GB2505561A

GB2505561A - Circuit arrangement for an electric protective device

Info

Publication number: GB2505561A
Application number: GB1313092.7A
Authority: GB
Inventors: Andreas Peters; Alexander Hueber; Jean-Mary Martel
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2012-08-29
Filing date: 2013-07-23
Publication date: 2014-03-05
Anticipated expiration: 2033-07-23
Also published as: CN103683182A; ITMI20131400A1; CN103683182B; DE102012215310A1; GB2505561B; DE102012215310B4; GB201313092D0

Abstract

A circuit arrangement 10 for an electric protective device comprises a first electric line 12, an electromagnetic isolating device 16 of a coil and plunger type, a switching device T1, a voltage divider 22 and a control device 18. The control device 18 detects the presence of a fault current and/or an arc in/on the electric line 12 and generates a trigger signal trig that activates the switching device T1. Once activated, the switching device T1, which may be a thyristor, allows a voltage U to be applied to the electromagnetic isolating device 16 and thereby isolates the electric line 12. The control device 18 is embodied to detect a zero crossing of the electric voltage U and to generate a trigger signal trig after a specified time or interval of time after the detected zero crossing, or at a particular voltage phase, so that the overall energy absorbed by the coil is controlled. The limits of a time interval may be calculated from static and/or dynamic force measurements on the electromagnetic isolating device 16 or an operating temperature of the electromagnetic isolating device 16.

Description

Circuit arrangement for an electric protective device The present invention relates to a circuit arrangement for an electric protective device. The present invention further relates to a method for operating an electric protective device.

Electric protective devices are typically used in electric wiring systems. Examples of these include residual current devices, by means of which fault currents to ground can be prevented, and arc fault protective devices, which protect electric wiring from damage due to arcing faults. These protective devices usually need a circuit arrangement containing analog and/or digital components, by means of which a fault current or an arc can be detected. Additionally, a trigger signal for activating an isolating device can be output with a circuit arrangement of this type, which trigger signal causes a circuit or an electric line in the wiring system in which the fault was identified to be electrically isolated from an electric supply device.

Whenever a fault current or an arc occurs, there is a need for an electromechanical coupling by means of which the circuit or line can be isolated from the supply. A very low-cost solution can be achieved by means of an electromagnetic isolating device operating according to the plunger coil principle. An electromagnetic isolating device of this type has a coil by means of which a plunger can be moved. As a result of the plunger being moved, an electric contact can be opened. This reguires a sufficiently high electromagnetic force to be provided by means of the coil so that the electric contacts can be separated by means of the plunger. The coil is usually connected to the electric voltage. Since supply voltages in a range from 50 V to 400 V AC are provided in electric systems for operating the individual components, it must be ensured on the one hand that the electromagnetic isolating device provides a sufficient force for opening the contacts even at a low electric voltage. On the other hand, the electromagnetic isolating device must not be damaged even at high electric voltages.

To fulfill these two reguirements, three different solutions have been pursued in the prior art. Firstly, a coil can be provided that can also be used for high electric voltages. To ensure that the coil will not be damaged even when subject to the high energies or powers occurring in such situations, there is a need for a large number of windings and corresponding wire cross-sections. A further possibility consists in using a coil that is dimensioned for smaller voltages and in limiting the electric power in the coil by means of a voltage regulator. Finally, use can be made of electromagnetic isolating devices that trigger at a very small electric power. For example, magnetic switches can be used for this purpose. All the embodiments described need additional installation space in the electric protective device and give rise to additional costs.

It is therefore the object of the present invention to provide a circuit arrangement of the type referred to in the introduction, by means of which a protective device can be operated more simply and more cost-effectively.

This object is achieved by a circuit arrangement having the features of claim 1 and by a method having the features of claim 8. Advantageous developments of the present invention are disclosed in the dependent claims.

