JPH0534798B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high frequency heating device that has a double insulation structure and eliminates the need for grounding work.

Conventional configurations and their problems Conventional high-frequency heating devices with a ground terminal (hereinafter simply referred to as microwave ovens), for example, do not allow electrical current to leak to accessible metal parts of the microwave due to insulation deterioration. Electric shock could occur if touched, so the idea was to ensure safety by installing grounding work on the ground terminal to bypass the electric shock current and reduce the electric shock current flowing through the human body to a safe level.

However, even if a grounding terminal is provided, grounding work must be done after the stove is purchased, and there is a possibility that the work will not be done for various reasons, making it difficult to ensure safety.

In other words, in the case of high-rise condominiums, it is sufficient to have a ground terminal installed at the outlet, but since only about 30% of the outlets are currently equipped with this, the majority of cases require the ground wire to be extended from a few meters to more than 10 meters. This method is not implemented due to the high cost of construction, as it requires driving a ground pole into the ground. In particular, transfer/
When moving to a new home, grounding work must be redone, making it increasingly difficult to carry out.

Also, even if you are not in a high-rise apartment building, you may have to make a hole in the wall for the ground wire to seal the aluminum sash window, or if you try to drive it into the ground, you will be told that the ground wire cannot be driven in because it is made of concrete. Currently, there are many cases where grounding work is not carried out due to various reasons. According to one survey, approximately 40 to 50% of microwave ovens are currently being used without being grounded.

Furthermore, if an earth pole were to be driven into the earth,
Even if grounding work has been done, the place where the grounding pole will be driven is dry or due to construction work.
If the surface is covered with gravel to improve drainage, low ground resistance will increase, making it impossible to ensure sufficient safety. In addition, there is a possibility of corrosion of the ground electrode or breakage of the ground wire, so the conventional method of installing a ground terminal is based on the premise of sufficiently reliable grounding work to ensure safety. Ta.

On the other hand, with the recent spread of microwave ovens, they have become lighter and more compact, and there is a tendency for microwave ovens to be used in any location other than the tabletop, and for devices that can be used without being fixed. However, conventional ranges with ground terminals require grounding work.
It was an inconvenience.

OBJECT OF THE INVENTION The present invention solves the above-mentioned conventional drawbacks.
The purpose is to completely separate the high-voltage secondary side of the isolation transformer from the power supply side, and maintain the conventional insulation specifications on the high-voltage secondary side, making the microwave a structure that prevents electric shock.

Structure of the Invention In order to achieve the above object, the present invention has the following structure.

In other words, by placing a metal between the high voltage side and the low voltage side and electrically shorting this metal to the chassis, even if the insulation on the high voltage side is damaged, the high voltage will leak to the low voltage side (high and low voltage This is to prevent any contact between the two. Specifically, it was done as follows.

(1) Since the core of the high-voltage coil is made of metal, the core is electrically shorted to the chassis.

(2) A metal plate is provided between the high voltage coil and the low voltage coil, and this metal plate is electrically shorted to the chassis.

(3) A metal partition is provided between the components on the high-voltage secondary side and the components on the low-voltage power supply side (including the primary coil), and this metal partition is electrically short-circuited to the chassis.

(4) Electrically connect one end of the high voltage secondary coil to the chassis.

The above configuration was adopted.

With this configuration, the high voltage secondary side is completely separated from the primary power supply side by the chassis, so even if insulation deterioration occurs on the secondary side, the high voltage on the secondary side will be transferred to the primary power source. This has the effect of preventing bridging to the power supply side and safely protecting the human body from electric shock caused by the high voltage of the range.

Description of examples The present invention will be explained below.

The double insulation structure referred to in this application refers to the following structure.

Double insulation structure is specified as an insulation structure that does not cause electric shock even if the equipment is not grounded. In other words, double insulation is insulation that consists of functional insulation and protective insulation. Here, the above-mentioned functional insulation is insulation that is necessary for equipment and provides basic protection against electric shock, and protective insulation is insulation that is necessary to ensure that electric shock can be prevented when functional insulation is broken. A structure consisting of independent insulation provided in addition to functional insulation.

