FR2791466A1 - Electronic command mechanism assisted electromagnet relay switching alternating current and having near zero volts nuller during closure and near zero amps nuller during opening. - Google Patents

Abstract

The electromangetic relay has a command operated (10,38,16,18,26) mechanical movement opening and closing a contact. The command mechanism has a voltage nuller which reduces the contact voltage near to zero volts during closure, and during relay opening maintaining the electrical contact current near zero amps during the change of direction of the alternating current.

Description

ELECTROMECHANICAL RELAY

ASSISTED SWITCHING

  The invention relates to an electromechanical relay assisted by switching by an electronic device. More specifically, the relay, intended to be inserted in an alternating current electrical circuit, includes control means improving its switching performance and

  ensuring a longer lifespan.

  The relays are designed on the one hand to support without abnormal heating the current of the electric circuit in which they are inserted and on the other hand to carry out the opening and the closing of the circuit

  electric charge without damage to its contacts.

  - Relays of the electromechanical type include one or more electrical contacts with mechanical displacement coupled to a mobile element of the magnetic circuit of an electromagnet. The electromagnet is controlled by feeding its coil which, by producing an induction flux in the magnetic circuit, causes the element to move

  the closing or opening of the electrical contacts of the relay.

  The electromechanical relays have delays between the moment the electromagnet is controlled by the supply of its coil and the actual closing or opening of its electrical contact. These delays

  are mainly due to the inertia of the moving element of the relay.

  The switching by an electromechanical relay of an electrical circuit under load, and particularly when the circuit is inductive, produces arcs between the contacts at the time of opening or closing of the

  circuit This phenomenon is commonly called sparking.

  Indeed, when the relay is closed, the current is established in the electrical circuit through the electrical contact producing one or more electric arcs due to rebound between the

mobile contact and fixed contact.

  On opening, the contact cuts the current flowing through the electrical circuit, which again produces arcs between the contacts, the greater the intensity of the current to be cut and

that the circuit is inductive.

  These repeating arcs inevitably degrade over time the

  contact and shorten its lifespan.

  The electrical contact usually comprises a fixed part and a mobile part each having studs made of a material which is a good electrical and thermal conductor. These pads, brought into contact when the relay closes, must have a low contact resistance in order to limit overheating during the passage of current. There is, after a certain number of openings and closings of the electrical contact under load, the appearance of a meniscus or metallic protuberance on the surface of one of the two studs. This protuberance occurs by the transfer, during successive cuts and closings l0 under load, of the metallic material from one pad to the other. This protuberance prevents direct contact between the studs, the contact being effected by means of the metallic protuberance having a much smaller contact surface than that which initially exists between the studs. One of the consequences is an abnormal heating of the contact

  and a decrease in its lifespan.

  In order to overcome the drawbacks of relays of the prior art, the invention provides an electromechanical relay intended to be inserted in an electric circuit with alternating current to effect its closing and its opening, the relay comprising an electrical contact with mechanical displacement, control means for controlling on the one hand the closing of the electrical contact in response to a first control signal and on the other hand the opening of the contact in response to a second control signal, characterized in that the control means comprise first means for: generating from the first control signal a signal for closing the electrical contact such that it closes during the passage of the voltage across the terminals of the electrical contact with a value close to zero volts when changing the sense of alternating voltage; and - generate from the second control signal an opening signal of the electrical contact such that it is opened during the passage of the current in the electrical contact by a value close to zero

  ampere when changing the direction of the alternating current.

  The idea of this invention is to make the closing and opening of the relay contacts coincide with the most favorable electrical states to preserve the characteristics of the relay and increase its

lifetime.

  In the relay according to the invention, the relay control means ensure that the contact closes when the voltage across its terminals is substantially zero and that it opens when the current flowing through said contact becomes substantially zero, which considerably decreases

  Sparking between the contacts and increases the service life of the contact.

