JP2003151826A - Electromagnet and open/close device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnet of high reliability and an operating mechanism for an open/close device by solving the problem that a reversely magnetizing magnetic flux penetrates only the periphery of an iron core due to a skin effect, a residual magnetic flux is large, and a canceling speed becomes low in a conventional electromagnet which keeps an attraction state with a permanent magnet and cancels an attraction state by reverse magnetization. SOLUTION: An electromagnet 1 is composed of a solenoid coil 4, a plunger 2a penetrating through the solenoid coil 4, and a stationary iron core 3 arranged so as to cover the solenoid coil 4. The solenoid coil 4 is excited to attract the plunger 2a, a magnetic flux generated by a permanent magnet 6 is made to pass through the plunger 2a and the opposed surface of the center leg 3d of the stationary iron core 3 to keep an attraction state, and a current flowing in the direction opposite to that of a current flowing in an attraction state is made to flow through the solenoid coil 4 to release the plunger 2a. A gap is provided at the center of either the plunger 2a or the center leg 3d, and a magnetic flux generated by the permanent magnet 6 is made to flow through the periphery with concentration. In an attraction state, the magnetic flux Φm of the permanent magnet 6 flows through the periphery of an iron core on the opposed surface with concentration, so that a releasing speed is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnet and a switchgear, and more particularly to an electromagnet that is inexpensive and has excellent operational stability, and an operating mechanism for a switchgear using the electromagnet.

[0002]

2. Description of the Related Art An operating mechanism of a switchgear includes an electric spring operating mechanism, a hydraulic operating mechanism, a pneumatic operating mechanism and the like.
Usually, these operating mechanisms have a large number of parts and the link mechanism is complicated, so that the manufacturing cost is relatively high.

As a method for simplifying the link mechanism, there is an operation mechanism using an electromagnet. For example, Japanese Patent Laid-Open No. 5-2
In the vacuum contactor described in Japanese Patent No. 34475, an electromagnet is used for closing, the charged opening spring is released at the same time as closing, and the contacts are opened.

In the operating mechanism disclosed in Japanese Patent Publication No. 10-505940, a plunger that penetrates two coils for making and breaking is provided, and it is made to make or break by the force of an electromagnet to make a state of making or breaking. Is held by the attractive force of the permanent magnet.

[0005]

The conventional electromagnet that maintains the closed state or the closed state by the attractive force of the permanent magnet needs a countermeasure for the eddy current, resulting in a problem of cost increase. When the electromagnet is applied to a switchgear, the rise time of the magnetic flux in the electromagnet must be about 20 ms or less in order to satisfy the regulation of the rated breaking time.

Since an eddy current is generated in the iron core due to the rapid change in the magnetic flux, the range in which the magnetic flux actually permeates is only d = √ (2 / μωσ) = 2.6 [mm] from the surface of the iron core. It is only in the range. This is the so-called skin effect. here,
The relative magnetic permeability of the iron core is 300 and the electrical conductivity is 10 ⁷ S / m.

Therefore, it is difficult to cancel the magnetic flux inside the iron core even if a reverse excitation current is passed through the coil, and the operating time becomes long and the operating speed decreases.

As countermeasures against eddy current, until now, an iron core has been constructed by using a laminated steel sheet having an insulating coating on the surface, or a slit is provided on a plunger as described in Japanese Utility Model Laid-Open No. 56-15509. It is designed to do.
However, both of these lead to higher costs.

It is an object of the present invention to provide an electromagnet which is inexpensive and excellent in operation stability, and an opening / closing device provided with the electromagnet as a drive source for an operating mechanism of a switch.

[0010]

In order to achieve the above-mentioned object, the present invention comprises a solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core having a solenoid coil inside, and excites the solenoid coil. Attracts the plunger, and the magnetic flux generated by the permanent magnet is applied to the surface facing the plunger and the center leg of the fixed iron core to maintain the attracted state, and a current in the direction opposite to that during attraction is applied to the solenoid coil to attract the plunger. In the electromagnet releasing
We propose an electromagnet in which at least one of the plunger around the facing surface and the central leg of the fixed iron core has a gap in the central portion.

