SK15162003A3 - Circuit arrangement for a residual-current circuit breaker - Google Patents

Abstract

The invention relates to a circuit arrangement for a residual-current circuit breaker comprising a detection device (10) for a residual current in a supply network (12). A conditioning circuit (20) for the residual current is preferably connected downstream of the detection device. The arrangement also comprises an energy storage circuit (30), which is charged in accordance with the detected residual current, a trigger (40), which monitors the charged state of the energy storage circuit (30) and a contact unit (50) for generating a tripping voltage pulse for a tripping element (60) for an isolator of at least one consumer that is fed by the supply network (12). According to the invention, the trigger (40) causes the contact unit (50) to generate a tripping voltage pulse for the tripping element (60), once the energy storage circuit (30) has attained a predetermined charged state, (set charged state) and the circuit arrangement is provided with a second trigger (40'), which blocks the contact unit (50) until the energy storage circuit (30) has attained an additional predetermined charged state, (minimum charged state).

Description

Circuit layout for leakage circuit breaker

Technical field

The invention relates to circuit arrangement for a leakage circuit breaker comprising a leakage current detection device in a power supply network, in particular a leakage current conditioning circuit, an energy storage circuit that is charged as a function of the leakage current detected, a threshold switch which monitors the state of charge of the energy storage circuit and a switching element for generating a trigger voltage pulse for the disconnector trigger of at least one mains-powered consumer, and a threshold switch upon reaching a predetermined charge state of the energy storage circuit prompts the switching element generating a trigger voltage pulse.

BACKGROUND OF THE INVENTION

A leakage circuit breaker or leakage current monitoring switch of the kind mentioned is known, for example, from DE 41 12 169 A1 and DE 44 29 007. In these circuit arrangements, the first threshold switch is usually formed by a Zener diode and the switching element is an electronic switch, for example a thyristor.

Due to the increasing load on the power supply systems by various disturbances, such as the water currents of upstream luminaires, switched mains parts, as well as motor frequency converters or thunderstorms, there is a problem with leakage circuit breakers that often even small disturbances can lead to unwanted tripping of the circuit breaker against leakage current.

Especially in the case of switching elements formed by thyristors, in this context, an inadvertent tripping of the circuit breaker against leakage current often occurs by switching on the switching element via the head. It is also possible that the energy storage circuit discharges after an unwanted premature switching on of the switching element by means of the trigger element without being disconnected from the mains. This may result in the circuit breaker not tripping. Do not discuss the issue in the above-mentioned documents.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an arrangement of leakage circuit breakers at the beginning of the aforementioned type, which eliminates the disadvantages described and allows to suppress as much as possible the incorrect start or failure of the leakage circuit breaker or increase interference immunity.

According to the invention, this is achieved by providing a second threshold value switch which blocks the switching element until a further predetermined state of charge (minimum state of charge) of the energy storage circuit is reached.

Interferences below the threshold given by another predetermined charge state can no longer result in the triggering of the switching element. In this way, a faulty tripping of the circuit breaker against leakage current can be safely prevented.

In order to prevent the leakage circuit breaker from tripping, in a further embodiment of the invention, it can be ensured that the additional predetermined state of charge (minimum state of charge) of the energy storage circuit lies above the state of charge required for the trigger element to function.

According to a further variant of the invention, it can be ensured that the second threshold value switch is formed by a self-guided, field-weakened gate-type transistor (J4) with channel N. This provides a particularly simple and functionally reliable circuit arrangement.

According to a further variant of the invention, it can be ensured that the field-controlled transistor (J4) is integrated with other semiconductor elements on a single chip. This allows integration into a particularly small and space-saving wiring.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail with reference to the accompanying drawings, in which particularly preferred exemplary embodiments are shown. It states:

1 shows a block diagram of a known leakage circuit breaker;

2 shows a simplified block diagram of a leakage circuit breaker according to the invention with a second switch 4 (P of the threshold value; FIG.