  In an embodiment of the relay providing an additional improvement in the lifetime of the relay, the control means also comprise second means for: - generating consecutive closing signals producing alternating consecutive closings of the electrical contact such as when a closure takes place during one of the two alternations of the alternating voltage, the next closure takes place during the other alternation, thus alternating with each closure the direction of current flow in the contact; and, - generate consecutive opening signals producing alternating consecutive openings of the electrical contact such that when an opening is made during one of the two alternations of the current in the contact, the next opening is made during the other alternation , interrupting alternately at each opening, in one direction then

  in the other direction, the current in the contact.

  The alternation of the current flow direction, during consecutive opening and closing of the contact, at the moment of the appearance of the arc due to switching, has the advantage of significantly reducing the

  metal deposition phenomenon on one of the two studs.

  An important aspect of this invention resides in the fact that the control means of the relay ensure the maintenance over time of the electrical characteristics of the relay and make it possible to obtain a duration of

  relay life close to its mechanical life.

  In one embodiment, the relay according to the invention uses a microcontroller (10) comprising on the one hand inputs receiving the control commands from the relay, current information in the circuit and voltage information at the terminals of the electrical displacement contact. mechanical and on the other hand an output providing the control signals

  opening and closing of the relay.

  Other characteristics and advantages of the invention will appear

  on reading the description of examples of relays in which:

  - Figure 1 shows a block diagram of a relay according to the invention. - Figures 2a, 2b, 2c, 2d, 2e, 3a, 3b, 3c, 3d and 3e, show state diagrams of different elements of the relay during

a closing command.

  - Figures 4a, 4b, 4c, 4d, 4th, 5a, 5b, 5c, 5d and 5e, represent state diagrams of different elements of the relay during

an opening command.

  Figure 1 shows a block diagram of a relay according to the invention inserted in an electrical circuit CE with alternating current and

  nominal voltage U at its supply terminals E1 and E2.

  The electrical circuit CE supplies a load 12 via

  an electrical contact 14 with mechanical displacement of the relay.

  The relay according to the invention essentially comprises: - a microcontroller 10 comprising calculation means in order to ensure the closing and opening of the electrical contact of the relay, - the electrical contact 14 with mechanical displacement actuated by a coil 16 of a electromagnet 18, a voltage detector 20 connected to the terminals of the electrical contact 14, a current detector 22 connected by two inputs 24 and 26 to the two terminals 28 and 30 of a shunt 32 in series in the electrical circuit CE, the shunt providing at its terminals 28 and 30 a proportional ul voltage

  at the value of current I in the electrical circuit.

  The microcontroller 10 has a logic input 34 connected to a CD control input of the relay, a control output 36 supplying via an amplifier 38 the coil 16 of the electromagnet 18. The microcontroller further comprises a input of current detection 40 and a voltage detection input 42 respectively connected to a current information output 44 of the current detector 22 and to a voltage information output 46 of the voltage detector 20. A first control signal, corresponding to a voltage Vc in the high state, applied through the CD control input of the relay, to the logic input 34 of the microcontroller, causes the electrical contact 14 of the relay to close. A second control signal, corresponding to a voltage Vc in the low state, applied to the same control input CD of the

  relay opens the same contact.

  We will then explain the operation of the relay using the diagram in Figure 1 and state diagrams over time.

different elements of the relay.

  1) closing of the relay (See figures 1, 2a, 2b, 2c, 2d, 2e and 3a, 3b, 3c, 3d, 3e) In an initial state before a time tOm, the relay is in the open state, the voltage Vc applied to the CD command input of the relay being low. FIG. 2a represents the control voltage Vc, of logic level, as a function of time. Figure 2b shows the voltage Dv at the output

  voltage information 46 of the voltage detector 20.

  The voltage information Dv is in the form of slots whose rising and falling edges occur respectively at time tvl, tv2, tv3, tv4, tv5 ..... tvn, of change of polarity of the alternations of the voltage V at the terminals of contact 14, a rising edge corresponding to the transition from alternating voltage V negative to alternating voltage V positive and a falling edge reverses it. The contact 14 being open before the time tOm, the voltage V across the contact is substantially equal to the

voltage U of the electrical circuit.