The present invention also comprises a solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core provided with the solenoid coil therein. The solenoid coil is excited to attract the plunger, and the center of the plunger and the fixed iron core. In the electromagnet, the magnetic flux generated by the permanent magnet is applied to the surface facing the leg to maintain the attracted state, and a current in the direction opposite to that during attraction is applied to the solenoid coil to release the attracted state of the plunger. Therefore, we propose an electromagnet in which a hollow is formed at the center of the central leg of the fixed iron core.

The present invention further comprises a solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core having a solenoid coil inside. The solenoid coil is excited to attract the plunger, and the center of the plunger and the fixed iron core. In the electromagnet, the magnetic flux generated by the permanent magnet is applied to the surface facing the leg to maintain the attracted state, and a current in the direction opposite to that during attraction is applied to the solenoid coil to release the attracted state of the plunger. Therefore, we propose an electromagnet in which the central leg of the fixed iron core is made of steel pipe.

The present invention comprises a solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core having a solenoid coil inside. The solenoid coil is excited to attract the plunger, and the center leg of the plunger and the fixed iron core is provided. The magnetic field generated by the permanent magnet is applied to the facing surface of the solenoid to maintain the attracted state, and a current in the opposite direction to that during attraction is applied to the solenoid coil to release the attracted state of the plunger. We propose an electromagnet in which a hollow is formed and the facing surface of the central leg of the fixed iron core is a flat surface.

The present invention also comprises a solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core having a solenoid coil inside. The solenoid coil is excited to attract the plunger, and the center of the plunger and the fixed iron core. At the center of the facing surface of the plunger, in the electromagnet, the magnetic flux generated by the permanent magnet is applied to the surface facing the leg to maintain the attracted state, and the current in the opposite direction to that at the time of attraction is applied to the solenoid coil to release the attracted state of the plunger. We propose an electromagnet in which a recess is formed in the central part of the center leg of the fixed iron core.

The present invention further comprises a solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core having a solenoid coil inside. The solenoid coil is excited to attract the plunger, and the center of the plunger and the fixed iron core. At the center of the facing surface of the plunger, in the electromagnet, the magnetic flux generated by the permanent magnet is applied to the surface facing the leg to maintain the attracted state, and the current in the opposite direction to that at the time of attraction is applied to the solenoid coil to release the attracted state of the plunger. We propose an electromagnet in which a hollow is formed in the part and the central leg of the fixed iron core is made of steel pipe.

The present invention comprises a solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core having a solenoid coil inside. The solenoid coil is excited to attract the plunger, and the center leg of the plunger and the fixed iron core is provided. In the electromagnet, the magnetic flux generated by the permanent magnet is applied to the opposite surface of the solenoid to maintain the attracted state, and a current in the opposite direction to that during attraction is applied to the solenoid coil to release the attracted state of the plunger. We propose an electromagnet in which the facing surface of the central leg of is flat.

The present invention also comprises a solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core provided with the solenoid coil inside. The solenoid coil is excited to attract the plunger, and the center of the plunger and the fixed iron core. In the electromagnet that flows the magnetic flux generated by the permanent magnets on the surface facing the leg to maintain the attracted state, and the current in the opposite direction to that during attraction is applied to the solenoid coil to release the attracted state of the plunger, the plunger is made of steel pipe, We propose an electromagnet in which a hollow is formed in the center of the center leg of a fixed iron core.

The present invention further comprises a solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core having a solenoid coil inside. The solenoid coil is excited to attract the plunger, and the center of the plunger and the fixed iron core. In the electromagnet that flows the magnetic flux generated by the permanent magnets on the surface facing the leg to maintain the attracted state, and the current in the opposite direction to that during attraction is applied to the solenoid coil to release the attracted state of the plunger, the plunger is made of steel pipe, We propose an electromagnet in which the central leg of the fixed core is made of steel pipe.

