IL157637A

IL157637A - Circuit arrangement for a residual-current circuit breaker

Info

Publication number: IL157637A
Application number: IL157637A
Authority: IL
Original assignee: Moeller Gebaudeautomation Gmbh
Priority date: 2001-06-12
Filing date: 2003-08-28
Publication date: 2008-11-26
Also published as: PL199098B1; AT410735B; EE200300479A; CZ20033308A3; HU226289B1; DE50204331D1; SK287930B6; WO2002101901A3; AU2002348706B2; CN1320716C; HUP0400190A2; SK15162003A3; NO333802B1; PL366764A1; ATA9092001A; ES2246411T3; EE04653B1; EP1399998A2; CN1515058A; EP1399998B1

Description

■>» vn on t»>i>tt *m»*) iiav iu»« Circuit Arrangement For A Residual-Current Circuit Breaker Moeller Gebaudeautomation KG A circuit arrangement for a residual-current circuit breaker The invention relates to a circuit arrangement for a residual-current circuit breaker comprising a detection device for a residual current in a supply network, which detection device is provided in outgoing circuit with a conditioning circuit for the residual current, an energy storage circuit which is charged in accordance with the detected residual current, a trigger which monitors the charged state of the energy storage circuit, and a contact unit for generating a tripping voltage pulse for a tripping element for an isolator of at least one consumer that is fed by the supply network, with the trigger causing the contact unit to generate a tripping voltage pulse for the tripping element once the energy storage circuit has attained a predetermined charged state (set charged state).

Residual-current circuit breakers or residual-current monitoring switches of the mentioned kind are known from DE 41 12 169 Al and DE 44 29 007 for example. In such circuit arrangements, the first-i'trigger is formed by a Zener diode and the contact unit by an electronic switch, e.g. a thyristor.

As a result of the increasing strain on electric supply networks with different disturbances such as the leakage currents of preheat ballasts, switched-mode power supplies as well as frequency converters of motor drives or effects from lightning surges, the problem arises in connection with the use of residual-current circuit breakers that even minor disturbances can lead to the unintended triggering of the residual-current circuit breaker.

Especially in the case of contact units formed as thyristors, it frequently occurs in this connection that the unintended triggering of the residual-current circuit breaker occurs through overhead triggering of the contact unit. It is also possible that the energy storage circuit will discharge after the unintended premature triggering of the contact unit via the tripping element. This can lead to the non-triggering of the residual-current circuit breaker. This problem has not been mentioned in the documents as cited above.

It is the object of the present invention to provide a circuit arrangement for residual-current circuit breakers of the kind mentioned above which eliminates the disadvantages as described above and allows suppressing a false tripping or non-tripping of the residual-current circuit breaker in the best possible way and to generally achieve an increase in the immunity to disturbances.

This is achieved in accordance with the invention in such a way that a second trigger is provided which blocks the contact unit until the energy storage circuit has attained an additional predetermined charged state (minimum charged state).

Interference effects below the threshold given by the further predetermined charged state can thus no longer lead to the tripping of the contact unit. The false tripping of the residual-current circuit breaker can thus be prevented securely.

In order to prevent the non-tripping of the residual-current circuit breaker, it may be provided in a further embodiment of the invention that the further predetermined charged state (minimum charged state) of the energy storage circuit lies over the charged state required for the functioning of the tripping element.

According to a further variant of the invention it can be provided that the second trigger is formed by a self-conducting N-channel depletion-type junction field-effect transistor (J4). An especially simple and functionally reliable circuit arrangement is thus obtained.

According to a further embodiment of the invention it can be provided that the field-effect transistor (J4) is integrated on a chip together with other semi-conductor elements. This allows the integration to form especially small and compact circuits.

