Title of Invention

A TRIP DEVICE

Abstract

ABSTRACT A CURRENT TRANSFORMER NOTABLY FOR A TRIP DEVICE BY FAULT CURRENT SENSITIVE TO PULSED CURRENTS AND A TRIP DEVICE EQUIPPED WITH SUCH A TRANSFORMER This current transformer (1) mainly comprises a magnetic core toroid (2), primary windings formed by the active conductors of an electrical installation to be protected, and a secondary winding (3) at the terminals of which a differential fault signal is established when a differential fault occurs in the primary windings. This transformer (1) is characterized in that the magnetic core of the above-mentioned toroid presents a ratio between the dynamic induction elevation at 400 Mz and the dynamic induction elevation at SO Hz greater than 0.7, for a field intensity amplitude of about 35 mAt/cm. The trip device (D) comprises a transformer (1) as described above, a tripping relay (4) and a secondary circuit (5) connecting said relay (4) to the transformer (1). The above-mentioned secondary circuit (5) comprises a capacitor (8) connected in series with the secondary winding (3) or a full-wave rectifier (6, 7). (figure 6)

Full Text

The present invention relates to a current transformer, notably for a differential trip device by fault cun-ent sensitive to pulsed curents, of the kind comprising a magnetic core toroid, primary windings formed by the active conductors of an installation to be protected and a secondary winding at the terminals of which a differential fault signal is established when a differential fault occurs in the primary windings. The invention also reiates to a trip device comprising in addition to a transformer such as described above, a tripping relay of a current breaking apparatus connected to the above-mentioned secondary winding by a secondary connection circuit an-anged to bring about tripping when said signal exceeds a preset threshold. Trip devices by fault current have been used for many years for protection of machines and people. For protection of people, the tripping current can be about 30 mA, whereas it is in a range of about 300 to 500 mA for protection of machines. However, during the last few years, more and more electronic devices with cun-ent rectifier effect have been incorporated in numerous electrical apparatuses. These rectifier effects may generate a DC component liable to influence the operation of the differential device. The increased use of electronic trip devices, notably in household appliances, also requires the latter to respond in complete safety not only to alternating currents but also to pulsed DC fault currents. The limit values defined for trip devices of this kind have been set by the standard VDE 0664. Trip devices of the previously mentioned kind are known, which meet this specific requirement, wherein the magnetic core of the transfonner toroid is made of a crystalline material designed for this use. The main quantities characteristic of these materials are the induction amplitude AB for a sinusoidal excitation current, the static induction elevation 48 stat for a half-wave rectified sinusoidal excitation current, and the dynamic induction elevation AB dyn for a full-wave rectified sinusoidal excitation current. In these trip devices, it is known to fit a capacitor between the transformer secondary winding and the relay tripping winding in order to increase the sensitivity of the trip device by increasing the power at the level of the relay. An oscillating circuit is thus formed by the secondary winding and the capacitor. The resonance frequency of this oscillating circuit then,has to be tuned with the frequency of the voltage in the secondary winding due to the fault current. Tuning of this resonant circuit is performed by defining the number of turns of the secondary winding based on the capacitance values prescribed for the capacitor, and the tripping conditions of the trip device are determined. However, the number of turns finally set simply represents a compromise between the different forms of fault current. European Patent application EP-0,563,606 describes a current transformer for a trip device, enabling safe interruption of a user circuit subjected to pulsed currents to be obtained, tripping being performed in a manner practically independent from the form of the fault current. These results are obtained due to the use of a magnetic core made of a nanocrystalline material presenting the following magnetic characteristics : Br/Bs 0.6T, for a field intensity amplitude of lOOmA/cm, DBdyn max > 0.7T and DBdyn/'^B > 0.7, these magnetic cores having been achieved in two stages, wherein Br is the remanence induction, Bs is the induction at saturation, DBdyn is the dynamic induction elevation and DBdyn/^B is the ratio between the dynamic induction elevation and the induction amplitude. Yet the magnetic quantities defined in this patent are measured at the frequency of 50 Hz, whereas the pulsed currents defined in the VDE 0664 may have harmonics higher than 50 Hz of large amplitude. This results in this type of trip device not being able to be used advantageously for electrical apparatuses comprising for example thyristors whose opening angle is 135°, the amplitude of the 400 Hz harmonic still corresponding for this angle to 30% of that of the harmonic at 50 Hz. The present invention overcomes these problems and proposes a current transformer and a trip device comprising such a