3 shows a circuit arrangement of an embodiment of a leakage circuit breaker according to the invention;

4 shows a further simplified circuit arrangement of an embodiment of a leakage circuit breaker according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The leakage circuit breakers, shortly called FI circuit breakers, contain a protective monitoring and reporting circuit breaker. FI switches generally monitor electrical installations and disconnect the grid connection before leakage current coming from the grid and flowing into the ground becomes dangerous to humans. For this purpose, FI switches are installed in such a way that leakage currents above a certain value lead to disconnection or disconnection of the supply network. Rated leakage current Ι _Δη , ie. the maximum tolerable leakage current is usually about 30 mA, with the FI switch disconnecting only after a certain tolerance time of about 10 ms. These values result from the magnitude of currents and frequencies dangerous to humans that can lead to cardiac fibrillation.

Figure 1 shows the modular structure of the known circuit breaker FI in the form of a block diagram.

For installations without leakage current, ie. without leakage current to the ground, the operating current flows from the mains to the appliance and from there again to the mains. When a leakage current is discharged into the ground in the event of a fault, the current flowing to the appliance is greater than that flowing back. This leakage current can be dangerous to the earth when flowing through a person into the ground or lead to serious injury. The difference current between the effluent and the effluent, which corresponds to the effluent, is determined by detecting device T.

The device consists of a summation current transformer which comprises a magnetic core, for example an annular core. The individual conductors that form the primary winding of the summation current transformer may be routed in one or more turns around the summation current transformer ring or, at a corresponding magnitude of the expected current flows, simply pass through the summation current transformer ring. The current difference in the conductors forming the primary winding creates a magnetic field in the secondary winding wound equally around the annular core of the summation current transformer, which induces a voltage in the secondary winding.

The detection device 10 or the summation current transformer thus detects the differential current or leakage current that is generated and converts this current into a voltage for further processing.

The output voltage of the detecting device 10 is generally applied to the conditioning circuit 20. This is advantageous so that the FI switches can safely detect different types of leakage current, such as pulsating DC leakage currents and AC leakage currents and DC leakage currents. The adjustment circuit 20 is therefore different in each case and is adapted for the particular use of the circuit breaker FI.

The conditioning circuit 20 is preferably a simple rectifier circuit that directs the leakage AC current.

The current produced by the voltage difference lying on the detection device 10 or the conditioning circuit 20 is fed further to the energy storage circuit 30. When a leakage current is generated, the energy storage circuit 30 is charged. The state of charge depends on the magnitude and duration of the leakage current. Such energy storage circuits 30 are mainly used in delay switches FI.

However, individual leakage currents whose duration is below the tolerance time preferably do not accumulate a slow charge of the energy storage circuit 30. This ensures that only a leakage current greater than the rated leakage current and lasting longer than the tolerance time leads to a charge of the energy storage circuit. 30 and, further, to trigger the FI switch.

The energy storage circuit 30 may be formed, for example, by a capacitor or an R-C member that discharges separately.

The state of charge of the energy storage circuit 30 is monitored by the threshold switch 40. Upon reaching a certain charging state, hereinafter referred to as the desired state of charge of the electrical storage circuit 30, this threshold switch 40 sells a control pulse to the downstream switching element 50, which further leads to the disconnection of the switch FI.

For this so-called. the normal triggering of the circuit breaker FI is a predetermined voltage setpoint applied to the energy storage circuit 30, which is determined by the rated leakage current Ι _Δη and the tolerance time.

The threshold switch 40 is preferably formed by a Zener diode having a very precisely defined breakdown voltage.

The control pulse transmitted by the threshold switch 40 serves to control the switching element 50.

This element acts as a power switch and generates a trigger voltage pulse for trigger element 60. In the case of a mains voltage-dependent switch FI, trigger element 60 uses, for example, the energy accumulated in the energy storage circuit 30 to generate a trigger voltage pulse.

The switching element 50 is generally formed by an electronic switch. The electronic switch is preferably a self-amplifying switching element, for example a thyristor. In addition to thyristors, other elements such as transistors or electronic relays can also be used.

The thyristors switch separately at typical switching voltages. For normal triggering of the switch FI, a separate thyristor switch-on is not used, but a control signal coming from the first threshold switch 40 which leads to the switching of the switching element 50.

The trigger voltage pulse generated by the switching element 50 is applied to the trigger 60, which disconnects the appliance from the mains.

The trigger element 60 may be designed as a permanent magnet trigger (PMA). In this case, the coil moves an anchor which disconnects the appliance from the mains 12 by means of a switch lock and a contact device.