The invention is now described in closer detail by reference to especially preferable embodiments shown in the enclosed drawings, wherein: Fig. 1 shows a block diagram of a known residual-current circuit breaker; Fig. 2 shows a simplified block diagram of a residual-current circuit breaker in accordance with the invention with a second trigger 40'; Fig. 3 shows a circuit arrangement of an embodiment of a residual-current circuit breaker in accordance with the invention; Fig. 4 shows a simplified further circuit arrangement of an embodiment of a residual-current circuit breaker in accordance with the invention.

Residual-current circuit breakers (also known as leakage-current mcbs) comprise protective circuit breakers, monitoring switches and alarm switches. Generally, residual-current circuit breakers monitor electrical installations and cut off the connection to the mains network before any current flowing from the mains and to earth can become hazardous for humans. For this purpose, residual-current circuit breakers are designed in such a way that residual currents above a certain value lead to the disconnection or breaking of the supply network. The rated residual current ΙΔη, i.e. the maximum tolerable residual current is usually approx. 30 mA, with the residual-current circuit breaker switching off only after a tolerance period of approx. 10 ms.

These values are obtained from amperages and frequencies which are dangerous for humans and can lead to cardiac flutter.

Fig. 1 shows the modular arrangement of a known residual-current circuit breaker in the form of a block diagram.

In a faultless installation, i.e. without a residual current discharged to earth, the service current flows from the mains to the consumer and from there back to the mains again. If as a result of a defect a residual current is discharged to earth, the current flowing towards the consumer is higher by this amount than the current flowing back. This residual current can be hazardous and lead to serious injuries when it flows through a human.jThe differential current between the current flowing back and forth which corresponds to the residual current is recognized by the detection apparatus 10.

It consists of a summation current transformer which comprises a magnet core such as an annular core. The individual conductors which form the primary windings of the summation current transformer can be guided in one or several windings about the ring of the summation current transformer or, in the case of a respective strength of the expected flows of current, simply through the ring of the summation current transformer. The differential current in the conductors forming the primary windings produces a magnetic field in the secondary windings of the summation current transformer which are also wound around the annular ririg, which magnetic field induces a voltage in the secondary winding.

The detection apparatus 10 or the summation current transformer thus detects the occurring differential current or residual current and converts the same into a voltage for further processing.

The voltage applied to the output of the detection apparatus 10 is generally supplied to a conditioning circuit 20. This is advantageous in order to enable the secure recognition of different types of residual current, e.g. pulsating DC residual currents and AC residual currents and residual currents with DC components, by the residual-current circuit breaker. The conditioning circuit 20 is therefore designed differently on a case to case basis and adjusted to the special application of the residual-current circuit breaker.

The conditioning circuit 20 preferably concerns a simple rectifier circuit which rectifies the AC residual current.

The current produced by the voltage difference applied to the detection apparatus 10 and the conditioning circuit 20 is forwarded to an energy storage circuit 30. The energy storage circuit 30 is charged when a residual current occurs. The charged state depends on the strength and the ' Ί/Ι ίΗ duration of the residual current. Such energy storage circuits 30 are especially used in the case of delayed residual-current circuit breakers.

Individual residual currents whose duration lies beneath the tolerance period preferably do not lead to the accumulated slow charging of the energy storage circuit 30. This ensures that only a residual current larger than the rated residual current and longer than the tolerance period will lead to the charging of the energy storage circuit 30 and subsequently to the tripping of the residual-current circuit breaker.

The energy storage circuit 30 can be formed by a capacitor or by an RC element for example which discharges automatically.

The charged state of the energy storage circuit 30 is monitored by a trigger 40. On reaching a specific charged state which is designated below as set charged state of the energy storage circuit 30, said trigger 40 forwards a control pulse to the downstream contact unit 50, which subsequently leads to the cut-off of the residual-current circuit breaker.

For this so-called normal tripping of the residual-current circuit breaker 30, a set charged state is predetermined for the voltage applied to the energy storage circuit 30, which set charged state is adjusted to the rated residual current ΙΛπ and the tolerance period.

The trigger 40 is preferably formed by a Zener diode which has a precisely defined breakdown voltage.