However, currently, there are no clear standards or design standards for double insulation against high voltages of around 2000V, and no international consensus has been established regarding the double insulation structure of insulating paper 18. Currently, there are no microwave ovens with double insulation structure.

Therefore, in the present invention, in addition to functional insulation, the power supply side is shielded with metal, and even if the high voltage secondary side breaks down, the secondary high voltage side and the metal are bridged, and the primary power supply side is not bridged. The structure is designed to prevent electric shock accidents. That is, in the present invention, the above structure is referred to as double insulation in the sense that it does not cause an electric shock accident.

Hereinafter, a specific example will be described based on the drawings.

In Fig. 1, a magnetron 2 is connected to a chassis 1, and as a power source for driving the magnetron 2, there are an isolation transformer 3, a high voltage capacitor 4, and a high voltage diode 5, which are installed together at the rear of the range. . isolation transformer 3
In this case, a primary coil 6 and a high voltage secondary coil 7 connected to the power supply side are wound in sections, and a metal plate 8 is provided between them as a cross-contact prevention plate. This metal plate 8
is electrically short-circuited to the core 16 of the isolation transformer 3. Further, a metal partition wall 22 extending from the magnetron 2 is installed interposed between the low voltage primary coil and the high voltage secondary wiring. This metal partition wall 22
is electrically shorted to the chassis along with the magnetron cathode. In addition, 2 of isolation transformer 3
One end of the secondary coil 7 is electrically short-circuited to the core of the insulation transformer 3. Furthermore, the core 16 of the insulating transformer 3 is attached to the chassis 1 in an electrically short-circuited manner. Therefore, core 16,
The metal plate 8, the metal partition wall 22, and one end of the high-voltage secondary coil 7 are electrically short-circuited via the chassis 1, and therefore are at substantially the same potential.

The above is the configuration on the high voltage side.

On the other hand, the configuration of the low-voltage primary power source side is as described below.

That is, the power cord 9 is connected to the operation panel 10, and parts directly connected to the primary power source, such as the control circuit drive power transformer 11, the cooling motor 12, and the relay 13, are connected to the metal wall such as the magnetron 2 and the insulation transformer 3. It is separated from the next-side high-pressure section and installed close to the front where the operation panel (not shown) is located.
Note that these parts directly connected to the primary power source are double insulated from the power source and accessible parts such as the chassis 1.
A door 14 is provided at the front to take in and take out food, which is an object to be heated.

FIG. 2 is a perspective view of the insulating transformer 3. The primary coil 6 has a terminal 15 for wiring to the power supply circuit, and is connected to the core 16 by an insulating paper 17.
Double insulated. The high-voltage secondary coil 7 is separated from the primary coil 6 and is separated by a required spatial distance, e.g.
It is divided at a distance of at least mm. It is also insulated from the core 16 by an insulating paper 18,
Not double insulated. In other words, approximately 2000V alternating current is generated in the high voltage secondary circuit, but for double insulation it is necessary to provide a spatial distance of 20 mm or more between the core 16 and the primary coil 6, but this is not possible with an isolation transformer. 3 is too large to be practical.

In the present invention, the metal plate 8, the metal partition wall 22, etc. are provided, and the distance of the metal plate 8 from the secondary coil 7 and the distance between the components on the secondary high voltage side and the metal partition wall 22, etc.
By making the distance from the secondary coil 7 to the primary coil 6 and the distance between the high-voltage secondary side parts and the low-voltage primary power side parts sufficiently small, the insulation transformer 3 can be made with dimensions almost the same as before. In addition, the secondary high voltage side is connected to 1 while maintaining the conventional insulation of the parts on the secondary high voltage side.
This range can be completely separated from the secondary power source and has a double insulation structure.

The operation of the above configuration will be explained below.

FIG. 3 shows an electric circuit according to an embodiment of the present invention.

Suppose that the human body 19 is operating the microwave and is touching the heating chamber, for example. The heating chamber and the metal part of the box form a chassis 1.

Currently, the range is connected to the power source drawn from the pole transformer, so one end 2 of the 100V power source 20
1 is grounded to the earth.

a cooling motor 12 directly connected to a 100V power supply circuit;
Relay 13, control circuit drive power transformer 11, power cord 9, and primary coil 6 of insulation transformer 3
All power supply side parts such as the chassis 1 are protected by double insulation, so there is no need to worry about electrical leakage.

On the other hand, the secondary coil 7 of the isolation transformer 3 has approximately
A high voltage of 2000V is generated. One end 22 of the secondary coil 7 is connected to the core 1 of the transformer 3 on the chassis 1.
6. Metal plate 8 directly connected to core 16 and metal partition wall 2 extending as shown in FIG.
2 substantially separates the low-voltage power supply side and the high-voltage side, so in the unlikely event that the secondary coil 7 on the secondary high-voltage side
Even if the insulation deteriorates at point A, there will be no cross-contact where the high voltage from the secondary coil 7 directly flows into the primary coil 6.

For example, consider a case where a high voltage is conducted to the chassis 1 as a result of insulation deterioration. When the conductive point A is connected to the chassis 1 via a low resistance r, the current flows only through the chassis 1 and the human body 19
It never flows.

That is, since one end of the secondary coil 7 is electrically short-circuited to the chassis, both ends of the secondary coil are short-circuited via the resistor r, and a short-circuit current flows. A current flows through the primary coil to compensate for this short circuit current. In a normal design, the current value generated by such a short circuit is abnormally large compared to the rated current. Therefore, this abnormal current activates a safety device and the power is cut off. In this case, since chassis 1 is metal, the resistance of the metal is much smaller than the resistance of the human body, so a closed circuit of coil → chassis → coil is formed, but a closed circuit of coil → chassis → human body → chassis → coil is not formed. Therefore, no current flows through the human body,
No electric shock accidents will occur.

On the other hand, as shown in Figure 4, in the case of a conventional microwave oven with a ground terminal, if a bridge occurs between the primary coil 6 and the secondary coil 7, a high voltage of 2000V will be applied to the human body 19, causing an electrical shock current. flows and becomes extremely dangerous. When the primary coil 6 and the secondary coil 7 are bridged with a resistance value R (R≒0), a circuit shown by the arrow is formed, including a power supply of 100V and a high voltage secondary voltage.
Since a voltage of 2000V is applied to this circuit, if the resistance of the human body is reduced to 500Ω, for example, a current of nearly 20A will pass through the human body, causing instant death. At this time,
Even if a conventional microwave oven were equipped with a ground terminal, and if it were grounded to the ground with a 100 ohm resistance as specified, approximately 3.4A of current would flow through the human body. If this current were to flow through the human body, it is currently internationally considered that the flow-time product for a current flow of 30 mA sec is the safe limit that does not cause death due to cardiac shock. If this continues, it becomes dangerous.

Therefore, even if the earth is grounded, if a bridge occurs due to poor insulation between the primary and secondary coils of an isolation transformer, it is extremely dangerous and safety cannot be guaranteed. It can be said that it is not.

In this regard, with the present invention, there is no risk of electric shock due to the secondary high voltage of 2000V, so compared to the conventional method,
It can be said that the structure is extremely safe.

In FIG. 1, the high voltage capacitor 4 and high voltage diode 5, which are components of the secondary high voltage circuit, are separated from the components of the power supply circuit by the core 6 of the transformer 3, the metal case of the magnetron 2, and the metal partition 22. Separated.

In other words, the distance between the components on the high voltage secondary side and the chassis is configured to be shorter than the distance between the components on the low voltage power supply side and the components on the high voltage secondary side. , there is no risk of it being connected to the low voltage power supply side.

FIG. 5 shows another embodiment in which a cooling air guide is effectively utilized as another metal partition to separate high-voltage side electrical components and low-voltage power source side components.

Usually, the cooling fan motor 12 is placed at the rear to cool the magnetron 2 and the high voltage transformer 3. In order to effectively guide the cooling air to the magnetron 2 and high-voltage transformer 3, an air guide 23 with an orifice is used, and the hot air after cooling the magnetron 2 is guided to the heating chamber, and the energy of the hot air is used to assist in raising the temperature of the heated object. The air guide 24 for this purpose is made of metal, and a part of the air guide extends out. B25 is configured to guide cold air to the back side of the transformer 3.

A metal partition wall 26 is attached to the transformer 3 so as to be directly connected to the core 16 and to separate the high voltage wiring 26 to the magnetron 2 from the coil 6 on the low voltage power source side.

With the above configuration, the air guides 23 and 24 provided for the cooling structure and the air guide B2
5 and the metal partition wall composed of the metal plate 8, the metal partition wall 26, the magnetron 2, and the transformer core 16, it is possible to substantially completely separate the components on the power supply side and the components on the high voltage secondary side.

Therefore, in FIG. 5, the power cord 9, the operation panel 1
0. By making only the parts directly connected to the primary power supply side circuit, such as the power transformer 11 for driving the control circuit, the cooling motor 12, and the relay 13, a double insulation structure,
This means that double insulation of the range can be achieved.

As described above, according to the present embodiment, in the insulation transformer in which one end of the high voltage secondary side is directly connected to the chassis, the high voltage secondary coil and the low voltage power supply side primary coil are wound separately, and the secondary coil and the primary coil are wound separately. Between the next coils,
In addition to providing a metal plate directly connected to the core, the distance between the metal plate and the secondary coil is shorter than the distance between the secondary coil and the primary coil, and the metal partition wall 26 or other metal partition wall directly connected to the chassis is used. high voltage 2
By making the distance between the next side parts and the chassis shorter than the distance between the high voltage secondary side parts and the power supply side parts, and by doubly insulating the primary coil and the parts connected to the power supply side from the chassis. This not only eliminates the need for grounding work, but also prevents electric shocks caused by high voltage on the secondary side, making it possible to create a range that is extremely safe compared to conventional microwave ovens.

Effects of the Invention As described above, according to the present invention, it is possible to realize a microwave oven with a double insulation structure although it has an extremely simple structure, and it has many effects such as high safety and ease of use as described below. Obtainable.

(1) Since grounding work is not required, there are not only no construction costs but also the following advantages.

It has become possible to freely choose the location where the microwave oven is installed, and especially lightweight and compact microwave ovens can now be moved to the required location for use.

(b) When it comes to grounding work, the work itself depends on the situation after purchasing the range, and over time there were concerns about corrosion of the ground electrode and breakage of the ground wire, but these worries have completely disappeared. .

(2) Since the microwave oven has a double insulation structure with almost the same shape as the conventional one, the dimensions of the microwave oven remain the same and the cost is low. When considering construction costs, it has actually become cheaper.

(3) In a conventional range with a ground terminal, for example, 2
It was almost impossible to prevent electric shock if the secondary high voltage bridged the primary coil, but with the present invention, this worry is completely eliminated, making it possible to use an extremely safe range. I was able to make it happen.

[Brief explanation of the drawing]

Fig. 1 is a side view of a microwave oven that is an embodiment of the present invention, Fig. 2 is a perspective view of the insulation transformer, Fig. 3 is a circuit diagram of the same embodiment, and Fig. 4 is a conventional lens with a ground terminal. FIG. 5, which is a diagram illustrating the path of electrocution current, is a diagram showing an embodiment in which a metal wall is effectively constructed using a cooling air guide. 1...Shiashi, 2...Magnetron, 3...
Insulation transformer, 6...Primary coil, 7...Secondary coil, 8...Metal plate, 16...Core, 19...
Human body, 20...Power source, 21...One end of the power source that is grounded, 22...Metal partition wall, 23, 24...
Air guide, 25... Air guide B, 26...
...metallic wall.

Claims (1)

[Claims] 1. An insulating transformer consisting of a core, a low-voltage primary coil and a high-voltage secondary coil that are wound in sections, a metal plate provided between the primary coil and the secondary coil, and components on the high-voltage secondary side. and a metal partition provided to prevent contact with components on the low voltage power supply side, electrically short-circuiting the core, one end of the high voltage coil, the metal plate, and the metal partition to the chassis, and connecting the high voltage 2 A high-frequency heating device configured such that a distance between a next-side component and the metal partition wall is smaller than a distance between a high-voltage secondary-side component and a low-voltage power source-side component.