FR2775847A1 - Differential protection for electrical circuits incorporating compensation for normal leakage currents - Google Patents

Abstract

Where supply conductors (N, P1) are connected to equipment such as filters a disturbing current (Ip) is generated by the leakage impedances (8,9) which influences the differential current (Id) being measured by the ring transformer (1). The disturbing effect may be compensated by connecting equivalent impedances (13,14) to the supply side and feeding their combined compensating current (Ic) through the ring transformer (1) in the reverse sense

Description

-1i

  DIFFERENTIAL PROTECTION DEVICES, ELECTRICAL APPARATUS

  AND ELECTRICAL INSTALLATION COMPRISING SUCH A DEVICE

  The invention relates to a differential protection device comprising: - main electrical supply conductors, - means for determining differential current supplying a signal representative of differential currents flowing in said main conductors, and - actuator means connected to the means of determination as well as a device

  electrical and an electrical installation comprising such a device.

  Differential protection devices are generally used to monitor or protect loads or parts of an electrical installation against current leakage to the earth or an earth of the installation. This leakage current is manifested in particular by a current

  differential or zero sequence in main supply conductors.

  In known differential protection devices such as relays, circuit breakers or differential switches, the differential current is detected by devices which determine the vector sum of the currents flowing in the main supply conductors. In known manner, the devices for determining differential current

  comprise toroids having a magnetic circuit which surrounds said main conductors.

  The toroids have a secondary winding providing a signal representative of the differential current. This signal is generally applied to actuators, such as in particular trigger relays, signaling relays, processing circuits or, for example,

display devices.

  If a differential current exceeds for example a predetermined threshold, the differential protection device triggers the opening of the main contacts of the circuit breakers or differential switches, or signals this threshold being exceeded. Current leakages producing a differential current are generally in phase with the supply voltage of the main conductors. For example, when the devices are used for the protection of persons

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  or to detect insulation faults, leakage currents can pass through charges

essentially resistive.

  However, impedant loads other than resistive loads can cause leakage currents between main conductors and the earth or earth of an installation. For example, electrical appliances may include filtering devices connected between supply conductors and an earth conductor. These filtering devices generally include inductors and capacitors which generate leakage currents having phase shifts due to the capacitive or inductive components of the impedances they pass through. Capacitive leakage currents can also be generated by capacitors

  of lines formed between the main conductors and the earth of an installation.

  When the number of devices comprising capacitive or inductive loads between the line conductors and the earth becomes large, the leakage current detected by the differential devices increases and the tripping threshold may be exceeded. These capacitive or inductive currents then disturb the operation of the differential tripping devices by making them sensitive to disruptive leakage currents which are not representative of insulation faults. These disturbances are particularly frequent when the trigger threshold is very low, for example, when the device is used to

  protecting people from direct contact.

  The object of the invention is a differential protection device less sensitive to

  disruptive leakage, as well as an apparatus and an installation comprising such a device.

  According to the invention, the differential protection device comprises means for compensating for disturbing differential currents connected to at least one of the main conductors and acting on the determination means to modify the signal representative of

differential currents.

  In a preferred embodiment, the compensation means generate in the detection means a compensation current having an opposite direction with respect to a

  disturbing differential current likely to flow in main conductors.

  According to a particular embodiment, the determination means comprise a torus

  adder surrounding main conductors.

  Advantageously, the compensation means comprise at least one impedant circuit connected between at least one first main conductor and one at least one return conductor. Preferably, said at least one first main conductor is a main conductor

  upstream upstream of said determination means.

  According to a first variant, said return conductor is a main conductor downstream downstream

said determination means.

  According to a second variant, said return conductor is an earth conductor connected to

a mass of an installation.

  According to a first development, the compensation means comprise a conductor

  compensation crossing the toroid and connected in series with the impedant circuit.

  According to a second development, the compensation means include at least one

  compensation winding wound on the toroid and connected in series with the impedant circuit.

  Preferably, the impedant circuit includes at least one capacitor.

  The actuator means comprise a relay connected to a secondary winding of the toroid.

  In one embodiment, the device comprises main contacts connected in series with main conductors, the actuator means causing said main contacts to open when a differential current exceeds a predetermined tripping threshold.