Thus, in the case of normal start-up, the following picture follows. The leakage current having a minimum rated leakage current and flowing longer than the tolerance time will cause the energy storage circuit 30 to charge up to the desired charge state. When the desired charging state is reached, the threshold switch 40 acts on the switching element 50 with a control pulse which causes the element to be switched on or connected. As a result, the trigger trigger pulse generated further leads to the trigger element 60 which disconnects the appliance from the mains.

The circuit arrangement according to the invention can be used for mains-voltage-independent as well as line-voltage-dependent FI switches. However, for a mains voltage-independent switch FI, the energy accumulated in the energy storage circuit 30 must be sufficient to allow safe disconnection from the mains by the trigger 60. Thus, the energy storage circuit 30 and the threshold switch 40 should be brought into line with the rated leakage current. as well as the trigger element 60.

The arrangement outlined in Figure 1 has the disadvantage that certain necessary voltage peaks from the mains under energized voltage may not result in the charging of the energy storage circuit 30 to the desired charge value, but may result in the switching element 50 or thyristor being energized. switch on through the head). The disturbances may come through a network, i.e. own. leakage-induced normal triggering or, on the other hand, from the trigger element 60 or the permanent magnet actuator (PMA).

This unintentional closing of the switching element 50 generally results in disconnection of the appliance from the mains by the trigger element 60. This erroneous triggering of the circuit breaker FI is unwanted.

It is also possible that the switching element 50 generates a trigger voltage pulse, but this is not sufficient to cause the trigger 60 to disconnect from the mains. This is particularly possible with mains-independent FI switches. The FI switch does not start. At the same time, however, further charging of the energy storage circuit 30 is prevented because the opening of the switching element 50 follows a steady flow of current from the energy storage circuit 30 through the trigger element 60. It is possible that the FI switch does not start in the following procedure even with leakage current above rated leakage current . This failure can lead to endangering people.

The core of the invention is to provide measures to prevent disturbances from triggering the switching element 50 below a predetermined threshold. This is achieved by providing a second threshold value switch 40 '.

Figure 2 shows the modular structure of a known FI switch in the form of a block diagram that illustrates the difference with known FI switches.

According to the invention, in the embodiment shown of the switching element 50, a second threshold switch 40 'is provided upstream. The second threshold switch 40 'blocks or locks the switching element 50 and releases it only after a certain state of charge of the energy storage circuit 30, hereinafter referred to as the minimum charge state, has been reached.

For this, the switching element 50 must have a second control input, by means of which the switching element 50 can be adjusted in such a way that interconnection is prevented. This may for example be the second control input of the thyristor tetrode.

With the circuit arrangement according to the invention, it is possible to lay a threshold or a minimum state of charge so that a number of incoming erroneous starts are suppressed. This provides improved interference immunity. To achieve maximum immunity to interference, the minimum charge state can be dimensioned according to the use of the switch F1.

Naturally, the minimum state of charge must not be chosen greater than the desired state of charge, otherwise normal start-up would be avoided.

As the threshold or minimum state of charge, for example, half of the set state of the charge state corresponding to the leakage current with the size of the nominal leakage current can be selected. With this default value, more than half of typical errors or disturbances on the FI switch in the power supply networks can be suppressed.

Preferably, the minimum state of charge should be selected such that when just the minimum state of charge is applied to the output of the energy storage circuit 30, the energy accumulated in the energy storage circuit 30 is sufficient to allow the trigger 60 to be disconnected from the grid. This can safely prevent the case of non-starting described above.

Figure 3 shows the circuit arrangement elements of the circuit breaker FI according to the invention. The circuit arrangement modules 10, 20, 30, 40, 50 and 60 correspond to the known delay switch FI.

Tx 1 denotes the summation current transformer on the supply network 12. The summation current transformer Tx1 constitutes a detection device 10 in accordance with the invention. The leakage current is detected by the summation current transformer Txl, but also in the arrangement of the connections there are also special disturbances.

After the secondary winding of the summation current transformer there is a modification circuit 20.

The conditioning circuitry 20 first includes a resistor R1 which serves to damp the annular wound cores with too high a secondary voltage.

The capacitor C1 serves to adapt to the secondary inductance. This makes it possible to tune the resonance of the conditioning circuit 20 to 50 Hz, or to the mains frequency.

