Title of Invention	A PROCESS FOR CONTROLLING A DEVICE COMPRISING ELECTROMAGNET FOR OPENING OR CLOSING ELECTROMAGNET OF A CIRCUIT BREAKER
Abstract	A control device and opening or closing electromagnet of a circuit breaker, the device comprising at least one coil connected in series with an electronic switch to the terminals of a supply voltage, means for measuring a first voltage, representative of the supply voltage, and means for control of the electromagnet, comprising means for comparison, connected to the mans for measuring the first voltage and to a control electrode of the electronic switch, to compare the first voltage with inrush and drop-out thresholds, characterized in that the means for comparison compare the first voltage with distinct first and second inrush thresholds and with a drop-out threshold, so as to monitor the flow of an inrush current in the coil during an inrush phase of preset duration when the first voltage reaches one of the inrush thresholds.

Title of Invention

A PROCESS FOR CONTROLLING A DEVICE COMPRISING ELECTROMAGNET FOR OPENING OR CLOSING ELECTROMAGNET OF A CIRCUIT BREAKER

Abstract

A control device and opening or closing electromagnet of a circuit breaker, the device comprising at least one coil connected in series with an electronic switch to the terminals of a supply voltage, means for measuring a first voltage, representative of the supply voltage, and means for control of the electromagnet, comprising means for comparison, connected to the mans for measuring the first voltage and to a control electrode of the electronic switch, to compare the first voltage with inrush and drop-out thresholds, characterized in that the means for comparison compare the first voltage with distinct first and second inrush thresholds and with a drop-out threshold, so as to monitor the flow of an inrush current in the coil during an inrush phase of preset duration when the first voltage reaches one of the inrush thresholds.