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  Preferably, the compensation means generate in the detection means a signal representative of a compensation current of value equal to or less than half the value

  the predetermined trigger threshold.

  Advantageously, the device comprises an auxiliary contact connected in series with the impedant circuit.

  Preferably, the state of the auxiliary contact is representative of the state of the main contacts.

  According to a third development, the device comprises selection means associated with the

  impedant circuit and making it possible to change the impedance of said impedant circuit.

  For example, the selection means include electronic switching means

  connected to at least two capacitors of said impedant circuit.

  Advantageously, it includes monitoring means connected to main conductors and receiving a signal representative of a differential current to determine

  values representative of disturbing differential currents.

  The monitoring means are connected to the selection means for selecting the impedance of the impedant circuit as a function of the values representative of currents

disruptive differentials.

  An electrical device according to the invention comprises at least one protection device

  differential as defined above.

  An electrical installation according to the invention comprises at least one protection device

  differential as defined above.

  Preferably, an electrical installation includes:

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  - a differential protection module comprising the main contacts, the means for determining differential current and the actuator means connected to the determination means and acting on the opening of the main contacts, and - a compensation module comprising the impedant circuit connected to main conductors. Advantageously, the electrical installation comprises an auxiliary contact module connected

  in series with the compensation module.

  In another embodiment, the installation comprises: - a breaking module comprising the main contacts, - a differential module associated with the breaking module and comprising the means for determining differential currents and the actuator means, and - a module compensation comprising the impedant circuit connected to conductors

  main and differential module.

  Other advantages and characteristics will emerge more clearly from the description which follows.

  to follow, of particular embodiments of the invention, given by way of nonlimiting examples, and represented in the appended drawings in which:

  Figure 1 shows the diagram of a known differential protection device.

  FIG. 2 represents the diagram of a known device associated with a switching device.

  FIG. 3 represents a differential protection device according to a first mode of

realization of the invention.

  FIG. 4 represents a differential protection device according to a second mode of

realization of the invention.

  FIG. 5 represents a differential protection device according to the invention associated with a

three-phase switching device.

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  FIG. 6 represents a development of the embodiment of FIG. 4.

  FIG. 7 represents an installation comprising a device according to the invention connected in a modular fashion. FIG. 8 represents a differential protection device according to a third mode of

realization of the invention.

  FIG. 9 represents an installation produced in a modular form and comprising a

  device according to FIG. 8 associated with a circuit breaker.

  FIG. 10 represents a device according to the invention comprising a selection device

compensation impedances.

  FIG. 11 represents the diagram of a compensation device intended to be used in

  installations with non-linear loads.

  The known differential protection device shown in FIG. 1 comprises a summing toroid 1 which surrounds main conductors 2 of an electrical distribution network. A secondary winding of the toroid is connected to a relay 3 which controls the opening of an electrical contact 4 when a secondary current Id passing through the relay exceeds a predetermined threshold. The current Id flowing in the secondary winding of the toroid is representative of the vector sum of the currents flowing in the main conductors. Said current Id representative of the differential current can also be a signal

supplied to a processing unit.

  In FIG. 2, the differential protection device is associated with a breaking device 5 comprising main contacts 6 connected in series with the main conductors. In this case, the relay 3 causes the opening of the main contacts when the secondary current flowing through the relay exceeds a predetermined tripping threshold. The breaking device can be, for example, a switch or a circuit breaker. The

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  main conductors are generally phase conductors and possibly the neutral conductor of an electrical distribution network, for example, in the diagram in FIG. 2, a first conductor P1 corresponds to a phase and a second conductor N

corresponds to the neutral conductor.

  Upstream of the differential protection device, the neutral and earth conductors can, in this case, be connected by an impedance Z. Depending on the earthing system chosen for the installation, the value of the impedance Z can be weak, zero, or of any value. If the sum of the currents flowing in the main conductors is not zero, a secondary current representative of a leakage current is generated in the secondary winding of the torus 1. For example, if a current flowing in the phase conductor P1 does not fully return via the neutral conductor, the toroid detects a differential current, or leakage current, and the relay is actuated if the detected current exceeds a threshold. The leakage current which does not pass through the toroid is generally diverted towards the earth or the earth of the installation. In the diagram of figure 2, the mass or the earth are represented

by an earth conductor 7.

