CH619328A5 - Safety device for detecting defects in an electrical supply circuit - Google Patents

Abstract

When a defect occurs in the supply circuit (1, 2, 3), supplying a machine or an apparatus to be monitored, a current is created between the neutral point (4) of the electric circuit to be monitored and the earth wire (8). This current gives rise to a biased leakage current (24) applied to the base of a transistor (13) which becomes conducting. The collector current of the transistor (13) actuates an element (16) of a power relay and an alarm (12). Thus, the supply circuit (1, 2, 3) is cut. This device operates regardless of the condition of earthing of the machine or the apparatus to be monitored and it allows the protection of the user of a machine operating under high current strength and whose earthing is defective. <IMAGE>

Description

The present invention relates to a safety device for detecting faults in an electrical supply circuit, i s comprising an electrical monitoring circuit connected to the supply circuit and comprising a relay.

Such a device can be inserted on the power supply of a machine to detect a possible fault, in particular a short circuit or an insulation fault, and ensure the protection of the user.

Electric safety devices are known. The known systems are heavy and expensive. A single system generally ensures the safety of all the machines in a workshop. A single faulty machine stops all 25 machines in the workshop. Furthermore, the known systems are mounted between the earth of the machine and a phase of the supply circuit. If the ground wire is faulty, the fault is not detected. Finally, the known safeties are not inserted between two phase wires of the power supply. su

The present invention aims to avoid these drawbacks by providing a safety device ensuring, in all cases, the safety of the user and, incidentally, of the machine, without disturbing the operation of other powered machines, motors or devices. by the same electrical circuit. To this end, the security device according to the invention has the characteristics specified in claim 1.

According to one embodiment, an alarm indicator is mounted on the power circuit, which is supplied by a rectifier bridge, each branch of which comprises a diode. This alarm indicator -111 can be, for example, a lamp or a horn.

According to another embodiment, the safety device is supplied either by the secondary of a transformer independent of the machine to be monitored, the mass of which is not earthed, or by a transformer, the primary of which is connected 45 on the machine supply circuit.

According to one embodiment, the power circuit under DC voltage includes a very high value capacity intended to protect the transistor by absorbing possible sudden variations in the voltage of the power circuit. su

According to one embodiment, in which the protection device is mounted on a machine supplied with single-phase alternating current, the tripping circuit becomes conductive when an imbalance appears between the two supply wires, creating a potential difference at the terminals of the 55 very high-value resistor connected in parallel between the base circuit (connected to the first wire) and the emitter circuit of the transistorized circuit connected to the machine's ground wire.

According to one embodiment, in which the safety fi0 device is inserted directly on an electric circuit supplied with direct current and comprises two transistors forming an amplifier, the monitoring voltage is then supplied by the current source, the first terminal of which is connected, through the relay, to a first terminal of the load circuit, while the (, 5 trigger circuit is interposed between the second terminal of the current source and the second terminal of the load circuit, the base of the first transistor being connected to ground so that the appearance of a short-circuit current reverses the polarity of the solid-state amplifier and interrupts the supply circuit. This simplified assembly is particularly intended to allow the opening of the battery circuit on a motor vehicle.

The accompanying drawing shows by way of example different embodiments of the device according to the invention.

FIG. 1 is the diagram of a safety device according to the invention, interposed between the ground wire and the center of the star of the three three-phase supply wires of an electric machine.

Figure 2 is an enlarged view showing the position of the relay in normal operation.

FIG. 3 is a view similar to FIG. 2 showing the stopping of the machine and the triggering of an alarm when an insulation fault occurs.

Figure 4 is a view of a variant of the device mounted on a single-phase supply.

FIG. 5 is the diagram of another variant of a security device with adjustable detection threshold and comprising an amplifier stage on the triggering circuit.

FIG. 6 illustrates another connection method allowing use for a direct or alternating current supply.

Figure 7 is a circuit diagram of a security device used as a control device.

Figure 8 shows the electrical diagram of a switching and switching device for the power circuit.

FIG. 9 is a view of the electrical mounting of a triggering relay of the detector circuit.

FIG. 10 shows a simplified safety device inserted in the battery circuit of a motor vehicle.