The inventive circuit arrangement for an electric protective device comprises an electric line, an electromagnetic isolating device which is embodied to isolate the electric line electrically in the event of an electric voltage being applied, a switching device which is embodied to apply the electric voltage to the electromagnetic isolating device in response to a trigger signal, a control device for detecting the presence of a fault current and/or an arc in/on the electric line and for generating the trigger signal for the switching device in the event of a fault current and/or an arc occurring, the control device being embodied to detect a zero crossing of the electric voltage and to generate the trigger signal for the switching device as a function of the detected zero crossing.

The circuit arrangement can be used for a residual current protective device and/or an arc fault protective device. The circuit arrangement can be disposed in a housing of an electric protective device. The circuit arrangement comprises at least one electric line to which an electric voltage, in particular an alternating-current electric voltage, can be applied. The circuit arrangement can also be used in multiphase systems. In addition, the circuit arrangement includes an electromagnetic isolating device of the protective device, which can be embodied in accordance with the plunger coil principle. The terminals of the electromagnetic isolating device can be connected to the electric line. To operate the electromagnetic isolating device, the latter can be supplied with the electric voltage. A switching device, which is embodied as a thyristcr for example, is used for this purpose, said device enabling the electromagnetic isolating device to be connected to the electric line and an additional ground line. Once the electromagnetic isolating device is connected to the line and the ground line, the electric voltage is present at their connecting terminals. This induces a current to flow through the coil of the electromagnetic isolating device. The electromagnetic forces of the coil cause a movable plunger of the electromagnetic isolating device to be moved.

As a result of the plunger being moved, a contact of the electric line can be separated.

The circuit arrangement additionally includes a control device which is embodied to detect a fault current and/or an arc in/on the electric line or in a line connected to the electric line. Alternatively, the control device can receive a signal from an external detection device by means of which a fault current and/cr arc is detected. Upon a fault current and/cr an arc being detected, the control device can output a trigger signal to the switching device, the conseguence of this being that the switching device applies the electric voltage to the electromagnetic isolating device. As a result of the electric voltage being applied to the electromagnetic isolating device, the electromagnetic isolating device is activated and separates the electric line.

When the electromagnetic isolating device or its coil is connected to the electric voltage at any given time, the electric current flows through the coil until the voltage reaches the next zero crossing. This means that the electric current flows through the coil at most for the time duration of a half-wave. The control device is additionally embodied to detect the zero crossing of the voltage and activate the switching device as a finction of the detected zero crossing.

The energy consumption of the coil can be adjusted and reduced as a result. This makes it possible to use an electromagnetic isolating device having a coil that has a smaller number of windings and/or a smaller wire cross-section. It is therefore possible to make savings in terms of costs and installation space.

The control device is preferably embodied to generate the trigger signal for the switching device on a timed basis after a predetermined time duration after the detected zero crossing. The period of time during which the electric current flows through the coil of the electromagnetic isolating device can therefore be adjusted precisely.

In a further embodiment, the control device is embodied to generate the trigger signal for the switching device on a timed basis after a defined lower threshold value and before a defined upper threshold value for the time duration after the detected zero crossing. In other words, a time interval is therefore defined in which the control device activates the switching device. The threshold values can be stored in a memory of the control device. The electromagnetic isolating device of the electric protective device can therefore be activated particularly precisely.

It is furthermore advantageous if the control device is embodied to determine the defined lower threshold value as a function of a current operating temperature of the electromagnetic isolating device. The control device can be connected to a temperat-ire sensor that is coupled to the electromagnetic isolating device. The electromagnetic isolating device can therefore be activated particularly reliably.

In one embodiment, the control device is embodied to generate the trigger signal for the switching device as a function of a triggering time of the electromagnetic isolating device. The triggering time corresponds to the time duration between the time at which the electromagnetic isolating device is connected to the voltage and the time until the electric line is isolated electrically by means of the electromagnetic isolating device. By taking account of the triggering time of the isolating device, reliable operation of the electric protective device can be ensured.

In one embodiment, the control device is embodied to ascertain the zero crossing on the basis of a mean value and/or an rms value of the electric voltage. Additionally, the voltage can be rectified before detection by means of the control device.

