electronic signal processing has the purpose of separating the switch sound from background and interference noise.

This achieves that the acoustic sensor 130 or 130' responds with sufficient probability only to the switch sounds which originate from triggering by short circuit and have a duration of, for example, 5 to 10 msec.

Both the messages concerning the switch state and the acoustic messages are transmitted without delay to the controller 600 via the data bus 1000, and the controller 600 decides by means of a window whether the two signals originate from the same event, namely the shut-off by short circuit, and developed independently from each other. For this purpose, the window is made operative by the signal received first by the controller 600 and is closed after a predetermined time period T. If the controller 600 receives also the other signal within the window, triggering upon short circuit is assumed on the basis of the coincidence of the triggering signal and the acoustic signal in time.

With the address of the emitting switch, switch X in Figure the short-circuit event is associated with the same, whereby the identification 1037zljrb 12 of the switch state "triggering upon short circuit" is realised for each individual distributor switch within the distributor cabinet 500.

Figure 11 shows a signal sequence of messages of a triggering event and an acoustic event as received by the controller 600 via the data bus: if the second signal appears within the window which was not triggered by the first signal, the controller 600 recognises a triggering by short circuit and associates the same with the address of the transmitting switch, switch X. If, however, the second signal is outside the window triggered by the first signal, namely the switch Y, the trigger message Is considered by the controller 600 as a triggering by overcurrent of the transmitting switch Y rather than a triggering upon short circuit. In that case, the acoustic message is considered a spurious signal by the controller 600 and is cancelled.

1037z/jrb -13- The claims defining the invention are as follows: 1. An electromechanical switchgear with at least one movable contact and associated drive in a switchgear housing with magnetic field sensor means for noncontacting identification of the switching states and optionally additional sensors such as acoustic sensors or the like, the sensor signals of which indicate switching states defined by logic functions, wherein said sensor means are arranged inside a separate sensor housing at a suitable location, and wherein for the monitoring of switching states said sensor housing is laterally coupled to said switchgear housing, wherein neither a mechanical or optical active connection nor an electrical line connection exists from said switchgear housing and/or power conductors connected thereto into the interior of said sensor housing.

2. A switchgear according to claim 1, wherein said magnetic field sensors are located in said sensor housing, wherein said magnetic field sensors measure position-dependent magnetic fields of permanent magnets and are provided as sensor means for identifying an on/off switching state, overcurrent tripping and contact fusion in said sensor housing.

3. A switchgear according to claim 1, wherein a sensor for measuring the magnetic field of the current flowing in the switchgear is provided as sensor means •for short-circuit tripping in the sensor housing.

4. A switchgear according to claim 2, wherein an acoustic sensor is 2 provided as sensor means for detecting switching noise in said sensor housing, a signal from said acoustic sensor being analyzed together with an overcurrent tripping signal from said magnetic field sensors, for the purpose of short-circuit identification.

5. A switchgear according to claim 2, wherein detection of said on/off switching position takes place using a static differential Hall effect sensor as one of said *og 30 magnetic field sensors.

••go 6. A switchgear according to claim 2, wherein detection of the overcurrent tripping takes place using a static differential Hall effect sensor as one of said magnetic field sensors.

7. A switchgear according to claim 4, wherein at least one of said magnetic field sensors is assigned a storage means for the formation of an "electronic memory" [n:\libpp]01087:IAD

Claims (12)

