Magnetic contactor having phase angle adjuster

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic contactor which energizes or de-energizes the coils of an electromagnet to attract or repel a movable iron core to or from a fixed iron core, thereby opening or closing a contact.

2. Description of Prior Art

A conventional magnetic contactor will be described in accordance with FIG. 26, which is a sectional view of the electromagnet of the magnetic contactor. The structure of the magnetic contactor is largely divided into a movable section consisting of a movable iron core 1, and a movable contactor (not shown) coupled with the movable iron core 1, and a fixed section made up of a fixed iron core 20, coils 21, etc. The fixed iron core 20 is contained in a mount (not shown) via a rubber plate 22 or an impact cushioning member. The coils 21 are wound around bobbins 24 and fitted to the center pole of the fixed iron core 20. A conical tripping spring 31 is disposed between the center pole of the movable iron core 1 and the bobbins 24.

The operation of the magnetic contactor will now be described with reference to FIG. 26. When current flows in the coils 21, the fixed iron core 20 is magnetized to generate magnetic attraction between itself and the movable iron core 1, causing the movable iron core 1 to be attracted to the fixed iron core 20 against the tripping spring 31. In the process of this joint operation, the contact of the movable contactor (not shown) is pressed against the contact of a fixed contactor and is closed. When the current to the coils 21 is shut off, the magnetic attraction between the fixed iron core 20 and the movable iron core 1 terminates and the tripping spring 31 causes the movable iron core 1 to move to the original position, opening the contacts. The power of the electromagnet is thus switched on-off directly.

Another conventional magnetic contactor will be described in accordance with FIGS. 27(a) and 27(b), showing a "contact actuation circuit" disclosed in Japanese Laid-Open Patent Publication No. SHO51-32297, and related graph. This contact actuation circuit is designed to set the actuation phase angle of a coil to a phase angle where chattering rarely occurs. In FIG. 27(a), the coil 21, an alternating-current power supply 100 and a control rectification device 41 are connected in series with each other via an actuation switch 11. Also, the power supply 100 and a phase signal generation circuit 40 are connected in series with each other via the actuation switch 11. The phase signal generation circuit 40 is designed to generate a trigger signal which is supplied to the control rectification device 41 when the voltage of the alternating-current power supply 100 reaches a value V.sub.BO.

FIG. 27(b) shows a relationship between the voltage V.sub.BO of the phase signal generation circuit 41 and the voltage waveform of the power supply 100. As shown in this drawing, the phase angle corresponding to the voltage V.sub.BO is 25.degree. . Therefore, when the actuation switch 11 is closed between 0.degree. and 25.degree. , the coil 21 is energized. On the other hand, when the switch 11 is turned on at the phase angle of 25.degree. or more, there is a delay until the next cycle of 0.degree. to 25.degree. is reached, and the control rectification device 41 is then caused to conduct to energize the coil 21, thereby reducing the occurrence of contact chattering.

In the first conventional magnetic contactor, as described above, the actuation phase angle of the power supply is optional, whereby the collision velocity of the movable iron core 1 against the fixed iron core 20 varies greatly.

In the second conventional device, the phase angle is set to a phase at which contact chattering is reduced. However, the velocity at which the movable iron core 1 collides against the fixed iron core 20 cannot be sufficiently suppressed for the following reason. Namely, in order to reduce contact chattering, the collision velocity of the movable and fixed contacts is set to a low value halfway through a stroke in which the movable iron core 1 is attracted to the fixed iron core 20. On the other hand, in order to decrease the impact generated when the movable iron core 1 collides with the fixed iron core 20, the velocity at almost the last point in the stroke of the movable iron core 1 is reduced, which is different from the reduction of the velocity at a specific passage point in the stroke of the movable iron core 1.

In order to review the above points, an example is shown in FIG. 28, wherein a vertical axis V, representing an attraction velocity of a movable iron core 1, relates to a horizontal axis X, representing the movement of a movable iron core 1 of the electromagnetic contactor. In FIG. 28, an actuation phase angle .alpha. of the power supply is 35.degree. and 90.degree. , and the iron core collides with a fixed contact (contactor) when the iron core 1 is about 4 mm in stroke.