Full Text	The invention relates to a process for controlling a device comprising electromagnet for opening or closing electromagnet of a circuit breaker, said device comprising at least one coil connected in series with an electronic switch to the terminals of a supply voltage, means for measuring a first voltage, representative of the supply voltage, and means for control of the electromagnet, comprising means for comparison, connected to the means for measuring the first voltage and to a control electrode of the electronic switch, to compare the first voltage with inrush and drop-out thresholds. BACKGROUND OF THE INVENTION Circuit breakers generally comprise a certain number of electrical auxiliaries, more particularly closing electromagnets (XF) or opening electromagnets, notably shunt releases (MX) or under-voltage releases (MN). The electromagnets used in under-voltage releases (MN) have different operating characteristics from those used in shunt releases (MX) or in closing electromagnets (XF). The control devices which are associated thereto are consequently different. SUMMARY OF THE INVENTION The object of the invention is to achieve a standard control device able to be used indifferently with the three above-mentioned types of auxiliaries and guaranteeing a satisfactory operating safety in all cases. According to the invention this object is achieved by the fact that the means for comparison compare the first voltage with distinct first and second inrush thresholds and with a drop-out threshold, so as to monitor the flow of an inrush current in the coil during an inrush phase of preset duration when the first voltage reaches one of the inrush thresholds. According to a development of the invention, at the end of an inrush phase the control means control, during a holding phase, the flow in the coil of a holding current weaker than the inrush current, the device comprising means for measuring the current flowing in the coil, the control means comprising means for regulating the holding current, with means for comparing the current with a preset setpoint value, and means for commanding switching to a new inrush phase when, during a holding phase, the current is less than or equal to a preset fraction of the setpoint value during a second preset duration. According to another development of the invention, the means for measuring the first voltage comprise numerical means for determining the rms voltage, comprising sampling means and a finite impulse response filter having an equation of the form: where U2j is a sample of the first voltage, n > 2, m > 1, the weighting coefficients aj not all being identical. BRIEF DESCRIPTION OF THE DRAWINGS Other advantages and features will become more clearly apparent from the following description of particular embodiments given as non-restrictive examples only and represented in the accompanying drawings in which: FIGS. 1 and 2 represent schematically, in cross-section, particular embodiments, of known type, of electromagnets used for an under-voltage release (MN) and, respectively, in a shunt release (MX) or for a closing electromagnet of a circuit breaker. FIG. 3 illustrates a control device in which the invention can be implemented. FIG. 4 illustrates the additional elements of a device according to FIG. 3 in the case of an electromagnet with double coil. FIG. 5 represents a particular embodiment of a flowchart of operation of a device according to the invention. FIG. 6 illustrates a particular embodiment of a sub-routine corresponding to a holding phase of the flowchart according to FIG. 5. FIGS. 7a and 7b respectively illustrate the variations, versus time, of the signals U2 and lb in a device according to FIG. 3, when the voltage U2 increases slowly. FIGS. 8a and 8b respectively illustrate the variations, versus time, of the signals U2 and lb in a device according to FIG. 3 in case of a micro-break and in case of a supply voltage drop. FIG. 9 represents a particular embodiment of a sub-routine for measuring the voltage U2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An electromagnet conventionally comprises a movable core, movement of which to a position in which the electromagnet is actuated is caused by flow of an inrush current. It is then held in this position by the flow of a weaker, holding current. An electromagnet of the type represented in FIG. 1 is, conventionally, used in under-voltage releases (MN). It comprises an armature 1 inside which a coil 2 is arranged. The coil 2 surrounds a fixed core 3, secured to the armature 1, and a movable core 4. A spring 5 is fitted between the fixed core and the movable core so as to separate the movable core 4 from the fixed core 3. In the rest position of the electromagnet, represented in FIG. 1, a plunger 6 securedly affixed to the movable core 4 protrudes out from the armature. Application of a supply voltage to the terminals of the coil 1 causes excitation of the electromagnet. Flow of an inrush current in the coil 1 causes movement of the movable core 4 in the direction of the fixed core 3, against the spring 5. When the cores come into contact, the plunger 6 no longer protrudes out from the armature 1. The inrush phase lasts sufficiently long to enable a complete movement of the movable core 4 which comes into contact with the fixed core 3. Subsequently, flow of a high inrush current is no longer necessary to hold the movable core in the actuation position of the electromagnet and, conventionally, only a weaker holding current is maintained in the coil 1. When the supply voltage is insufficient, the current flow in the coil 1 is interrupted. The energy of the spring 5 then urges the movable core 4 to the position represented in FIG. 1 and the plunger 6, securedly affixed to the movable core, causes opening of the associated circuit breaker in the case of an under-voltage release. Opening of the circuit breaker being performed by the action of the spring 5, the latter must be relatively powerful. Consequently, the energy required to bring the cores into contact when excitation of the electromagnet takes place, thus allowing closing of the circuit breaker, is relatively high. The supply voltage of the electromagnet must consequently be sufficient to ensure that the cores come into contact in all cases when an electromagnet command is performed. Conventionally, for an under-voltage release coil having a rated voltage A of 100V, an inrush threshold of about 70 V and a drop-out threshold of about 30V are used. An electromagnet of the type represented in FIG. 2 is, conventionally, used in shunt releases (MX) and as closing electromagnet (XF) of a circuit breaker. It also comprises a coil 2 in an armature 1. A plunger 7 securedly affixed to a movable core 8 passes through a fixed core 9, secured to the armature 1. In the rest position of the electromagnet, represented in FIG. 2, a spring 10 keeps the cores separated from one another, the plunger then not protruding outside the armature. In case of actuation of the electromagnet an inrush current flowing in the coil 2 causes movement of the movable core, and consequently of the plunger 7, which then protrudes outwards, thus allowing either opening of the associated circuit breaker in the case of a shunt release (MX) or closing thereof in the case of a closing electromagnet (XF). It is therefore the electromagnetic energy supplied by the coil which causes actuation of the circuit breaker. As previously, an inrush phase is followed by a holding phase, during which the current flowing in the coil is weaker. When the voltage is lower than a drop-out threshold, the current flow in the coil is interrupted and the movable core 8 is moved away from the fixed core 9 by the action of the spring 10. Switching to this position not having any action on the circuit breaker, the spring 10 does not have to be powerful It is therefore a relatively weak spring in comparison with the spring 5. The supply voltage necessary for actuation of the electromagnet is consequently less than that necessary in the case of an electromagnet according to FIG. 1. Conventionally, for a coil of a shunt release having a rated supply voltage A of 100V, an inrush threshold of about 20V and a drop-out threshold of about 10V are used. The control device illustrated in FIG. 3 can be used either for control of an electromagnet according to FIG. 1 for an under-voltage release or for control of an electromagnet according to FIG. 2 for a shunt release or a closing electromagnet of a circuit breaker. The coil 2 is connected in series with an electronic switch, preferably formed by a transistor Tl, and a measuring resistor Rl to the terminals of a supply voltage Ua. Conventionally, a freewheel diode Dl is connected in parallel with the coil 2. The supply voltage Ua is obtained by rectification, by means of a diode bridge rectifier 11, of an AC voltage Ul supplied by the conductors of a power system 12 to which a circuit breaker is connected, opening or, should this