In order to achieve the above object, the present invention proposes a switchgear including any one of the above electromagnets as a drive source of a switch operating mechanism.

In the present invention, since the central portion of at least one of the plunger around the facing surface and the central leg of the fixed iron core is a gap, the magnetic flux of the permanent magnet is formed on the facing surface of the plunger and the fixed iron core where the attractive force acts. Will flow concentratedly in the peripheral part of the iron core, and even if no special eddy current countermeasures are taken,
It is possible to provide an electromagnet that is inexpensive and has excellent operational stability, and an opening / closing device that includes this electromagnet as a drive source of an operating mechanism, because most of the magnetic flux can be canceled by the reverse excitation current of the solenoid coil.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of an electromagnet and an operating mechanism of a switchgear according to the present invention will be described with reference to FIGS.

[0022]

Embodiment 1 FIGS. 1 to 4 show the structure of Embodiment 1 of an electromagnet according to the present invention. FIG. 1 is a diagram showing a state in which a plunger is attracted and held by an attraction force of a permanent magnet. FIG. 2 is a diagram showing an operation of sucking the plunger. FIG. 3 is a diagram showing an operation of sucking the plunger immediately before completion. FIG. 4 is a diagram showing an operation for releasing the suction state of the plunger.

The electromagnet 1 of the first embodiment is composed of a T-shaped movable iron core 2, a fixed iron core 3 and a coil 4. The movable iron core 2 that can move in the vertical direction is a plunger 2 made of a magnetic material.
It consists of a and a steel plate 2b. The magnetic plunger 2a and the steel plate 2b are fixed by a bolt 5. Fixed iron core 3
Is formed by screwing disk-shaped steel plates 3a and 3b from both ends of a cylindrical iron core 3c, and a coil 4 is provided therein.

A central leg 3d having a recess 12 formed in the center is fixed to the steel plate 3b below the fixed core, and the central leg 3d and the plunger 2a are opposed to each other. Steel plate 3 above the fixed core
An annular permanent magnet 6 is mounted on a, and the permanent magnet 6 and the steel plate 2b of the movable iron core 2 are opposed to each other. The permanent magnet 6 is magnetized in the thickness direction. The plunger 2a has a connecting member 9
Is connected to the spring 7 and the driven object 8 by. The spring 7 is held between the mount 10 and the spring retainer 11,
It expands and contracts as the electromagnet 1 moves.

In the electromagnet 1 thus constructed,
When the coil 4 is excited with the plunger released, the magnetic flux Φ
c is generated, and the plunger 2a, as shown in FIG.
The suction force Fp works. The movable iron core 2 is
It is driven downward, charges the spring 7, and moves the driven object 8 downward.

Immediately before the attraction is completed, as shown in FIG. 3, the magnetic flux Φc and the magnetic flux Φm of the permanent magnet 6 are combined to not only enhance the attractive force Fp but also the steel plates of the permanent magnet 6 and the movable iron core 2. The attraction force Fm is also generated between 2b.

Even after the attraction is completed and the excitation of the coil 4 is stopped, as shown in FIG. 1, the magnetic flux Φm of the permanent magnet 6 causes
The attraction forces Fp and Fm act and the spring 7 remains charged. This is the so-called magnetic latch system.

In order to release the attracted state, as shown in FIG. 4, a current in the opposite direction to that at the time of attraction may be applied to the coil 4 for reverse excitation. Since the magnetic flux generated on the facing surface of the plunger 2a and the central leg 3d is canceled and the attractive force Fp is reduced, the charging force of the spring 7 drives the movable iron core 2 upward.

The structure of the first embodiment is characterized in that the central leg 3d
Part of. FIG. 5: is a figure which shows the structure of the conventional electromagnet in the attraction | suction state. The magnetic flux Φm of the conventional permanent magnet 6 disperses and flows over the entire facing surface between the plunger 2a and the central leg 3d. In this conventional example, when releasing the attracted state by reverse excitation, the magnetic flux Φc due to the current of the coil 4 penetrates only into the plunger outer peripheral portion Cs due to the skin effect of the iron core.
In the region inside of that, the magnetic flux Φm remains.