transformer, presenting a better sensitivity, particulariy to pulsed currents for opening angles of up to 135° and more. For this purpose, the object of the present invention is to achieve a current transformer of the kind previously mentioned, characterized in that the magnetic core of the above-mentioned toroid presents a ratio between the dynamic induction elevation at 400 Hz and the dynamic induction elevation at 50 Hz greater than 0.7, for a field intensity amplitude of about 35 mA t/cm, (tesla/cm). Advantageously, the magnetic core of the toroid presents a remanence ratio Br/Bs 0.6T, for a field intensity amplitude of 100 mA/cm, a maximum dynamic induction elevation greater than 0.7T, and a ratio between the dynamic induction elevation and the induction amplitude AB dyn / ^B > 0.7. Advantageously, the magnetic core is made from a soft magnetic iron based alloy made up of at least 50% of fine crystal grains of a size smaller than 100 nm and containing, in addition to an iron content greater than 60 % (at) [wherein (at) is atomic percentage], 0.5 to 2 % of copper, 2 to 5 % at least of one of the following metals, niobium, tungsten, tantalum, zirconium, hafnium, titanium and/or molybdenum, 5 to 14 % of boron and 14 to 17 % of siHcon. According to a particular embodiment, the magnetic core of the toroid is made of a nanocrystalline material. According to another embodiment, the magnetic core of the toroid is made of an amorphous material. An object of the invention is also to achieve a trip device by fault current comprising a transformer having the previously mentioned characteristics taken either alone or in combination, a tripping relay and a secondary circuit connecting the relay to the transformer, this trip device being characterized in that the above-mentioned secondary circuit comprises a capacitor connected in series with the secondary winding. According to another embodiment, the secondary circuit comprises a full-wave rectifier. Advantageously, this rectifier comprises two diodes respectively connecting the two ends of the secondary winding to one of the ends of the coil of the relay, the other end of which is connected to a mid-point of the secondary winding. According to another embodiment, this rectifier comprises a diode bridge connecting the two ends of the secondary winding respectively to the two ends of the coil of the relay. Advantageously, the secondary circuit comprises in addition a storage capacitor and means for comparison connected to the storage capacitor and comprising a monitoring output connected to control means of the relay, so as to supply a tripping signal to the relay if the value of the voltage of the capacitor is greater than a preset threshold. Advantageously, the means for comparison comprise a comparator or a voltage threshold diode. Preferably, the control means of the relay comprise a thyristor. Accordingly the present invention provides a trip device by fault current sensitive to pulsed currents, comprising a current transformer, a trip relay and a secondary circuit connecting said relay to the transformer comprising a toroid with a magnetic core, primary windings formed by the active conductors of an electrical installation to be protected and a secondary winding at the terminals of which winding a differential fault signal is established when a differential fault occurs in the primary windings, the said secondary winding is connected to the trip relay by the secondary circuit located to bring about tripping when said signal exceeds a preset threshold, characterized in that the magnetic core of the above-mentioned toroid presents a ratio between the dynamic induction elevation ABdyn at 400 Hz and the dynamic induction elevation ABdyn at 50 Hz greater 0.7, for a field intensity amplitude H of about 35 mAt/cm and that the said secondary circuit comprises a full-wave rectifier, said rectifier comprising two diodes respectively connecting the two ends of the secondary winding to one of the ends of the coil of the relay, the other end whereof is connected to a mid-point of the secondary winding. But other advantages and features of the invention will become more clearly apparent from the following description, referring to the accompanying drawings given as examples only and in which: Figure 1 is a graphic representation illustrating the breakdown of a pulsed current signal, for an opening angle of 0° (rms value of the current in mA, according to the frequency in Hz). Figure 2 illustrates the breakdown of a pulsed current signal, for an opening angle of 90° Figure 3 illustrates the breakdown of a pulsed current signal, for an opening angle of Figure 4 is a graphic representation illustrating the dynamic induction elevation (relative to 50 Hz), according to the frequency (in Hz), for a peak field intensity amplitude H of 34 mAT/cm, and Figure 5, 6, 7 and 8 represent schematically four different embodiments of the trip device according to the invention. In figures 5, 6, 7 and 8, four embodiments can be seen of a trip device D according to the invention, designed to be incorporated in or associated to an electrical circuit breaker (not represented) for breaking the active conductors supplying an electrical installation to be protected. This trip device D comprises commonly to the four embodiments, a differential transfomner 1 fomied by a magnetic core toroid 2 comprising a primary vending (not