be the case, closing of which circuit breaker can be controlled by the coil 2. An output SI of a control circuit 14, preferably a microprocessor-based circuit, is connected to a control electrode of the transistor Tl to which it supplies control signals. An input El of the control circuit 14 is connected to the mid-point of a resistive divider formed by two resistors R2 and R3, connected in series to the terminals of the supply voltage Ua. The signals applied to the input El are representative of the voltage U2 at the terminals of the resistor R3, itself representative of the supply voltage Ua of the electromagnet, which is itself representative of the voltage Ul of the power system 12. The control circuit 14 is also connected to the terminals of the resistor Rl, so as to receive on an input E2 signals lb representative of the current flowing in the coil when the transistor Tl is turned on. In the case of a shunt release (MX) or of a circuit breaker closing electromagnet (XF), a control means enables a control order to be supplied to the electromagnet. The electromagnet is actuated on receipt of this order provided that the supply voltage Ua is sufficient. In FIG. 3, the control means is formed by a pushbutton 15 arranged between one of the power system conductors and one of the input terminals of the rectifier 11. The control means may apply a control order directly to a control input, not represented, of the microprocessor-based control circuit 14. In this case, as in the case of an under-voltage release (MN), the rectifier 11 is permanently connected to the power system 12. FIG. 4 illustrates the complementary elements of an embodiment with double coil. An inrush coil 16 is connected in series with a transistor T2 and a measuring resistor R4 to the terminals of the supply voltage Ua. A free-wheel diode D2 is connected in parallel with the inrush coil 16. The control electrode of the transistor T2 is connected to an output S2 of the control circuit 14. If the current in the inrush coil 16 has to be regulated during the inrush phase, the point common to R4 and T2 is connected to an input E3 of the circuit 14. The control circuit 14 can be achieved by any suitable, analog or digital, means. In a preferred embodiment, it comprises a microprocessor which performs sampling, with a sampling period Te, of the signals applied to its inputs El, E2 and E3, analog-to-digital conversion of these signals, comparison of these signals with setpoint values during the holding and inrush phases, and control of the transistors Tl and T2. The control circuit 14 of a device according to the invention uses two distinct inrush thresholds and a drop-out threshold. It can thus be used indifferently with the different types of electromagnets. The inrush and drop-out thresholds selected are compatible both with existing electromagnets and with the norms of the circuit breaker auxiliaries involved. A particular embodiment of a flowchart of operation of a microprocessor-based device according to the invention, represented in FIG. 5, will be explained in greater detail hereafter, with reference to the wave shapes of the signals U2 and lb, represented in FIGS. 7a and 7b in which the voltage U2 increases slowly up to its rated value U2n. In an initialization step Fl, an indicator M is set to a first logic state, 0 in FIG. 5. Then in a step F2 a time indicator ta is set to 0. Then the microprocessor of the control circuit 14 goes on to a step F3 of measurement (sampling and conversion) of the voltage U2 applied to the input El. The microprocessor then goes on to a step F4 of comparing the voltage U2 with the drop-out threshold Sr. If the voltage U2 is greater than or equal to the threshold Sr (YES output of F4), then, in a step F5, the voltage U2 is compared with a first inrush threshold Sa.sub.l. If the voltage U2 is lower than the threshold Sa.sub.l (NO output of F5), the microprocessor goes back to the input of the step F3 of measurement of U2 for monitoring of a new voltage sample. This corresponds, in FIG. 7a, to the moments prior to the time tl. If on the other hand, at F5, the voltage U2 is greater than or equal to the threshold Sa.sub.l (YES output of F5), the microprocessor goes on to a step F6 in which it checks if the indicator M is still at zero. If this is the case (YES output of F6), the microprocessor goes on to a step F7 corresponding to an inrush phase. The transistor Tl, or T2 in the embodiment with double coil of FIG. 4, is then controlled by the control circuit 14 so that a current lb whose value is equal to a setpoint value lea flows in the coil 2, or in the inrush coil 16 in the case of a double coil, during the inrush phase. In FIG. 7b this phase ends at a time t2. The duration of the inrush phase is preset, for example 80 ms, so as to ensure in all cases correct contact of the fixed and movable cores of the electromagnet. At the end of the inrush phase, in a step F8, the indicator M is set to logic state 1, then the microprocessor goes on to a step F9 corresponding to a holding phase. During the holding phase, the transistor Tl is controlled so that the coil 6 has flowing through it a current lb whose value is equal to a setpoint value Icm (FIG. 7b), lower than lea, sufficient to keep the cores of the electromagnet into contact. During the holding phase the microprocessor continues monitoring the voltage U2 by going back, in parallel with going to step F9, to the input of step F2. If, at the step F6, the indicator M is not zero (NO output of F6), this means that the electromagnet is in a holding phase. The microprocessor then checks, in a step F10, if the voltage U2 is equal to or greater than a second inrush threshold Sa2. If this is not the case (NO output of F10), this therefore means that the voltage U2 is comprised between the thresholds Sai and Sa2 and that the coil has the holding current flowing through it. This state corresponds to the state represented between the times t2 and t3 in FIGS. 7a and 7b. The microprocessor then goes back to the input of step F3, continuing monitoring of U2. If on the other hand, at the step F10, U2 is greater than or equal to Sa.sub.2 (YES output of F10), the microprocessor then goes to the step F7 causing a new inrush phase between the times t3 and t4, then to a holding phase after the time t4. If, at the step F4, the voltage U2 is lower than the drop-out threshold Sr (NO output of F4), the indicator ta is incremented (ta = ta + Ata) in a step Fl 1. Then, in a step F12, ta is compared with a preset time, 15 ms in FIG. 5. If the time indicator ta is not equal to 15 ms (NO output of F12), the microprocessor goes back to the input of the step F3. If on the other hand ta is equal to 15 ms (YES output of F12), this means that the voltage U2 has been lower than the drop-out threshold for 15 ms. The microprocessor then causes (step F13) switching to an unlatching phase, during which the current flowing in the coil, or in the coils in the case of a double coil, is annulled. The drop-out threshold Sr and the maximum time ta are chosen so that the electronic control circuit gives an unlatching order before the electromagnet drops by itself. In a preferred embodiment, the first inrush threshold, Sai, is representative of a voltage comprised between-40 and 50%, preferably 45%, of the rated supply voltage of the electromagnet and the second inrush threshold, Sa2, is representative of a voltage comprised between 70 and 85%, preferably 80%, of the rated supply voltage of the electromagnet. The drop-out threshold Sr for its part corresponds to a voltage of about 30% of the rated supply voltage. In the case of a slow increase of the supply voltage, as represented in FIG. 7a, when the voltage U2 reaches the first threshold Sai, at the time tl, switching to inrush phase (tl-t2) automatically brings into contact the cores of an electromagnet with a weak spring, i.e. of the type used for a shunt release (MX) or for a closing electromagnet (XF). If on the other hand the electromagnet, with a powerful spring, is of the type used for an under-voltage release (MN), this inrush phase is insufficient. When the voltage U2 reaches the second threshold Sa2, at the time t3, the control circuit causes a new switching to inrush phase (t3-t4). This new inrush phase does not have any influence if the cores of the electromagnet were already brought into contact during the first inrush phase. If on the other hand this was not the case, then the cores come into contact during this second inrush phase. In the case of a fast increase of the supply voltage, the first inrush phase may be sufficient in all cases. To increase the reliability of the control device, the latter preferably also comprises means for detecting micro-breaks of the supply voltage Ua. Such a micro-break, or transient voltage interruption, may in fact make the electromagnet drop out when the latter is in holding phase. As described above, an unlatching phase is only introduced by the microprocessor if the