  Since the relay is in the open state, it is desired to close it at time tOm by applying the first control signal to its control input CD in the form of a logic level at the high state of the control voltage Vc. . The first control signal is transmitted to the logic input 34 of the microcontroller which triggers a sequence of

relay closing.

  We will suppose that the closing of the contact of the relay at a time t2m must be carried out during the passage of the voltage V across the contact of the negative alternation towards the positive alternation, that is during a rising edge of the voltage information Dv. To this end, the microcontroller 10 takes into account, by the voltage information Dv applied to its voltage detection input 40, the instants tvl, tv2, tv3, tv4, tv5 ..... tvn, at which the edges of rise and fall corresponding to changes in polarity of the voltage V across the terminals of contact 14. The

  derived from the voltage information Dv can be used for this purpose.

  The microcontroller calculates a first waiting time dTOm, when closing near a rising voltage edge, after the appearance of the first control signal from the relay at time tOm, to generate at the control output 36 of the microcontroller at the end of the waiting time, at a time tl m, a signal to close the electrical contact of the relay, this first waiting time dTOm being such that the contact is opened at a

  instant close to the change in voltage alternation.

  The closing signal is represented in FIG. 2c by the passage, at time t1m, of the logic output 36 of the microcontroller from the low state (0 in the figure) to the high state (1). The change to state 1 of the logic output 36 causes the coil 16 of the electromagnet 18 of the relay to be supplied via the amplifier 38 and the closing of the electrical contact 14 after a delay on closing corresponding dT1 at the characteristic delay time of the electromechanical relay between its command at time tlm (the supply of the coil 16) and the closing of the electrical contact at a

next t2m instant.

  The first dTOm timeout is calculated by the microcontroller -

  taking into account the duration T of the period of the alternating voltage U of the electric circuit, the instant tOm of closing command in a

  period T and the delay on closing dT1 characteristic of the relay.

  The microcontroller 10 can for example, in the case of FIGS. 2a, 2b, 2c, 2d and 2e, carry out the calculation of the first waiting time dTOm as follows: Let dTCm be the time difference between the instant tv2 of rising edge of the voltage information Dv preceding the closing signal of the relay at time tOm, the first waiting time dTOm will be given by: dTOm = T - (dTCm + dT1) Let Vmax be the maximum voltage at the terminals of contact 14 open and VE the voltage across the same contact when it closes at time t2m. The voltage Vs will be of very low value, close to O volt, by

  relation to the maximum of the voltage Vmax at the terminals of the contact.

  The closing of the contact with a voltage Vs at its terminals of very low value and therefore of a voltage Us in the electrical circuit of the same amplitude does not produce an electric arc between the contacts when the current is established also as a consequence of very low amplitude compared to

  maximum current in the electrical circuit.

  Figures 3a, 3b, 3c, 3d and 3e show the diagrams at the same points of the relay as for Figures 2a, 2b, 2c, 2d and 2e but for the following closing sequence of the relay to that described above. During this following sequence, the microcontroller will close the contact 14 at a time t2d, during the passage of the voltage V across the terminals of the contact from positive alternation to negative alternation, unlike the previous sequence; this passage corresponding to a falling edge of

the voltage information Dv.

  As for the calculation of the first waiting time, the microcontroller calculates a second waiting time (dTOd), when closing close to a voltage drop edge, after the appearance of the first relay control signal at the instant tOd, to generate at the control output (36) of the microcontroller, at the end of the second waiting time at a time t1d, a signal for closing the electrical contact of the relay, this second waiting time ( dTOd) being such that the contact is closed

  takes place at a time close to the change in voltage alternation.

  The second waiting time dTOd is calculated by the microcontroller in the same way as the first taking into account the duration T of the period of the alternating voltage U of the electric circuit, of the instant of closing command in a period and the delay

closing dT1.