  When an electrical installation or devices connected to the installation include inductive or capacitive loads that must be connected to earth or ground, inductive or capacitive Ip currents flow to the earth conductor. These charges are represented in FIG. 2 by impedances 8 and 9 connected respectively between the conductors P1 and N and the earth 7. Such charges are found in particular in the filtering devices or in the form of stray capacitances between the main conductors and earth or mass. Thus, in the embodiment of Figure 2, the phase current of the main conductors does not return entirely by the neutral. The differential current Ip generated by the currents flowing in these loads is detected by the

  toroid and risk of disturbing the operation of the differential protection devices.

  A protection device according to embodiments of the invention makes it possible to completely or partially overcome the disturbing effects of the currents flowing in

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  impedant, capacitive or inductive loads, located between main conductors and the

  ground or earth downstream of the differential protection device.

  In a differential protection device according to an embodiment of the invention, the detection of differential current is compensated by causing a compensation current flowing in said opposite direction and of the same nature as the current flowing in the

  capacitive or inductive disturbing loads.

  FIG. 3 shows a first embodiment of a protection device according to the invention. In this embodiment, a compensation conductor 10 crosses the torus to circulate a compensation current Ic. This compensation current Ic compensates

  the effects of the disturbing differential current Ip.

  To generate said compensation current, an impedant circuit 11 is connected between main conductors upstream of the toroid and a first part of the conductor of

compensation 10 downstream of the torus.

  A second part of the compensation conductor upstream of the toroid is connected to the

  earth conductor 7 to close the circuit.

  The impedant circuit can for example comprise a first impedance 13 connected to the phase conductor P1 and a second impedance 14 connected to the neutral conductor N. These impedances are of the same nature as the corresponding disturbing impedances

8 and 9 respectively.

  For optimal compensation, the impedances 13 and 14 of the impedant circuit can be of the same value as the disturbing impedances respectively 8 and 9. However, when the disturbing impedances are not fixed, for example when filters are installed on portable devices or devices connected to the network so

  periodic, it is preferable not to generate too high a compensation current.

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  In a preferred embodiment, the compensation current is lower than the actuation threshold of the relay. To increase operating safety and take account of the precision of the relay actuation thresholds, the compensation current Ic can be

  advantageously equal to or less than half the actuation threshold.

  Generally, the impeding disturbing loads are capacitive loads. In this case, the impedant circuit includes capacitive impedances 13 and 14 produced by capacitors. The impedances connected to the same main phase or neutral conductor are of the same nature, for example capacitive, the compensation is then independent of the network frequency. Consequently, if the frequency of the alternating voltage of the network increases, the current flowing in capacitive impedances increases in the same proportions and that flowing in inductive impedances decreases. Thus, the interference leakage current compensation is independent of the frequency of the supply network and of the shape

  currents or voltages present in the network.

  The diagram in FIG. 3 represents a differential protection device integrated in a switch or circuit breaker box. This device is installed in an installation where the main conductors N and P1 can be electrically isolated from the earth or ground conductor 7. The conductor 7 can also relate to an equipotential bonding. In some installations, the neutral conductor is connected to the earth line upstream of the

  electrical distribution network through a low impedance.

  FIG. 4 represents a diagram of a differential protection device according to the invention used in an installation where the neutral conductor is connected to earth. In this case, the impedant current diverted to earth essentially passes through the impedance 8 connected to the phase conductor. To compensate for the impeding leakage current, the compensation circuit 11 includes an impedance 13 connected between the phase conductor upstream of the toroid 1 and the neutral conductor downstream of the toroid. It is not necessary to add, in this case, an additional compensation conductor 10 since the conductor of

  neutral is itself connected to earth upstream of the torus.

  l0 2775847 If the load 8 is capacitive, the impeding compensation circuit 11 includes a capacitor 13 connected between the upstream phase P1 and the downstream neutral conductor. In this embodiment, the disturbing leakage current Ip flows in the phase conductor and the compensation current Ic flows in the neutral conductor in the opposite direction. So

  diagram, the main contacts 5 are, for example, circuit breaker contacts.