The conditioning circuit 20 further comprises a voltage doubling guide. The bridge bridge with Delon circuit is formed by diodes D1 and D2 and capacitors C2 and C3.

Zener diode D3 is placed behind the rectifier bridge circuit as a voltage reference element. This Zener diode D3 limits the voltage of the conditioning circuit 20. This prevents the accumulator capacitor C4 to be charged too quickly at higher leakage currents (from 5χΙ _Δη ).

An energy storage circuit 30 is further downstream of the conditioning circuit 20. This circuit in the embodiment shown comprises a constant current source, which is formed by a field-effect gate transistor J1 (FET) and a resistor R2. Resistor R2 is used to set the desired constant current. The field-effect transistor (FET) is operated in the back-up area. The constant current source allows the current to flow, which depends only to a small extent on the applied voltage. In this way, the storage capacitor is only gradually charged and the start-up behavior is delayed. However, it is not necessary to provide a constant current source.

The core of the energy storage circuit 30 is comprised of a storage capacitor C4, which is charged when leakage current is generated.

The accumulator capacitor C4 is discharged by means of a resistor R3. As a result, short leakage currents whose duration is below the tolerance time of the switch F1 do not lead to a continuous charging of the energy storage circuit 30.

The first threshold switch 40, which in a known manner monitors the voltage at the output of the energy storage circuit 30, is formed by a Zener diode D4 connected in the reverse direction. If the voltage applied to the Zener diode D4 reaches its breakdown voltage, the first control input GK of the switching element 50 will be coupled to the output of the energy storage circuit 30 by the Zener diode D4.

The resistor R8 connected in series with the Zener diode D4 serves to set the voltage connected to the Zener diode D4 and thus to set the desired charge state.

Since the set state of the adjustable breakdown voltage 30 of the adjustable diode Zener diode D4 and the resistor R8, the points P3 and P4 are connected by a resistor R5. Thereby, the threshold switch 40 produces a control pulse for the first control input GK of the switching element 50.

In the illustrated embodiment, the switching element 50 or the electronic switch is formed by a thyristor replacement circuit with anode lead A and cathode lead K, as well as anode lead GA and anode lead GK. The thyristor replacement circuit further comprises a pnp transistor Q1 and a npn transistor Q2. whose collectors and bases are alternately connected, as well as the resistance R6.

The anode lead A or the emitter pnp of the transistor Q1 is at the output potential of the energy storage circuit 30. The cathode lead K is connected to the trigger element 60 ..

The thyristor replacement circuit serves as an electronic switch. In normal network operation, i. in the absence of leakage current, the thyristor is blocked, i. that no current can flow between the anode lead A and the cathode lead K and further through the trigger element 60.

Upon reaching the desired charge state, the cathode-side GK supply acts on the cathode side via a energized Zener diode D4 to trigger a control pulse that leads to a thyristor replacement circuit.

The cathode-side GK supply determines the base emitter voltage npn of transistor Q2 through a resistor R5. Thus, a positive supply voltage at the cathode side of the GK leads to the setting of the npn transistor Q2. This causes transistors 01 and Q2 to adjust to one another and to be regulated within a short period of time due to interaction.

The thyristor replacement circuit also remains conductive after the control pulse.

The switching element 50 can naturally consist instead of two bipolar transistors, also a single thyristor tetrode, with an anode-side gate and a cathode-side gate, which is made as a separate component. This tetrode can be connected or disconnected by the control leads.

The capacitor C7 is not an essential part of the switching element 50. However, it constitutes an additional protection capacity against erroneous triggering, since the interference emanating from the trigger element 60 or the permanent magnet actuator (PMA) is attenuated. Particularly at a minimum state of charge substantially below the setpoint, the capacitor C7 is advantageous. The second threshold switch 40 'blocks the switching element 50 until the minimum state of charge of the energy storage circuit 30 is reached, which means that there is no danger of the circuit breaker FI not tripping by switching the switching element 50 on incorrectly. state of charge and below the desired state of charge. These erroneous starts are far suppressed by capacitor C7.

According to the invention, the second control lead GA of the switching element 50 is connected to the second threshold switch 40 '.