The control pulse as emitted by the trigger 40 is used for controlling the contact unit 50.

It acts as a power circuit breaker and produces a tripping voltage pulse for the tripping element 60. In the case of a residual-current circuit breaker that is functionally independent of line voltage, the contact unit 50 uses the energy stored in the energy storage circuit 30 in order to generate the tripping voltage pulse.

The contact unit 50 is generally formed by an electronic switch. This electronic switch is preferably a self-amplifying contact unit, e.g. a thyristor. In addition to thyristors, other components such as transistors or electronic relays can be used.

Thyristors fire at a typical gate trigger voltage automatically. It is not the gate trigger voltage of the thyristor that is used for the normal tripping of the residual-current circuit breaker. Instead, the control signal coming from the first trigger 40 is used, which leads to the conduction-through of the contact unit 50.

The voltage tripping pulse as generated by the contact unit 50 is forwarded to a tripping element 60 which severs the consumer from the mains.

The tripping element 60 can be arranged as a permanent magnet tripping element. An armature is moved by means of a coil, which armature performs the severing of the consumer from the supply network 12 by means of a breaker mechanism and a contact apparatus.

The following picture is obtained for normal tripping. A residual current which at least has the strength of the rated residual current and flows over a longer period than the tolerance period produces the charging of the energy storage circuit 30 until the set charged state. On reaching the set charged state the trigger 40 sends a control pulse to the contact unit 50 which makes the same fire or contact-through. The thus generated tripping voltage pulse is forwarded to the tripping element 60 which severs the consumer from the mains.

The circuit arrangement in accordance with the invention can be used for residual-current circuit breakers which are dependent on or independent of line voltage. In the case of residual-current circuit breakers which are independent of line voltage the energy stored in the energy storage circuit 30 must be sufficient in order to allow a secure severing from the mains by the tripping element 60. Energy storage circuit 30 and the trigger 40 must thus be adjusted both to the rated residual current as well as the tripping element 60.

The arrangement as explained in fig. 1 comes with the disadvantage that certain unavoidable peak voltages below the gate trigger voltage from the mains network will not lead to the charging of the energy storage circuit 30 to the set charged state but to the firing of the contact unit 50 or the thyristor (so-called overhead firing). The disturbances can come through the mains network, through the own residual current induced by the normal tripping for example or from the other side, namely the tripping element 60 or the permanent magnet tripping element.

The unintended firing of the contact unit 50 generally leads to the severing of the consumer from the mains network by the tripping element 60. This false tripping of the residual-current circuit breaker is undesirable.

It is also possible that the contact unit 50 generates a tripping voltage pulse which is not sufficient in order to effect the severing from the mains network by the tripping element 60. This is especially possible in the case of residual-current circuit breakers which are independent on line voltage. The residual-current circuit breaker thus does not trip. At the same time, a further charging of the energy storage circuit 30 is prevented because there is a continuous flow of current from the energy storage circuit 30 through the tripping element 60 by the opening of the contact unit 50. It is thus possible that the residual-current circuit breaker does not trip subsequently even in a residual current over the rated residual current. Humans can be endangered by this failure to trip.

The core of the invention is that measures are provided preventing that disturbances below a predetermined threshold can lead to the tripping of the contact unit 50. This is achieved by providing a second trigger 40'.

Fig. 2 shows the modular arrangement of a known residual-current circuit breaker in the form of a block diagram which explains the difference over conventional residual-current circuit breakers.

In accordance with the invention, the contact unit 50 is provided upstream with a second trigger 40' in the embodiment as shown in fig. 2. The second trigger 40' blocks or locks out the contact unit 50 and releases the same only after reaching a specific charged state of the energy storage circuit 30, which state is designated below as minimum charged state.

For this purpose the contact unit 50 must comprise a second control input via which the contact unit 50 can be controlled in such a way that switching through is prevented. This can be the second control input of a tetrode thyristor.