  The microcontroller 10 memorizes the polarity of the alternation during which a closure was made (for a low voltage Vs at the terminals of the contact 14) in order to effect the next closure with the reverse polarity. For example, if the closure was carried out during a negative alternation with a low negative voltage -Vs, the next closure will be controlled by the microcontroller so that it is carried out during the positive alternation, with low voltage + positive Vs. For example, the microcontroller 10 will calculate the first waiting time dTOm, so that the contact is closed very shortly (relative to the period T) before the change of alternation across the contact, which will systematically obtain a low negative voltage -Vs across the contact when closing during a negative half-wave (i.e. during a voltage rising edge) and a low voltage + positive Vs when closing during a positive alternation (either during a voltage falling edge); the relative stability of the relay delay time on closing dT1 between two consecutive closings

  allowing to obtain such an operation.

  The direction of the arc between the closing contacts will thus be alternated during successive closings avoiding the formation of the menisci of

  metal due to the transfer of material from one pad to another of the contact.

  1) opening of the relay (see figures 1, 4a, 4b, 4c, 4d, 4th and 5a, 5b, 5c, 5d, 5e) In an initial state before a time t10m, the relay is in the closed state, the voltage Vc applied to the CD command input of the relay being high. FIG. 4a represents the control voltage Vc of logic level as a function of time. FIG. 4b represents the voltage Di at the output

  current information 44 of the current detector 20.

  With the contact closed, the current of the electrical circuit passes through the electrical contact 14 and the shunt 32 supplying the microcontroller, through

  the current detector 22, the current information Di.

  The current information Di is in the form of slots whose rising and falling edges occur respectively at times til, ti2, ti3, ti4 ..... tin, of change of polarity of the alternations of current I in the electrical circuit, a rising edge corresponding to the passage from negative current alternation to positive current alternation and a

falling edge the reverse.

  The relay being in the closed state, it is opened at the instant t12m by applying the second control signal to its CD input in the form of a logic level of the control voltage Vc in the low state. The second control signal is transmitted to logic input 34 of the

  microcontroller which triggers a relay opening sequence.

  We will suppose that the opening of the contact of the relay at time t1l2m must be carried out during the passage of the current in the contact of the negative alternation towards the positive alternation, that is to say during a rising edge of the current information Sun. To this end, the microcontroller 10 takes into account the current information Di applied to its current detection input, the instants til, ti2, ti3, ti4 ..... tin, at which the rising and falling edges occur. corresponding to changes in polarity of the

current in contact 14.

  In the same way as when closing the relay, the microcontroller calculates a third waiting time dTlOm, when opening close to a rising current edge, after the appearance of the second control signal from the relay to l instant t10m, to generate at the control output 36 of the microcontroller, at the end of the waiting time at a time tl lm, a signal for opening the electrical contact of the relay, this third waiting time dT10Im being such that the contact is opened at an instant

  t12m close to the change in alternating current.

  The opening signal is represented in FIG. 4c by the passage, at time tllm, of the control output 36 of the microcontroller from the high state (1 in the figure) to the low state (0). The passage to the low state of the control output 36 of the microcontroller produces the interruption of the supply of the coil 16 of the electromagnet 18 and the opening of the electrical contact 14 after a delay of delay in the opening dT2 of the electromechanical relay contact corresponding to the difference in time between the disappearance of the command at time t lm (interruption of supply to the coil 16) and the opening of the

  electrical contact at the next t12m instant.

  Let Imax be the maximum current in contact 14 closed and IE the

  currents in the same contact when it opens at time t12m.

  The current Is will be of very low value, compared to the maximum current Imax in the contact. The opening of the contact with a circuit current lF of

  very low value does not produce an electric arc between the contacts.

  Figures 5a, 5b, 5c, 5d and 5e show the diagrams at the same relay points as for Figures 4a, 4b, 4c, 4d and 4th but for the following relay opening sequence to that described above. During this following sequence the microcontroller will open the contact 14 at a time t12d, during the passage of the current in the contact, from the positive alternation to the negative alternation, unlike the previous sequence; this passage corresponding to a falling edge of

current information Di.

  The microcontroller calculates a fourth waiting time (dTO10d), when opening near a falling current front, after the appearance of the second control signal from the relay at time t10d, to generate at the output of command (36) of the microcontroller, at the end of the fourth waiting time at a time t11d, a signal to open the electrical contact of the relay, this fourth waiting time (dTO10d) being such that l0 the opening of the contact takes place for a short time close to change

alternating current.

