DE2920287A1 - FAULT CURRENT PROTECTION DEVICE - Google Patents

Description

Residual current protective device

The invention relates to a residual current protective device with a fault current detector and a breaker arrangement.

Residual current protective devices respond to residual currents that especially in the case of so-called double-insulated devices without earthing, as a result of insulation faults flow to earth. Such fault currents are particularly dangerous in the case of handheld devices, in particular personal care devices such as electrically operated toothbrushes, which are used by the user be operated in a damp environment. These protective devices should be designed in such a way that they can operate at sufficiently low currents Respond quickly enough to avoid the risk of electric shock.

So far known residual current protective devices are designed in the form of permanently installed sockets and open when responding of the fault current detector a mechanical switch arrangement, which is then automatically secured by the user can be closed again by pressing a button. These permanently installed facilities can therefore not use the electrical Properties of very specific electrical devices, such as electrically operated personal care devices, are adapted, they are furthermore, it is relatively expensive and large, and there is also the possibility of uncontrolled restart by the user very dangerous. Finally, the sensitivity threshold lies in the known devices with conventional mechanical breaker switches at about 10 mA, which often complies with modern strict safety regulations not enough.

As is well known, the mean statistical perception threshold is at 50 Hz at about 1 mA, while the critical current which is used for

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Avoidance of severe damage or even fatal blows the immediate disconnection of the current is required, is around 15 mA, because at such a current strength the person concerned can generally no longer let go of the live device or device part. Except Of course, the current intensity also affects the duration of the passage of the current plays a decisive role through the body, so that protective devices should switch off in the event of fault currents within time intervals well below 100 ms.

The invention is based on the object of a residual current protective device to create, which can be optimally adapted to a certain type of electrical device, inexpensive and space-saving as well as with a particularly low response threshold can be produced and, after it has responded once, cannot be switched on again by the user can.

This object is achieved according to the invention by the in claim 1 specified features solved.

In this way it is achieved that every electrical device, in particular every personal care device, such as an electrically operated toothbrush, can be equipped directly with a plug, which contains a protective device optimally adapted to this device. However, it is also possible that with a protective device according to the invention equipped plugs are available separately and then, as required, instead of the normal plug, with a specific electrical device or can be connected to its supply line.

Particularly useful refinements of the invention emerge from the subclaims. The use of a toroidal tape core made of a nickel alloy with a maximum permeability of about 300,000 a field strength amplitude of approximately Ο, ΟΙΑ / cm as current or Pulse converter allows the production of protective devices with a

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Response threshold below 5 mA, preferably around 1 mA. Preferably the pulse generated when a fault current occurs in the secondary winding of such a current converter is used to ignite a Triacs used which one in series with one of the fuses and through which a current flows, for example five to twenty times greater than the rated current for the electrical device in question is. In this case, only a small amount of power is required to trigger the device because, as is well known, a triac only has a very small control power requires, and in addition, the comparatively high current ensures that the fuse will burn out quickly.

The contacts of an electret relay can also be used as a switch, -which quickly close the auxiliary circuit containing the fuse when a fault current occurs, which in turn is excited by the output pulse of a secondary winding on the toroidal core of the current transformer. It is preferably also possible to arrange the relay contacts of a bistable electret relay directly in the wires of the supply line, dispensing with special fuses, and in this way to use them directly as interrupter contacts.

The invention is based on the drawings of exemplary embodiments explained in more detail. Show it:

Fig. 1 is a view of a two-pole plug in natural size, in which a protective device according to the invention is housed, and

2-5 the circuit diagrams of four exemplary embodiments of a residual current protective device according to the invention

According to FIG. 2, the connector poles a and b of a connector 10 according to FIG. 1,

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for example for one with 50 Hz AC voltage of 220V too operating electrical hand-held device is intended, connected to the wires 1 and the supply line to the electrical device M. The core 1 leads over a fuse 3 and the primary winding Wl of a current transformer to one terminal of the motor of the electrical device M, while the other wire 2 via a further fuse 4 and a further primary winding W2 of the current transformer and the on-off switch 6 with the other motor terminal of the device M is connected. The plug pole a is also via a two-way thyristor circuit T2 and a resistor R2 is connected to the other wire 2 on the side of the fuse 4 facing away from the other connector pole b, while conversely the Connector pole b via a resistor Rl and a two-way thyristor circuit Tl and the fuse 3 is connected to the first-mentioned connector pole a. In the case of the circuits T1 and T2, it can preferably be a triac each or, if necessary, thyristors connected in antiparallel in each case. The control electrode of each of the two Zweiwegthyr is tor circuits Tl or T2 is connected to one end of a secondary winding W3 or W4 of the current transformer, whose other ends each to the connecting line between the relevant circuit T1 or T2 and the. associated resistor Rl or R2 connected are.