The circuit arrangement in accordance with the invention allows placing the threshold or the minimum charged state in such a way that the majority of the occurring false trippings is suppressed. An improved immunity to disturbances is thus achieved. In order to achieve a maximum immunity from disturbances, the minimum charged state can be dimensioned according to the application of the residual-current circuit breaker.

It is obvious that the minimum charged state must not be chosen higher than the set charged state because otherwise the normal tripping would be prevented.

Half the set charged state which corresponds to a residual current in the level of the rated residual current can be chosen as threshold or minimum charged state. With this default it is possible to suppress more than half the typical errors or disturbances on the residual-current circuit breaker in supply networks.

Preferably, the minimum charged state must be chosen in such a way that in the case of application of this minimum charged state on the output of the energy storage circuit 30 the energy stored in the energy storage circuit 30 is sufficient in order to allow the tripping element 30 the severing from the mains network. The case of the failure to trip as explained above can thus securely be prevented.

Fig. 3 shows the elements of the circuit arrangement of a residual-current circuit breaker in accordance with the invention. The modules 10, 20, 30, 40, 50 and 60 of the circuit arrangement correspond to a known delayed residual-current circuit breaker.

A summation current transformer on the supply network 12 is designated with reference numeral T l . The summation current transformer Txl forms the detection apparatus 10 within the terms of the invention. The residual current is detected through the summation current transformer Txl . Other disturbances also reach the circuit arrangement.

The conditioning circuit 20 is connected in outgoing circuit with the secondary winding of the summation current transformer.

The conditioning circuit 20 comprises at first a resistor Rl which is used for damping annular strip-wound cores with too high secondary voltage.

The capacitor CI is used for adjustment to the secondary inductivity. This allows obtaining a resonant adjustment of the conditioning circuit 20 to 50 Hz or to the mains frequency.

The conditioning circuit 20 further comprises a rectification with voltage doubling. The rectifier bridge circuit with Delon rectifier is formed by the diodes Dl and D2 and the capacitors C2 and C3.

The rectifier bridge circuit is provided in outgoing circuit with a Zener diode D3 as voltage reference element. The voltage of the conditioning circuit 20 is limited with this Zener diode D3. It prevents a too rapid charging of the storage capacitor C4 connected in outgoing circuit in the case of higher residual currents (from 5 x ΙΛΠ).

An energy storage circuit 30 is provided in outgoing circuit of the conditioning circuit 20. It comprises in the illustrated embodiment a constant-current source which is formed by the depletion-type junction FET Jl and the resistor R2. The resistor R2 is used for setting the desired constant current. The FET is operated in the cut-off region. The constant current source allows a current to flow which depends only to a very low extent on the applied voltage. In this way the storage capacitor is charged only gradually and a time-delay in the tripping behavior is obtained. The provision of a constant current source is not mandatory, however.

The core of the energy storage circuit 30 consists of the storage capacitor C4 which is charged during the occurrence of a residual current.

The storage capacitor C4 discharges intentionally through the resistor R3. As a result, short residual currents whose duration is below the tolerance period of the residual-current circuit breaker will not lead to a continuous charging of the energy storage circuit 30.

The first trigger 40 which monitors the voltage at the output of the energy storage circuit 30 in the known manner is formed by a Zener diode D4 which is switched in the blocking direction. Once the voltage applied to the Zener diode D4 reaches its breakdown voltage, the first control input GK of the contact unit 50 is connected with the output of the energy storage circuit 30 by the Zener diode D4.

The resistor R8 which is connected in series with the Zener diode D4 is used for setting the voltage applied to the Zener diode D4 and is thus used for setting the set charged state.

From the set charged state of the energy storage circuit 30 which is adjustable by the breakdown voltage of the Zener diode D4 and the resistor R8, the points P3 and P4 are connected through the resistor R5. A control pulse is produced on the first control input GK of the contact unit 50 by the trigger 40.

