FR2653610A1 - SELECTIVE DIFFERENTIAL SWITCH WITH FAULT CURRENT. - Google Patents

Abstract

The residual current fault interrupter has a magnetic hold trip (22) which is connected directly to the secondary winding (28) of a totalizing current transformer (24) through a capacitor (34). On two main conductors (P1, N1) controlled by the residual current circuit breaker, a direct current supply circuit (40) is connected, from which the magnetic hold release (22) can be energized. continuous in the same direction as the permanent holding magnet, through at least one diode (46, 48). On the secondary winding or on a tertiary winding (60) of the totalizing current transformer, an amplifier (54) is connected, which can control after the expiry of the time set by a time delay element (56), an electronic switching circuit ( 50) bypassing the output terminals of the DC power supply circuit (40). The residual current fault interrupter is simple in construction and requires only a small number of turns for the secondary winding of the totalizing current transformer. In addition, the differential fault current switch is insensitive to overvoltages, parasitic currents and mechanical vibrations and shocks.

Description

:. The invention relates to a differential switch with fault current,

  with delay, comprising a totalizing current transformer, a polarized trip unit with magnetic holding, and an electric time delay element combined with the trip unit with magnetic holding. In a known version of a fault current differential switch of the type mentioned above (Revue Siemens 42, 1968, fascicule 6, pages 492-494), the trip delay is ensured by an RC circuit connected to the output I0 terminals of a bridge rectifier device, provided in the

  secondary circuit of the totalizing current transformer.

  Owing to the wide dispersion range of such a timing device based on simple RC circuits, this known execution of a fault current differential switch has a certain inaccuracy in response from the trigger connected thereafter. Another known embodiment of a differential switch of the type mentioned at the start (DE-AS 27 45 464) avoids this drawback because a delay capacitor is charged using an electronic circuit, the essential component of which consists in a constant current regulator assembly comprising a transistor and a Zener diode, and which is connected to the secondary winding of the totalizing current transformer via a rectifier bridge. This arrangement provides a limited constant current, with the consequence of a constant time delay independent of the importance of the fault current, which however is insufficient to satisfy the conditions of a switch.

  selective differential with fault current.

  Finally, we know from DE-PS 31 27 331 an electronic assembly for differential switch with fault current with time delay, in which the excitation winding of the trip device is preceded by a contact with threshold value, which when is activated, discharges the energy accumulated in the time delay capacitor in the excitation winding of the trip unit. Also in this arrangement, the delay capacitor is charged via --2-- a capacitor current regulator, connected to the secondary winding of the totalizing current transformer through a full-wave rectifier , this arrangement making the trigger delay constant, practically independent of the magnitude of the fault current. All of the known differential fault current interrupters mentioned above thus have drawbacks and are moreover costly to manufacture due to the use of full-wave rectifiers and energy storage capacitors, moreover they require totalizing current transformers having a high number of turns in the secondary winding, in order to induce in the event of tripping the response voltage necessary for electronic mounting. The object of the invention is to avoid these drawbacks and to create a differential fault current switch with time delay which, while ensuring sufficient insensitivity against accidental trips, remains however of simple construction and operates with a limited number of turns in the secondary winding of the transformer

totalizing current.

  According to the invention, this objective is achieved by the fact that the polarized trip unit with magnetic holding is connected directly to the secondary winding of the totalizing current transformer with a capacitor in series, only on two main conductors controlled by the differential switch with fault current a DC power supply circuit is connected, by means of which the magnetic holding release can be excited in direct current in the same direction as the holding magnet through at least one diode, and only on the secondary winding or another special winding of the totalizing current transformer an amplifier is connected, which can control after expiration of a delay fixed by a time delay element, an electronic switching circuit shorting the terminals

  output of the DC power supply circuit.