represented) fomried by the active conductors passing through the toroid 2, and a secondary winding 3 connected to the coil of a tripping relay 4, of the polarised type, by a secondary connecting circuit 5. The secondary circuit 5 of the trip device D, represented in figure 5, is formed by a capacitor 8 connected in series with the secondary winding 3 of the transfomier 1 and the polarised relay 4. In the second embodiment of the trip device described in figure 6, this secondary circuit 5 comprises two diodes 6, 7 connected on input respectively to the two ends of the secondary winding 3, and on output to the positive pole of the tripping relay 4, whereas the negative pole of the relay 4 Is connected to a mid-point 3a of the secondary winding 3. In the embodiment illustrated in figure 7, the secondary circuit 5 comprises a diode bridge P comprising four diodes 9 to 12. In the embodiment illustrated in figure 8, the secondary circuit 5 comprises a tuning capacitor 13 connected in parallel with the secondary winding 3 of the toroid 2 and a rectifier bridge P, whose outputs are connected in parallel to a storage capacitor 14, which is connected in parallel with the relay 4 and a thyristor 15 mounted in series, and a threshold circuit 16 comprising a control output connected to the thyristor 15. According to the first three embodiments, the tripping relay 4 commands tripping of the circuit brealter when the fault signal delivered to the coil of the relay 4, when a fault cun-ent appears in the primary windings, exceeds a preset tripping threshold. In the fourth embodiment, the threshold circuit 16 supplies a tripping signal to the relay 4 via the thyristor 15 when the voltage at the terminals of the storage capacitor 14 exceeds a certain threshold. It can be noted that the tripping relay 4 is advantageously of the polarised type using a single half-wave of the signal or a full-wave. In the first embodiment, the purpose of the capacitor 8 is to compose a shaping filter with the inductances of the detector toroid 2 and of the tripping relay 4. The value of the capacitor is determined by the usual means for calculating and determining filters; it takes account of the number of turns of the secondary winding 3 and coil 4 and of the magnetic materials implemented for designing the toroid 2. The use of such a shaping filter of the fault signal delivered by the tonsid 2 enables the same tripping threshold of the protective device to be kept in AC operating conditions, in half-wave or full-wave rectified fault current operating conditions, etc. In the embodiments illustrated in figures 6, 7 and 8, the pulsed cun-ent thresholds are rendered symmetrical by the rectifiers (two diodes or diode bridge). Referring to figures 1, 2 and 3, the breakdown of a class A signal (pulsed currents) (42 mA RMS 50 Hz) can be observed for different opening angles (a) respectively a = 0". 90° and 135°. It can thus be seen that for opening angles of 0 or 90° (figures 1 and 2), the pulsed currents can have harmonics greater than 50 Hz, of small amplitude. It can on the other hand be seen that, for an opening angle of 135° (figure 3), which may be the case for gradation thyristors, the pulsed cun-ents can have harmonics of large amplitude. In this figure 3, it can in fact be seen that for a = 135°, the amplitude of the 400 Hz harmonic still corresponds to about 30 % of the amplitude of the fundamental harmonic. According to the invention, the magnetic core of the toroid 2 of the transformer 1 presents a ratio between tiie dynamic induction elevation at 400 Hz and the dynamic induction elevation at 50 Hz greater than 0.7, for a field intensity amplitude of about 35 mA t/cm. Due to this magnetic characteristic of the core, an improvement of operation in class A is observed, that is to say a lowering of the tripping thresholds for pulsed currents, at least up to this angle of 135°. It can be noted that this threshold reduction for a = 135° will be about 15%. Referring to figure 4, it can be seen that for a nanocrystalline material whose curve (a) represents the relationship between the AByn relative to 50 Hz and the frequency, this characteristic can be verified. It can on the other hand be seen that it is not verified for a material of crystalline type whose same curve is represented in (b). A nanocrystalline material will therefore preferably be used. Advantageously, this magnetic core could be fomied by a soft magnetic iron based alloy made up of at least 50% of crystallites of a size smaller than lOOnm and containing the following atomic percentage : in addition to an iron content greater than 60 %, 0.5 to 2 % of copper. 