The control device can include an analog-to-digital converter that is connected to a computing device. A zero crossing of the electric voltage can therefore be determined in a simple manner.

In a further embodiment, a voltage divider is connected between the control device and the electric line. What can be achieved by this means is that only a part of the electric voltage drops at the control device. A partial voltage of this type, the amplitude of which can amount to only a few percent of the amplitude of the electric voltage, can easily be detected in the control device by means of conventional electronic components or computing devices.

The inventive method for operating an electric protective device comprises providing an electric line, providing an electromagnetic isolating device which is embodied to isolate the electric line electrically in the event of an electric voltage being applied, providing a switching device which is embodied to apply the electric voltage to the electromagnetic isolating device in response to a trigger signal, detecting the presence of a fault current and/or an arc in/on the electric line by means of a control device, generating the trigger signal for the switching device by means of the control device in the event of a fault current and/or an arc occurring, detecting a zero crossing of the electric voltage by means of the control device, and generating the trigger signal for the switching device by means of the control device as a function of the detected zero crossing.

The advantages and developments described hereintofore in connection with the inventive circuit arrangement can be transferred in an identical manner to the inventive method.

Preferably, the trigger signal for the switching device is generated by means of the control device on a timed basis after a defined lower threshold value and before a defined upper threshold value for the time duration after the detected zero crossing.

In one embodiment, the defined upper threshold value before which the trigger signal for the switching device is generated is ascertained by means of static and dynamic force measurements on the electric isolating device. Corresponding measurements can be carried out on the electromagnetic isolating device at the time of configuration of the circuit arrangement. The triggering time of the electric isolating device can therefore be reliably determined.

In a further embodiment, the defined lower threshold value after which the trigger signal for the switching device is generated is ascertained on the basis of calculations and/or load tests carried out on the electromagnetic isolating device. Different values for the amplitude of the electric voltage or temperature effects can also be taken into account at the same time. The electromagnetic isolating device can therefore be operated particularly reliably as a function of the ambient conditions.

The present invention will now be explained in more detail with reference to the attached drawing, in which the single figure shows a circuit arrangement in a schematic representation.

The exemplary embodiment described in more detail below represents a preferred embodiment of the present invention.

The figure shows a schematic representation of a circuit arrangement 10 for an electric protective device. An electric protective device of this type can be a residual current detector (RCD) or an arc fault detection device (AFDD) . The circuit arrangement 10 has a first electric line 12 and a second electric line 14. The electric lines 12, 14 are connected to an electric supply device that is not shown here, for example to a power grid. An electric voltage U, in particular an alternating-current electric voltage, is applied between the two electric lines 12, 14. Tn the present case the second electric line is connected to a ground terminal 20.

Furthermore, the circuit arrangement 10 has an electromagnetic isolating device 16 that comprises a coil Li and a plunger that is not shown here. The electromagnetic isolating device 16 is constructed in accordance with the plunger coil principle. When an electric current flows through the coil Li, the plunger is moved and corresponding contacts in the electric line 12 are opened. The electric line 12 is therefore electrically isolated from the supply device or the electric voltage U. The circuit arrangement 10 additionally has a switching device Ti. The switching device Tl can be embodied as a thyristor for example. The two electric lines 12 and 14 can be connected by means of the switching device Ti. This causes an electric current to flow through the coil Li and the electric line 12 to be isolated. Additionally provided is a first diode Dl which is connected in series with the coil Li. The electric current flowing through the coil Li can be rectified by means of the diode Di. A second diode D2 in the reverse direction in parallel with the coil Li prevents voltage surges arising due to the current flowing into the coil Li.

Furthermore, the circuit arrangement 10 has a control device 18. Depending on the application, a fault current or an arc in one of the electric lines 12, 14 can be detected by means of the control device 18. An external detection device can also be provided for detecting a fault current or identifying an arc, which device sends a corresponding signal to the control device 18 in the event of a fault current or arc occurring.

Upon a fault current and/or arc being sensed, a trigger signal trig is output by means of the control device 18. Said trigger signal trig is transmitted to the switching device Ti. After the trigger signal trig is received, the switching device 18 is closed, with the result that the voltage U is applied to the coil Li and an electric current flows through the coil Li.