  Thanks to this solution, the invention benefits from the known mode of direct supply of the magnetic hold release, for example according to DE-AS 20 44 302 and DE-PS 20 36 497 concerning -3- a differential switch with non-fault current time delay, thanks to the voltage induced in the totalizing current transformer when a fault current appears, and achieves the time delay required for tripping by superimposing this voltage with a DC voltage generated by a supply circuit in direct current taken from the network and which reinforces the magnetic field of the permanent magnet of the trip unit with magnetic holding, until the secondary winding or an additional winding of the totalizing current transformer, after expiration of the time delay by the connection of a delay circuit connected to an amplifier, short-circuits the superimposed DC voltage and thus allows the de tripping of the trip device during the next half-wave of the shunt current emanating from the secondary winding of the totalizing current transformer. On the other hand, the time delay can be adjusted in such a way that the differential fault current switch can be used as a differential fault selective current switch, in order to prevent, in low voltage tap-off distributions including in the differential switch circuit with fault current of the apparatuses as well in the main distribution as in the secondary distributions, that a cut of all the user devices connected to the main distribution intervenes following a fault of insulation in the

bypass distribution.

  The advantages of the invention are as follows: - no reduction in safety, - no full-wave rectifier and no electronic assembly having to react for an extremely low power, resulting in lower manufacturing costs; - No need to provide on the secondary winding of the totalizing current transformer a voltage of 6 volts or the like, thus the number of turns of the secondary winding can be kept low, with the consequence of another compression of the cost price; -4- - high insensitivity to accidental tripping by shock voltages or stray currents, as well

  only by mechanical bumps or jolts.

  Advantageous embodiments of the invention emerge from the

subclaims.

  The invention will be described in detail below, with reference

to the accompanying drawings, of which: -

  Fig.1 shows a first embodiment of the differential trip trigger release circuit according to the invention, in the form of a block diagram. Fig. 2 shows a modified embodiment, in which the various block circuits are replaced

by electronic components.

  In these two embodiments, in the example proposed, the phase conductor and the neutral conductor of a single-phase low-voltage distribution 10 have been designated by P and respectively by N, of which a branch line 12 supplies a device ( not shown). the bypass line 12 therefore consists of two conductors Pi and Ni, which can be cut by the contacts 14 of a differential switch with bipolar fault current shown only schematically. The contacts 14 are connected by means of an operating system 16 to a control 18 making it possible to connect and disconnect the contacts normally. The operating system 16 has a holding lock 20 which can be released by a polarized trip unit with magnetic holding 22 , in order to cut the contacts 14 when

  the occurrence of a fault current in the bypass 12.

  The detection of a fault current is ensured by a totalizing current transformer 24 having a toroidal core 26 simply shown, by which the conductors Pi,

  Neither of the bypass 12 pass as primary winding.

  The O-ring core 26 also carries a secondary winding consisting of a relatively small number of turns 28, the output terminals of which are connected by the conductors 30, 32 to the input terminals of the magnetic retaining release 22, more precisely in series with a capacitor 34 which in the example described is inserted into the conductor 32. However, the capacitor 34 can also consist of one or more

-'- 5--

  capacitors inserted in each of conductors 30 or 32. The

  function of the capacitor 34 will be specified later.

  The conductors Pi, Ni are connected by connecting wires to a DC power supply circuit 40, simply shown diagrammatically in FIG. 1 by a block, and the output terminals of which are connected by the conductors 42, 44, to the conductors 32, 30, downstream of the capacitor 34. Therefore, when the normal operating voltage which is for example 230 volts circulates in conductors Pi and Ni, the excitation winding of the magnetic holding release is traversed by a direct current, more precisely so that the attraction force exerted by the permanent magnet of the magnetic holding release on its armature finds it strengthened. In this regard, the capacitor 34 prevents the DC power supply circuit from being short-circuited by the secondary winding 28 of the totalizing current transformer 24. On the conductor 42 are provided two rectifying diodes 46, 48 connected in cascade , and polarized so that they allow the direct current specified above to pass from the DC power supply circuit 40 to the magnetic hold release 22, while blocking any current in the opposite direction. In addition, there is provided between the conductors 42, 44 an electronic switching circuit 50, usefully consisting of a thyristor. During the reaction of the electronic switching device 50, the output terminals of the DC power supply circuit 40 are short-circuited, so that the magnetic hold release 22 is then no longer supplied with DC power intended for to build strength

  of attraction of the trigger armature.

  For the control of the electronic switching device, an auxiliary circuit 52 with amplifier 54 is provided, the output of which is connected to an electronic timing element 56, the output of which is connected by a conductor to the control input of the electronic device switching 50. In the example described, the amplifier 54 is, in accordance with FIG. 1, connected by its inputs to a third tertiary winding or winding 60 of the current transformer

  totalizer via conductors 62, 64.