As shown in FIG. 28, both in the case of an actuation phase angle of 35.degree. , and in the case of an actuation phase angle of 90.degree. , the velocity V upon actuation of a contactor is about 0.6 m/s when the iron core is about 2.5 mm in stroke. However, the velocity V when the iron core collides with the fixed iron core 20 varies according to an actuation phase angle of a power source. Namely, the velocity V is about 1.6 m/s in case of .alpha. of 90.degree. , and is four times as large as the velocity V about 0.4 m/s in case of .alpha. of 35.degree. . The chattering time of the contactor depends on the actuation velocity, and the larger the actuation velocity is, the longer the chattering time is. Therefore, in the example illustrated in FIG. 28, the chattering times are substantially the same, but the collision force in the case of 90.degree. is 4 times that of the collision force in the case of 35.degree. . Hence, although the velocity at which the movable iron core 1 in the process of movement makes contact was decreased to reduce chattering, the velocity at which the movable iron core 1 collides with the fixed iron core 20 increased, decreasing the life of the magnetic contactor.

Further, although the impact of the movable iron core 1 was small, contact chattering was likely to occur, whereby arc discharges were generated at the contact, reducing the life of the contact.

SUMMARY OF THE INVENTION

It is accordingly a first object of the present invention to overcome the above-mentioned problems by providing a long-life magnetic contactor which can reduce impact of a movable iron core by controlling the phase angle at which the coils of the magnetic contactor are energized.

It is a second object of the present invention to provide a long-life magnetic contactor which can reduce impact of a movable iron core, and to provide a contact which can prevent arc discharges.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a curve showing the operation of a magnetic contactor according to the present invention.

FIG. 3 is an actuation phase angle setting circuit according to the present invention.

FIGS. 4(a)-4(f) show waveform diagrams and timing charts for illustrating the operation of the circuit shown in FIG. 1.

FIG. 5 is a graph showing the operation of the magnetic contactor according to the present invention.

FIGS. 6(a)-6(e) illustrate actual waveform diagrams according to the present invention.

FIGS. 7(a)-7(d) illustrate actual waveform diagrams according to the present invention.

FIGS. 8(a)-8(c) illustrate actual waveform diagrams according to the present invention.

FIG. 9 is a circuit diagram showing another embodiment of the present invention.

FIG. 10 is a circuit diagram showing another embodiment of the present invention.

FIG. 11 is a circuit diagram showing an actuation phase angle detector of the present invention.

FIG. 12 is a circuit diagram showing another embodiment of the present invention.

FIG. 13 is a circuit diagram showing another embodiment of the present invention.

FIG. 14 is a circuit diagram showing another embodiment of the present invention.

FIG. 15 is a circuit diagram showing a current detector of the present invention.

FIG. 16 is a circuit diagram showing the other embodiment of the present invention.

FIG. 17 is a diagram showing an embodiment wherein a microprocessor is used.

FIG. 18 is a flowchart illustrating the operation of the microprocessor in FIG. 17.

FIGS. 19(a)-19(b) illustrate diagrams showing an impact cushioning device.

FIGS. 20(a)-20(c) illustrate perspective views showing elastic bodies.

FIGS. 21(a)-21(b) are diagrams showing an impact cushioning device.

FIG. 22 is a circuit diagram showing an embodiment for preventing arc discharges at a contact.

FIGS. 23(a)-23(g) show timing charts illustrating the operation of the device in FIGS. 21(a)-21(b).

FIG. 24 is a diagram showing a contact arc prevention circuit where there is a normally closed contact.

FIG. 25 is a diagram showing a contact arc prevention circuit where there is a three-phase alternating-current power supply.

FIG. 26 is a sectional view showing the structure of a conventional magnetic contactor.

FIGS. 27(a)-27(b) respectively illustrate a circuit diagram and a graph of conventional art disclosed in Japanese Laid-Open Patent Publication No. SHO51-32297.