  In the same way as during closings, the third and fourth waiting times are calculated by the microcontroller taking into account the duration T of the period of the alternating current in the electrical circuit, respectively times t10m (rising edge) and t10d (falling edge) for opening control in a period T and the second delay in opening dT2 As for closing, the microcontroller 10 memorizes the polarity of the alternation during which an opening is carried out in order to carry out the next opening with reverse polarity; if the opening was made during a negative alternation with a low current - the negative, the next opening will be controlled by the microcontroller so that it takes place during the positive alternation, with a weak current + the positive. The microcontroller 10 will calculate the third and fourth waiting times (dT1 Om, dTl Od) so that the opening of the contact takes place very shortly before the change of alternation of current in the electrical circuit, this which will systematically obtain a low current - the negative in the contact during an opening during a negative half-wave (i.e. during a rising current front) and a low current + Is positive during a opening during a positive alternation

  (either during a current falling edge).

  The direction of the arc between the opening contacts will thus be alternated during successive openings avoiding the formation of the menisci of

  metal due to the transfer of material from one pad to another of the contact.

  Another method avoiding the formation of metal menisci would be to randomize the control of the relay with respect to the half-waves so that, overall, we find the operation described above. The relay according to the invention, by closing and opening the electrical contact respectively in synchronism with a passage through a value close to zero of the voltage and current of the electrical circuit, ensures switching without arcing whatever either the phase difference existing between the current I and the voltage U of the electric circuit due to the

  lo impedance characteristic of the load of the electric circuit.

  The measurement of the current I in the electric circuit supplying the current information Di is not limited to the use of a shunt, other devices can be used among which we find, Hall effect sensors, magnetoresistors , the optical couplers, or

  any other system that may be suitable.

  The use of a microcontroller to control the relay allows it to provide the best possible self-adaptation functionality.

switching performance.

  At a given moment in the operation of the relay, the microcontroller includes, for example in a memory, the delay times for opening and closing (dT1, dT2) of the relay necessary for calculating the waiting times. These delay times (dTl1, dT2) are liable to vary over time through aging, wear of the relay mechanism, or other causes. These variations in the delay times can be large enough for the closings and openings of the electrical contact controlled by the microcontroller to occur at times when the

  currents and voltages have important values producing arcs.

  The information at the output of the voltage detector and of the current detector is used by the microcontroller to detect the instants of the changes of alternations and the instants of closing and opening of the contact of the relay and if necessary automatically correct the waiting times. (dTOm, dTOd, dT10m, dT10d); for this purpose the microcontroller calculates the means of the last delay times measured respectively at closing (dT1) and at opening (dT2), in order to determine new waiting times respectively at closing (dTO'm, dTO ' d) and on opening (dT 10'm, dT 10'd) to automatically maintain the closing (t2m, t2d) and opening (t1 2m, t1 2d) instants at values such as closing and l contact opening occurs respectively when the voltage and

current are close to zero.

  For example, the microcontroller can measure the delay times (dT1, dT2) as follows: - on closing (see Figures 2a to 2e), close to a rising edge (tv4) of the voltage information Dv, the contact closes at an instant TF; an annex circuit 50 of the voltage detector connected to the terminals of the relay contact detects the mechanical closure of the contact and supplies the microcontroller with a pulse 52 at the closing instant TF. The microcontroller determines a new closing delay time dTl 'by calculating the difference between the time tl m, of the first control signal and the

time at closing TF.

  - on opening (see FIGS. 4a to 4e), close to a falling edge (ti4) of the current information Di, the contact opens at time TO; the appended circuit 50 connected to the terminals of the relay contact detects the mechanical opening of the contact and supplies the microcontroller with a pulse 54 at the time of opening TO. The microcontroller determines the new opening delay time dT2 'by calculating the difference between the time tllm of the

  second control signal and the opening time TO.

  Similar measurements and calculations are carried out by the microcontroller for the closings and openings of the contact during falling edges of the voltage (tv5) and current (ti5) information, (see figures

3a to 3 and 5a to 5e).