Therefore, even if the reverse excitation is performed, the attractive force Fp does not decrease so much and a predetermined operation speed is often not obtained. In the conventional electromagnet, the plunger 2a is used as a countermeasure.
It is necessary to adopt an eddy current prevention measure in which a slit is provided in the slit, an eddy current prevention measure in which the plunger is made of laminated steel plates insulated from each other, and as a result, the cost is increased.

On the other hand, in the electromagnet 1 of the first embodiment, the recess 12 is formed at the center of the central leg 3d. Since the magnetic flux Φm of the permanent magnet 6 flows concentratedly on the outer peripheral portion of the iron core on the surface where the plunger 2a and the central leg 3d face each other, most of the magnetic flux can be canceled by reverse excitation regardless of the skin effect. That is, the suctioned state can be released at high speed and stably without increasing the cost.

Further, by concentrating the magnetic flux on the opposing surfaces of the plunger 2a and the central leg 3d, the attractive force Fp
Also has the effect of increasing. The attractive force Fp is given by Fp = (B ² / 2μ ₀ ) S by the magnetic flux density B of the iron core and the facing area S.

In order to increase the attractive force Fp, it is better to increase the magnetic flux density B as much as possible instead of the facing area S. The electromagnet 1 according to the first embodiment includes a plunger 2a.
The magnetic flux is concentrated only in the vicinity of the facing surface between the central leg 3d and the central leg 3d, and the attractive force can be increased without significantly increasing the magnetic resistance of the entire magnetic path. In other words, the size of the permanent magnet for obtaining a predetermined attractive force can be reduced, and the cost can be reduced.

[0034]

Second Embodiment FIG. 6 is a diagram showing the structure of a second embodiment of the electromagnet according to the present invention. The electromagnet 1 of the second embodiment is
Instead of the central leg 3d of the fixed iron core 3 of the first embodiment, the recess 2c is formed in the plunger 2a. The central leg 3d of the fixed iron core 3 has a simple columnar shape, and the other portions are the same as those of the electromagnet of the first embodiment.

Also in the second embodiment, as in the first embodiment, the magnetic flux Φm of the permanent magnet 6 in the attracted state flows concentratedly on the peripheral portion of the iron core on the facing surface between the plunger 2a and the central leg 3d. Therefore, the magnetic flux can be canceled by the reverse excitation, and the release speed is improved without taking any special eddy current countermeasure. Further, in the electromagnet 1 according to the second embodiment, the mass of the movable iron core 2 is reduced as compared with the first embodiment, so that there is an effect that the operating speed is further increased.

[0036]

Third Embodiment FIG. 7 is a diagram showing the structure of a third embodiment of the electromagnet according to the present invention. In the electromagnet 1 of the third embodiment, the plunger 2a is composed of a steel pipe. The movable iron core 2 is configured by screwing the plunger 2a into the annular steel plate 2b, and the connecting member 9 for connecting to the drive target is connected to the movable iron core 2 via the member 2d. Other parts are the same as the electromagnet of the first embodiment.

[0037]

Fourth Embodiment FIG. 8 is a diagram showing the structure of a fourth embodiment of the electromagnet according to the present invention. In the electromagnet 1 of Embodiment 4, the central leg 3d is made of a steel pipe. The center leg 3d is screwed and fixed to the annular steel plate 3b below the fixed iron core. Other parts are the same as the electromagnet of the first embodiment.

In the third and fourth embodiments, the magnetic flux Φm of the permanent magnet 6 in the attracted state is the same as in the first embodiment.
However, it flows concentratedly in the peripheral portion of the iron core on the facing surface between the plunger 2a and the central leg 3d. Therefore, regardless of the presence or absence of the skin effect, the magnetic flux can be completely canceled by the reverse excitation, and the release speed is improved without taking any special eddy current countermeasure.

Further, the electromagnet 1 according to the third and fourth embodiments.
Then, there is an effect that the weight of the iron core can be reduced and the cost can be further reduced by using the steel pipe.

The plunger 2a which is the subject of the present invention
Considering the combination of the shapes of the central leg 3d, there is a possibility that each of the plunger 2a and the central leg 3d may adopt three types of shapes, that is, the facing surface is flat, the facing surface is hollow, and the steel pipe. Therefore, although there are 3 × 3 = 9 combinations, the combination in which the facing surfaces are flat is
Since this is the conventional example of FIG. 5, eight types excluding this are the embodiments of the present invention.

Although the four types of the first to fourth embodiments have been described here, it is easy for those skilled in the art to realize the remaining four types of combinations by referring to the description of the four types of embodiments. You will understand.

When forming a depression on the opposing surface,
Also in the case of using a steel pipe, in consideration of the skin effect, rather than reducing the diameter and arranging it at a position closer to the connecting member 9, as in each of the above-described embodiments, a diameter closer to the outside, that is, closer to the solenoid coil 4, is set. It is better to do.

[0043]

Fifth Embodiment FIG. 9 is a view showing the structure of the operating mechanism of a switchgear using the electromagnet of the present invention. In the fifth embodiment, the electromagnet according to any one of the first to fourth embodiments is applied to the operating mechanism of the switchgear. Here, an example in which the vacuum circuit breaker 20 is used as the switchgear will be described, but the present invention may be applied to general switchgear such as a gas circuit breaker or a disconnector.

The vacuum valve 30 is kept in a vacuum state by a vacuum container composed of upper and lower end plates 32 and an insulating cylinder 33. A fixed contact 37 and a movable contact 38 are arranged in the vacuum valve 30, and the contact and separation thereof realize closing and closing.

The fixed contact 37 is fixed to the fixed conductor 35 and is electrically connected to the fixed feeder 39.
On the other hand, the movable contact 38 is fixed to the movable conductor 36,
It is connected to the movable side feeder 62 via the flexible conductor 61. Both ends of the bellows 34 are connected to the movable conductor 36 and the end plate 32. The fixed contact 37 and the movable contact 3 while maintaining the vacuum state by the bellows 34.
It is possible to connect and disconnect with 8.

The vacuum valve 30 and the electromagnet 1 are connected via the shaft 41, and the driving force generated by the electromagnet 1 is applied to the movable conductor 36. The movable conductor 36 is the insulating rod 6
By means of 3, it is electrically insulated from the operating mechanism and is connected to the lever 42 fixed to the shaft 41. Movable iron core 2 of electromagnet 1
Is connected to the lever 44 by the connecting member 9. When the coil 4 is excited, the movable iron core 2 is driven downward, that is, the movable conductor 34 moves upward, and the switchgear is closed.

Upon closing, the contact pressure spring 43 and the opening spring 45 are charged at the same time. The contact pressure spring 43 is a spring that applies contact pressure to the contact at the time of closing, and the opening spring 45 is a spring that opens the contact. The contact pressure spring 43 is housed in the insulating rod 63. On the other hand, the opening spring 45 is connected to the operation mechanism unit 4
It is sandwiched between the top plate 46 of 0 and the member 11 fixed to the connecting member 9. At the completion of the closing, the attraction force of the permanent magnet 6 causes the shaft 41 to be in a non-rotating state, and the closing state is maintained. In the closed state, the contact pressure spring 43 and the opening spring 45 both remain in a compressed state, and therefore, when the electromagnet 1 is reversely excited, the contacts are opened by the charge energy of both springs.

In the fifth embodiment, the electromagnet 1 of any of the first to fourth embodiments is applied to the operating mechanism, and the recess 12 is formed in at least one of the plunger 2a and the center leg of the fixed iron core 3. The magnetic flux generated by the permanent magnet 6 concentrates on the peripheral portion of the iron core in the vicinity of the facing surface between the plunger 2a and the fixed iron core 3. Therefore,
When an electric current in the opposite direction to that at the time of turning on is applied to the coil 4, most of the magnetic flux Φm of the permanent magnet 6 can be canceled at this facing portion. Therefore, the opening speed is increased and the breaking performance is improved without taking special measures against eddy current. That is, a low-cost and highly reliable operation mechanism can be obtained.

[0049]

According to the electromagnet of the present invention and the opening / closing device which employs this electromagnet as the drive source of the operating mechanism, the magnetic flux Φm of the permanent magnet in the attracted state is the peripheral portion of the iron core at the surface facing the plunger and the central leg. Because it concentrates on
Release speed increases without special eddy current measures
It is possible to obtain a low-cost and highly reliable electromagnet and a switchgear including the electromagnet as a drive source of an operating mechanism.

[Brief description of drawings]

FIG. 1 is a diagram showing a state in which a plunger is attracted and held by an attraction force of a permanent magnet in Embodiment 1 of an electromagnet according to the present invention.

FIG. 2 is a diagram showing an operation of attracting the plunger in the first embodiment of the electromagnet according to the present invention.

FIG. 3 is a diagram showing an operation of attracting the plunger immediately before completion in the first embodiment of the electromagnet according to the present invention.

FIG. 4 is a diagram showing the operation of releasing the attracted state of the plunger in the first embodiment of the electromagnet according to the present invention.

FIG. 5 is a diagram showing a structure of a conventional electromagnet in a suction state.

FIG. 6 is a view showing an attracting state of the second embodiment of the electromagnet according to the present invention.

FIG. 7 is a diagram showing a state of attraction of an electromagnet according to a third embodiment of the present invention.

FIG. 8 is a diagram showing a suction state of an electromagnet according to a fourth embodiment of the present invention.

FIG. 9 is a diagram showing a structure of an operating mechanism of a switchgear using the electromagnet of the present invention.

[Explanation of symbols]

1 electromagnet 2 movable iron core 2a Plunger 2b steel plate 2c hollow 2d member 3 fixed iron core 3a steel plate 3b steel plate 3c Cylindrical iron core 3d central leg 4 coils 5 Volts 6 permanent magnet 7 spring 8 Drive target 9 Connection member 10 mounts 11 Spring hold 20 vacuum circuit breaker 30 vacuum valve 32 end plate 33 Insulation cylinder 34 Bellows 35 fixed conductor 36 Movable conductor 37 fixed contact 38 Moving contact 39 Fixed side feeder 40 Operation mechanism 41 shaft 42 lever 43 Contact pressure spring 44 lever 45 Opening spring 46 Top plate 61 Flexible conductor 62 Movable feeder 63 insulating rod F suction force Fm suction force Fp suction force Φ magnetic flux Φm Magnetic flux of permanent magnet 6 Φc Magnetic flux due to current in coil 4

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toru Tanimizu             1-1-1 Kokubuncho, Hitachi-shi, Ibaraki Stock             Hitachi, Ltd. Electric Systems Division F-term (reference) 5E048 AB01 AC05 AD02                 5G028 AA01 AA08 DB05

Claims (10)

[Claims] 1. A solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core provided with the solenoid coil therein. The solenoid coil is excited to attract the plunger, and the plunger and the fixed iron core are connected to each other. In an electromagnet that flows a magnetic flux generated by a permanent magnet on the surface facing the central leg to maintain the attracted state, and causes a current in a direction opposite to that during attraction to flow through the solenoid coil to release the attracted state of the plunger. An electromagnet, characterized in that a central portion of at least one of the plunger around the core and the central leg of the fixed iron core is a void. 2. A solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core provided with the solenoid coil therein. The solenoid coil is excited to attract the plunger, and the plunger and the fixed iron core are connected to each other. In an electromagnet that flows a magnetic flux generated by a permanent magnet on the surface facing the central leg to maintain an attracted state, and causes a current in a direction opposite to that during attraction to flow through the solenoid coil to release the attracted state of the plunger. An electromagnet, wherein the facing surface is a flat surface, and a recess is formed in the center of the central leg of the fixed iron core. 3. A solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core having the solenoid coil therein. The solenoid coil is excited to attract the plunger, and the plunger and the fixed iron core are connected to each other. In an electromagnet that flows a magnetic flux generated by a permanent magnet on the surface facing the central leg to maintain an attracted state, and causes a current in a direction opposite to that during attraction to flow through the solenoid coil to release the attracted state of the plunger. An electromagnet, wherein the facing surface is a flat surface, and the central leg of the fixed iron core is made of a steel pipe. 4. A solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core provided with the solenoid coil therein. The solenoid coil is excited to attract the plunger, and the plunger and the fixed iron core are connected to each other. In an electromagnet that flows a magnetic flux generated by a permanent magnet on the surface facing the central leg to maintain an attracted state, and causes a current in a direction opposite to that during attraction to flow through the solenoid coil to release the attracted state of the plunger. An electromagnet, wherein a recess is formed in the center of the facing surface, and the facing surface of the central leg of the fixed iron core is a flat surface. 5. A solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core provided with the solenoid coil therein. The solenoid coil is excited to attract the plunger, and the plunger and the fixed iron core are connected to each other. In an electromagnet that flows a magnetic flux generated by a permanent magnet on the surface facing the central leg to maintain an attracted state, and causes a current in a direction opposite to that during attraction to flow through the solenoid coil to release the attracted state of the plunger. An electromagnet, characterized in that a recess is formed in the center of the facing surface, and a recess is formed in the center of the central leg of the fixed iron core. 6. A solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core provided with the solenoid coil therein. The solenoid coil is excited to attract the plunger, and the plunger and the fixed iron core are connected to each other. In an electromagnet that flows a magnetic flux generated by a permanent magnet on the surface facing the central leg to maintain an attracted state, and causes a current in a direction opposite to that during attraction to flow through the solenoid coil to release the attracted state of the plunger. An electromagnet, wherein a recess is formed in the central portion of the facing surface, and the central leg of the fixed iron core is made of a steel pipe. 7. A solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core provided with the solenoid coil therein. The solenoid coil is excited to attract the plunger, and the plunger and the fixed iron core are connected to each other. In an electromagnet that flows a magnetic flux generated by a permanent magnet on the surface facing the central leg to maintain an attracted state, and causes a current in a direction opposite to that at the time of attraction to flow through the solenoid coil to release the attracted state of the plunger, wherein the plunger is An electromagnet comprising a steel pipe, wherein the facing surface of the central leg of the fixed iron core is a flat surface. 8. A solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core provided with the solenoid coil therein. The solenoid coil is excited to attract the plunger, and the plunger and the fixed iron core are attracted to each other. In an electromagnet that flows a magnetic flux generated by a permanent magnet on the surface facing the central leg to maintain an attracted state, and causes a current in a direction opposite to that at the time of attraction to flow through the solenoid coil to release the attracted state of the plunger, wherein the plunger is An electromagnet, comprising a steel pipe, wherein a hollow is formed at the center of the central leg of the fixed iron core. 9. A solenoid coil, a plunger penetrating the solenoid coil, and a fixed iron core provided with the solenoid coil therein. The solenoid coil is excited to attract the plunger, and the plunger and the fixed iron core are connected to each other. In an electromagnet that flows a magnetic flux generated by a permanent magnet on the surface facing the central leg to maintain an attracted state, and causes a current in a direction opposite to that at the time of attraction to flow through the solenoid coil to release the attracted state of the plunger, wherein the plunger is An electromagnet comprising a steel pipe, wherein the central leg of the fixed iron core is a steel pipe. 10. A switchgear provided with the electromagnet according to claim 1, as a drive source of a switch operating mechanism.