voltage U2 remains lower than the drop-out threshold Sr for at least 15 ms. A shorter break, for example 10-11 ms, must not lead to switching to an unlatching phase. However, to prevent a possible unscheduled unlatching of the electromagnet, the control circuit 14 which detects such a micro-break switches to a new inrush phase. In the particular embodiment illustrated in FIGS. 6, 8a and 8b, detection of a micro-break during a holding phase is based on monitoring of the holding current lb in the coil 2. When the current lb is lower than a preset function, preferably comprised between 1/4 and 1/2, of the setpoint value Icm during a preset period, preferably about a few milliseconds, a new inrush phase is caused. In the sub-routine of FIG. 6, a holding phase begins with an initialization step F14, during which a time indicator tb is set to zero. Then, in a step F15, the current lb is measured. For this, the transistor Tl is temporarily turned on, enabling sampling and analog-to-digital conversion of the signals applied to the input E2 of the control circuit 14. Then the microprocessor performs in parallel detection of micro-breaks and regulation of the current lb to the setpoint value Icm, in a step F16 which loops back on the input of step F15. To detect micro-breaks, the microprocessor compares the current lb with a threshold equal to Icm/2 (or Icm/4) in a step F17. If (NO output of F17) the current lb is greater than this threshold (before the time t5 in FIG. 8b)s the microprocessor then goes back to the input of step F14. If on the other hand (between t6 and t7) the current lb is lower than or equal to this threshold, then the microprocessor goes (YES output of F17) to a step F18 during which the time indicator tb is incremented (tb = tb + Atb). Then in a step F19, the time indicator tb is compared to 5 ms. If tb is lower than 5 ms (NO output of F19), then the microprocessor loops back on the input of step F15 for a new measurement of lb. On the other hand if tb=5 ms (YES output of F19) this means that the current lb has been lower than the threshold Icm/2 for 5 ms and the microprocessor causes a new inrush phase (step 7), at the time t7. If a micro-break was really involved, the voltage U2 has already returned to its rated voltage or returns thereto at the beginning of the inrush phase, at a time t8, and the current can take the value lea during the time the inrush phase lasts, before a new switching to holding phase at a time t9. If on the other hand, as represented in FIG. 8a, the voltage drop starting at a time tlO lasts for more than 15 ms, this voltage drop first causes a current drop, which is detected 5 ms later, at tl 1, as a micro-break causing switching to an inrush phase. However, as the voltage is not re-established, the current lb continues to drop and keeping the voltage U2 below the dropout threshold Sr for at least 15 ms (FIG. 8a) leads the microprocessor to cause an unlatching phase at the time tl2 (step F13 of FIG. 5) during which the current in the coil is annulled. Measurement of the voltage U2 by the control circuit 14 must have a satisfactory precision whether the supply voltage Ua, from which it is derived, is a DC voltage or a full-wave rectified AC voltage as in the embodiment of FIG. 3. Moreover, in the case of a rectified AC voltage, the frequency of the AC voltage must be able to vary in frequency ranges comprised between 45 and 65 Hz and 360 and 440 Hz. In the case of a circuit breaker, the voltage can be disturbed by harmonics and measurement must be fast because with opening electromagnets the circuit breaker must open in less than 40 milliseconds. In addition, the required operating temperature ranges from -40° C. to +125° C. In known circuit breaker opening and closing electromagnets, voltage measurement is generally performed by means of a low-pass analog filter. This filter supplies a mean value of the voltage to be measured with a poor precision (more than 10% in general) and requires the use of a very precise, very stable in temperature capacitor, which is expensive and voluminous. To overcome these drawbacks, measurement of the voltage is preferably achieved by numerical electronic processing supplying a rms value of the voltage U2 by means of a finite impulse response (FIR) filter. In a preferred embodiment, the voltage U2 is sampled with a sampling period Tc=625\|is. Preferably, a new computation is performed every 8 samples, i.e. every 5 milliseconds. The microprocessor uses 24 samples for each computation. In the particular embodiment illustrated in FIG. 9, measurement of U2 starts with an initialization step F20, during which an indicator i is set to 0. Then the microprocessor of the control circuit 14 goes on to a step F21 of measuring and storing a sample U2j. It then checks, in a step F22, if the indicator i has reached the value 7. If this is not the case (NO output of F22) it goes on to a step F23 of incrementing i (i = i + 1) before looping back on the input of step F21 for measurement of a new voltage sample. If, at the step F22, i=7, this means that 8 successive samples of U2 have been stored. In this case (YES output of F22), the microprocessor goes on to a step F23 of computation of a first partial sum Al of the square of the last 8 measured samples / 7 V o J . Then, in a step F24, the microprocessor computes a value of U2 obtained by the weighted sum of three successive partial sums Al, A2 and A3 (U2=A1+2A2+A3). It should be noted that initially the sums Al, A2 and A3 had been set to zero during the step Fl (FIG. 5). In a step F25 the new partial sum A3 takes the value of A2 and the new partial sum A2 takes the value of Al. The microprocessor then loops back to the input of step F20, enabling, after 8 new samples have been measured, a new computation of U2 to be performed taking the last 24 samples measured into account. The value of U2 thus obtained is representative of its rms value, measured numerically by means of a finite impulse response filter having an equation of the type: U2=ai Al+a2 A2+ - - - +aj Aj + - - - +an An m-with4/ = ]T£/2,2 0 in which the weighting coefficients aj are different, and where n > 2 and m > 1. The rms value of the voltage U2 is thus computed from the weighted sum of n partial sums of m squares of samples U2*. In the preferred embodiment of FIG. 9, n=3, m=8, ai =a3 =1 and a2 =2. The FIR filter used may be of another type, the number of samples, weighting coefficients, and sampling frequency depending on the precision and speed required. For example, Harming, Hamming, rectangular-shaped etc., windows can be used. WE CLAIM: 1. A process for controlling a device comprising electromagnet for opening or closing electromagnet of a circuit breaker, the device comprising at least one coil (2) connected in series with an electronic switch (Tl) to the terminals of a supply voltage (Ua), said process comprising the steps of measuring a first voltage (U2), representative of the supply voltage; comparing the first voltage (U2) with distinct first and second inrush thresholds (Sai, Sa2) and with a drop-out threshold (Sr); monitoring the flow of an inrush current (lea) in the coil during an inrush phase of preset duration when the first voltage (U2) reaches one of the inrush thresholds (Sai, Sa2). 2. The process according to claim 1, wherein the first inrush threshold (Sai) is representative of a voltage of about 40 to 50% of the rated supply voltage of the electromagnet and the second inrush threshold (Sa2) is representative of a voltage of about 70 to 85% of the rated supply voltage of the electromagnet. 3. The process according to any one of the claims 1 and 2, wherein the electromagnet belongs to an under voltage release. 4. The process according to any one of claims 1 and 2, wherein the electromagnet belongs to a shunt release. 5. The process according to any one of the claims 1 to 4, comprising the steps of controlling, during the holding phase and at the end of an inrush phase, the flow in the coil (2) of a holding current weaker than the inrush current; measuring the holding current (lb) flowing in the coil; regulating the holding current and comparing the holding current with a set point value (Icm); switching to a new inrush phase when, during a holding phase, the current (lb) is less than or equal to a preset fraction of the set point value during a second preset duration (tb). 6. The process according to claim 5, wherein said fraction is between lA and XA of the setpoint value (Icm). 7. The process according to any one of the claims 5 and 6, wherein the second preset duration (tb) is about a few milliseconds. 8. The process according to any one of the claims 1 to 7, comprising the step of determining the rms voltage using sampling means and a finite impulse response filter having an equation of the form: where U21 is a sample of the first voltage, n > 2, m > 1, the weighting coefficients aj not all being identical. 9. The process according to claim 8, wherein n = 3, aj = a3 = 1 and a2 = 2.