This causes the plunger to be moved and the electric line 12 to be separated. If the switching device Ti is embodied as a thyristor, the control signal trig can be transmitted as an electric current or current pulse to the gate terminal of the thyristor, with the result that the thyristor fires and is switched in the forward direction.

Tn the present exemplary embodiment, the control device 18 is connected to the electric line 12. This makes it possible for the electric voltage U to be monitored by means of the control device 18. Toward that end, the control device 18 is connected via a voltage divider 22. The voltage divider 22 comprises the two resistors Ri and R2 connected in series. By connecting the two resistors Ri and R2 in series it is possible for the electric power to be distributed correspondingly over the two resistors Rl und R2. Just one electric resistor can also be used instead of the resistors Ri and R2. The voltage divider 22 additionally includes the resistor R3, which is connected in series with the resistors Ri and R2. On account of the voltage divider 22, only a part of the electric voltage U or a voltage rectified by the diode Di is transmitted to the control device 18. For example, the electric resistors can be selected such that a partial voltage of 0.5% of the amplitude of the voltage U drops at the control device 18.

The control device 18 is embodied to deteot a zero crossing of the electric voltage U. For this purpose the control device 18 has an analog-to-digital converter by means of which the partial voltage of the electric voltage U can be digitized.

Furthermore, the control device 18 can have a computing device in the form of a microcontroller, an ASTO or a comparator, by means of which the zero crossing of the voltage U is determined on the basis of the mean value or rms value of the partial voltage dropping at the control device 18.

When the electromagnetic isolating device 16 or the coil Li is connected to the voltage U at any given time, the electric current flows through the coil Li until the electric voltage U reaches the next zero crossing. This means that the electric current flows through the coil Li at most for the time duration of a half-wave, In the case of an electric voltage U having a frequency of 5 Hz, the time duration of a half-wave amounts to 10 ms. The maximum energy consumption Ernax resulting in this case can be calculated as a function of the period T, the electric voltage U, the angular frequency o, the time t, and the electric resistance R1 of the coil Li: E = U2 sin(oJ. t) By means of the control device 18, the switching device Ti can now be activated as a finction of the zero crossing of the electric voltage U. In particular, the control device 18 can also trigger the switching device Il on a timed basis after a predetermined time duration. A phase angle cx can also be assigned instead of the time duration. The energy consumption E(a) as a function of the phase angle a is calculated according to the following formula: rn2 U2 sin(w t) E(a) = _____________ If the contrcl device 18 triggers the switching device Ti at a phase angle a cf 9Q°, that is tc say after a time duration cf ms after the zero crossing of the electric voltage U, the energy consumption can be reduced by a factor of 2. If triggering of the switching device Ti by means of the control device 18 is effected at a phase angle a of 115° or after a time duration of around 6.3 ms after the zero crossing, the energy consumption can be reduced by a factor of 4.

Furthermore, a time interval after reaching the zero crossing of the electric voltage U can also be defined, in which time interval the control device 18 triggers the switching device Ti. instead of a time interval, an angular interval can also be defined. A lower threshold value and an upper threshold value are therefore defined for the time duration, with the control device 18 triggering the switching device Ti in the time interval between the lower and upper threshold values.

The triggering time of the electromagnetic isolating device 16 can also be taken into account here. The threshold values can be stored in a memory of the control device 18 specifically for the electromagnetic isolating device 16, for example in the form of a mathematical function or a table. The threshold values can have been ascertained by means of calculations and measurements on the electromagnetic isolating device 16 that were carried out previously.

The upper threshold valie of the time duration can be ascertained in advance on the basis of static or dynamic force measurements on the electromagnetic isolating device 16. The upper threshold value of the time duration can be ascertained by theoretical calculations or load testing. Idditionally, the control device 18 can be embodied to detect the temperature of the electromagnetic isolating device 16 at the present time and to adjust the lower time threshold value as a function of the temperature.