  The assembly described above operates as follows: -6- When there is no voltage in the conductors Pi, Ni, no DC voltage appears consequently at the DC power supply circuit 40, similarly nothing does not appear at the output of amplifier 54. The system then functions exactly as a differential switch with non-delayed fault current. When the conductors P1, Ni are at 230 volts, as long as no fault current is present, nothing appears at the outputs of the amplifier 54 and of the timing element 56. The thyristor 50 mounted at the rest of the timer element 56 remains blocked. The DC voltage delivered by the DC power supply circuit 40 acts across the terminals of the magnetic hold release 22, but in such a way that, as a consequence of its polarity, the field of the permanent magnet of the magnetic hold release 22 is finds it strengthened. Therefore, the magnetic hold trigger cannot absolutely trigger: its insensitivity

  vis-à-vis accidental trips is increased.

  If a fault current then appears, it induces in the secondary winding 28 of the totalizing current transformer 24 an alternating voltage, the negative half-waves of which weaken the DC voltage across the terminals of the trip device, however without immediate action. Likewise, in the tertiary winding 60 of the totalizing current transformer 24, a voltage is induced, which will be filled by the amplifier 54 and then led to the delay element 56. This element applies with a certain delay a

  voltage on the trigger of thyristor 50 and makes it conductive.

  Due to the unlocking of the thyristor 50, the DC power supply circuit 40 is short-circuited, which allows the magnetic hold release to trigger under the action of the next half wave of weakening of the magnetic field emanating of the secondary winding of the totalizing current transformer 24. The two diodes 46, 48 connected in cascade are used to decouple the DC power supply circuit from the secondary winding 28 of the current transformer

totalizer 24.

  The modified variant illustrated in FIG. 2 concerning a differential fault current switch according to the invention, is not different from that of FIG. 1 -7- that by the fact that the tertiary winding 60 is suppressed and that the amplifier 54 is connected to the secondary winding 28 of the totalizing current transformer in parallel with the magnetic holding release 22. In addition, the various blocks 40, 54, 56 are replaced by electronic circuits

  can constitute these blocks by way of examples.

  Thus, the DC power supply circuit 40 consists according to FIG. 2 into a series resistor 66 and a diode 68, followed by a smoothing capacitor 70 connected between the two conductors 42, 44. In addition, it is possible to connect a further Zener diode 72 in parallel to the smoothing capacitor. The function of the Zener 72 diode is mainly to provide a regulated supply voltage

to amplifier 54.

  The timer element 56 is in the form of an RC circuit and consists of an ohmic resistor 74 and a

capacitor 76.

  The operation of the assembly shown diagrammatically in FIG. 2 is identical to that of the exemplary embodiment according to FIG. A. The invention is obviously not limited to differential switches with bipolar fault current for use in single-phase low-voltage distributions, but is adaptable in the same way to polyphase distributions, in particular to three-phase installations, by the use of differential current switches

four-pole defect.

-8-

Claims (5)

  1. Differential fault current switch with time delay, comprising a totalizing current transformer, a polarized trip unit with magnetic holding and an electric timing element combined - with the trip unit with magnetic holding, characterized in that the trip unit with magnetic holding ( 22) is connected directly to the secondary winding (28) of the totalizing current transformer (24) in series with a capacitor (34), only on two main conductors (P1 Ni) controlled by the differential fault current switch a direct current supply circuit (40) is connected, by means of which the magnetic holding release (22) can be excited in direct current in the same direction as the holding magnet through at least one diode (46, 48) , and that on the secondary winding (28) or on a tertiary winding (60) of the totalizing current transformer (24), an amplifier (54) e st connected, which can control after expiration of a time period fixed by a timing element (56), an electronic switching circuit (50) bypassing the terminals of   output of the DC power supply circuit (40).   2. Differential fault current switch according to claim 1, characterized in that the circuit   switching electronics (50) consists of a thyristor.   3. Differential fault current switch according to   Claims 1 or 2, characterized in that the element of   time delay (56) consists of an RC circuit.   4. Differential fault current switch according to   one of the preceding claims, characterized in that   that the DC power supply circuit (40) comprises at least one diode (68) with a capacitor thereafter smoothing (70).   5. Differential fault current switch according to claim 4, characterized in that a Zener diode (72)   is connected in parallel to the smoothing capacitor.