2 to 5 % at least of one of the following metals, niobium, tungsten, tantalum, zirconium, hafnium, titanium and/or molybdenum, 5 to 14 % of boron and 14 to 17 % of silicon. When this transformer 1 is used in a trip device D of the type described in figure 5, additional magnetic characteristics will be advantageous to obtain both a great sensitivity to pulsed current faults and a regular tripping threshold, which characteristics are the following : a remanence ratio Br/Bs 0.6 T for H = 100 mA/cm, DByn max > 0.7 T and DByn/'^B > 0.7. These magnetic values could be obtained by two successive themial treatments performed on a magnetic band obtained by dipping (amorphous alloy strip cooled rapidly). The first thermal treatment consists of a nanocrystallisation treatment, with appiiration of a longitudinal magnetic field (following the direction of the band), whereas the second treatment will be performed under a transverse field. When the transformer 1 of the invention is used in a trip device D according to figures 6, 7 and 8, the same properties can be obtained with lower magnetic characteristics, notably DByn (100 mAt/cm) According to another embodiment of the invention, this magnetic core could be made of amorphous material, for this type of material does not present high magnetic losses, a suitable treatment of the core giving it the appropriate magnetic characteristics in compliance with the invention, i.e. DByn (400 Hz) / DByn (50 Hz) > 0.7, for H = 35 mAt/cm. A current transformer and fault current trip device, presenting an improved sensitivity to pulsed currents (lower tripping threshold), especially when used with electrical apparatuses having opening angles able to reach 135" or even more, have therefore been achieved by means of the invention. Naturally, the invention is not limited to the embodiments described and illustrated which have been given as examples only. Thus the invention also applies to trip devices presenting a different secondary circuit, for example comprising parallel-mounted capacitors, zener diodes etc. On the contrary, the invention comprises all the technical equivalents of the means described as well as their combinations if these are made according to the spirit of the invention. WE CLAIM: 1. A trip device by fault current sensitive to pulsed currents, comprising a current transformer (1), a trip relay (4) and a secondary circuit (5) connecting said relay to the transformer comprising a toroid (2) with a magnetic core, primary windings formed by the active conductors of an electrical installation to be protected and a secondary winding (3) at the terminals of which winding a differential fault signal is established when a differential fault occurs in the primary windings, the said secondary winding is connected to the trip relay by the secondary circuit located to bring about tripping when said signal exceeds a preset threshold, characterized in that the magnetic core of the above-mentioned toroid (2) presents a ratio between the dynamic induction elevation ABdyn at 400 Hz and the dynamic induction elevation ABdyn at 50 Hz greater 0.7, for a field intensity amplitude H of about 35 mAt/cm and that the said secondary circuit (5) comprises a full-wave rectifier (6, 7; 9 to 12), said rectifier comprising two diodes (6, 7) respectively connecting the two ends of the secondary winding (3) to one of the ends of the coil of the relay (4), the other end whereof is connected to a mid-point (3a) of the secondary winding (3). 2. The trip device as claimed in claim 1, wherein the magnetic core of the toroid (2) presents a remanence ratio Br/Bs 0.6T, for a field intensity amplitude of 100 mA/cm, a maximum dynamic induction elevation AB dyn greater than 0.7T, and a ratio between the dynamic induction elevation and the induction amplitude AB dyn /^B > 0.7. 3. The trip device as claimed in claim 1 or 2, wherein the magnetic core is made from a soft magnetic iron-based alloy, composed of more than 50 % of fine crystal grains of a size smaller than 100 nm and containing, in addition to an iron content greater than 60 % (at), 0.5 to 2 % of copper, 2 to 5 % at least of one of the following metals, niobium, tungsten, tantalum, zirconium, haftiium, titanium and/or molybdenum, 5 to 14 % of boron and 14 to 17 % of silicon. 4. The trip device as claimed in any one of the preceding claims, wherein the magnetic core of the toroid (2) is made of a nanocrystalline material. 5. The trip device as claimed in claim I, wherein the magnetic core of the toroid (2) is made of an amorphous material. 6. The trip device as claimed in any one of the claims 1 to 5, wherein the said rectifier comprises a diode bridge P respectively for connecting the two ends of the secondary winding (3) to the two ends of the coil of the relay (4). 7. The trip device as claimed in any one of the preceding claims, wherein that secondary circuit (5) comprises in addition a storage capacitor(14) and means for comparison (16) connected to the storage capacitor (14) and comprising a monitoring output connected to control means (15) of the relay (4) so as to supply a tripping signal to the relay (4) if the value of the voltage of the capacitor (14) is greater than a preset threshold. 8. The trip device as claimed in claim 7, wherein the means for comparison (16) comprise a comparator. 9. The trip device as claimed in claim 7, wherein the means for comparison (16) comprise a voltage threshold diode. 10. The trip device as claimed in any one of the claims 7 to 9, wherein the control means for the relay (4) comprise a thyristor (15). 11. A trip device, substantially as herein described with reference to the accompanying drawings.

Documents:

603-mas-1996 abstract duplicate.pdf

603-mas-1996 abstract.jpg

603-mas-1996 abstract.pdf

603-mas-1996 claims duplicate.pdf

603-mas-1996 claims.pdf

603-mas-1996 correspondence others.pdf

603-mas-1996 correspondence po.pdf

603-mas-1996 description (complete) duplicate.pdf

603-mas-1996 description (complete).pdf

603-mas-1996 drawings duplicate.pdf

603-mas-1996 drawings.pdf

603-mas-1996 form-1.pdf

603-mas-1996 form-26.pdf

603-mas-1996 form-4.pdf

603-mas-1996 petition.pdf