By controlling the triggering of the switching device Tl it is possible to reduce the time duration of the current flow through the coil Ll and consequently the energy consumption of the coil Li. This enables an electromagnetic isolating device 16 to be used that has a coil Li having a smaller number of windings and/or a smaller wire cross-section. Savings can therefore be made in terms of costs and installation space.

List of reference symbols Circuit arrangement 12 Line 14 Line 16 Isolating device 18 Control device Ground terminal 22 Voltage divider Di Diode D2 Diode Li Coil Ri Resistor R2 Resistor R3 Resistor trig Trigger signal Ti Switching device U Voltage

Claims

Claims 1. A circuit arrangement (10) for an electric protective device having -an electric line (12), -an electromagnetic isolating device (16) which is embodied to isolate the electric line (12) electrically in the event of an electric voltage (U) being applied, -a switching device (Ti) which is embodied to apply the electric voltage (U) to the electromagnetic isolating device (16) in response to a trigger signal (trig), -a control device (18) for detecting the presence of a fault current and/or an arc in/on the electric line (12) and for generating the trigger signal (trig) for the switching device (Ti) in the event of a fault current and/or arc occurring, characterized in that -the control device (18) is embodied to detect a zero crossing of the electric voltage (U) and to generate the trigger signal (trig) for the switching device (Ti) as a function of the detected zero crossing.
2. The circuit arrangement (10) as claimed in claim 1, characterized in that the control device (18) is embodied to generate the trigger signal (trig) for the switching device (Ti) on a timed basis after a predetermined time duration after the detected zero crossing.
3. The circuit arrangement (10) as claimed in claim 1 or 2, characterized in that the control device (18) is embodied to generate the trigger signal (trig) for the switching device (Ti) on a timed basis after a defined lower threshold value and before a defined upper threshold value for the time duration after the detected zero crossing.
4. The circuit arrangement (10) as claimed in claim 3, characterized in that the control device (18) is embodied to determine the defined lower threshold value as a function of a current operating temperature of the electromagnetic isolating device (16)
5. The circuit arrangement (10) as claimed in one of the preceding claims, characterized in that the control device (18) is embodied to generate the trigger signal (trig) for the switching device (Ti) as a function of a triggering time of the electromagnetic isolating device (16)
6. The circuit arrangement (10) as claimed in one of the preceding claims, characterized in that the control device (18) is embodied to ascertain the zero crossing on the basis of a mean value and/or an rms value of the electric voltage (U).
7. The circuit arrangement (10) as claimed in one of the preceding claims, characterized in that a voltage divider (22) is connected between the control device (18) and the electric line (12)
8. A method for operating an electric protective device by -providing an electric line (12), -providing an electromagnetic isolating device (16) which is embodied to isolate the electric line (12) electrically in the event of an electric voltage (U) being applied, -providing a switching device (Ti) which is embodied to apply the electric voltage (U) to the electromagnetic isolating device (16) in response to a trigger signal (trig), -detecting the presence of a fault current and/or an arc in/on the electric line (12) by means of a control device (18) , and -generating the trigger signal for the switching device (Ti) by means of the control device (18) in the event of a fault current and/or arc occurring, characterized by -detection of a zero crossing of the electric voltage (U) by means of the control device (18), and -generation of the trigger signal (trig) for the switching device (Ti) by means of the control device (18) as a function of the detected zero crossing.
9. The method as claimed in claim 8, characterized in that the trigger signal (trig) for the switching device (Ti) is generated by means of the control device (18) on a timed basis after a defined lower threshold value and before a defined upper threshold value for a time duration after the detected zero crossing.
10. The method as claimed in claim 9, characterized in that the defined upper threshold value before which the trigger signal (trig) for the switching device (Tl) is generated is ascertained by static and/or dynamic force measurements on the electric isolating device (16)
11. The method as claimed in claim 9 or 10, characterized in that the defined lower threshold value after which the trigger signal (trig) for the switching device (Tl) is generated is ascertained on the basis of calculations and/or load tests carried out on the electromagnetic isolating device (16)