Full Text

The invention relates to a process for controlling a device comprising electromagnet for opening or closing electromagnet of a circuit breaker, said device comprising at least one coil connected in series with an electronic switch to the terminals of a supply voltage, means for measuring a first voltage, representative of the supply voltage, and means for control of the electromagnet, comprising means for comparison, connected to the means for measuring the first voltage and to a control electrode of the electronic switch, to compare the first voltage with inrush and drop-out thresholds.
BACKGROUND OF THE INVENTION
Circuit breakers generally comprise a certain number of electrical auxiliaries, more particularly closing electromagnets (XF) or opening electromagnets, notably shunt releases (MX) or under-voltage releases (MN). The electromagnets used in under-voltage releases (MN) have different operating characteristics from those used in shunt releases (MX) or in closing electromagnets (XF). The control devices which are associated thereto are consequently different.
SUMMARY OF THE INVENTION
The object of the invention is to achieve a standard control device able to be used indifferently with the three above-mentioned types of auxiliaries and guaranteeing a satisfactory operating safety in all cases.
According to the invention this object is achieved by the fact that the means for comparison compare the first voltage with distinct first and second inrush thresholds and with a drop-out threshold, so as to monitor the flow of an inrush current in the coil during an inrush phase of preset duration when the first voltage reaches one of the inrush thresholds.

According to a development of the invention, at the end of an inrush phase the control means control, during a holding phase, the flow in the coil of a holding current weaker than the inrush current, the device comprising means for measuring the current flowing in the coil, the control means comprising means for regulating the holding current, with means for comparing the current with a preset setpoint value, and means for commanding switching to a new inrush phase when, during a holding phase, the current is less than or equal to a preset fraction of the setpoint value during a second preset duration.
According to another development of the invention, the means for measuring the first voltage comprise numerical means for determining the rms voltage, comprising sampling means and a finite impulse response filter having an equation of the form:
where U2j is a sample of the first voltage, n > 2, m > 1, the weighting coefficients aj not all being identical.
BRIEF DESCRIPTION OF THE DRAWINGS
Other advantages and features will become more clearly apparent from the following description of particular embodiments given as non-restrictive examples only and represented in the accompanying drawings in which:
FIGS. 1 and 2 represent schematically, in cross-section, particular embodiments, of known type, of electromagnets used for an under-voltage release (MN) and, respectively, in a shunt release (MX) or for a closing electromagnet of a circuit breaker.
FIG. 3 illustrates a control device in which the invention can be implemented.

FIG. 4 illustrates the additional elements of a device according to FIG. 3 in the case of an electromagnet with double coil.
FIG. 5 represents a particular embodiment of a flowchart of operation of a device according to the invention.
FIG. 6 illustrates a particular embodiment of a sub-routine corresponding to a holding phase of the flowchart according to FIG. 5.
FIGS. 7a and 7b respectively illustrate the variations, versus time, of the signals U2 and lb in a device according to FIG. 3, when the voltage U2 increases slowly.
FIGS. 8a and 8b respectively illustrate the variations, versus time, of the signals U2 and lb in a device according to FIG. 3 in case of a micro-break and in case of a supply voltage drop.
FIG. 9 represents a particular embodiment of a sub-routine for measuring the voltage U2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
An electromagnet conventionally comprises a movable core, movement of which to a position in which the electromagnet is actuated is caused by flow of an inrush current. It is then held in this position by the flow of a weaker, holding current.
An electromagnet of the type represented in FIG. 1 is, conventionally, used in under-voltage releases (MN). It comprises an armature 1 inside which a coil 2 is arranged. The coil 2 surrounds a fixed core 3, secured to the armature 1, and a movable core 4. A spring 5 is fitted between the fixed core and the movable core so as to separate the movable core 4 from the fixed core 3. In the rest position of the electromagnet, represented in FIG. 1, a plunger 6 securedly affixed to the

movable core 4 protrudes out from the armature. Application of a supply voltage to the terminals of the coil 1 causes excitation of the electromagnet. Flow of an inrush current in the coil 1 causes movement of the movable core 4 in the direction of the fixed core 3, against the spring 5. When the cores come into contact, the plunger 6 no longer protrudes out from the armature 1. The inrush phase lasts sufficiently long to enable a complete movement of the movable core 4 which comes into contact with the fixed core 3. Subsequently, flow of a high inrush current is no longer necessary to hold the movable core in the actuation position of the electromagnet and, conventionally, only a weaker holding current is maintained in the coil 1. When the supply voltage is insufficient, the current flow in the coil 1 is interrupted. The energy of the spring 5 then urges the movable core 4 to the position represented in FIG. 1 and the plunger 6, securedly affixed to the movable core, causes opening of the associated circuit breaker in the case of an under-voltage release. Opening of the circuit breaker being performed by the action of the spring 5, the latter must be relatively powerful. Consequently, the energy required to bring the cores into contact when excitation of the electromagnet takes place, thus allowing closing of the circuit breaker, is relatively high. The supply voltage of the electromagnet must consequently be sufficient to ensure that the cores come into contact in all cases when an electromagnet command is performed. Conventionally, for an under-voltage release coil having a rated voltage A of 100V, an inrush threshold of about 70 V and a drop-out threshold of about 30V are used.
An electromagnet of the type represented in FIG. 2 is, conventionally, used in shunt releases (MX) and as closing electromagnet (XF) of a circuit breaker. It also comprises a coil 2 in an armature 1. A plunger 7 securedly affixed to a movable core 8 passes through a fixed core 9, secured to the armature 1. In the rest position of the electromagnet, represented in FIG. 2, a spring 10 keeps the cores separated from one another, the plunger then not protruding outside the armature. In case of actuation of the electromagnet an inrush current flowing in the coil 2 causes movement of the movable core, and consequently of the plunger 7, which then protrudes outwards, thus allowing either opening of the associated circuit breaker in the case of a shunt release (MX) or closing thereof in the case of a closing electromagnet (XF). It is therefore the electromagnetic energy supplied by the coil which causes actuation of the circuit breaker. As

