JPH1027671A - Corona discharge device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a corona discharge device which can emit a negative ion in a condition suppressing emission of a positive ion. SOLUTION: A corona discharge element 2 is set up in a device so as to place a lengthwise direction in parallel to an inflow direction (arrow mark 9) of air to a corona discharge device main unit. An induction electrode 3 is arranged in the windward side of an insulating layer 1. A discharge electrode 5 is formed in belt shape, to be arranged in a lee side along the center line in a lengthwise direction of the insulating layer 1 in a position upward from the induction electrode 3 in the insulating layer 1. A windward side of the discharge electrode 5 is opposed to the windward side of the induction electrode 3 by interposing the insulating layer 1. By connecting a high voltage output terminal of a negative potential drive power source 7 to the discharge electrode 5 and an earth terminal to the induction electrode 3, the discharge electrode 5 in a lee side is in high voltage. By a creeping discharge generated in the vicinity of the discharge electrode 5, ozone and a positive/negative ion are generated, most part of the negative ion is released to outside the device with ozone by a flow of air passing in the corona discharge device. Emitting to outside the device of the positive ion is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corona discharge device having a corona discharge element for generating ozone and ions from the air by surface corona discharge.

[0002]

2. Description of the Related Art Conventionally, in a corona discharge device, a negative AC high voltage is applied to a discharge electrode and an induction electrode which constitute a corona discharge element and face each other with an insulating layer interposed therebetween, and a creeping surface is formed near the discharge electrode. 2. Description of the Related Art There is known an apparatus which generates a discharge and thereby releases ozone and negative ions generated from the atmosphere to the outside.

[0003]

By the way, in the corona discharge device having the above-described structure, in spite of the fact that only negative ions of the generated ions should be emitted to the outside of the device, the corona discharge device is actually used. In some cases, positive ions were released together with negative ions. Therefore, the purpose of the corona discharge device, which emits only negative ions, cannot be achieved.

Accordingly, it is an object of the present invention to provide a corona discharge device capable of emitting negative ions while suppressing the emission of positive ions.

[0005]

A corona discharge device according to a first aspect of the present invention includes a corona discharge element for generating negative ions from air by creeping corona discharge between a plurality of electrodes. The electrode to which a negative voltage is applied among the plurality of electrodes of the element is disposed downstream of the airflow.

With this structure, positive ions generated from the air by the surface corona discharge are collected by the electrode to which a negative voltage is applied, which is located downstream of the air flow, while being discharged to the outside of the device by the air flow. Therefore, the positive ions are prevented from being released out of the apparatus.

In a preferred embodiment according to the first aspect of the present invention, there is provided a collecting electrode for collecting positive ions generated from the air by a creeping corona discharge. This collecting electrode is preferably arranged downstream of the air flow of the plurality of electrodes.

[0008] With this configuration, the positive ions that are not collected at the electrode to which the negative voltage is applied due to the strong air flow are collected at the collecting electrode, so that the positive ions are discharged outside the apparatus. Is prevented. In addition, when the collecting electrode and the electrode to which the negative voltage is applied are combined as one electrode on the corona discharge element, or when the electrode to which the negative voltage is applied is more air than the area where the creeping corona discharge occurs. Even if it has a portion extending to the downstream side of the flow, it is possible to prevent the positive ions from being released out of the apparatus. The same applies to the case where the area of the part of the electrode to which the negative voltage is applied, which extends to the downstream side of the airflow, is made larger than the area of the part where the creeping corona discharge occurs.

In another preferred embodiment, the electrode to which a negative voltage is applied among the plurality of electrodes surrounds the other electrodes.

With this configuration, the corona discharge element can be designed regardless of the direction of the air flow.

A corona discharge element according to a second aspect of the present invention includes a plurality of electrodes for generating a creeping corona discharge, one of the plurality of electrodes surrounding the other.

In a preferred embodiment according to the second aspect of the present invention, another electrode is provided.

In another preferred embodiment other than the above,
One of the plurality of electrodes extends in a predetermined direction from a portion where the creeping corona discharge occurs, and the area of the extended portion is set to be larger than the area of the portion where the creeping corona discharge occurs.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIGS. 1 and 2 show an embodiment of a corona discharge element provided in the corona discharge device of the present invention. FIG. 1 is a plan view showing an embodiment of a corona discharge element, and FIG. It is sectional drawing which shows one Embodiment of an element.