FIG. 28 is a characteristic curve of a conventional electromagnetic contactor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

An embodiment of a magnetic contactor according to the present invention will be described with reference to FIG. 1, wherein an alternating-current power supply 100, an electromagnet 101 with contract 102 and a phase switch 103 incorporating a switch device are connected in series with each other, and a signal generator 104, designed to generate an operation signal to actuate the switch, is connected with the phase switch 103. The phase switch 103 controls the supply of voltage from the alternating-current power supply 100 to the coils 101 so that the voltage is switched on with a delay of a given phase angle .alpha. after zero (hereinafter referred to as the "actuation phase angle"). The signal generator 104 contains a normally open contact 200, and outputs an on-off command to the phase switch 103 depending on whether the normally open contact 200 is open or closed.

A relationship between the actuation phase angle .alpha. and a collision velocity Vm, at which the movable iron core 1 collides against the fixed iron core 20 is shown in FIG. 2. The vertical axis represents the collision velocity Vm, while the horizontal axis represents the actuation phase angle .alpha.. The collision velocity Vm varies greatly between approximately 0.4 and 1.6 m/s according to variation in the actuation phase angle .alpha.. The actuation phase angle .alpha. is set to any of points 140, 141, 142 and 143 where the collision velocity Vm decreases. Around the points, the values of "Vm" is small, and the differential value dVm/D.alpha. thereof is close to zero. In general, the collision force by the iron core is proportional to the collision velocity. Therefore, the smaller the collision velocity, the smaller the collision force, and the longer the life time of the iron core. However, taking an error of actuation into consideration, the actuation phase .alpha. is set to be in a range of about .+-.5%. It is to be understood that if the permissible range of the collision velocity is varied, other phase angles may be used.

Specific setting means for the actuation phase angle .alpha. of the phase switch 103 will now be described in accordance with FIG. 3, wherein the alternating-current power supply 100, the electromagnet 101 and the phase switch 103 are connected in series with each other, and the signal generator 104 is connected to the phase switch 103. An actuation phase angle detector 180B, provided as a phase angle adjustment device, is connected to the phase switch 103. The actuation phase angle .alpha. can be optionally set by the actuation phase angle detector 180B by means of a variable resistor. The detailed structure of the actuation phase angle detector 180B is given in an embodiment described later. A probe 500A of a non-contact laser Doppler velocimeter 500 is disposed in parallel to a top projection 20a of the movable iron core 1.

In the above configuration, the normally open contact 200 is closed to place the phase switch 103 in an on-ready state, and the actuation phase angle .alpha. of the switch 103 is set by the variable resistor in the actuation phase angle detector 180B. In such a setting, the phase switch 103 is turned on to energize the coils 101, whereby the movable iron core 1 is operated and the velocity displayed on an indicator 500B is visually checked by a measurer. The series of operations are repeated for each setting of the actuation phase angle .alpha. with the variable resistor, and the actuation phase angle .alpha. at which the velocity of the movable iron core 1 decreases is set with the variable resistor.

It is to be understood that while the velocity of the movable iron core 1 was directly detected as described above, the variation L of the movable iron core 1 may be measured by means of a differential transformer using movement time t measured simultaneously, where L/t is computed to detect the velocity of the movable iron core 1 indirectly.

The operation of the present embodiment will be described with reference to waveform diagrams illustrated in FIGS. 4(a)-4(g). First, the actuation phase angle .alpha. is set to a phase angle equivalent to point 140 in FIG. 2. Then, the normally open contact 200 in the signal generator 104 is closed at time T0, as shown in FIG. 4(b). The closure of the contact causes the phase switch 103 to turn on at time T2 with a delay of the given phase angle .alpha. after time T1, as shown in FIG. 4(c). Therefore, a hatched voltage 111 is applied to the electromagnet 101 as shown in FIG. 4(a), and a current 112 flows in the electromagnet 101 as shown in FIG. 4(d), causing magnetic force to attract the movable iron core 1 to the fixed iron core 20. As shown in FIG. 4(e), because of inertia, the movable iron core 1 begins to move at time T11 soon after the current 112 has started to flow. The iron core 1 gradually gathers velocity, and collides with the fixed iron core 20 at time T5. Also, there are changes in the current 112, as shown in FIG. 4(d), between acceleration at time T11 and the collision at time T5. The attraction for the movable iron core 1, which is proportional to the square of the current, is zero at point T4 when the current 112 is zero (hereinafter referred to as the "zero cross point"). Hence, the movable iron core 1 loses velocity, pushed by the counterforce of the tripping spring 31, etc., and the collision velocity is minimized at time T5 just when the movable iron core 1 collides against the fixed iron core 20. Also, as shown in FIG. 4(f), the contact 102 is closed at time T12 when the movable iron core 1 is in the process of being attracted.