previously, an inrush phase is followed by a holding phase, during which the current flowing in the coil is weaker. When the voltage is lower than a drop-out threshold, the current flow in the coil is interrupted and the movable core 8 is moved away from the fixed core 9 by the action of the spring 10. Switching to this position not having any action on the circuit breaker, the spring 10 does not have to be powerful It is therefore a relatively weak spring in comparison with the spring 5. The supply voltage necessary for actuation of the electromagnet is consequently less than that necessary in the case of an electromagnet according to FIG. 1. Conventionally, for a coil of a shunt release having a rated supply voltage A of 100V, an inrush threshold of about 20V and a drop-out threshold of about 10V are used.
The control device illustrated in FIG. 3 can be used either for control of an electromagnet according to FIG. 1 for an under-voltage release or for control of an electromagnet according to FIG. 2 for a shunt release or a closing electromagnet of a circuit breaker.
The coil 2 is connected in series with an electronic switch, preferably formed by a transistor Tl, and a measuring resistor Rl to the terminals of a supply voltage Ua. Conventionally, a freewheel diode Dl is connected in parallel with the coil 2. The supply voltage Ua is obtained by rectification, by means of a diode bridge rectifier 11, of an AC voltage Ul supplied by the conductors of a power system 12 to which a circuit breaker is connected, opening or, should this be the case, closing of which circuit breaker can be controlled by the coil 2. An output SI of a control circuit 14, preferably a microprocessor-based circuit, is connected to a control electrode of the transistor Tl to which it supplies control signals. An input El of the control circuit 14 is connected to the mid-point of a resistive divider formed by two resistors R2 and R3, connected in series to the terminals of the supply voltage Ua. The signals applied to the input El are representative of the voltage U2 at the terminals of the resistor R3, itself representative of the supply voltage Ua of the electromagnet, which is itself representative of the voltage Ul of the power system 12. The control circuit 14 is also connected to the terminals of the resistor Rl, so as to receive on an input E2 signals lb representative of the current flowing in the coil when the transistor Tl is turned on. In the case of a shunt release (MX) or of a circuit breaker closing

electromagnet (XF), a control means enables a control order to be supplied to the electromagnet. The electromagnet is actuated on receipt of this order provided that the supply voltage Ua is sufficient. In FIG. 3, the control means is formed by a pushbutton 15 arranged between one of the power system conductors and one of the input terminals of the rectifier 11. The control means may apply a control order directly to a control input, not represented, of the microprocessor-based control circuit 14. In this case, as in the case of an under-voltage release (MN), the rectifier 11 is permanently connected to the power system 12.
FIG. 4 illustrates the complementary elements of an embodiment with double coil. An inrush coil 16 is connected in series with a transistor T2 and a measuring resistor R4 to the terminals of the supply voltage Ua. A free-wheel diode D2 is connected in parallel with the inrush coil 16. The control electrode of the transistor T2 is connected to an output S2 of the control circuit 14. If the current in the inrush coil 16 has to be regulated during the inrush phase, the point common to R4 and T2 is connected to an input E3 of the circuit 14.
The control circuit 14 can be achieved by any suitable, analog or digital, means. In a preferred embodiment, it comprises a microprocessor which performs sampling, with a sampling period Te, of the signals applied to its inputs El, E2 and E3, analog-to-digital conversion of these signals, comparison of these signals with setpoint values during the holding and inrush phases, and control of the transistors Tl and T2.
The control circuit 14 of a device according to the invention uses two distinct inrush thresholds and a drop-out threshold. It can thus be used indifferently with the different types of electromagnets. The inrush and drop-out thresholds selected are compatible both with existing electromagnets and with the norms of the circuit breaker auxiliaries involved.
A particular embodiment of a flowchart of operation of a microprocessor-based device according to the invention, represented in FIG. 5, will be explained in greater detail hereafter, with reference to the wave shapes of the signals U2 and lb, represented in FIGS. 7a and 7b in which

the voltage U2 increases slowly up to its rated value U2n.
In an initialization step Fl, an indicator M is set to a first logic state, 0 in FIG. 5. Then in a step F2 a time indicator ta is set to 0. Then the microprocessor of the control circuit 14 goes on to a step F3 of measurement (sampling and conversion) of the voltage U2 applied to the input El.
The microprocessor then goes on to a step F4 of comparing the voltage U2 with the drop-out threshold Sr. If the voltage U2 is greater than or equal to the threshold Sr (YES output of F4), then, in a step F5, the voltage U2 is compared with a first inrush threshold Sa.sub.l. If the voltage U2 is lower than the threshold Sa.sub.l (NO output of F5), the microprocessor goes back to the input of the step F3 of measurement of U2 for monitoring of a new voltage sample. This corresponds, in FIG. 7a, to the moments prior to the time tl. If on the other hand, at F5, the voltage U2 is greater than or equal to the threshold Sa.sub.l (YES output of F5), the microprocessor goes on to a step F6 in which it checks if the indicator M is still at zero. If this is the case (YES output of F6), the microprocessor goes on to a step F7 corresponding to an inrush phase.
The transistor Tl, or T2 in the embodiment with double coil of FIG. 4, is then controlled by the control circuit 14 so that a current lb whose value is equal to a setpoint value lea flows in the coil 2, or in the inrush coil 16 in the case of a double coil, during the inrush phase. In FIG. 7b this phase ends at a time t2. The duration of the inrush phase is preset, for example 80 ms, so as to ensure in all cases correct contact of the fixed and movable cores of the electromagnet. At the end of the inrush phase, in a step F8, the indicator M is set to logic state 1, then the microprocessor goes on to a step F9 corresponding to a holding phase. During the holding phase, the transistor Tl is controlled so that the coil 6 has flowing through it a current lb whose value is equal to a setpoint value Icm (FIG. 7b), lower than lea, sufficient to keep the cores of the electromagnet into contact.
During the holding phase the microprocessor continues monitoring the voltage U2 by going