The contact unit 50 or the electric switch is formed in the illustrated embodiment by an alternate thyristor circuit with an anode connection A and a cathode connection K as well as a gate connection GA on the anode side and a gate connection GK on the cathode side. The alternate thyristor circuit contains a pnp transistor Ql and an npn transistor Q2 whose collectors and bases are alternatingly mutually connected, as well as a resistor R6.

The anode connection A or the emitter of the pnp transistor Ql lies on the potential of the output of the energy storage circuit 30. The cathode connection K is connected with the tripping element 60.

The alternate thyristor circuit is used as an electronic switch. In normal operation of the mains network, i.e. in the case that there is no residual current, the thyristor is blocked, i.e. no current can flow between the anode connection A and the cathode connection K and further via the tripping element 60.

On reaching the set charged state, the gate connection GK on the cathode side is subjected to a control pulse via the firing Zener diode D4, which pulse leads to the firing of the alternate thyristor circuit.

The gate connection GK on the cathode side determines the emitter-base voltage of the npn transistor Q2 through the resistor R5. A positive voltage on the cathode-side gate connection GK thus leads to the triggering of the npn transistor Q2. This ensures that the transistors Ql and Q2 mutually trigger each other and are forced to trip fully within a very short time period through the mutual influence.

The alternate thyristor circuit remains conductive even after the control pulse.

Instead of two bipolar transistors, the contact unit 50 can also consist of a tetrode thyristor with a gate on the anode and cathode side which is configured as a separate component. It can be activated and deactivated via the gates. The capacitor C7 is a component that is not absolutely necessary for the contact unit 50. It forms an additional protective capacity against false tripping because disturbances originating from the tripping element 60 or the permanent magnet tripping element are dampened. The provision of the capacitor C7 is especially advantageous in the case of a minimum charged state which is considerably below the set charged state. Although the second trigger 40' blocks the contact unit 50 until reaching the minimum charged state of the energy storage circuit 30 (which is why there is no likelihood of non-tripping of the residual-current circuit breaker by a false firing of the contact unit 50), a false tripping of the residual-current circuit breaker can still occur at values above the minimum charged state and below the set charged state. These false trippings are substantially suppressed by the capacitor CI.

In accordance with the invention, the second control connection GA of the contact unit 50 is connected with a second trigger 40'.

The second trigger 40' is formed in the circuit as outlined in fig. 3 by a field-effect transistor J4 with gate connection G, drain connection D and source connection S.

A self-conducting N-channel depletion-type junction field-effect transistor (n-JFET) is used as a field-effect transistor J4. It is conductive without the application of a control voltage UGS- The connection between the drain connection D and the source connection S only becomes high-resistance following the application of a negative control voltage UGS which is higher than the manufacturer-dependent threshold voltage (threshold voltage: Uth). A typical value of the threshold voltage is 5 volts.

In the present circuit, the drain connection D of the field-effect transistor J4 is placed on the basis of the pnp transistor Ql .

The gate connection G of the field-effect transistor J4 is connected with the zero potential 0 and the source connection S with the output of the energy storage circuit 30. The voltage applied to the output of the energy storage circuit 30 is thus used as the control voltage UGS- In this arrangement the field-effect transistor J4 is conductive until reaching the threshold voltage Uth on the output of the energy storage circuit 30. As a result, the source S and the drain D of the field-effect transistor J4 and thus the basis and the emitter of the pnp transistor Ql are short-circuited. The pnp transistor Ql is thus blocked and thus also the entire alternate thyristor circuit. A false firing of the contact unit 50 is thus reliably prevented.

When the charged state of the energy storage circuit 30 and thus the potential on the source connection rises (which is the case on the occurrence of a residual current to be switched off), a triggering of the field-effect transistor J4 with negative gate voltage with respect to source is obtained. The field-effect transistor J4 becomes high-resistant on reaching the threshold voltage.

As a result, the base and the emitter of the pnp transistor Ql are no longer short-circuited and the transistors Ql, Q2 are released for switching through the tripping voltage pulse to the tripping element 60.