The contact 102 is closed near the current zero cross point T4 when the electromagnet 101 is energized at a phase angle at which the collision velocity is reduced as indicated by time T12 in FIG. 4(f). Accordingly, an effect identical to that of this embodiment is produced by turning the phase switch 103 on near the point when the contact 102 closes after the electromagnet 101 has been energized and at the actuation phase angle .alpha. at which the current flowing in the electromagnet 101 is zero.

Embodiment 2

Another embodiment of the present invention will be described in accordance with FIG. 5, wherein the vertical axis represents a period of time when the movable iron core 1 has energized the electromagnet 101 until it collides with the fixed iron core 20 (hereinafter referred to as the "attraction time"); namely, the time from T2 when a phase switch 103 is turned on, to time T5 when the movable iron core 1 collides with the fixed iron core 20 in FIGS. 4(a)-4(f). The abscissa designates calculation and experimental data showing the actuation phase angle .alpha.. As shown in FIG. 5, the attraction time t more than doubles from 11 to 26 ms at the power supply frequency of 60 Hz.

As described previously, the actuation phase angle .alpha. at a low collision velocity Vm is at points 140, 141, 142 and 143 in FIG. 2. However, the attraction time at points 141 and 142 in FIG. 2 is longer than that illustrated in FIG. 5. Since the phase angle at a low collision velocity is also smaller in width at points 141, 142, the phase angle at these points is not preferable. The operating width of the phase angle is large at point 143, but the phase angle equivalent to point 143 is 135.degree. , which is converted into a time of 6.25 ms on the assumption that the frequency of the alternating-current power supply 100 is 60 Hz. Since the actuation phase angle .alpha. must also be considered for the ordinary operation time of the magnetic contactor, the length of time of 6.25 ms from when the operation signal is generated to turn on the switch until the actuation of the magnetic contactor is complete (hereinafter referred to as the "full operation time") is not preferable to maintain the performance level of the magnetic contactor. Hence, the actuation phase angle of approximately 35.degree. , equivalent to point 140, is the most preferable phase angle when the full operation time and the like are taken into consideration.

It is to be noted that there are many magnetic contactor types which are classified by electromagnet operation forms (such as plunger and flat plate types), contact capacitances, etc., which are characterized by different attraction times and collision velocities. Also, the attraction time and the like differ depending on the mounting direction of the magnetic contactor. However, actuation impact can be reduced by selecting the actuation phase angle at which the collision velocity for each magnetic contactor decreases and the attraction time is short, and by energizing the electromagnet 101 at the selected actuation phase angle.

The actual operation waveform of the magnetic contactor will now be described in accordance with FIGS. 6(a)-6(c), wherein the normally open contact 200 in the signal generator 104 is closed at time T0 as shown in FIG. 6(b), and the phase switch 103 is turned on at the actuation phase angle .alpha. of approximately 35.degree. to apply a hatched voltage 150 to the electromagnet 101, as shown in FIG. 6(a). When the voltage is applied, a current 151 flows in the electromagnet 101, as shown in FIG. 6(c), to cause magnetic attraction, and the movable iron core 1 begins to move at time T11 and is caused to move at an acceleration velocity 152 by the attraction as shown in FIG. 6(d). The contact 102 is closed at time T12 immediately before the movable iron core 1 collides with the fixed iron core 20 as shown in FIG. 6(e), and subsequently, the movable iron core 1 collides with the fixed iron core 20 at a low velocity at time T5. The acceleration of the movable iron core 1 is lost because the electromagnet current at time T4 is zero.

The length of time 154, between the current zero cross point 155 and the collision, is approximately 4 ms. According to experimental results, the length of time 154 is between 1 and 5 ms.