back, in parallel with going to step F9, to the input of step F2.
If, at the step F6, the indicator M is not zero (NO output of F6), this means that the electromagnet is in a holding phase. The microprocessor then checks, in a step F10, if the voltage U2 is equal to or greater than a second inrush threshold Sa2. If this is not the case (NO output of F10), this therefore means that the voltage U2 is comprised between the thresholds Sai and Sa2 and that the coil has the holding current flowing through it. This state corresponds to the state represented between the times t2 and t3 in FIGS. 7a and 7b. The microprocessor then goes back to the input of step F3, continuing monitoring of U2. If on the other hand, at the step F10, U2 is greater than or equal to Sa.sub.2 (YES output of F10), the microprocessor then goes to the step F7 causing a new inrush phase between the times t3 and t4, then to a holding phase after the time t4.
If, at the step F4, the voltage U2 is lower than the drop-out threshold Sr (NO output of F4), the indicator ta is incremented (ta = ta + Ata) in a step Fl 1. Then, in a step F12, ta is compared with a preset time, 15 ms in FIG. 5. If the time indicator ta is not equal to 15 ms (NO output of F12), the microprocessor goes back to the input of the step F3. If on the other hand ta is equal to 15 ms (YES output of F12), this means that the voltage U2 has been lower than the drop-out threshold for 15 ms. The microprocessor then causes (step F13) switching to an unlatching phase, during which the current flowing in the coil, or in the coils in the case of a double coil, is annulled. The drop-out threshold Sr and the maximum time ta are chosen so that the electronic control circuit gives an unlatching order before the electromagnet drops by itself.
In a preferred embodiment, the first inrush threshold, Sai, is representative of a voltage comprised between-40 and 50%, preferably 45%, of the rated supply voltage of the electromagnet and the second inrush threshold, Sa2, is representative of a voltage comprised between 70 and 85%, preferably 80%, of the rated supply voltage of the electromagnet. The drop-out threshold Sr for its part corresponds to a voltage of about 30% of the rated supply voltage.

In the case of a slow increase of the supply voltage, as represented in FIG. 7a, when the voltage U2 reaches the first threshold Sai, at the time tl, switching to inrush phase (tl-t2) automatically brings into contact the cores of an electromagnet with a weak spring, i.e. of the type used for a shunt release (MX) or for a closing electromagnet (XF). If on the other hand the electromagnet, with a powerful spring, is of the type used for an under-voltage release (MN), this inrush phase is insufficient. When the voltage U2 reaches the second threshold Sa2, at the time t3, the control circuit causes a new switching to inrush phase (t3-t4). This new inrush phase does not have any influence if the cores of the electromagnet were already brought into contact during the first inrush phase. If on the other hand this was not the case, then the cores come into contact during this second inrush phase. In the case of a fast increase of the supply voltage, the first inrush phase may be sufficient in all cases.
To increase the reliability of the control device, the latter preferably also comprises means for detecting micro-breaks of the supply voltage Ua. Such a micro-break, or transient voltage interruption, may in fact make the electromagnet drop out when the latter is in holding phase. As described above, an unlatching phase is only introduced by the microprocessor if the voltage U2 remains lower than the drop-out threshold Sr for at least 15 ms. A shorter break, for example 10-11 ms, must not lead to switching to an unlatching phase. However, to prevent a possible unscheduled unlatching of the electromagnet, the control circuit 14 which detects such a micro-break switches to a new inrush phase.
In the particular embodiment illustrated in FIGS. 6, 8a and 8b, detection of a micro-break during a holding phase is based on monitoring of the holding current lb in the coil 2. When the current lb is lower than a preset function, preferably comprised between 1/4 and 1/2, of the setpoint value Icm during a preset period, preferably about a few milliseconds, a new inrush phase is caused.
In the sub-routine of FIG. 6, a holding phase begins with an initialization step F14, during which

a time indicator tb is set to zero. Then, in a step F15, the current lb is measured. For this, the transistor Tl is temporarily turned on, enabling sampling and analog-to-digital conversion of the signals applied to the input E2 of the control circuit 14. Then the microprocessor performs in parallel detection of micro-breaks and regulation of the current lb to the setpoint value Icm, in a step F16 which loops back on the input of step F15. To detect micro-breaks, the microprocessor compares the current lb with a threshold equal to Icm/2 (or Icm/4) in a step F17. If (NO output of F17) the current lb is greater than this threshold (before the time t5 in FIG. 8b)s the microprocessor then goes back to the input of step F14. If on the other hand (between t6 and t7) the current lb is lower than or equal to this threshold, then the microprocessor goes (YES output of F17) to a step F18 during which the time indicator tb is incremented (tb = tb + Atb). Then in a step F19, the time indicator tb is compared to 5 ms. If tb is lower than 5 ms (NO output of F19), then the microprocessor loops back on the input of step F15 for a new measurement of lb. On the other hand if tb=5 ms (YES output of F19) this means that the current lb has been lower than the threshold Icm/2 for 5 ms and the microprocessor causes a new inrush phase (step 7), at the time t7. If a micro-break was really involved, the voltage U2 has already returned to its rated voltage or returns thereto at the beginning of the inrush phase, at a time t8, and the current can take the value lea during the time the inrush phase lasts, before a new switching to holding phase at a time t9. If on the other hand, as represented in FIG. 8a, the voltage drop starting at a time tlO lasts for more than 15 ms, this voltage drop first causes a current drop, which is detected 5 ms later, at tl 1, as a micro-break causing switching to an inrush phase. However, as the voltage is not re-established, the current lb continues to drop and keeping the voltage U2 below the dropout threshold Sr for at least 15 ms (FIG. 8a) leads the microprocessor to cause an unlatching phase at the time tl2 (step F13 of FIG. 5) during which the current in the coil is annulled. Measurement of the voltage U2 by the control circuit 14 must have a satisfactory precision whether the supply voltage Ua, from which it is derived, is a DC voltage or a full-wave rectified AC voltage as in the embodiment of FIG. 3. Moreover, in the case of a rectified AC voltage, the frequency of the AC voltage must be able to vary in frequency ranges comprised between 45 and 65 Hz and 360 and 440 Hz. In the case of a circuit breaker, the voltage can be disturbed by harmonics and measurement must be fast because with opening electromagnets the circuit