  FIG. 5 represents a differential protection device according to FIG. 4 associated with a four-phase three-pole differential switch 16 P1, P2, P3 and a neutral N. In this three-phase embodiment of the disturbing leakage currents can pass through three impedances 8A respectively, 8B and 8C. These leakage currents are compensated by compensation impedances respectively 13A, 13B and 13C connected between the upstream phase conductors P1, P2, P3 and the downstream neutral conductor N. The neutral conductor connected to the earth upstream of the device passes the compensation current Ic in the opposite direction in relation to the disturbing leakage currents Ip. To prevent currents flowing in the impedant circuit from propagating in an installation downstream of the main contacts 6 of the breaking device 5, a device according to one embodiment of the invention comprises an additional contact 17 arranged in series with impedances of the impedant circuit 11. In this embodiment, the contact 17 is associated with the main contacts, the state of the contact 17 being representative of the state of the

contacts 5.

  To protect the compensation circuit, a protection device can also be connected in series with the compensation impedances. For example, in FIG. 5, fuses 18 are connected in series with the impedances 13A, 13B and 13C between the

  phase conductors upstream of the contacts 5 said impedances.

  When the conductors upstream and downstream of the toroid are accessible, the impedance 13 can be connected between the conductor P1 upstream of the torus but downstream of the main contacts, 6 and the neutral conductor downstream of the torus. Such a connection is shown in hll 2775847 diagram of the embodiment of Figure 6. Thus, the opening of the main contacts also stops the flow of compensation currents. Downstream line conductors

  toroid are therefore isolated from the upstream voltage if the contacts 5, 6 are open.

  Figure 7 shows a modular embodiment of a device according to the invention. In this installation, a differential protection module 20 such as a differential switch or circuit breaker is associated with a modular auxiliary contact 21 and a modular compensation block 22. The contact 21 is actuated at the same time as the main contacts of the module 20. Thus, the opening of the main contacts causes the opening of the contact 21. The compensation block 22, comprising for example at least one capacitor, is connected in series with contact 21 between the phase conductor P1 in

  upstream of module 20 and the neutral conductor downstream of said module 20.

  A fuse 18 can be connected between the module 21 and the conductor P1. This fuse can be a separate module or be inserted in the modular contact 21. It is also possible to introduce a protection fuse in block 22 in series with the impedances

compensation.

  The modular elements 20, 21 and 22 may preferably be arranged in the same

distribution board.

  The devices described above risk themselves generating disturbing leakage currents for upstream differential protection devices. In fact, in the case of the device in FIG. 3, the compensation current flowing in the compensation conductor 10 generates an additional leakage current for devices upstream. This disturbance does not exist in the case of the devices of FIGS. 4 to 7 because the compensation current returns via the neutral conductor and is therefore compensated for by

upstream of the torus.

  To limit the value of the compensation current while keeping maximum compensation efficiency, a device according to the invention comprises a winding of

  compensation 23 wound on the toroid to circulate a reduced compensation current.

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  The winding 23 replaces the compensation conductor 10 which had only one passage in the torus. An embodiment comprising such a winding is shown in FIG. 8. In this case, for equivalent compensation, the compensation current is reduced by a ratio corresponding to the number of turns of the compensation winding. For example, if the number of turns is equal to ten, the necessary compensation current Ic is ten times lower. Consequently, the disturbance produced by the compensation current will also be ten times smaller. Preferably, the number of

  compensation congestion turns can be between ten and one hundred.

  Advantageously, the compensation winding can also be used in devices where the neutral conductor is connected to earth as in FIGS. 4 to 7. In all cases, the winding has a first end connected to at least one impedance of the compensation circuit 11 and a second end connected to a ground or neutral return conductor as the case may be. The effects of the compensation winding on the toroid being greater than a single passage in said torus, in earth neutral installations the

  return conductor can be either the neutral conductor upstream or downstream of the toroid.

  Similarly, the compensation impedances can be connected upstream or downstream of the device. The compensation winding used to reduce the compensation current while maintaining maximum efficiency and also used to reduce the size and cost of the compensation impedances. Indeed, since the compensation current Ic decreases, the power of the impedances is also reduced in the same proportions, the reduction depending on the number of turns of the winding 23. For example, if the impedances are

  capacitors, the value of the capacitors is reduced as well as the size and cost.