The actuation phase angle .alpha. may be set at any point between the current zero cross point and a point 1 to 5 ms before the movable iron core 1 collides with the fixed iron core 20. It should be noted that when setting the actuation phase angle .alpha., if the current zero cross point is too close to time T5, the movable iron core 1 collides without its velocity decreasing. On the other hand, if the current zero cross point occurs too early, a backward current increases, which increases the attraction again and accelerates the movable iron core 1 again to increase the collision velocity.

The actual operation waveform of the magnetic contactor set to an improper actuation phase angle will be described in accordance with FIGS. 7(a)-7(d), wherein the normally open contact 200 in the signal generator 104 is closed at time T0, as shown in FIG. 7(b), and the phase switch 103 is turned on at the actuation phase angle .alpha. of 73.degree. to apply a hatched voltage 150 to the electromagnet 101, as shown in FIG. 7(a). When the voltage is applied to the electromagnet 101, a current 151 flows in the electromagnet 101, as shown in FIG. 7(c), to cause magnetic attraction, and the movable iron core 1 begins to move at time T11 and is caused to move at a relatively low acceleration velocity 162 as shown in FIG. 7(d). The movable iron core 1 moves past the current zero cross point 165 halfway, rapidly increases velocity 163 as the current increases, and collides against the fixed iron core 20 at time T5. As a result, the collision velocity of the movable iron core 1 is extremely high. Hence, a large sound is generated at the time of collision, making a remarkable difference as compared to the phase angle of 35 degrees.

Embodiment 3

Another embodiment of the present invention will be described in accordance with FIGS. 8(a)-8(c), which illustrate waveform diagrams showing how the electromagnet 101 is de-energized. The normally open contact 200 in the signal generator 104 is closed as shown in FIG. 8(b), the phase switch 103 is turned on as shown in FIG. 8(c), and a voltage 170 is applied to the electromagnet 101 to start a current 171, as shown in FIG. 8(a). In the electromagnet 101, which is an equivalent circuit of an inductance and a resistor connected in series, the current 171 often lags the voltage 170 of the electromagnet 101 by the phase angle of 60 to 80 degrees. This is because the electromagnet 101 is designed to minimize power loss, and therefore, the inductance component is larger than the resistor component. In this example, the current lags the voltage by a phase angle of 67 degrees.

When the normally open contact 200 in the signal generator 104 is opened at time T20, as shown in FIG. 8(b), a next voltage zero cross point 172 is detected, and the phase switch 103 is turned off at time T22 with a delay of the phase angle .beta. after time T21 at the voltage zero cross point 172, as shown in FIG. 8(c), to de-energize the electromagnet 101 at the current zero cross point.

Accordingly, since no energy is accumulated in the inductance of the electromagnet 101, a high voltage is not generated by de-energizing the electromagnet 101.

With no high voltage generated, the phase switch 103 consisting of semiconductors, etc., increases in reliability and noise generated by high voltages decreases.

Embodiment 4

Another embodiment of the present invention will be described in accordance with FIG. 9, wherein the electromagnet 101 is connected in series with the alternating-current power supply 100 via terminals S1 and S2 of a current switch section 181. One end of the electromagnet 101 and terminal VP of an actuation phase angle detector 180 are connected, and terminal SS of the actuation phase angle detector 180 is connected to terminal SD of the signal generator 104. The signal generator 104 generates the operation signal of the phase switch 103 by means of a photocoupler 201. Further, the phase switch 103 is comprised of the actuation phase angle detector 180 and the current switch section 181, which can be electrically opened and closed, and they are connected to each other at terminals PO and CC. The current switch section 181, e.g., a transistor or an FET (field-effect transistor), is designed to open or close an electric switch 207 or switch device under the control of an input signal.

In the actuation phase angle detector 180, the output of an invertor device 191, for inverting the output signal of the signal generator 104, is connected to the reset terminal of storage device 192, and the output of a zero cross detector 190, for detecting the zero cross of the voltage of the alternating-current power supply 100, is connected to the set terminal of the storage device 192. The output of the storage device 192, consisting of flip-flops, etc., is connected to the input of timer 193 which delays the signal output by the storage device 192 by a given length of time as a phase adjusting means. This timer 193 allows the delay time to be adjusted by a variable resistor 193A. In this example, the timer is a delay device or the like configured by an on-delay timer or a time-constant circuit made up of a resistor and a capacitor.