1. 8. A switchgear according to claim 5, wherein a movable contact is arranged on a contact carrier rotatable about an axis of rotation, wherein said Hall effect sensor detects a position of an axis of rotation of said contact carrier.
2. 9. A switchgear according to claim 7, wherein a detection of contact fusion takes place by logic coupling of a switching position signal from one of said magnetic field sensors and a contact shaft position signal from one other of said magnetic field sensors, wherein contact fusion is one of said switch states.
3. 10. A switchgear according to one of claims 2 to 7, wherein a position dependency of the magnetic fields of permanent magnets measured by said magnetic field sensors is produced by components of a switch mechanism which are to be monitored.
4. 11. A switchgear according to claim 9, with a drive bridge as a component of a drive mechanism of said associated drive, wherein a component of a switch mechanism of said switchgear housing to be monitored, for example said drive bridge, consists of ferromagnetic material.
5. 12. A switchgear according to claim 9, with a contact shaft and a latch as components of said drive mechanism of said associated drive, wherein a component of a switch mechanism of said switchgear housing to be monitored, for example said contact shaft and latch has a component made of ferromagnetic material.
6. 13. A switchgear according to claim 11, wherein said component made of ferromagnetic material has the form of an iron rod or hollow cylinder and for example has a length of approximately 4 mm and a thickness of approximately 4 mm. A switchgear according to claim 3, wherein a reed contact is 30 provided, as one of said magnetic field sensors, for the detection of short-circuit *fee tripping. S 15. A switchgear according to claim 14, wherein said reed contact is assigned a storage means for the formation of an "electronic memory".
7. 16. A switchgear according to claim 15, wherein said reed contact is shielded from external magnetic interference fields by a ferromagnetic shield. ln:\libpplOl 087:IAD
8. 17. A switchgear according to claim 4 and claim 6, wherein a signal for an acoustic event detected by said acoustic sensor and said signal for overcurrent tripping generated by a differential Hall effect probe are fed via time stages to an AND gate and a short-circuit event is indicated in the case of an overlapping of the two signals on a time scale.
9. 18. A switchgear according to claim 17, wherein said acoustic sensor is a capacitor microphone or a piezoelectric microphone which is arranged outside said switchgear housing.
10. 19. A switchgear according to one of the preceding claims, characterised by a multi-pole design. An arrangement comprising a plurality of switchgears according to any one of the preceding claims, having the following features: the identification of said on/off switching state and of said tripping state, in particular overcurrent- or short-circuit tripping, of said switchgears is effected by sensors; said switchgears are connected via a data bus to a monitoring device and report the occurrence of a tripping state without delay to said monitoring device; said switchgears are installed as distributor switches in a common distributor cabinet; detection of short-circuits in said distributor switches is effected by one or S 2 more acoustic sensors permanently installed at suitable measurement locations in said distributor cabinet; S. acoustic events, selected in accordance with acoustic level and a time characteristic, can be detected as possible short-circuit events and are reported without :delay as electric signals via said data bus to said monitoring device; said monitoring device cancels an acoustic message unless a tripping message 30 arrives within a preset time window; and Sg.. *eve*: said monitoring device establishes short-circuit tripping when an acoustic event signal and said tripping message arrive within said preset time window and assigns a S•short-circuit tripping to that distributor switch which has transmitted said tripping message.
11. 21. An electromechanical switch unit, substantially as herein described with reference to any one of the embodiments as illustrated in Figs. 2, 3, 4, 8 and 9. [n:\libpp]O01087:IAD 16-
12. 22. An arrangement with a plurality of switch units, substantially as herein described with reference to Figs. 10 and 11. DATED this Twenty-third Day of October 1998 Siemens Aktiengesellschaft Patent Attorneys for the Applicant SPRUSON FERGUSON ~0 a. eq.. C C C. a C a a. C C. CC 9 C C CC C. C. C CC CCC a a CC.. S C. 4e C C a 'a C. CC C CC CC tn:\iibpp]Ol 087:IAD 17 Abstract Electromechanical Switch Unit and Arrangement of a Plurality of such Switch Units Switching units can include means for non-contacting identification of the switch state. According to the invention, for identifying the switch state there are used magnetic-field sensors which are mounted at an appropriate point within and/or outside the unit's housing. Position-dependent magnetic fields are analysed for identifying the on/off switch state and for identifying triggering by overcurrent and fused contacts. The magnetic field of the flowing current is analysed to identify triggering by short circuit. Differential Hall effect sensors (10, 30, 40), on the one hand, and reed contacts on the other, are appropriate for this purpose. In a convenient development of the principal patent, there is an acoustic sensor (130) for detecting the switch sound and its signal, together with the signal for triggering by overcurrent, are used to identify a short circuit. Figure 3 1037z/jrb