  FIG. 9 represents a differential protection device according to the diagram of FIG. 8 produced in a modular form. This device which can be integrated into an electrical installation comprises a breaking module 24 such as a switch or a circuit breaker, a differential module 25 associated with the breaking module and a compensation module 22. The differential module comprises the toroid 1 comprising a winding secondary 26 connected to relay 3 for triggering contacts 6 of the cut-off module, conductors

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  main N and Pl crossing the torus and connected between output terminals 27 of the cut-off module and output terminals 28 of said differential module, and a compensation winding 23 wound on the torus and connected between two terminals 29 of compensation of said

differential module.

  Impedances 13 and 14 of the compensation module comprising output terminals 30 are connected to output terminals 28 of the differential module so as to be preferably disconnected when the contacts are opened 6. Impedances 13 and 14 are represented by capacitors having a common connection point connected to a first end of the winding 23 on a terminal 29. In this embodiment, a second end

  of the compensation winding 23 is connected to the earth conductor 7.

  In order to be able to precisely adjust the compensation, a device according to the invention shown in FIG. 10, includes a selection device 31 for selecting the values of the compensation impedances. In this embodiment of FIG. 10, the selection device comprises in particular a switching device 32 comprising contacts connected in series with three impedances 13D, 13E and 13F. The assembly constituted by the switching device 32 and the impedances 13D, 13E and 13F is connected in series with the compensation winding 23 between an upstream main conductor P1 and a return conductor. In this diagram, the return conductor is the neutral conductor

N downstream.

  The switching device 32 can be a switch controlled by a control member.

  manual control or by an electric control signal.

  The selection device makes it possible to connect one or more impedances 13D, 13E, 13F, in parallel combination so as to adjust the value of the compensation impedance and

  consequently the current Ic flowing in the winding 23.

  Advantageously, a device according to the invention comprises a control circuit 33 connected to the switching device 32 for automatically selecting the value of the compensation impedance. This control circuit is connected to main conductors N and P1

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  and to means 34 for measuring a signal representative of the differential current to determine the phase shift of the differential current relative to the supply voltage of the network. In order to minimize the effects of impedance disruptive leakage currents, the control circuit monitors the phase shift and controls the selection device 32 to adjust the compensation impedance. In this automatic selection mode, the contacts of the selection device are preferably made with electronic switching components such as triacs

or thyristors.

  In the diagram of FIG. 11, a differential protection device according to the invention is used in an electrical installation comprising a switching regulator 35 disposed downstream of said device. Switching regulators modify the characteristics of the line currents flowing in the main conductors. Generally, the frequencies of the currents or the frequency spectrum of the currents are often higher. In the example of FIG. 11, the device 15 includes a compensation winding 23 connected between the earth conductor 7 and compensation impedances 13 and 14 connected downstream of the regulator. Since disruptive leakage impedances 8 and 9 are also located downstream of the regulator 35, the compensation of the impedant leakage currents flowing in said impedances 8 and 9 will be correctly carried out by the impedances 13, 14 since the disturbing impedances and the compensation impedances are in this case connected in parallel. Thus, the disturbing leakage currents and the compensation current will be of the same nature even if the regulator 35 modifies the frequency and the shape of the circulating current.

in the main conductors.

  In this embodiment, the compensation impedances are connected downstream of the differential protection device. This connection method slightly increases the impeding leakage currents since the use of a compensation winding makes it possible to reduce said compensation current. Thus, even if in this case the impedant leakage current increases, an additional turn in the compensation winding is sufficient

  to cancel the effect of this increase.

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  In the devices described above, the determination of the differential current is carried out with a toroid. However, other detectors can be used to perform this function. In these same devices, the compensation current is represented flowing in the toroid, but it is also possible to directly combine signals representative of differential current and compensation current without passing the current Ic

directly in the torus.

  The devices according to the invention described above can be integrated into breaking devices such as circuit breakers or switches, be part of complex electrical devices, in particular removable electrical devices comprising charges to be protected, or be installed in installations electric in compact form or in

  modular form with several components.

  In the embodiments described above, devices according to the invention are used in networks with isolated neutral or earth neutral. However, they can also be used

  in other types of networks, for example in networks without neutral.