The operation of the present embodiment will be described in accordance with FIG. 9. An ON signal is generated via the photocoupler 201 of the signal generator 104 and inverted by the invertor device 191 to cancel the reset of the storage device 192. The zero cross detector 190 detects the zero voltage of the alternating-current power supply 100 and generates an output signal. This output signal is supplied by the timer 193, a given time later, as an ON signal to the current switch section 181. Accordingly, the current switch section 181 turns on at a given actuation phase angle to energize the electromagnet 101. By setting the delay time of the timer 193 at the phase angle at which the current switch section 181 turns on, the magnetic contactor can be set to the actuation phase angle at which the collision velocity decreases.

Embodiment 5

Another embodiment of the actuation phase angle detector will be described in accordance with FIG. 10, wherein terminal SS of an actuation phase angle detector 180B is connected to the input of the invertor device 191, which inverts an external signal supplied to terminal SS. The output of the invertor device 191 is connected to the reset terminals of the storage devices 192, 206 consisting of flip-flops, etc., to cancel the resets of the storage devices 192, 206 under the control of an ON signal. Terminal VP, connected to the alternating-current power supply, is connected to one input of a comparator 204 and the input of the zero cross detector 190. The output of the zero cross detector 190 is connected to the set terminal of the storage device 192.

A setting potentiometer 203 is connected to the other input of the comparator 204. The setting potentiometer 203 is designed to set a reference voltage used for comparison with the voltage of the alternating-current power supply 100. The output of the comparator 204 and that of the storage device 192 are respectively connected to the inputs of an AND device 205, and the output of the AND device 205 is connected to the set terminal of the storage device 206.

The operation of the present embodiment will be described in accordance with FIG. 10. An external ON signal is entered into terminal SS and inverted by the invertor device 191 to cancel the reset of the storage devices 192, 206. Also, the voltage of the alternating-current power supply 100 is applied to terminal VP and the zero cross detector 190 detects that the voltage is zero and outputs a signal. If the reset of the storage device 192 has been canceled, the output signal sets the storage device 192. Subsequently, when the voltage of the alternating-current power supply 100 exceeds the voltage set to the setting potentiometer 203, the output of the comparator 204 is switched on. The output from the comparator 204 and the output ON signal of the storage device 192 are ANDed by the AND device 205, and the storage device 206 is set under the control of the output signal from the AND device 205. Accordingly, the storage device 192 is set at the zero cross point of the voltage of the alternating-current power supply 100 after the storage devices 192, 206 have been reset by the external ON signal. Further, the comparator 204 outputs a signal if the voltage of the alternating-current power supply 100 exceeds the voltage set to the setting potentiometer 203, whereby the storage device 206 is set by the output of the AND device 205, and an output signal is generated at the phase angle at which the alternating-current voltage corresponds to the voltage set to the setting potentiometer 203. Replacement of the actuation phase angle detector 180 in FIG. 9 with the actuation phase angle detector 180B described above allows the phase angle to be set by the setting potentiometer 203 as described in Embodiment 4, whereby the magnetic contactor, set to the actuation phase angle at which the collision velocity decreases, can be configured.

Embodiment 6

Another embodiment of the present invention will be described in accordance with FIG. 11, wherein the electromagnet 101 is connected in series with the alternating-current power supply 100 via terminals S1 and S2 of a current switch section 181B. One end of the electromagnet 101 and terminal VQ of an OFF phase angle detector 180C are connected together and terminal ST of the OFF phase angle detector 180C and terminal SD of the signal generator 104 are connected. This signal generator 104 generates the operation signal of the phase switch 103 by means of an AND device 202. Terminal SE of the OFF phase angle detector 180C and terminal CC of the current switch section 181B are connected.