  This automatic adaptation of the waiting times to open and close the relay contact with favorable electrical states contributes

  notably to further increase its service life and reliability.

  For example, the relays of the prior art make it possible to carry out approximately 105 closing / opening cycles at nominal current. With the relay according to the invention ensuring alternating control on one then the other altemrnance, and a correction in time of the waiting times, the number of closing-opening cycles can reach 5.10 cycles at twice the nominal current. Another advantage of the relay according to the invention is the use for equivalent powers of smaller relays, therefore more economical, having a longer service life than that of current uncontrolled relays. The use of the relay according to the invention also ensures

  load switching without disturbance to the electrical circuit.

  The control means described comprising a microcontroller can easily be associated either with a switching couple composed of an electromechanical contact alone, or with a switching couple composed of a

  electromechanical contact assisted by a semiconductor.

Claims (15)

  1. Electromechanical relay intended to be inserted in an electrical circuit with alternating current to effect its closing and its opening, the relay comprising an electrical contact (14) with mechanical displacement, control means (10, 38, 16, 18,20 , 26) to control on the one hand the closing of the electrical contact in response to a first control signal and on the other hand the opening of the contact in response to a second control signal 10, characterized in that the control means comprise first means for: generating from the first control signal a signal for closing the electrical contact such that it closes during the passage of the voltage (V) across the terminals of the electrical contact by a value close to zero volts (-Vú, + Vs) when changing the direction of the alternation of the voltage; and - generate from the second control signal an opening signal of the electrical contact such that it is opened during the passage of the current in the electrical contact by a value close to zero   ampere (-Is, + le) when changing the direction of the alternating current.   2. Electromechanical relay according to claim 1, characterized in that the control means also comprise second means for: generating consecutive closing signals producing alternating consecutive closings of the electrical contact such as when a closing is carried out during a of the two half-waves of the alternating voltage, the next closing takes place during the other half-cycle, alternating the polarity of the voltage across the contact; and / or generate consecutive opening signals producing alternating consecutive openings of the electrical contact such that when an opening is made during one of the two alternations of the alternating voltage, the next opening is carried out during the other alternation ,   alternating the polarity of the current in the contact.   3. Electromechanical relay according to one of claims I or 2,   characterized in that the relay control means comprise a microcontroller (10) comprising, on the one hand, inputs receiving the relay control orders (Vc), current information (Di) in the circuit and voltage information ( Dv) at the terminals of the electric contact with mechanical displacement and on the other hand an output (36) supplying the   relay open and close control signals.   4. Electromechanical relay according to claim 3, characterized in that the electrical contact (14) with mechanical displacement is actuated by a coil (16) of an electromagnet (18), the relay further comprising a voltage detector (20) across the electrical contact (14), a current detector (22) of the current I traversing the electrical circuit (CE) and passing through the contact (14) of the relay, two inputs (24, 26) of the current detector (22) being connected to the two terminals (28, 30) of a shunt (32) in series in the electrical circuit (CE), the shunt supplying at its terminals (28,) a voltage ul proportional to the value of the current I in the circuit electric, the microcontroller (10) comprising a logic input (34) connected to a control input (CD) of the relay, a control output (36) supplying the coil (16) via an amplifier (38) of the electromagnet (18), the microcontroller further comprising a detection input tion of current (40) and a voltage detection input (42) connected   respectively to a current information output (44) of the   current (22) and at a voltage information output (46) of the voltage detector (20), a first control signal applied through the control input (CD) of the relay to the logic input (34) of the microcontroller , causing the electrical contact (14) of the relay to close, a second control signal, complementary to the first, applied to the same input of   control (CD) of the relay causing the opening of the same contact.   