As shown, the corona discharge device includes a corona discharge element including an insulating layer 1, an induction electrode 3, and a discharge electrode 5, and the induction electrode 3 and the discharge electrode 5 have a negative potential. A creeping discharge is generated in the vicinity of the discharge electrode 5 by connecting the driving power supply 7 to generate ozone and ions from the atmosphere.

Next, each part constituting the corona discharge element will be described.

The corona discharge element 2 has a rectangular shape having a predetermined thickness, and its length direction is the direction in which air flows into a corona discharge device main body (not shown) (indicated by an arrow 9 in FIG. 2). Are installed in a corona discharge device (not shown) so as to be in parallel with. The induction electrode 3 is formed in a rectangular shape, and is arranged in a region of the insulating layer 1 that is closer to the upstream side (ie, upwind) in the air inflow direction. Discharge electrode 5
Is a corona discharge element 2 together with the induction electrode 3, and is formed in a belt shape. The discharge electrode 5 is located at a position above the induction electrode 3 in the insulating layer 1 and is located downstream in the inflow direction of air along the longitudinal center line of the insulating layer 1 (that is, in the airflow direction).
(Leeward) It is located closer to you. The windward part of the discharge electrode 5 is opposed to the windward part of the induction electrode 3 with the insulating layer 1 interposed therebetween.

In this embodiment, a high-voltage AC power supply is used as the negative-potential drive power supply 7, and its high-voltage output terminal is connected to the discharge electrode 5 and its ground terminal is connected to the induction electrode 3, respectively. Thereby, the discharge electrode 5 located on the leeward side has a higher voltage than the induction electrode 3 located on the leeward side.

In the above configuration, ozone and positive and negative ions are generated by creeping discharge generated near the discharge electrode 5. Most of the generated positive and negative ions are discharged to the outside of the apparatus together with ozone by an air flow (arrow 9) passing through a corona discharge device (not shown). Is suppressed from being released out of the apparatus (see FIG. 2). This is a fact confirmed as a result of the inventors' experiments.

Therefore, in the corona discharge device for obtaining negative ions together with ozone from the atmosphere, as in the present embodiment, the electrode located on the leeward side (ie, the discharge electrode 5) is connected to the electrode ( That is, the configuration in which the voltage is set higher than that of the induction electrode 3) is based on new knowledge obtained as a result of an experiment conducted by the present inventors.

Hereinafter, the experiments performed by the present inventors and novel findings obtained by the experiments will be described in detail with reference to FIGS.

FIG. 3 is a characteristic diagram showing the relationship between the wind speed near the corona discharge element 2 and the ion concentration in the air. The data shown in FIG. 3 is obtained by sampling while changing the wind speed in the vicinity of the corona discharge element 2 by controlling the fan rotation speed in a state in which a negative AC high voltage is applied to the corona discharge element 2.

In FIG. 3, dashed lines a and b indicate the relationship between the wind speed and the ion concentration when the induction electrode 3 is set to a high voltage in the above-mentioned apparatus, that is, the electrodes located on the windward side. A broken line a indicates the relationship between the wind speed and the positive ion concentration, and a broken line b indicates the relationship between the wind speed and the negative ion concentration.

On the other hand, solid lines c and d are curves showing the relationship between the wind speed and the ion concentration when the discharge electrode 5 is set to a high voltage in the above-mentioned apparatus, ie, the electrodes located on the leeward side. Solid line c shows the relationship between wind speed and negative ion concentration,
The solid line d indicates the relationship between the wind speed and the positive ion concentration, respectively.

As is apparent from the figure, when the electrode on the windward side is set to a high voltage, the positive ion concentration becomes 1.20 m / wind.
The wind speed rises sharply from around sec and is 1.70 m / sec.
In the vicinity, the concentration of negative ions will exceed the
At 0 m / sec, a considerable difference occurs with the negative ion concentration. That is, it can be seen that the positive ions emitted from the corona discharge element 2 rapidly increase. On the other hand, when the electrode on the leeward side is set to a high voltage, the positive ion concentration changes to 0 or almost 0 while the wind speed increases from 1.00 m / sec to 2.00 m / sec. I do. That is, it can be seen that the positive ions emitted from the corona discharge element 2 are 0 or almost 0.

It is considered that such a phenomenon occurs due to the following reasons.

That is, of the positive and negative ions generated by the creeping discharge generated in the vicinity of the discharge electrode 5, the positive ions have the power of the air flow and the corona discharge element 2 kept at a negative potential. By the action of the combined force with the resulting Coulomb force, the particles are collected by the corona discharge element 2. Since the magnitude of this Coulomb force is determined according to the potential difference between the corona discharge element 2 and the positive ions, as shown in FIGS. 4 and 5, if the force of the air flow (that is, the wind speed) F1 is the same, The magnitude and direction of the resultant force F3 of the force F1 of the air flow and the Coulomb force F2 are:
It is determined by the magnitude of the Coulomb force F2.

FIG. 4 shows the three types of forces F1, F2 and F3 acting on the positive ions p when the discharge electrode 5 located on the leeward side is set to a high voltage. The three types of forces F1, F2 and F3 acting on the positive ions p when the induction electrode 3 located on the windward side is set to a high voltage are shown.

When the leeward discharge electrode 5 is set to a high voltage, the potential difference between the positive ions p and the discharge electrode 5 is naturally larger than when the leeward induction electrode 3 is set to a high voltage. Therefore, the Coulomb force F2 shown in FIG. 4 is necessarily larger than the Coulomb force F2 shown in FIG. Therefore, in the device shown in FIG. 4, positive ions p are collected near the discharge electrode by the combined force F3, whereas in the device shown in FIG. 5, positive ions p are collected near the discharge electrode by the combined force F3. Instead, they are released outside the device.

From the above experimental results, the present inventors have found that
A new finding was obtained that setting the electrode on the leeward side (discharge electrode 5 in the present embodiment) to a negative high voltage is an effective means for suppressing the release of positive ions from the corona discharge device. It is a thing.

FIG. 6 is a plan view showing a first modification of the above-described embodiment of the corona discharge element 2, and FIG. 7 is a cross-sectional view showing a first modification of the above-described embodiment of the corona discharge element 2. It is.

In the corona discharge element 2 of the present modification, the two induction electrodes 3 and 8 are arranged at predetermined intervals on the windward and leeward sides of the insulating layer 1 which is installed so that the length direction is parallel to the wind direction 11. Are placed apart from each other. Then, the discharge electrode 6 is partially located on the center of the insulating layer 1 along the longitudinal center line of the insulating layer 1 at a position above the induction electrodes 3 and 8 in the insulating layer 1 and partially with the induction electrodes 3 and 8. Are arranged so as to oppose to each other. In this configuration, the leeward induction electrode 8 is connected to the negative potential driving power source 7.
Is connected to the windward induction electrode 3 by the drive power supply 7.
Are connected to each other, thereby setting the induction electrode 8 side to a high voltage and setting the discharge electrode 6 to an electrically floating state.

Also in the above configuration, of the positive and negative ions generated by the creeping discharge generated near the discharge electrode 6,
Most of the negative ions are released to the outside of the apparatus together with the ozone by the air flow (arrow 11) passing through the inside of the corona discharge device (not shown), but the discharge of the positive ions to the outside of the apparatus is suppressed. This is also a fact confirmed as a result of the above-mentioned experiments performed by the present inventors in the apparatus shown in FIGS.

FIG. 8 is a plan view showing a second modification of the embodiment of the corona discharge element 2 described above.

The corona discharge element 2 of the present modified example has an insulating layer 1
In the position above the induction electrode 3 in FIG.
Consisting of a strip-shaped discharge portion 13a arranged at a central portion of the insulating layer 1 along the longitudinal center line so as to partially face the induction electrode 3, and a rectangular portion 13b surrounding the discharge portion 13a. The configuration is such that an electrode 13 is provided. In this configuration, a high voltage output terminal of a negative potential drive power supply (not shown) is connected to the discharge electrode 13, and a ground terminal (not shown) of the negative potential drive power supply is connected to the induction electrode 3, thereby raising the discharge electrode 13 side. It is set to voltage.

According to the above structure, the discharge region 13a and the ion generation region in the vicinity of the induction electrode 3 are surrounded by the rectangular portion 13b set to a high voltage, similarly to the discharge region 13a. A Coulomb force is generated between the portion 13a and between the positive ions and the rectangular portion 13b, so that the positive ions are not easily emitted to the outside of the apparatus. Therefore, it is possible to design a corona discharge device that ignores the wind direction.

FIG. 9 is a plan view showing a third modification of the embodiment of the corona discharge element 2.

The corona discharge element 2 of this modification has a configuration in which two induction electrodes 3 and 8 are arranged on the insulating layer 1 and a discharge electrode 13 having the structure shown in FIG.

In this modified example, the same effect as in the second modified example can be obtained.

FIGS. 10 and 11 show another embodiment of the corona discharge element 2 provided in the corona discharge device of the present invention. FIG. 10 is a plan view showing another embodiment of the corona discharge element 2. FIG. 11 is a sectional view showing another embodiment of the corona discharge element 2.

The corona discharge element 2 of this embodiment is obtained by improving the corona discharge element 2 having the structure shown in FIGS. 6 and 7 so that it can be applied even at a high wind speed. , An electrode (collecting electrode) 29 for collecting positive ions is provided leeward (in the direction indicated by the arrow 31).

That is, the two induction electrodes 23 and 28 are arranged at a predetermined interval toward the windward side of the strip-shaped insulating layer 21,
The discharge electrode 25 is connected to the induction electrodes 23, 2 in the insulating layer 21.
At a position higher than 8, the insulating layer 21 is disposed so as to partially face the induction electrodes 23 and 28 along the longitudinal center line. Further, a rectangular collecting electrode 29 having the same height as the discharge electrode 25 is arranged on the leeward side of the insulating layer 21.

In this configuration, the high-voltage output terminal of the negative potential drive power supply 7 is connected to the leeward induction electrode 28 and the collection electrode 29, and the ground terminal of the drive power supply 7 is connected to the leeward induction electrode 3. Thus, the induction electrode 28 side is set to a high voltage, and the discharge electrode 25 is electrically floated.

In the above configuration, ozone and positive and negative ions are generated by creeping discharge generated near the discharge electrode 25. Most of the generated positive and negative ions are discharged to the outside of the device together with ozone by an air flow (arrow 31) passing through the inside of the corona discharge device (not shown). For, release to the outside of the device is suppressed. This is also a fact confirmed as a result of experiments performed by the present inventors.

Therefore, in the above-described corona discharge device, as in the present embodiment, the collecting electrode 29 is provided on the most leeward side of the insulating layer 21 to connect the high voltage output terminal of the driving power source 7 to the vicinity of the discharging electrode 25. The positive electrode that failed to be collected by the collecting electrode 2
The configuration determined to be collected in 9 is based on new findings obtained as a result of experiments conducted by the present inventors.

Hereinafter, the experiments performed by the present inventors and the novel findings obtained by the experiments will be described with reference to FIGS.
This will be described in detail with reference to FIG.

FIG. 12 is a characteristic diagram showing the relationship between the wind speed near the corona discharge element 2 and the ion concentration in the air.

The data shown in FIG. 12 shows that the above-mentioned leeward induction electrode 8 is set to a higher voltage than the leeward induction electrode 3 and the discharge electrode 6 is electrically floated (FIG. 6 and FIG. FIG. 7) is used to sample the wind speed-ion concentration data in a higher wind speed region than in FIG. 3 by controlling the fan rotation speed.

In FIG. 12, the solid line e indicates the discharge electrode 25.
, And the solid line f is a characteristic curve showing the relationship between the wind speed and the positive ion concentration in the vicinity of the discharge electrode 25, respectively.

As is apparent from the figure, as the wind speed is increased, the positive ion concentration sharply increases from around 2.30 m / sec as compared with the negative ion concentration, and the wind speed becomes 2.40.
In the vicinity of m / sec, the concentration exceeds the negative ion concentration.
When the wind speed is around 4.10 m / sec, the wind speed becomes so high that a considerable difference occurs with the negative ion concentration. In other words, it can be seen that the amount of positive ions emitted outside the device increases sharply with an increase in the wind speed as compared with negative ions.

It is considered that such a phenomenon is caused by the following reasons.

That is, if the leeward induction electrode 8 is set to a high voltage as in the corona discharge device shown in FIGS. 6 and 7,
As already described, the Coulomb force F2 generated between the corona discharge element 2 and the positive ions is larger than when the windward induction electrode 3 is set to a high voltage.

However, even if the leeward induction electrode 8 is set to a high voltage in this way, as shown in FIG. 13, when the force F1 of the air flow increases sharply as shown in FIG. Positive ions p, which are carried further downwind than the position of the induction electrode 8 due to the combined force F3 of F2 and F2, cannot be collected near the discharge electrode 6, and increase rapidly. Therefore, FIG.
In the apparatus shown in FIG. 7, the positive ions p emitted to the outside of the apparatus increase rapidly.

From these experimental results, the present inventors have found that
The collection electrode 29 for the positive ions p further downwind than the induction electrode 8
And the fact that setting the collecting electrode 29 to a high negative voltage is also an effective means for suppressing the release of the positive ions p from the corona discharge device at high wind speed. Things.

FIG. 14 is a characteristic diagram showing the relationship between the wind speed near the corona discharge element 2 and the ion concentration in the air.

The data shown in FIG. 14 shows that the induction electrode 28 and the further downwind collection electrode 29 are set to a high voltage,
12 using a corona discharge device (shown in FIGS. 10 and 11) in which the discharge electrode 25 is electrically floated.
As in the case of, data of wind speed-ion concentration value in a high wind speed region are sampled.

In FIG. 14, the solid line g represents the discharge electrode 25.
, And the solid line h is a characteristic curve showing the relationship between the wind speed and the positive ion concentration near the discharge electrode 25, respectively.

As is apparent from the figure, the negative ion concentration is
The wind speed starts rising gradually from around 1.30 m / sec and reaches around 4.10 m / sec, whereas the positive ion concentration changes to zero despite the rise in wind speed. That is, it can be seen that the number of positive ions emitted from the corona discharge element shown in FIGS. 10 and 11 to the outside of the device is zero.

Comparing and comparing the experimental data shown in FIG. 12 with the experimental data shown in FIG. 14, the apparatus having the configuration shown in FIGS. 10 and 11 has a positive ion trapping performance even at a high wind speed. It is clear that this can be fully demonstrated.

FIG. 15 is a plan view showing a first modified example of another embodiment of the corona discharge element 2 described above, and FIG. 16 shows a first modified example of the above-described other embodiment of the corona discharge element 2. It is sectional drawing.

The corona discharge element 2 of this modification is the same as the corona discharge element 2 shown in FIGS. 10 and 11, except that only the dielectric electrode 23 on the windward side is used as the dielectric electrode.
Is extended to the leeward side (arrow 31), and the leeward end thereof is brought close to the collecting electrode 29. The discharge electrode 26 and the collecting electrode 29 are connected to the high voltage output terminal of the negative potential driving power source 7, and the dielectric electrode 23 is connected to the ground terminal of the driving power source 7, so that the discharge electrode 26 and the collecting electrode 29 are connected. It is set to a high voltage.

In the above-described configuration, the positive ions that have failed to be collected in the vicinity of the discharge electrode 26 at the time of high wind speed are surely collected at the collecting electrode 29. It can be prevented from being released outside. Therefore, in this modification, the same effects as those of the apparatus shown in FIGS. 10 and 11 can be obtained.

FIG. 17 is a plan view showing a second modification of the other embodiment of the corona discharge element 2 described above, and FIG. 18 shows a second modification of the above-described corona discharge element 2 in another embodiment. It is sectional drawing.

The corona discharge element 2 according to the present modification has an insulating layer 2
1, a dielectric electrode 23 is disposed on the leeward side, and a discharge electrode 30 having a configuration in which a band-shaped portion 30a and a rectangular-shaped portion 30b are integrated is arranged on the leeward side of the insulating layer 21 as shown in FIG.
Are arranged so as to face the dielectric electrode 23. The high voltage output terminal of the negative potential drive power supply 7 is connected to the discharge electrode 30 and the ground terminal of the drive power supply 7 is connected to the dielectric electrode 23, thereby setting the discharge electrode 30 side to a high voltage. .

Also in the above configuration, the positive ions that have failed to be collected in the vicinity of the strip portion 30a of the discharge electrode 30 at a high wind speed are:
Since it is reliably collected in the rectangular portion 30b, it is possible to prevent positive ions from being discharged out of the apparatus with an increase in wind speed. Therefore, also in this modification, FIGS.
The same effects as those of the device shown in FIG. 15 and the devices shown in FIGS. 15 and 16 can be obtained.

The contents described above relate to each embodiment of the present invention and the modifications thereof, and needless to say that the present invention is not limited to the above contents.

[0068]

As described above, according to the present invention,
A corona discharge device capable of emitting negative ions while suppressing emission of positive ions can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view of a corona discharge element according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the corona discharge element of FIG.

FIG. 3 is a characteristic diagram showing a relationship between a wind speed and an ion concentration near a corona discharge element.

FIG. 4 is an explanatory diagram showing a force acting on positive ions when a leeward electrode is at a negative potential high voltage.

FIG. 5 is an explanatory diagram showing a force acting on positive ions when a windward electrode is at a high negative voltage.

FIG. 6 is a plan view showing a first modification of the embodiment of the corona discharge element.

FIG. 7 is a sectional view showing a first modification of the embodiment of the corona discharge element.

FIG. 8 is a plan view showing a second modified example of the embodiment of the corona discharge element.

FIG. 9 is a plan view showing a third modification of the embodiment of the corona discharge element.

FIG. 10 is a plan view showing another embodiment of a corona discharge element.

FIG. 11 is a sectional view showing another embodiment of a corona discharge element.

FIG. 12 is a characteristic diagram showing a relationship between a wind speed and an ion concentration near a corona discharge element.

FIG. 13 is an explanatory diagram showing a force acting on positive ions at a high wind speed when a downwind electrode is set to a negative potential high voltage.

FIG. 14 is a characteristic diagram showing a relationship between a wind speed and an ion concentration near a corona discharge element.

FIG. 15 is a plan view showing a first modified example of another embodiment of the corona discharge element.

FIG. 16 is a sectional view showing a first modified example of another embodiment of the corona discharge element.

FIG. 17 is a plan view showing a second modified example of another embodiment of the corona discharge element.

FIG. 18 is a sectional view showing a second modified example of another embodiment of the corona discharge element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 21 Insulating layer 2 Corona discharge element 3, 8, 23, 28 Induction electrode 5, 6, 13, 25, 26, 30 Discharge electrode 7 Negative potential drive power supply 9, 11, 31 Wind direction 29 Collection electrode

Claims (11)

[Claims] 1. A corona discharge device including a corona discharge element that generates negative ions from air by creeping corona discharge between a plurality of electrodes, wherein an electrode to which a negative voltage is applied among a plurality of electrodes of the corona discharge element. Is disposed downstream of the air flow. 2. The corona discharge device according to claim 1, further comprising a collecting electrode for collecting positive ions generated from the air by the creeping corona discharge. 3. The corona discharge device according to claim 2, wherein the collecting electrode is disposed downstream of an air flow of the plurality of electrodes. 4. The corona discharge device according to claim 2, wherein the collection electrode and the electrode to which the negative voltage is applied are connected as one electrode on the corona discharge element. Corona discharge device. 5. The corona discharge device according to claim 1, wherein the electrode to which the negative voltage is applied has a portion extending further downstream of the airflow than a region where the creeping corona discharge is generated. A corona discharge device characterized by the above-mentioned. 6. The corona discharge device according to claim 5, wherein an area of a portion extending to a downstream side of the air flow is larger than an area of a portion where the creeping corona discharge is generated. 7. The corona discharge device according to claim 1, wherein an electrode to which a negative voltage is applied among the plurality of electrodes surrounds another electrode. 8. A corona discharge element having a plurality of electrodes for generating a creeping corona discharge, wherein one of the plurality of electrodes surrounds the other. 9. The corona discharge element according to claim 8, further comprising another electrode. 10. A corona discharge element having a plurality of electrodes for generating a creeping corona discharge, wherein one of the plurality of electrodes extends in a predetermined direction from a portion where the creepage corona discharge is generated. Characteristic corona discharge element. 11. The corona discharge element according to claim 10, wherein an area of the extended portion is larger than an area of a portion where the creeping corona discharge is generated.