In the OFF phase angle detector 180C, the output of the AND device 202 in the signal generator 104 is connected to the reset terminal of storage device 192, and the output of the zero cross detector 190, for detecting the zero cross of the voltage of the alternating-current power supply 100, is connected to the set terminal of the storage device 192. The output of the storage device 192, consisting of flip-flops, etc., is connected to the input of a timer 120 which delays the output signal a given time. The timer 120 allows the delay time to be adjusted by a variable resistor 120A. For example, the timer may be a delay device or the like configured by an on-delay timer or a time-constant circuit made up of a resistor and a capacitor. The output of the timer 120 is connected to the input of a drive circuit 208, and the outputs of the drive circuit 208 are respectively connected to the inputs of switching devices 209A and 209B, or switch means such as two FETs (field-effect transistors). The outputs of the switching devices 209A, 209B are connected in series with each other in opposite directions, diodes 216 and 217 are connected across the switching devices 209A and 209B, respectively, and a voltage absorbing device 211, for absorbing a high voltage, is connected between terminals S1 and S2.

The operation of the present embodiment will be described in accordance with FIG. 11. The AND device 202 in the signal generator 104 generates an ON signal and the output of the storage device 192 is off. The output of the invertor device 121 turns on, the timer supplies the ON signal to the input of the drive circuit 208 in a given period of time to provide the ON signal from the output of the drive circuit 208, whereby the switching devices 209A, 209B are turned on to energize the electromagnet 101.

Subsequently, the output of the AND device 202 in the signal generator 104 generates an OFF signal to cancel the reset of the storage device 192, and the zero cross detector 190 detects the zero voltage of the alternating-current power supply 100 and generates an output signal. This output signal is provided to switch on the output of the storage device 192, whereby the invertor device 121 inverts the OFF signal and the timer 193 outputs the OFF signal in a given period of time to send the OFF signal to the current switch section 181B. Accordingly, the current switch section 181B turns off at a given phase angle from the zero voltage point of the alternating-current power supply 100 to de-energize the electromagnet 101. By appropriately setting the delay time of the timer 120 at the phase angle at which the current switch section 181B turns off, the electromagnet 101 can be de-energized at the zero current of the electromagnet 101, whereby the magnetic contactor set to the phase angle at which high voltages are rarely generated can be configured.

Embodiment 7

Another embodiment of the present invention will be described in accordance with FIG. 12, wherein the electromagnet 101 and the alternating-current power supply 100 are connected in series with each other via terminals S1 and S2 of the current switch section 181 including a switch. Terminal ST of an OFF phase angle detector 180C is connected to terminal SD of the signal generator 104, and terminal VQ of the OFF phase angle detector 180C and terminal VP of the actuation phase angle detector 180, including a phase adjusting device, are connected to one end of the electromagnet 101. Terminal SE of the OFF phase angle detector 180C is connected to terminal SS of the actuation phase angle detector 180, and terminal PO of the actuation phase angle detector 180 is connected to terminal CC of the current switch section 181. It is to be noted that the actuation phase angle detector 180 is identical to the one illustrated in FIG. 10, and the OFF phase angle detector 180C is identical to the one illustrated in FIG. 11.

The operation of the present embodiment will be described in accordance with FIG. 12. First, the switch of the signal generator 104 is turned on to supply an ON signal to terminal ST of the OFF phase angle detector 180C. The OFF phase angle detector 180C generates the ON signal from terminal SE and the signal is supplied to terminal SS of the actuation phase angle detector 180. The actuation phase angle detector 180 detects that the voltage of the alternating-current power supply 100 is zero, generates the ON signal from its terminal PO in a given period of time, and supplies it to terminal CC of the current switch section 181 to turn on the current switch section 181, thereby energizing the electromagnet 101.

Subsequently, the switch of the signal generator 104 is turned off to supply an OFF signal to terminal ST of the OFF phase angle detector 180C, which then detects that the voltage of the alternating-current power supply 100 is zero. In a given period of time, the output of the OFF phase angle detector 180C is switched off, the OFF signal is supplied to terminal SS of the actuation phase angle detector 180 and is generated at terminal PO of the actuation phase angle detector 180 to turn off the current switch section 181, thereby de-energizing the electromagnet 101.

Embodiment 8

Another embodiment of the present invention will be described in accordance with FIG. 13, wherein on