The second threshold value switch 40 'is formed by a field-effect transistor J4 with a gate inlet G, a collector inlet D and an emitter inlet S.

As a field-controlled transistor J4, a stand-alone N-channel field-controlled gate transistor (NJFET) is used. This transistor is conductive without connection of control voltage U _G. The connection between the collector lead D and the emitter lead S will be highly resistive only after a negative control voltage U _G s> which is greater than the manufacturer-dependent threshold voltage (U _TH ) is connected. A typical threshold voltage value is at 5 V.

In the present embodiment, the collector D supply of the field-controlled transistor J4 is coupled to the pnp transistor Q1.

The supply of the field-controlled transistor J4 is coupled to zero potential 0 and the emitter supply S is connected to the output of the energy storage circuit 30. The voltage at the output of the energy storage circuit 30 thus serves as a control voltage U _G sV. threshold voltage U _TH at the output of the energy storage circuit 3.0. Thereby, the emitter S and the collector D of the field-controlled transistor J4 are short-circuited, and thus also the base and emitter pnp of transistor O1. Thus, the pnp transistor Q1 is blocked, and hence the entire thyristor replacement circuit. In this way, incorrect switching of the switching element 50 is reliably prevented.

When the charge state of the energy storage circuit 30, and hence the potential at the emitter supply, increases - as is the case of the leakage current to be disconnected - the field-controlled transistor J4 is set to a negative voltage against the emitter. When the threshold voltage is reached, the transistor J4 is controlled by a high-resistance field.

As a result, the bases and emitter pnp of transistor Q1 are no longer short-circuited, and transistors Q1 and Q2 are released to connect the trigger voltage pulse to the trigger element 60.

Thus, with given circuit arrangement values, the supply voltage pulses remaining at the supply G of the field-controlled transistor J4 below the threshold voltage U _T h do not lead to the switching of the thyristor or the switching element 50. By varying the semiconductor physical quantities the interference voltage threshold can be set arbitrarily close to the rated leakage current by the arrangement of the circuits.

Instead of a single-headed N-channel field effect transistor J4 (N-JFET), other transistors such as a P-channel (P-JFET) field-type gate transistor or self-conducting MOSFET N or P transistors are also possible. controlled by different polarity. The advantage of these components is that the MOSFETs and the field-controlled gate transistors are substantially symmetrical, i. the collector and emitter may be interchanged.

In order to make the circuit arrangement as small as possible, the field-controlled transistor, together with other semiconductor components, is preferably integrated on a single chip.

However, as shown in Figure 4 by block 42 ', as an alternative to field-effect transistor J4, a bipolar transistor, thyristor, voltage-controlled resistor, or relay can be used, which can be controlled by a voltage divider, splitter amplifier or comparator symbolized by block 4'.

It is essential here that the voltage connected to the energy storage circuit 30 is monitored by the second threshold switch 401 and the switching element 50 is released when the minimum charge state is reached.

Claims (4)

PATENT CLAIMS 1. A leakage circuit breaker circuit arrangement comprising: - a leakage current detection device (10) in the supply network (12), downstream of which a leakage current conditioning circuit (20) is connected in particular, - an energy storage circuit (30) which is charged depending on the detected leakage current, - a threshold switch (40) that monitors the charge state of the energy storage circuit (30), - a switching element (50) for generating a trigger voltage pulse for the trigger element (60) for the disconnector of at least one consumer powered from the mains (12), wherein the threshold switch (40) when reaching a predetermined charge state The circuit (30) provides a trigger for generating a trigger voltage pulse for the trigger element (60), characterized in that: - is equipped with a second threshold switch (40 '), - which blocks the switching element (50) until a further predetermined state of charge (minimum state of charge) of the energy storage circuit (30) is reached. Circuit arrangement according to claim 1, characterized in that another predetermined state of charge (minimum state of charge) of the energy storage circuit (30) lies above the necessary state of charge for the operation of the trigger element (60). Circuit arrangement according to claims 1 and 2, characterized in that the second threshold value switch (40 ') is formed by a self-conducting, field-controlled, depleted-type gate transistor (J4) with channel N. Circuit arrangement according to claim 1, 2 and 3, characterized in that the field-controlled transistor (J4), together with other semiconductor elements, is integrated on a single chip.