The two primary windings Wl and W2 are each a capacitor C1 or C2 connected in parallel. For the purpose of suppressing sparks when The switch 6 is also opened for this switch and the device M, a capacitor C4 and a resistor R4 connected in series with this connected in parallel.

The current transformer has a small toroidal band core 5, known per se, made of an alloy which preferably consists of 72-83% nickel with additions of copper and molybdenum and a maximum permeability M of 300,000 at 50 Hz and a field strength amplitude of

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about 0.01 A / cm. Such an alloy is, for example, under known by the trade name Ultraperm 10.

In the case under consideration, it is assumed that the electrical device M has a nominal current of 50 mA. The response threshold should be at a fault current of around 1 mA. The two primary windings Wl and W2 are wound in the same way and have a number of turns of z. B. 150 turns. The coil length, which in the practical versions of such current transformers is equal to the circumferential length of the toroidal tape core because of the overlapping of all windings, can be, for example, about 50 mm. From the above information, the magnetic field strength H results in a known manner, which is proportional to the product of the number of turns N current strength i divided by the coil length 1 and is linked to the induction B by the relationship B = ju.H. A field strength amplitude of 0.01 A / cm corresponds to an induction of approximately 0.4 Tesla at a ze of approximately 300,000.

As long as there are no fault currents, they compensate each other two primary windings W1 and W2 wound in the same direction and having the same number of turns induced effects, so that in the toroidal tape core 5 no magnetic flux is effective and the two two-way thyristor circuits T1 and T2 remain blocked. If now as a result of an insulation break or another insulation fault over the body of the person holding the device, a fault current can flow to earth, which is the connection shown in dashed lines in the circuit diagram according to FIG. 2 to the earth via which the body resistance is one piece of resistance R5 corresponds, then the primary winding Wl has a higher current flowing through it than the other primary winding W2 ^ 'Here it is assumed that the connector pole a is connected to voltage, while the other connector pole b is connected to the neutral conductor. The current asymmetry in the two Primary windings Wl and W2 result in a resulting magnetic flux in the toroidal tape core 5, which occurs during the first

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ORIGINAL INSFciO. ^

occurring half-wave in the secondary winding W3 or W4 an output pulse generated; this output impulse ignites, depending on the moment existing polarity, first the one and immediately thereafter the other two-way thyristor circuit T1 or T2. The resistors R1 and R2 are dimensioned in such a way that currents of approximately 0.5 to 1 A now flow through the circuits T1 and T2 and thus the fuses 3 and 4, respectively which corresponds to ten to twenty times the nominal device current of around 50 mA. Therefore fuses 3 and 4 respectively melt very quickly, so that after 5-20 ms, for example, both wires 1 and 2 are permanently disconnected from the network. The protective device According to the invention, regardless of the polarity of the plug, always interrupts both supply lines.

If, in the example according to FIG. 2, both fuses 3 and 4 have blown and the user then puts the plug back into the socket with the polarity reversed, then this is due to the high, but finite Blocking resistance of the two-way thyristor circuit Tl on wire 1 has a high potential or a practically corresponding to the mains voltage corresponding static charge; if the user touches the device or the defective insulation again, then as a result of one in this If there is a small fault current pulse it the primary winding Wl in the secondary windings one possibly the ignition of the two-way thyristor circuits Generate T1 or T2 causing impulse, which of course has to be prevented. Preventing this possible Effect happens with the help of the capacitors Cl and C2, which of the Primary winding Wl and W2 are connected in parallel and which have such a possible fault current pulse for the primary winding in question render ineffective.