5. Electromechanical relay according to one of claims 3 or 4,   characterized in that the microcontroller has means for calculating: - a first waiting time (dTOm), when closing near a rising voltage edge, after the appearance of the first relay control signal at time tOm, to generate at the control output (36) of the microcontroller, at the end of the waiting time at a time tm, a signal for closing the electrical contact of the relay, this first waiting time (dTOm ) being such that the contact is closed at an instant close to the change in alternation of voltage and; - a second waiting time (dTOd), when closing close to a voltage drop edge, after the appearance of the first relay control signal at time tOd, to generate at the output of the microcontroller (36), at the end of the second waiting time at a time tld, a signal for closing the electrical contact of the relay, this second waiting time 0 (dTOd) being such that the closing of the contact s '' performs at a moment   close to the change in alternation of voltage.   6. Electromechanical relay according to claim 5, characterized in that the first and second waiting times (dTOm, dTOd) are calculated by the microcontroller taking into account the duration T of the period of the alternating voltage U of the electrical circuit, of the instant (tOm, tOd) of closing command in a period T and of the delay in closing dT1 relay characteristic.   7. Electromechanical relay according to one of claims 3 to 6,   characterized in that the microcontroller comprises means for memorizing the polarity of the alternation during which was carried out   a closure in order to carry out the next closure with the reverse polarity.   8. Electromechanical relay according to one of claims 5 to 7,   characterized in that the microcontroller calculation means calculate the first and second waiting times (dTOm, dTOd) so that the contact is closed very shortly (relative to the period T) before the change of alternation at the terminals of the contact, making it possible to systematically obtain a low negative voltage (-VE) at the terminals of the contact during closing during a negative alternation and low positive voltage (+ VE) during a closure during a positive alternation.   9. Electromechanical relay according to one of claims 3 to 7,   characterized in that the microcontroller has means for calculating: - a third waiting time (dTO10m), when opening near a rising current edge after the appearance of the second control signal from the relay to the instant tO10m, to generate at the control output (36) of the microcontroller, at the end of the waiting time at a time tl 1 m, a signal to open the electrical contact of the relay, this third waiting time (dTlOm) being such that the contact is opened a short time before the change of alternating current and; - a fourth waiting time (dT10d), when opening near a falling current front, after the appearance of the second relay control signal at time tlOd, to generate at the output of control (36) of the microcontroller, at the end of the fourth waiting time at a time tl1 d, an opening signal of the electrical contact of the relay, this i5 fourth waiting time (dT1 Od) being such that the opening of contact   takes place a short time before the change of alternating current.   10. Electromechanical relay according to claim 9, characterized in that the third and fourth waiting times (dTO10m, dT10d) are calculated by the microcontroller taking into account the duration T of the alternating current period of the electric circuit, the '' instant (t10 Om, t10 d) of command to open in a period T and of the delay in opening dT2 relay characteristic.   11. Electromechanical relay according to one of claims 9 or   , characterized in that the microcontroller comprises means for memorizing the polarity of the alternation during which was carried out   an opening in order to carry out the next opening with reverse polarity.   12. Electromechanical relay according to one of claims 9 to   1 1, characterized in that the microcontroller calculation means calculate the third and fourth waiting times (dT10m, dT10d) so that the contact is opened very quickly (compared to the period T) before the change of alternation at the terminals of the contact, making it possible to systematically obtain a low negative current (-Is) at the terminals of the contact when opening during negative alternation and a low current (+ IF) positive when opened during a positive alternation.   13. Electromechanical relay according to one of claims 3 to   12, characterized in that the microcontroller has means for calculating the averages of the last measured delay times, respectively on closing (dT1) and on opening (dT2), in order to determine new waiting times, respectively at closing (dTOm, dTOd) and opening (dT1Om, dTlOd) in order to automatically maintain the closing (t2m, t2d) and opening (t12m, t12d) instants at values such as closing and opening contact occurs when the voltage and current are close to zero.   14. Electromechanical relay according to one of claims 3 to   13, characterized in that a current measurement providing the information of the current I in the electrical circuit is carried out by a device among which there are, Hall effect sensors, magnetoresistors,   optical couplers, or any other system that may be suitable.   15. Electromechanical relay according to one of claims 1 to   14, characterized in that the control means described, comprising a microcontroller, are associated either with a switching couple composed of an electromechanical contact alone, or with a switching couple composed of a   electromechanical contact assisted by a semiconductor.