breaker must open in less than 40 milliseconds. In addition, the required operating temperature ranges from -40° C. to +125° C.
In known circuit breaker opening and closing electromagnets, voltage measurement is generally performed by means of a low-pass analog filter. This filter supplies a mean value of the voltage to be measured with a poor precision (more than 10% in general) and requires the use of a very precise, very stable in temperature capacitor, which is expensive and voluminous.
To overcome these drawbacks, measurement of the voltage is preferably achieved by numerical electronic processing supplying a rms value of the voltage U2 by means of a finite impulse response (FIR) filter. In a preferred embodiment, the voltage U2 is sampled with a sampling period Tc=625|is. Preferably, a new computation is performed every 8 samples, i.e. every 5 milliseconds. The microprocessor uses 24 samples for each computation.
In the particular embodiment illustrated in FIG. 9, measurement of U2 starts with an initialization step F20, during which an indicator i is set to 0. Then the microprocessor of the control circuit 14 goes on to a step F21 of measuring and storing a sample U2j. It then checks, in a step F22, if the indicator i has reached the value 7. If this is not the case (NO output of F22) it goes on to a step F23 of incrementing i (i = i + 1) before looping back on the input of step F21 for measurement of a new voltage sample. If, at the step F22, i=7, this means that 8 successive samples of U2 have been stored. In this case (YES output of F22), the microprocessor goes on to a step F23 of computation of a first partial sum Al of the square of the last 8 measured samples

/ 7 V o J

. Then, in a step F24, the microprocessor computes a value of U2 obtained by the

weighted sum of three successive partial sums Al, A2 and A3 (U2=A1+2A2+A3). It should be noted that initially the sums Al, A2 and A3 had been set to zero during the step Fl (FIG. 5). In a step F25 the new partial sum A3 takes the value of A2 and the new partial sum A2 takes the value of Al. The microprocessor then loops back to the input of step F20, enabling, after 8 new samples have been measured, a new computation of U2 to be performed taking the last 24

samples measured into account.
The value of U2 thus obtained is representative of its rms value, measured numerically by means of a finite impulse response filter having an equation of the type:
U2=ai Al+a2 A2+ - - - +aj Aj + - - - +an An
m-with4/ = ]T£/2,2
0
in which the weighting coefficients aj are different, and where n > 2 and m > 1. The rms value of the voltage U2 is thus computed from the weighted sum of n partial sums of m squares of samples U2*.
In the preferred embodiment of FIG. 9, n=3, m=8, ai =a3 =1 and a2 =2.
The FIR filter used may be of another type, the number of samples, weighting coefficients, and sampling frequency depending on the precision and speed required. For example, Harming, Hamming, rectangular-shaped etc., windows can be used.

WE CLAIM:
1. A process for controlling a device comprising electromagnet for opening or closing
electromagnet of a circuit breaker, the device comprising at least one coil (2) connected in
series with an electronic switch (Tl) to the terminals of a supply voltage (Ua), said process
comprising the steps of measuring a first voltage (U2), representative of the supply voltage;
comparing the first voltage (U2) with distinct first and second inrush thresholds (Sai, Sa2)
and with a drop-out threshold (Sr); monitoring the flow of an inrush current (lea) in the coil
during an inrush phase of preset duration when the first voltage (U2) reaches one of the
inrush thresholds (Sai, Sa2).
2. The process according to claim 1, wherein the first inrush threshold (Sai) is representative of a voltage of about 40 to 50% of the rated supply voltage of the electromagnet and the second inrush threshold (Sa2) is representative of a voltage of about 70 to 85% of the rated supply voltage of the electromagnet.
3. The process according to any one of the claims 1 and 2, wherein the electromagnet belongs to an under voltage release.
4. The process according to any one of claims 1 and 2, wherein the electromagnet belongs to a shunt release.
5. The process according to any one of the claims 1 to 4, comprising the steps of controlling, during the holding phase and at the end of an inrush phase, the flow in the coil (2) of a holding current weaker than the inrush current; measuring the holding current (lb) flowing in the coil; regulating the holding current and comparing the holding current with a set point value (Icm); switching to a new inrush phase when, during a holding phase, the current (lb) is less than or equal to a preset fraction of the set point value during a second preset duration (tb).

6. The process according to claim 5, wherein said fraction is between lA and XA of the setpoint
value (Icm).
7. The process according to any one of the claims 5 and 6, wherein the second preset duration
(tb) is about a few milliseconds.
8. The process according to any one of the claims 1 to 7, comprising the step of determining
the rms voltage using sampling means and a finite impulse response filter having an equation
of the form:

where U21 is a sample of the first voltage, n > 2, m > 1, the weighting coefficients aj not all being identical.
9. The process according to claim 8, wherein n = 3, aj = a3 = 1 and a2 = 2.

Documents:

1141-mas-1999 abstract granted.pdf

1141-mas-1999 claims granted.pdf

1141-mas-1999 description(complete) granted.pdf

1141-mas-1999- abstract.pdf

1141-mas-1999- claims.pdf

1141-mas-1999- correspondence others.pdf

1141-mas-1999- correspondence po.pdf

1141-mas-1999- description complete.pdf

1141-mas-1999- drawings.pdf

1141-mas-1999- form 1.pdf

1141-mas-1999- form 26.pdf

1141-mas-1999- form 3.pdf

1141-mas-1999- form 5.pdf

1141-mas-1999- other documents.pdf

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Patent Number

214029

Indian Patent Application Number

1141/MAS/1999

PG Journal Number

13/2008

Publication Date

31-Mar-2008

Grant Date

23-Jan-2008

Date of Filing

24-Nov-1999

Name of Patentee

SCHNEIDER ELECTRIC INDUSTRIES S A

Applicant Address

40, AVENUE ANDRE MORIZET, F-92100 BOULOGNE BILLANCOURT,

Inventors:

#	Inventor's Name	Inventor's Address
1	GHISLAIN DURIF	6, CHEMIN DE LA DHUY-38240 MEYLAN,
2	MUSTAPHA CHELLOUG	12, RUE NORMANDIE NIEMEN-38130 ECHIROLLES,
3	JEAN-PIERRE NEREAU	134, RUE DE 1'INDUSTRIE-38170 SEYSSINET-PARISET,

PCT International Classification Number

H01H 47/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	9815552	1998-12-07	France