FIG. 11 illustrates a safety assembly on a machine working at high intensity.

There is shown in Figure 1, phases 1,2 and 3 of the three-phase supply of an electric machine. These three phases are mounted in a star, the center 4 of which is connected through a diode 5, to a terminal 6. The ground wire 8 of the power supply is connected, by a rectifying diode 9, to a terminal 7.

A monitoring circuit A detects electrical insulation faults between wires 1,2,3 and 8 of the power supply.

The secondary of a transformer 10 permanently maintains a continuous monitoring voltage across a bridge 11. This constant voltage is applied to the input of circuit A.

Circuit A includes an electromagnetic relay R at the terminals of which is mounted a detection indicator 12 which is in series with the emitter collector circuit of a transistor 13. The base of transistor 13 is connected to terminal 6, while a bypass 14 connects the emitter of the transistor to terminal 7. Terminals 6 and 7 finally constitute the terminals of a resistor 15 of very great value.

FIG. 2 represents the state of the various elements of the safety device when the wires 1, 2,3 and 8 are perfectly insulated. The terminals 6 and 7 of the resistor 15 are at the same potential V = 0. No current flows through the diode 5. The base 13b receiving no signal, the transistor 13 is not conductive. Despite the voltage applied to the collector 13c through the excitation winding 16 of the relay R, no current flows through the transmitter 13e. Contact 17 of relay R is not activated. The power circuit 18 and the solid-state holding circuit 19 are open (switches 17 and 13). No current flows through the detection device, the elements of which are protected by a filter constituted by a very high-capacity 21 (680 mF). In this figure, the arrow I shows schematically the cut-off members to be actuated by the winding 16.

When an anomaly occurs in the machine's power supply, and in particular when there is a fault in the electrical insulation, a current is established between the ground wire 8 and a

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phase. This short circuit 23 causes a potential difference between the terminals 6 and 7 of the resistor 15 (Figure 3). One of the alternations of the alternating current from the center 4 of the star is applied to the base of the transistor 13 (arrow 24). If the diodes 5 and 9 are oriented correctly, the transistor becomes conductive. A current appears in the winding 16 and the wire 14. The contact 17 of the relay is bonded, which causes the maintenance of the current in the winding 16 and the closing of the circuit through the indicator 12 which lights up. It can thus be seen that, when the transistor 13 becomes conductive, the emitting current (arrow i o 25) is derived in the two wires 14 and 19 respectively through the short circuit 23 and coming from the contact 17 of the cut-off relay.

The holding circuit is crossed by a current of intensity I while the transistorized tripping circuit is crossed by a current of very low intensity, substantially equal to the leakage current 23. The resistor 15 of very great value disposed between the terminals 6 and 7, and diodes 5 and 9, allow the bias of the base of the transistor even if the machine is not grounded. The detection is carried out for a current 23 20 of the order of a milli-ampere. Contact 22 allows manual resetting of the device, by opening circuit 18, after elimination of leakage current 23.

The construction shown in Figure 4 shows the device applied to a machine whose power is monophase. The base circuit of a transistor 30 is connected to a midpoint 38 of the power supply through a diode 31. The emitter circuit is connected to the terminal 33 of the resistor 15, to the diode 34 and to a ground wire 40 The DC voltage applied to the power circuit is supplied by the monitoring bridge 11 supplied from 1.1 of a secondary of a transformer 10 whose primary is connected to the power supply of the machine. Figure 4 shows an audible alarm system 35, for example, a horn. An insulation fault between the two phase wires 36 and 37 gives rise to a short-circuit current 39. The potential of the midpoint 38 15 is unbalanced. This causes a potential difference between the terminals 32 and 33 of the resistor 15. The protection and detection device is identical to that shown in the previous figures. The short-circuit current 39 causes the machine to ground and stop immediately. 4 (1

It is obvious that one can use all types of known power cut-off relays without departing from the scope of the invention. Likewise, the alarm device can be audible or luminous. The polarization of the base of the transistor, obtained by the diodes mounted on the supply wires, has a sign defined 45 by the nature of the transistor which can vary.

The main advantages of the present device are as follows:

- an anomaly is detected even if the machine is not grounded;

the low cost price of the device makes it possible to mount it on each of the machines in a workshop, so that the detection of an anomaly on one of them does not stop the entire workshop; 55

- The value of the resistance 15 is large enough for the intensity of the base current applied to the transistor to be substantially equal to that of the polarized half-waves, delivered by the diodes 5 and 9, or 31 and 34, the power on the machine remaining cut as long as a short-circuit current of 60 mA persists.

- Finally, this device allows instantaneous tripping of the machine's power relay, regardless of the state of the earthing. As soon as a short circuit current is detected, the machine stops and the user is protected from a mechanical or electrical incident.

A more elaborate variant of the security and detection device is shown in FIG. 5. The trigger circuit 100 associated with the resistor 15 comprises an amplifier circuit with two transistors 13 and 113, while an adjustable potentiometer 116 is disposed between the base circuit of the first transistor 13 and the emitter circuit of the second transistor 113. A “neutral” terminal 101 can also be connected to the center 4 of the star.

The potential at point 6 is applied to the base of the first transistor, while the emitter of the second transistor is connected, by circuit 14, to terminal 7. The collector circuits 13c and 113c of the two transistors of the trip circuit are connected to a terminal 118 of the power relay. The other terminal 117 of this relay R (or switching device) receives the DC monitoring voltage. This assembly is an adjustable amplifier assembly which makes it possible to adjust the intensity of the short-circuit current triggering the switching device to a predetermined value.

As soon as a potential difference appears between points 6 and 7, it is applied to terminals 116a and 116b of potentiometer 116. The basic current reverses the polarity of the amplifier transistors which become conductive as soon as this basic current reaches a value which can be adjusted via potentiometer 116. The monitoring circuit closes through indicator 12 mounted in parallel on the cut-off relay R.

An alternative embodiment is shown in FIG. 6. The principle of the security and detection device remains unchanged. On the other hand, the connection of this device to the electric machine to be monitored is modified. The wires 14 and 114 are connected to two opposite vertices of a bridge 111. This bridge is mounted in parallel by its two other vertices, on a resistor 115 of great value, the terminals 115a and 115b of which are connected directly to the common point 4 of the terminals to be checked and to the ground wire 8. This assembly makes it possible to produce a universal safety device, that is to say capable of detecting the insulation faults of a single-phase or three-phase alternative supply, with neutral point, or a continuous supply in high, low or medium voltage. The resistor 115 and the bridge 111 constitute a universal connection circuit designated by the reference number 110.

This construction is used for example in a security device provided with an independent power supply 112 (FIG. 7). This safety device comprises a tripping circuit 100 constituted by the circuits described above, this time including the resistor 15. This tripping circuit 100 is connected to the universal connection circuit 110, the outputs of which are: one grounded 8 , the other connected by a wire 104 to one of the terminals 1,2,3,101,102,103 connected to the common point 4. A contact 120 makes it possible to connect the universal connection circuit 110 to the tripping circuit 100.

FIG. 8 shows an embodiment of the switching device R interposed on the power circuit.

A diac 121 supplied through a resistor 122 and a contactor 123 controls the opening or closing of this circuit. This electronic element controls a triac 124 mounted on the power circuit. When an insulation fault appears, the diac 121 causes the triac 124 to open and the supply of the load P to be cut off (FIG. 8).

FIG. 9 is a detailed view of an embodiment of a trigger relay R fitted in particular with a control and detection device to allow, after earthing 8, to check the good insulation of each of the terminals 1, 2 , 3,101,102 and 103, mass 8 may not be connected to earth.

As in the previous figures, and in particular Figures 5 and 6, the rectangles identified by the numbers 100 and 110 represent, respectively:

100: a part of the security device, comprising the

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monitoring and reading circuit and the transistorized detection and amplification circuit;

110: a diode bridge rectifier which allows the reading of a leakage current between two conductors 1,2,3 and 101.

In the left part of FIG. 9, there is shown,

schematically an assembly called "universal controller 200" equipped with a trigger relay R, for monitoring by the circuit 100 both three-phase or single-phase alternating current terminals 1,2,3,101 as direct current terminals 102,103. This universal controller 200 includes: l (l

- Contacts 201 of a manual switch;

the contacts 202 of a relay R serving as a power switch and connected, through the rectifier circuit 110, to the monitoring and detection circuits shown diagrammatically by the rectangle 100.

Finally, at the far left of FIG. 9, there is next to the relay R for the safety triggering, a contact 22 which the operator can actuate manually when he wants to reset the circuits, that is to say say to put the assembly back into operation after a cut made automatically by the detection assemblies 110 and 100 (rectifier, amplification, monitoring and detection circuits).

The present safety device can be adapted to the electric battery circuit of a motor vehicle. The monitoring voltage is directly supplied by the battery, or direct current source 130, through a contact 131 of a relay R, and 25 of the diodes 132, 133, 134 and 135 (FIG. 10). The electric battery circuit represented in this figure 10 is an ignition and lighting circuit, comprising spark plugs supplied by a distributor connected to the positive 132a and negative 133a poles of the battery or DC source 130. 1 (1

In the safety device of FIG. 10, the relay R a,

on the one hand, a coil interposed on the conductor 139 and,

on the other hand, a contact 131 which works on opening and is provided with a timing device.

The load circuit, formed by the transistor 113 and the diodes -15 132, 133 and 135 is supplied with direct current under a monitoring voltage trapped in a capacity 160 interposed between the points a and b which are the fault detection points.

40

The trip circuit includes relay R and a double reset contactor 136.137. The contact 136 is interposed on the basic circuit of the transistor 13, and it is mechanically connected to the contact 137 which equips a supply loop 138 also provided with the contact 131. At rest, the contact 136 is closed, and the contact 137 is open. The double contactor is actuated by a push button. It is provided with a timing system. Finally, the circuits of the device are connected, through the diodes 133 and 135, suitably oriented, to ground 8. 50

When the engine suddenly changes speed (starting, or rapid acceleration) a transient imbalance appears between points a and b. An inadvertent cut by the safety device is avoided by:

- the timing of contacts 131, 136 and 137; 55

- the supply loop 138.

Thus, the cut is only caused by a lasting imbalance, according to the following operation (Figure 10):

a) to start, the contact 136 is opened; the current flows through the loop 138 where the contacts 131 and 137 are closed and w, feeds the relay R through the diode 132 and the conductor 139 for starting the vehicle;

b) the contact 136 which closes is released; the device can then detect a fault between the bridges a and b;

c) in the event of a fault at points a or b, a current appears between the defective point and ground 8. It is applied, by closed contact 136, to the basic circuit of transistor 13. The transistors 13 and 113 become conductive. The detector current flows through the relay R by closing on the contact 136. The contact 131 of the relay opens and cuts the electrical supply circuit 138, while the two poles 132a and 133a of the source 130, and the first and the second terminals of the charging circuit are grounded 8 through the diodes 133 and 135.

The device of FIG. 10 generally comprises an alarm system (not shown) instantaneously triggered by the passage of the detector current in the relay R. On the other hand, the opening of the contact 131 takes place only after a time delay provided for the operation of contacts 131, 136 and 137. In this way, we can distinguish two main cases of imbalances:

- imbalance due to a transient regime: it is signaled by the alarm but its short duration does not cause the power to cut off;

- lasting imbalance (insulation fault or the like): the device ensures safety during operation by performing the cut-off after a determined period of time after the alarm.

In this assembly, the sensitivity is adjusted so that the detection and safety device cannot cause a sudden cut while the alternator (or the dynamo) of the vehicle is running at a speed higher than idling.

Likewise, the universal device of FIG. 6 can be used on board an airplane in flight. The device is not earthed and there is no question of suddenly cutting off all electrical and electronic, AC or DC networks. Any insulation fault between the cabin and the aircraft on the one hand and the circuits under surveillance on the other hand, triggers an alarm which signals to the crew a fault to be corrected before this fault s 'worsen.

Another application is shown in FIG. 11, intended in particular for electric machines having to operate with a high amperage (for example from 10 to a few hundred amps). Each machine 140 in a workshop is continuously protected by power fuses 141.

As we have seen previously, each machine 140 is also equipped with an individual safety device 142, protecting the user against an insulation fault.

We know machines operating for example at more than 100 amps. The fuses (or disruptors) 141 are calculated to protect the machine in the event of a short circuit, for example between two of the supply phases. However, the switches do not trip if the short circuit is "partial". We can thus have a short-circuit current of 5 to 10 amps. The machine remains protected, but the user is in danger of electric shock.

As shown in FIG. 11, a first safety device 142 protects the machine 140 individually from other machines in the workshop. A second safety device 143 is connected in parallel to the power supply circuit 150, by supply conductors 151, detection 152, grounding "machine" 153. The imbalance caused by a leakage current gives rise to a voltage on the detection circuit (inside 143) and causes the contact 146 to close and the relay R of the trip circuit 148 to open.

The security device 143 provides protection for the user. It is supplied by the machine circuit through fuses 144 which, for example, melt at 100 mA.

When no fault (insulation, short circuit) is detected, the current in fuses 144 is zero. The machine is operating normally. The detector circuit 143 is at rest.

A short circuit between two phases, or between a phase and the earth of the machine, creates a derivative current through the fuses 144 to the detector device 143. As soon as this current becomes dangerous, the fuses 144 and 145 are cut. This causes

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the opening of the contactor 146 of the power circuit 148, and the interruption of the power supply to the machine, or the triggering of an alarm 147. The user is thus protected against any electrical fault (poor insulation, short circuit) . While the power disrupters 141 are calculated as a function of the load of the machine used, the safety fuses 144 are independent of the power of the machine: they only aim to protect the user.

VS

5 sheets of drawings

Claims (6)

619,328 2 CLAIMS circuit to allow proper biasing of the transistor 1. Safety device for detecting faults in a detector circuit, which makes it possible to detect an insulation fault or an electrical supply, comprising an electrical anomaly monitoring circuit on an electric device supplied connected to the supply and comprising a relay, alternating current by the supply circuit. rised in that the monitoring circuit is maintained, permanently 5 7. Device according to claim 1, for a nence circuit, under a DC voltage, supplied by a three-phase supply circuit feeding a machine, characterized in rectifier (11 ), while said relay (R), the contacts of which are that the basic current is supplied by a circuit connected to the center arranged so as to cause the breaking of (4) of said three-phase supply circuit, mounted in star, tan supply circuit, is connected to a trip circuit - say that the emitter circuit is connected on the one hand to the ground wire (8) ment which includes at least one transistor (13) mounted from the 10 de this supply, and on the other hand to a terminal of the relay in the following way: cut-off, so that when an anomaly appears, causing - its base (13b) is connected to the cathode of a diode (5, the circulation of a current in the conductor between point 31) which is connected to one of the ends of a resistor (15), the neutral (4) and the ground wire (8), the tripping circuit is a diode and the resistance being inserted in a branch which becomes polarized, becomes conductive and causes the opening of the relay connects an electrical zero point (4, a, 38 ) of the electrical circuit 15 to cut off the power of the machine. monitor with a ground wire (8); 8. Device according to claim 6, for a circuit - the collector (13c) of the transistor is connected to a terminal of the three-phase supply supplying a machine, characterized in relay (R); what the solid-state trip circuit is connected - the transmitter (13e) is connected to a conductor connecting the other between two phase wires of the three-phase power supply, the polarized end of the resistor (15) and the ground wire (8), the latter 20 tion of the transistor then being due to an imbalance between them being neutral in normal operation, this device being phases of the machine. arranged so that the potential difference, created in the 9. Device according to claim 1, characterized in that branch between the electrical zero point (4, a, 38) and the wire the monitoring circuit is supplied by the secondary of a ground (8) when a fault appears in the power supply circuit independent of the circuit to be monitored and whose tation gives rise to a current which flows in this mass is not connected to earth . branch as well as in the conductor connected to the base of the transistor 10. Device according to claim 1, characterized in this tor, this fault current causing the polarization and the change that the relay comprises a triac (124) controlled by the circuit state control of the transistor which becomes conductive, authorizing tripping from a diac (121), so that the triac current flow from the collector (13c) to the emitter instantly cuts the circuit power supply to monitor. (13e), which opens the relay (R) and cuts the m 11. Device according to claim 1, characterized in this supply circuit, the transistor (13) remaining polarized, therefore that the monitoring circuit is connected on the one hand to the circuit ensuring the triggering of the relay and the detection of the supply fault to be checked and on the other hand to the ground wire by one as long as this fault lasts, and this regardless of the state of bridge (111) each branch of which has a diode, so that the electrical circuit to be monitored is grounded or that the device makes it possible to check an electrical supply electrical device supplied with current by the circuit on which 35 also alternatively three-phase or single-phase that 'detection is carried out. continued. 2. Device according to claim 1, characterized in that 12- Device according to claim 1, characterized in that an alarm indicator (12) is mounted at the terminals of the relay (R) 1ue 'e supply circuit comprises a commu-device and in that said rectifier assembly (11) is constituted by an additional tation (200) arranged to allow raccor-bridge each branch of which comprises a diode. 40 from the monitoring circuit to 1 or 1 other of several circuits 3. Device according to claim 2, characterized in that to be checked (1,2,3,101,102,103), these circuits being supplied with the alarm indicator is light or sound. alternating or direct current, at variable voltages 4. Device according to claim 1, for a circuit (fig- 9). single-phase power supply, characterized in that the circuit of 13. Device according to claim 1 for a trigger circuit is connected to a midpoint (38) of the power circuit 45 supplied by a direct current source, characterized in electrical mentation, so that when an insulation fault on the tripping circuit comprises a first and one appears between the two supply wires (36,37), a second transistors (13,113) is established, the basic circuit of the first leakage current, which is biased through a transistor circuit (13) being connected to ground (8) and the two rectifier transistors (31,34) and applied to the base of the transistor for the (13> 113) constituting a polarized transistorized amplifier, making it conductive, the detection of the fault being ensured whatever 5 "short-circuit current reversing the polarity of this amplifier-is the state of the earthing of a device connected to the circuit breaker and cutting the monitoring circuit of ci food power supply. tion in DC current to be monitored, this device being further characterized in that it includes a triggering alarm 5. Device according to claim 1, characterized in that instantaneous actuated by the relay (R), which comprises a trip circuit is equipped with a first and a 55 timed contact (131) associated with reset contacts second transistor (13,113) arranged in such a way that the base of the (136,137) also timed in order to delay the operation of the first transistor (13) is connected on the one hand to ground and on the other hand to the tripping circuit and to avoid breaking on the other hand to the emitter of the second transistor (113) through a poten- the DC power supply when an adjustable tiometer (116) appears; the emitter of the first transistor is faulty due to a transient imbalance (fig. 10). connected to the base of the second transistor and the two collectors are M) 14. Device according to claims 11 and 12, characterized connected to the same terminal (118) of the relay (R), so that the in that the circuit power supply includes an alarm (147) assembly is an adjustable amplifier assembly allowing it to be arranged to be triggered by an insulation fault, without adjusting the current of the supply circuit to a predetermined value (fig. 11). short circuit triggering the relay (R). 15. Use of the device according to claim 13, for 6. Device according to claim 1, characterized in that 6s detect the faults of electrical insulation in a circuit ali-the circuits of the base and of the emitter of the transistor of the circuit of menté by a source of direct current (130) , characterized in triggering each comprise a diode (5,9), these dios that the circuits of the device are supplied directly by the rectifying the alternations of the alternating current of electric short-circuit to be monitored between the electric zero point (a) and 3 619,328 ground (8), the DC monitoring voltage being supplied by the source (130) and stored in a capacitor (160), the positive terminal (132a) of the source (130) being connected, through the relay (R) , at a first terminal of the load circuit formed by said transistors (13,113), diodes (132,133,135) and said capacitance (160), while the trigger circuit, formed by the relay (R) which controls the timed contact ( 131) and said reset contacts (136,137), is arranged between the negative terminal (133a) of the source and the second terminal of the load circuit (13,113,132,133,135,160). m