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Claims (24)

  1. Differential protection device comprising: - main conductors (2, N, Pi, P2, P3) of electrical supply, - means (1) for determining the differential current supplying a signal (Id) representative of the differential currents flowing in said main conductors, and - actuator means (4) connected to the determination means, device characterized in that it comprises compensation means (10, 11, 13, 14, 23) of disturbing differential currents connected to at least one of the main conductors and acting on the determination means to modify the signal representative of differential currents. 2. Device according to claim 1, characterized in that the compensation means generate, in the detection means, a compensation current (Ic) having an opposite direction with respect to a disturbing differential current (Ip) capable of flowing in main conductors.   3. Device according to one of claims 1 or 2, characterized in that the means of   determination include a summing toroid (1) surrounding the main conductors.   4. Device according to any one of claims 1 to 3, characterized in that the means   of compensation include at least one impedant circuit (11, 13, 13A-13F, 14) connected   between at least a first main conductor and at least one return conductor.   5. Device according to claim 4, characterized in that said at least one first main conductor is an upstream main conductor (P1-P3, N) upstream of said means of determination.   6. Device according to one of claims 4 or 5, characterized in that said conductor   return is a downstream main conductor (P I-P3, N) downstream of said determination means. 17 2775847   7. Device according to one of claims 4 or 5, characterized in that said conductor   return is an earth conductor (7) connected to a ground of an installation.   8. Device according to any one of claims 4 to 7, characterized in that the means   compensation comprises a compensation conductor (10) passing through the torus and   connected in series with the impedant circuit.   9. Device according to any one of claims 4 to 8, characterized in that the means   compensation comprises at least one compensation winding (23) wound on the   toroid (1) and connected in series with the impedant circuit (11).   10. Device according to any one of claims 4 to 9, characterized in that the circuit   impedant has at least one capacitor (13, 14).   11. Device according to any one of claims 3 to 10, characterized in that the   actuator means comprise a relay (3) connected to a secondary winding (26) of the toroid.   12. Device according to any one of claims 1 to 11, characterized in that it   comprises main contacts (5, 6) connected in series with main conductors (2), the actuator means causing the opening of said main contacts when   differential current exceeds a predetermined tripping threshold.   13. Device according to claim 12, characterized in that the compensation means generate in the detection means a signal representative of a compensation current of   value equal to or less than half the value of the predetermined triggering threshold.   14. Device according to any one of claims 4 to 13, characterized in that it   comprises an auxiliary contact (17) connected in series with the impedant circuit.   15. Device according to claim 14, characterized in that the state of the auxiliary contact (17)   is representative of the state of the main contacts (5, 6). 18 2775847   16. Device according to any one of claims 4 to 15 characterized in that it   comprises selection means (31, 32) associated with the impedant circuit and making it possible to   change the impedance of said impedant circuit.   17. Device according to claim 16 characterized in that the selection means comprise electronic switching means (32) connected to at least two   capacitors (13D, 13E, 13F) of said impedant circuit.   18. Device according to any one of claims 1 to 17 characterized in that it   comprises monitoring means (33) connected to main conductors and receiving a signal representative of a differential current to determine values representative of   disturbing differential currents.   19. Device according to claim 18 characterized in that the monitoring means (33) are connected to the selection means (31, 32) for selecting the impedance of the circuit   impedant as a function of the values representative of disturbing differential currents.   20. Electrical device characterized in that it includes a protection device   differential according to any one of claims 1 to 19.   21. Electrical installation characterized in that it comprises at least one device according to one   any of claims 1 to 19.   22. Electrical installation according to claim 21 characterized in that it comprises: - a differential protection module (20) comprising the main contacts, the means for determining differential current and the actuator means connected to the determination means and acting on the opening of the main contacts, and a compensation module (22) comprising an impedant circuit (11) connected to main conductors. 19 2775847   23. Electrical installation according to claim 21 characterized in that it comprises a   auxiliary contact module (21) connected in series with the compensation module.   24. Electrical installation according to claim 20 characterized in that it comprises: - a cut-off module (24) comprising the main contacts, - a differential module (25) associated with the cut-off module and comprising the determination means (1) of differential currents and the actuator means, and - a compensation module (22) comprising the impedant circuit (11) connected to   main conductors and to the differential module.