The example according to FIG. 3 differs from the example according to FIG. 2 only in the fact that the secondary winding W'3, one end of which with the Ignition electrode of the two-way thyristor circuit Tl is connected to

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its other end directly to wire 1 and thus to the end in question the primary winding "WTl is, while the other secondary winding" W'4, one end of which lies on the ignition electrode of the two-way thyristor circuit T 2, with its other end directly on wire 2 and thus on the relevant end of the primary winding "Wl is connected. Through this measure is achieved that the windings Wl and W'3 on the one hand and W2 and ¥ '4, on the other hand, can each consist of a common winding with a corresponding center tap, which is what makes the production and simplified the structure. In particular, one of the two common windings can also be used, while saving insulation thickness, made of enamel wire, while only the other common winding has a higher insulation, for example a plastic insulation needs.

The rest of the structure of the circuit shown in Figure 3, its elements with the same reference numerals as the corresponding elements of the circuit according to Figure 2, and the function of this circuit are the same as described for the example according to FIG.

In the example according to FIG. 4, the one connector pole a connected wire 1 of the supply line a rapidly responding fuse 3 and a primary winding Wl of a current transformer that again has a toroidal tape core 5 of the type described in the preceding examples, while in the connected to the other connector pole b Wire 2 a corresponding fuse 4 and the other primary winding W2 of the current converter £ j are connected. Between the others The motor of the electrical device M with the on-off switch 6 of this device is in turn located at the ends of the two primary windings mentioned. the In this case, the breaker arrangement consists of a known electret relay 7, which is connected in series with a diode D to a secondary winding W5 of the current transformer. An electret relay has one an existing thermoplastic anchor, which

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is permanently charged with electrical charge carriers of a sign. This plate-shaped anchor can be tilted freely between two metallic electrodes, which can be charged in one sense or the other. Of the charged armature is in each case on that metallic electrode, which is charged opposite to the charge of this armature; if now the two Electrodes are reloaded, then the relay armature is charged by the other electrode, which is now charged with the opposite charge attracted and practically folds down at the moment. This is an extremely sensitive, bistable relay, which is practically only requires a vanishing performance. At the relay armature, depending on Application, on one side or on both sides metallic contacts are attached, which then in one of the two relay positions or in both Lay the electrical connection to one or the other fixed electrode. The relay armature can of course also in a known manner with in be connected to separate electrical circuits lying contacts, which are switched by the electret relay.

In the example according to Figure 4 relay contacts 8 and 9 of the relay 7 are provided, of which one relay contact 8 has one connector pole a via the fuse 4 with the other connector pole b and the relay contact 9 this connector pole b via the other fuse 3 with the connector pole a connects. Both relay contacts are normally open and are closed when the electret relay 7 is energized; this results in a strong current flow through the fuses 3 and 4, which are quickly burned out in this way and thereby permanently separate the two wires 1 and 2 from the mains. The current transformer works as described in the previous examples. As long as there is no fault current flows, the effects generated by the two primary windings W1 and W2, which are wound in the same sense and have the same number of turns, neutralize each other _As a result of the current asymmetry then occurring in the two primary windings W1 and W2, s becomes a magnetic flux

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generated in the toroidal core 5, which has a corresponding, the relay exciting pulse from the secondary winding W5 results in the z. B. Can have 250 turns.

FIG. 5 shows a particularly simple circuit in which, without Fuses the relay contacts 18, 19 of an electret relay 17 directly as normally closed contacts, i.e. normally closed interrupter contacts, in the wires 1, 2 of the supply line, so that when the relay 17 is energized, both wires 1,2 directly through the opening relay contacts be disconnected from the mains. The relay excitation takes place via a full-wave rectifier working with diodes in a Graetz circuit G, so that the time of the current flow after a fault in a 50 Hz network is limited to a maximum of 10 ms. The relay 17 is preferred intended only for a one-time function and elastic, e.g. B. biased by a spring so that the opening stroke when responding the contacts 18, 19, which then remain in their opening position, can be made large enough to cover a sufficiently long interrupter path to obtain.

The fault current detector 5 and the other components in the example according to FIG. 5 correspond to those according to FIG Example according to Figure 4, the diode D can be replaced by a full-wave rectifier.

Known electret relays require, for example, 6 V pulses and only 10-20 / tW for switching.