With the stated values, the voltage pulses which are fed into the circuit arrangement and which remain on the gate connection G of the field-effect transistor J4 below the threshold voltage Uth do not lead to the firing of the thyristor or the contact unit 50. By changing the semi-conductor-physical values of the field-effect transistor J4 it is possible to vary this value within certain limits, so that the circuit arrangement can be used to set the interference voltage threshold in relation to the rated residual current in any desirable way.

Instead of the self-conducting N-channel depletion-type junction field-effect transistor (n-JFET) J4 it is also possible to use other transistors such as P-channel depletion-type (p-JFET) and self-conducting N- or P-MOSFET transistors. They need to be triggered with different polarity, however. The advantage in these components is that MOSFETs and depletion-type junction FETs are principally symmetrical, i.e. drain and source can be switched.

For the production of the smallest possible circuit arrangements, the field-effect transistor is preferably integrated together with the other semi-conductor components on a chip.

A bipolar transistor, thyristor, voltage-controlled resistor or a relay can obviously also be used as an alternative to the field-effect transistor J4 (as indicated in fig. 4 by block 42') which can be triggered by a voltage divider, difference amplifier or comparator, as symbolized by the block 4Γ.

The relevant aspect in this connection is that the voltage applied to the energy storage circuit 30 is monitored by the second trigger 40' and the contact unit 50 is released on reaching the minimum charged state of the contact unit 50.

Claims

1. A circuit arrangement for a residual-current breaker, comprising - a detection apparatus for a residual current in a supply network, which detection apparatus is preferably provided in outgoing circuit * with a conditioning circuit for the residual current; - an energy storage circuit which is charged in accordance with the detected residual current; - a trigger which monitors the charged state of the energy storage circuit, and - a contact unit for generating a tripping voltage pulse for a tripping element for an isolator of at least one consumer that is fed by the supply network, with the trigger causing the contact unit to generate a tripping voltage pulse for the tripping element once the energy storage circuit has attained a predetermined charged state (set charged state), where a second trigger is provided, characterized in that the second trigger blocks the contact unit reaching a further predetermined charged state (minimum charged state) of the energy storage circuit. A circuit arrangement as claimed in claim 1 , characterized in that the further predetermined charged state (minimum charged state) of the energy storage circuit lies above the charged state required for the functioning of the tripping element. A circuit arrangement as claimed in claim 1 and 2, characterized in that the second trigger is formed by a self-conducting N-channel depletion-type junction filed-effect transistor. A circuit arrangement as claimed in claim 1 , 2 and 3, characterized in that the field-effect transistor is integrated on a chip together with the other semi-conductor elements. FOR THE APPLICANT Yitzhak Hess & Partners By: 157637/2 CLAIMS

1. A circuit arrangement for a residual-current breaker, comprising - a detection apparatus for a residual current in a supply network, which detection apparatus is preferably provided in outgoing circuit * with a conditioning circuit for the residual current; - an energy storage circuit which is charged in accordance with the detected residual current; - a trigger which monitors the charged state of the energy storage circuit, and - a contact unit for generating a tripping voltage pulse for a tripping element for an isolator of at least one consumer that is fed by the supply network, with the trigger causing the contact unit to generate a tripping voltage pulse for the tripping element once the energy storage circuit has attained a predetermined charged state (set charged state), where a second trigger is provided, characterized in that the second trigger blocks the contact unit reaching a further predetermined charged state (minimum charged state) of the energy storage circuit. A circuit arrangement as claimed in claim 1 , characterized in that the further predetermined charged state (minimum charged state) of the energy storage circuit lies above the charged state required for the functioning of the tripping element. A circuit arrangement as claimed in claim 1 and 2, characterized in that the second trigger is formed by a self-conducting N-channel depletion-type junction filed-effect transistor. A circuit arrangement as claimed in claim 1 , 2 and 3, characterized in that the field-effect transistor is integrated on a chip together with the other semi-conductor elements. FOR THE APPLICANT Yitzhak Hess & Partners By: