JP2012087654A - Gas blower and method of detecting abnormality of inside of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas blower which enables the reduction of the stop time of electric power devices required for the repair or replacement of the gas blower by detecting the abnormality of the inside of the gas blower to efficiently perform the preparatory operations for the repair or replacement, and also provide a method of detecting the abnormality of the inside of the gas blower.SOLUTION: The gas blower 20 includes a rotatable impeller 21 having a plurality of blades 27, a casing 23 covering the impeller 21, and a motor 26 for rotating the impeller 21. A direct current power supply 22 for supplying a direct current voltage to the impeller 21 is connected to the impeller 21, and a float electrode 24 is disposed near the casing 23. The impeller 21 and the float electrode 24 are electrically insulated from each other. A voltage measurer 28 is connected to the float electrode 24 through a potential measuring terminal 25. A surveillance monitor 32 is connected to the voltage measurer 28.

Description

  The present invention relates to a gas blower monitoring technique mainly used to forcibly circulate an insulating gas in gas-insulated power equipment, and more particularly, a gas blower capable of detecting an internal abnormality and an internal abnormality detection method thereof About.

  In general, gas-insulated power devices such as transformers and reactors generate heat due to loss of iron cores and windings. Therefore, the insulating gas sealed in the apparatus main body tank is required to have a function as a cooling medium as well as a function as an insulating medium. In particular, an insulating gas sealed in a large-capacity power device having a large calorific value needs to have a high cooling capacity. Therefore, in a large-capacity electric power device, a forced circulation method for forcibly circulating the insulating gas is adopted as a method for cooling the device, instead of the self-cooling method for naturally circulating the insulating gas.

  In gas-insulated power equipment that employs the forced circulation system, a gas blower or a gas cooler is attached to the equipment body tank via a connection pipe. Among these, the gas blower is a blower that rotates an impeller having a plurality of blades to generate a gas flow, and forcibly feeds an insulating gas into the apparatus main body tank and circulates it.

  By the way, when some abnormality occurs in the gas blower and the circulating flow rate of the insulating gas is less than a predetermined amount, the heat inside the device is not sufficiently discharged and the internal temperature rises. If the high temperature state continues for a long time inside the device main body tank, or if the temperature becomes abnormally high for a short time and abnormal overheating occurs locally, the surrounding insulators are rapidly deteriorated and deteriorated.

  As a result, the lifetime of the device is remarkably shortened, and in the worst case, there is a risk of causing breakdown and causing damage to the device. In order to avoid such a worst situation, forced-circulation gas-insulated power equipment performs emergency stop control of equipment when it detects a gas blower failure to avoid equipment damage. ing.

  In the power equipment that performs the emergency stop control described above, it is important to reliably detect a failure of the gas blower. For this reason, various techniques for monitoring the operating state of the gas blower have been proposed. For example, in patent document 1, the operation state of a gas blower is monitored by measuring the electric power generated by the impeller generator. More specifically, an impeller generator is disposed in a connection pipe between the gas blower and the gas cooler. Then, if the flow of the insulating gas operates the impeller generator and the generated power amount becomes smaller than a predetermined reference value, it can be determined that the flow rate of the insulating gas has decreased.

  Further, as a conventional technique for monitoring other than the gas flow rate, a technique for monitoring the magnitude of vibration of the gas blower surface, a technique for monitoring a motor current value for driving the gas blower, and the like are known. In the former, an abnormality of the gas blower can be detected from the outside of the gas blower, and in the latter, an electrical failure of the gas blower can be detected.

Japanese Patent Laid-Open No. 9-199337

  According to the above-described conventional technology, the power device is urgently stopped when a failure of the gas blower is detected so that the malfunction of the gas blower does not seriously affect the power device. In other words, when the power equipment is stopped, the gas blower is completely out of order and is almost impossible to operate. Therefore, it is indispensable to repair or replace the gas blower when restoring the stopped power equipment.

  Such gas blower repair / replacement work often takes time, including preparation work. Specifically, the period required for repairing and replacing the gas blower, that is, the period in which the gas-insulated power equipment is forced to stop may range from several weeks to several months.

  Among them, among the work included in the repair and replacement work of the gas blower, the preparation work tends to be prolonged. This includes preparatory work starting from internal inspections to confirm the damage status, investigation of the cause of failure, arrangement of repair parts or alternative blowers, and processing of insulating gas in the equipment body tank after the equipment is stopped. This is because a plurality of operations are included.

  Moreover, most of these preparatory work must be carried out step by step, such as finding out the cause of failure and then arranging for repair parts or alternative blowers corresponding to the cause. Therefore, in the preparatory work related to the repair / replacement of the gas blower, it is difficult to carry out a plurality of work in parallel and the work efficiency is low.

  Therefore, regarding the preparatory work for repairing / replacement of the gas blower, it is desired not to start the preparatory work after the gas blower has completely failed, but to start the work that can be prepared at the earliest possible stage. In order to meet this demand, it is effective to detect a sign of failure at an early stage by detecting this with high sensitivity when an abnormality occurs inside the gas blower.

  However, in the prior art, emergency stop control of electric power equipment is performed on the assumption that the gas blower has completely failed. In other words, the conventional gas blower monitoring technology determines that the failure of the gas blower has progressed sufficiently, and even if a mechanical abnormality occurs inside the gas blower, the operation of the gas blower can be continued. , Such an internal abnormality was not detected.

  Although there is a possibility of failure of the gas blower, for the time being, an internal abnormality in which the operation of the gas blower can be continued is typically the loss of several blades among the numerous blades of the impeller. . The conventional gas blower monitoring technique does not detect such internal abnormalities one by one, but only detects that the gas blower has completely failed as described above.

  Thus, in the prior art, an internal abnormality of the gas blower that does not immediately lead to a failure is not detected. For this reason, the work efficiency of the preparatory work was low except that the gas blower was completely broken and the preparatory work was started. Therefore, the period during which the gas-insulated power equipment is stopped when the gas blower is repaired or replaced is inevitably prolonged.

  The present invention has been proposed in view of such a situation, and does not detect a failure of the gas blower, but detects an internal abnormality of the gas blower that is a sign of the failure, thereby carrying out preparation work for repair or replacement. It is an object of the present invention to provide a gas blower that can be efficiently advanced in advance and that can shorten the period of stoppage of power equipment accompanying the repair / replacement of the gas blower, and a method for detecting an internal abnormality thereof.

  In order to achieve the above object, the present invention provides a gas blower for forcibly circulating an insulating gas to a power device, wherein a motor is accommodated in the casing, and the AC voltage is supplied to the motor. A supply means is connected, and an impeller is attached to the rotating shaft of the motor in an electrically insulated state. A DC voltage supply means for supplying a DC voltage to the impeller is connected to the impeller, and in the vicinity of the casing. A float electrode is attached in an electrically insulated state, and a potential measurement terminal for extracting the potential of the float electrode to the outside is installed in the float electrode, and a voltage induced in the float electrode is measured in the potential measurement terminal Voltage measuring means is connected to the voltage measuring means, and the voltage measuring means monitors voltage measured by the voltage measuring means. It is continued, the voltage monitoring means for measuring the voltage of the voltage measuring means, and characterized in that it is configured to monitor the variation range of the AC voltage component superposed on the DC voltage.

  The present invention also provides an interior of a gas blower in which an impeller is attached to a rotating shaft of a drive motor in a casing in an electrically insulated state, and a float electrode is attached in the electrically insulated state in the vicinity of the casing. In the method for detecting an abnormality, during the operation of the gas blower, the DC voltage supply step for supplying a DC voltage to the impeller, the voltage measurement step for measuring the voltage induced in the float electrode, and the voltage measurement step were used. A voltage monitoring step for monitoring the voltage, wherein the voltage monitoring step monitors the fluctuation range of the AC voltage component superimposed on the DC voltage with respect to the voltage measured in the voltage measurement step.

  According to the gas blower and the internal abnormality detection method of the present invention, the gas blower is operated in a state where a DC voltage is applied to the impeller which is originally non-voltage, and when the impeller rotates normally, the float electrode located near the impeller By using the fact that the induced voltage fluctuates periodically, the fluctuation range of the AC voltage component superimposed on the DC voltage is monitored with respect to the voltage induced on the float electrode. When the range is exceeded, it is possible to detect abnormalities inside the gas blower, detect early signs of failure, and proceed efficiently with gas blower repair and replacement preparations. -It is possible to shorten the power equipment outage period due to replacement.

The block diagram of 1st Embodiment of the gas blower of this invention. The schematic diagram which shows typically normal operation of 1st Embodiment from the upper surface. The schematic diagram which shows typically the operation | movement at the time of abnormality of 1st Embodiment from the upper surface. The graph which shows the float electrode voltage waveform at the time of normal. The graph which shows the float electrode voltage waveform when one impeller is lost. The block diagram of the 2nd Embodiment of this invention. The block diagram of the 3rd Embodiment of this invention.

(1) Configuration of First Embodiment (1-1) The configuration of the first embodiment according to the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing an outline of the first embodiment of the present invention, FIGS. 2 and 3 are schematic views of the gas blower 20 shown in FIG. 1 as viewed from above, and FIG. FIG. 3 shows a state during abnormal operation. FIG. 4 is a graph showing the voltage waveform of the float electrode 24 when the impeller 21 is operating normally, and FIG. 5 is a diagram showing the float electrode when the blade 27 attached to the impeller 21 is lost and operated. It is a graph which shows 24 voltage waveforms.

  As shown in FIG. 1, the gas blower 20 has a squirrel-cage shape that forcibly circulates an insulating gas through a power device. The gas blower 20 is provided with a casing 23. The casing 23 is formed by connecting two cylindrical shapes having different diameters, and a conductive impeller 21 is provided on the upper side having a larger diameter, and a motor 26 for driving the impeller 21 is provided on the lower side having a smaller diameter. It is stored.

  The impeller 21 is disposed so as to be rotatable with the rotation shaft in the vertical direction, and is attached in a state of being electrically insulated from the rotation shaft of the motor 26. The impeller 21 is covered with a casing 23 and is electrically insulated from surrounding structures. Further, a plurality of blades 27 are attached to the outer peripheral portion of the impeller 21 along the circumferential portion.

  The motor 26 is provided with an AC power supply terminal 31. An AC power supply 30 is connected to the AC power supply terminal 31. The AC power supply 30 supplies an AC voltage to the motor 26. Further, a DC voltage application terminal 29 is installed in the vicinity of the AC power supply terminal 31. A DC power supply 22 is connected to the DC voltage application terminal 29. The DC power source 22 supplies a DC voltage to the impeller 21.

  Further, a float electrode 24 is fixed near the casing 23. The float electrode 24 is electrically insulated from the ground, and is connected to a potential measurement terminal 25. The potential measuring terminal 25 is for drawing out the potential of the float electrode 24 to the outside of the casing 23, and is connected to a voltage measuring device 28.

  The voltage measuring device 28 is a device for measuring a voltage induced in the float electrode 24, and a monitor monitor 32 is connected thereto. The monitor monitor 32 has a display monitor for displaying the measurement result of the voltage measuring device 28, and monitors the fluctuation range of the AC voltage component superimposed on the DC voltage with respect to the voltage measured by the voltage measuring device 28. ing.

(1-2) Gas Blower Internal Abnormality Detection Method In the gas blower 20 having the above configuration, the internal abnormality of the gas blower 20 is detected by monitoring with the monitoring monitor 32 as follows. First, prior to detecting an internal abnormality of the gas blower 20, the voltage measuring device 28 is connected to the potential measuring terminal 25. Then, a DC voltage is supplied from the DC power supply 22 to the impeller 21 via the DC voltage application terminal 29 in a state where the gas blower 20 is operated (DC voltage supply step).

  As shown in FIGS. 2 and 3, by supplying a DC voltage to the impeller 21, each blade 27 has a positive charge 41, and the entire impeller 21 has a uniform potential. At this time, a capacitance 42 exists between the blade 27 and the float electrode 24, and a capacitance 43 exists between the float electrode 24 and the casing 23. Here, the DC voltage applied to the impeller 21 is divided by the electrostatic capacity 42 between the blade 27 and the float electrode 24 and the electrostatic capacity 43 between the float electrode 24 and the casing 23, and thus the float electrode 24. A voltage is induced in.

  This voltage induction phenomenon is established even in the operating state of the gas blower 20 in which the impeller 21 rotates by the driving force of the motor 26. Therefore, in a state where the gas blower 20 is operated, the voltage induced in the float electrode 24 is measured by the voltage measuring device 28 (voltage measuring step), and the measurement result of the voltage measuring device 28 is constantly monitored by the monitoring monitor 32 ( Voltage monitoring step).

Now, when the DC voltage 41 is supplied from the DC power supply 22 to the impeller 21 of the gas blower 20 in operation, the i-th blade 27 attached to the impeller 21 will be considered. The generated voltage of the float electrode 24 at this time is the vector Vi, the capacitance 42 between the i-th blade 27 and the float electrode 24 is C1i, the capacitance 43 between the float electrode 24 and the casing 23 is C2, and the DC power source 22 Assuming that the DC voltage supplied to the impeller 21 is E, the magnitude of the voltage vector Vi generated at the float electrode 24 can be expressed by the following equation (1).

  Here, since the float electrode 24 is fixed in the vicinity of the casing 23, the distance between the float electrode 24 and the casing 23 does not change. Therefore, C2 of the capacitance 43 between the float electrode 24 and the casing 23 does not change. On the other hand, since the gas blower 20 is in operation and the blade 27 of the impeller 21 is moving on the circumference at a constant speed, the distance between the blade 27 and the float electrode 24 changes at a constant period.

The radius of the impeller 21 is r, the angular frequency of the impeller 21 is ω, the circumference is π, the shortest distance between the blade 27 and the float electrode 24 is a, the number of blades 27 attached to the impeller 21 is N, and the number of the blade 27 If i is i (i = 0,... N−1), and the distance between the i-th blade 27 and the float electrode 24 is represented by a vector li in complex notation, the following equation 2 is obtained.

Moreover, the electrostatic capacitance between opposing flat plates is inversely proportional to the distance between the two. From this, if the electrostatic capacity when the distance between the blade 27 and the float electrode 24 is the shortest distance a is Cm, the electrostatic capacity C1i between the i-th blade 27 and the float electrode 24 is expressed by the following Equation 3. Can be represented.

そのときのｉ番目のブレード２７からフロート電極２４に誘起される電圧Ｖｉは、上記式４により、次の式５のベクトルとして表される。

Here, the distance between the i-th blade 27 and the float electrode 24, that is, the magnitude of the vector li can be derived from the following Equation 4.

The voltage Vi induced from the i-th blade 27 to the float electrode 24 at that time is expressed as a vector of the following expression 5 by the above expression 4.

In view of the above formula 5, the voltage Vi induced from the i-th blade 27 to the float electrode 24 periodically varies with the angular frequency of the impeller 21. Since Formula 5 is a case where one of the N blades 27 attached to the impeller 21 is considered, the voltage vector V induced from the total number N of blades is expressed by the following Formula 6.

(1-3) When the gas blower 20 is normal If the number of blades 27 attached to the impeller 21 is 51 (N = 51), for example, from the above equation 6, the induced voltage of the float electrode 24 in this case The time change is shown in the graph of FIG. This graph is displayed on the monitor 32.

  As apparent from the graph shown in FIG. 4, it can be seen that the induced voltage of the float electrode 24 is a small alternating voltage superimposed on the direct current voltage. The monitoring monitor 32 monitors the fluctuation range of the AC voltage component superimposed on the DC voltage with respect to the voltage measured by the voltage measuring device 28. In the graph of FIG. 4, the fluctuation range falls within a predetermined range. Will be.

  That is, the periodic waveform in the induced voltage of the float electrode 24 is not disturbed. Accordingly, the distance between each blade 27 and the float electrode 24 changes at a constant period. This indicates that the impeller 21 is rotating normally, and the gas blower 20 can be regarded as operating normally.

(1-4) When an internal abnormality occurs in the gas blower 20 On the other hand, when one of the blades 27 attached to the impeller 21 is lost, the voltage vector V induced from the blade 27 is expressed by the following equation 7 Can be calculated.

  From Equation 7, the time change of the induced voltage of the float electrode 24 when the number of blades 27 attached to the impeller 21 is reduced from 51 to 50, for example, is as shown in the graph of FIG. This graph can also be displayed on the monitor 32. Also in the graph of FIG. 5, it can be seen that the AC voltage is superimposed on the DC voltage as in the graph of FIG.

  However, at the position of the lost blade 27, the ground capacitance C1i does not increase when passing in front of the float electrode 24. For this reason, the induced voltage of the float electrode 24 becomes small based on the formula 1, and a large voltage drop occurs at the timing when the position of the lost blade 27 passes in front of the float electrode 24.

  Here, the monitoring monitor 32 monitors the fluctuation range of the AC voltage component superimposed on the DC voltage with respect to the voltage measured by the voltage measuring instrument 28. However, the fluctuation range exceeds the predetermined range. The periodic waveform in the induced voltage of the float electrode 24 is disturbed. In response to this monitoring result, the impeller 21 can determine that one blade 27 has been lost, and an internal abnormality of the gas blower 20 can be detected.

(1-5) Other examples of internal abnormality of gas blower 20 In the above description, the loss of the blade 27 is given as an example of the abnormality occurring inside the gas blower 20, but in this embodiment, the bearing abnormality of the impeller 21 A rotation abnormality due to imbalance of the impeller 21 can also be detected as an internal abnormality of the gas blower 20.

  That is, the induced voltage of the float electrode 24 varies according to the change in the distance between the float electrode 24 and the blade 27. Therefore, even when the bearing of the impeller 21 is shaken due to a bearing breakage or when the rotating shaft is eccentric due to the imbalance of the impeller 21, the distance between the float electrode 24 and the blade 27 deviates from a periodic change. .

  Therefore, the periodic voltage fluctuation of the float electrode 24 when the impeller 21 is normal is measured in advance with respect to the bearing and the rotating shaft of the impeller 21. When the fluctuation width of the AC voltage component superimposed on the DC voltage exceeds the normal range with respect to the voltage fluctuation of the float electrode 24, the bearing abnormality of the impeller 21 or the rotation abnormality due to the imbalance of the impeller 21 is It can be detected as an internal abnormality.

(1-6) Operational Effects The operational effects of the first embodiment described above are as follows. That is, in the first embodiment, the gas blower 20 is operated in a state in which the DC power source 22 applies a DC voltage to the impeller 21 that is electrically insulated. The induced voltage generated in the float electrode 24 fixed in the vicinity of the casing 23 is monitored by the monitor monitor 32.

  At that time, when an induced voltage waveform in which an AC voltage component having an amplitude exceeding a predetermined fluctuation range is superimposed on the DC voltage is observed, an abnormality has occurred in the distance between the blade 27 and the float electrode 24. It will be. In this way, the occurrence of internal abnormality of the gas blower 20 can be detected with high sensitivity.

  The internal abnormality of the gas blower 20 described above does not cause a serious failure that immediately causes the gas blower 20 to become inoperable, and the gas blower 20 can be continuously operated for the time being. For this reason, time delay is possible until the gas blower 20 reaches a complete failure.

  Therefore, by detecting such an internal abnormality as a sign of a failure, preparation work relating to repair / replacement of the gas blower 20 can be advanced from the time of detection. More specifically, preparatory work for repair / replacement preparation work is possible, such as arranging parts or alternative blowers that are expected to be repaired, and preparatory work for processing the insulating gas in the equipment tank. It is possible to proceed in a range.

  As a result, even after an appropriate time has elapsed since the detection of an internal abnormality in the gas blower 20, even if the gas-insulated power device is urgently stopped due to a complete failure of the gas blower 20, sufficient preparations are in place. Repair and replacement work of the gas blower 20 can be performed very smoothly. As a result, it is possible to greatly shorten the long-term power equipment outage period of several weeks to several months, which can contribute to the improvement of economy.

(2) Configuration of Second Embodiment (2-1) Next, a gas blower according to a second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a configuration diagram showing an outline of the second embodiment.

  As shown in FIG. 6, a rectifier 51 is installed in the gas blower 20 </ b> A according to the second embodiment in electrical parallel with the AC power supply terminal 31 for driving the motor 26. That is, the power supply to the motor 26 and the power supply to the rectifier 51 can be performed simultaneously. In such a second embodiment, as an alternative to the DC power source 22, a rectifier 51 that rectifies an AC voltage is attached in the gas blower 20A.

(2-2) Operational Effects In the second embodiment described above, it is possible to supply the DC voltage obtained from the rectifier 51 to the impeller 21, and compared to the first embodiment, a DC voltage application terminal 29 is provided. In addition, the DC power source 22 can be omitted. Therefore, in addition to the operational effects of the first embodiment, there is an operational effect that the configuration can be further simplified.

(3) Third Embodiment (3-1) Configuration Subsequently, a gas blower according to a third embodiment of the present invention will be described with reference to FIG. FIG. 7 is a configuration diagram showing an outline of the third embodiment.

  In the gas blower 20B shown in FIG. 7, the lower surface of the casing 23 that covers the impeller 21 and the lower surface of the impeller 21 are opposed to each other, and a high-charged body 61 (on the casing 23 side in FIG. 7) is provided on one side. On the other side, low charge bodies 62 (on the impeller 21 side in FIG. 7) are respectively attached.

  The high charged body 61 is made of a material having a high charge column such as nylon, and the low charged body 62 is made of a material having a low charge row such as vinyl chloride. These charging bodies 61 and 62 are always in contact with each other, and when the impeller 21 rotates, static electricity is generated by friction between the two to supply a DC voltage to the impeller 21.

(3-2) Operational Effect In the third embodiment as described above, a DC voltage can be applied to the impeller 21 by generating static electricity from the charging bodies 61 and 62. Therefore, members such as the DC voltage application terminal 29, the DC power supply 22, and the rectifier 51 can be omitted as compared with the first and second embodiments. Thereby, compared with 2nd Embodiment, it is possible to further simplify the structure.

(4) Other Embodiments The present invention is not limited to the above-described embodiments, and the configuration and location of each member can be changed as appropriate. Specifically, the float electrode 24 may be fixed to the upper surface of the casing 23 instead of near the side surface of the casing 23. In such an embodiment, the vibration of the gas blower 20 is most noticeable on the upper surface of the casing 23, which is advantageous for detecting abnormal vibration of the impeller 21. In addition to measuring and monitoring the induced voltage of the float electrode 24, the internal abnormality of the gas blower 20 can be detected more accurately by measuring and monitoring the voltage, current, frequency, etc. of the power source together. Become.

20, 20A, 20B ... gas blower 21 ... impeller 22 ... DC power supply 23 ... casing 24 ... float electrode 25 ... potential measurement terminal 26 ... motor 27 ... blade 28 ... voltage measuring device 29 ... DC voltage application terminal 30 ... AC power supply 31 ... AC Power supply terminal 32 ... Monitoring monitor 41 ... Blade positive charge 42 ... Capacitance 43 between blade and float electrode 43 ... Capacitance 51 between float electrode and casing ... Rectifier 61 ... High charging body 62 ... Low charging body

Claims (4)

In a gas blower that forcibly circulates insulating gas to power equipment,
A motor is housed in the casing,
AC voltage supply means for supplying an AC voltage to the motor is connected to the motor,
An impeller is attached to the rotating shaft of the motor in an electrically insulated state,
The impeller is connected to DC voltage supply means for supplying a DC voltage to the impeller,
A float electrode is attached in an electrically insulated state near the casing,
The float electrode is provided with a potential measuring terminal for extracting the potential of the float electrode to the outside,
Voltage measuring means for measuring a voltage induced in the float electrode is connected to the potential measuring terminal,
Further, the voltage measuring means is connected to a voltage monitoring means for monitoring the voltage measured by the voltage measuring means,
The gas monitoring unit, wherein the voltage monitoring unit is configured to monitor a fluctuation range of an AC voltage component superimposed on a DC voltage with respect to a voltage measured by the voltage measuring unit.   The gas blower according to claim 1, wherein a rectifier for rectifying an alternating voltage is installed as the direct voltage supply means in parallel with the alternating voltage supply means. Of the opposed surfaces of the impeller and the casing, a high charged body having a high charged column level is attached to one side, and a low charged body made of a material having a low charged column level is attached to the other side so that they are always in contact with each other. And
2. The gas blower according to claim 1, wherein the high-charged body and the low-charged body are configured to generate static electricity by friction when the impeller rotates to supply a DC voltage to the impeller. In a method for detecting an internal abnormality of a gas blower in which an impeller is attached to a rotating shaft of a drive motor in a casing in an electrically insulated state and a float electrode is attached in an electrically insulated state in the vicinity of the casing. ,
A DC voltage supply step for supplying a DC voltage to the impeller during operation of the gas blower;
A voltage measuring step for measuring a voltage induced in the float electrode;
Including a voltage monitoring step of monitoring the voltage measured in the voltage measuring step;
In the voltage monitoring step, the fluctuation range of the AC voltage component superimposed on the DC voltage is monitored for the voltage measured in the voltage measuring step.

Images