The current transformers described, which have a fault current Measure the current difference that occurs in the two supply lines extremely sensitive when using a suitable toroidal tape core, so that, as mentioned, it is already below fault currents about 5 mA, preferably at already 1 mA, respond; the described

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In addition, interrupter arrangements only require an extremely low power to control them and also speak extremely quickly. The residual current protective devices described are therefore in particular with rapidly responding fuses, which, in the event of a fault, apply currents of ten to twenty times the rated device current can be, or with electret relays that act directly as a breaker, from which they can be properly and reliably in addition, can be produced inexpensively and in very small dimensions.

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Claims (11)

V 2920237 ■ Φ- PATENT CLAIMS ( 1. JFeMerstrom protective device with a fault current detector and ^ -one of this, controlled interrupter arrangement, characterized in that this protective device in a plug (10) which is on the supply line of a mains-operated electrical device, in particular a handheld device, or for such an electrical device is intended, housed and the interrupter arrangement (Tl, Rl, 3; T2, R2, 4) is set up to permanently disconnect all wires (1,2) of the supply line from the network. 2. Protection device according to claim 1, characterized in that in each wire (1, Z) of the supply line a fast-responding fuse (3, 4) is arranged and each fuse (3, 4) is also in a circuit which has a two-way thyristor Circuit (Tl, T2) and a resistor (Rl, R2) in series therewith, which is significantly smaller than the resistance of the connected electrical device (M), and that the two-way thyristor circuits (Tl, T2) are set up to to be ignited by the output of the fault current detector (5). 3. Protection device according to claims 1 or 2, characterized in that that the fault current detector is a current transformer in the form a toroidal tape core (5) with a high maximum permeability, preferably made of a nickel alloy with a maximum permeability from about 250,000-300,000 at a field strength amplitude of about 0.01 A / cm, and in the case of a two-pole plug is two Primary windings (W1, W2) and at least one in each of the two wires (1, 2) of the supply line, wound in the same direction, and at least one Secondary winding (W3, W4) carries. 4. Protection device according to claim 3, characterized in that 8/87 22 the primary windings ("Wl, W2) of the current converter rs capacitors (Cl, C2) are connected in parallel. 5. Protection device according to claims 1 to 4, characterized in that that the fuse (3,4) in each wire (1,2) of the supply line is on the one hand in series with the relevant primary winding (Wl, W2) of the current transformer (5) and on the other hand via the two-way thyrostor circuit (Tl, T2) and the resistor (Rl, R2) in series with it is connected to the pole (b, a) of the other wire (2, 1) of the supply line, and that for each of the two ignition circuits of the two-way thyristor circuits (Tl, T2) each have a secondary winding (W3, W4) on the toroidal core (5) is provided. 6. Protection device according to claim 5, characterized in that the primary winding (Wl or W2) in one wire (1 or 2) and the Secondary winding (W "3 or W'4) in the ignition circuit of the two-way thyristor circuit (Tl or T2), which is in the circuit of the fuse (3 or 4) of the relevant wire (1 or 2), the two halves of one common winding with one connected to the relevant wire (1 or 2) Are center tapping. 7. Protection device according to claim 1, characterized in that the interrupter arrangement has a bistable electret relay (7) which is in series with a rectifier in the output circuit of the fault current detector and normally open relay contacts (8 ₄ 9), each in a circuit that one of the connector poles (a or b) is connected to this last-mentioned connector pole (b or a) connects. 8. Protection device according to claim 1, characterized in that 9098Α8 / Θ722 the interrupter arrangement has a bistable eletret relay (17), which is in series with a rectifier (G), preferably a full wave rectifier, in the output circuit of the fault current detector (5) and normally closed relay contacts (18, 19}, which are each arranged in one of the wires (11,12) of the supply line and when energized of the relay (17) are opened. 9. Protection device according to claim 8, characterized in that the Electret relay (17) intended for a one-time function, mechanical biased relay is. 10. Protection device according to claim 7, 8 or 9, characterized in that the fault current detector is a current transformer in the form of a toroidal tape core (5) with a high maximum permeability and two in each of the two wires (1,2) of the supply line, in the same sense wound primary TATicklungs ("WTl, WZ) and a secondary winding (" V \ T5) to which the electret relay (7, 17) is connected via the rectifier (D; G). 11. Protection device according to one of claims 1, 2, 7 or 8, characterized marked that the on-off switch (6) of the electrical device (M) and its motor is one in series with a resistor (R4) Capacitor (C4) is connected in parallel. 984870722