JP2021038867A - Induction furnace and method for driving induction furnace - Google Patents

Induction furnace and method for driving induction furnace Download PDF

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JP2021038867A
JP2021038867A JP2019159349A JP2019159349A JP2021038867A JP 2021038867 A JP2021038867 A JP 2021038867A JP 2019159349 A JP2019159349 A JP 2019159349A JP 2019159349 A JP2019159349 A JP 2019159349A JP 2021038867 A JP2021038867 A JP 2021038867A
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terminal
switch
coil
induction furnace
intermittent
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JP7408953B2 (en
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宏隆 華表
Hirotaka Hanaomote
宏隆 華表
悠二 早瀬
Yuji Hayase
悠二 早瀬
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Fuji Electric Co Ltd
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Fuji Electric Co Ltd
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/06—Control, e.g. of temperature, of power
    • H05B6/067—Control, e.g. of temperature, of power for melting furnaces
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B14/00—Crucible or pot furnaces
    • F27B14/06—Crucible or pot furnaces heated electrically, e.g. induction crucible furnaces with or without any other source of heat
    • F27B14/061—Induction furnaces
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B14/00—Crucible or pot furnaces
    • F27B14/08—Details peculiar to crucible or pot furnaces
    • F27B14/20—Arrangement of controlling, monitoring, alarm or like devices
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • General Induction Heating (AREA)
  • Crucibles And Fluidized-Bed Furnaces (AREA)
  • Waste-Gas Treatment And Other Accessory Devices For Furnaces (AREA)

Abstract

To provide an induction furnace, even if the resistance value of an insulator is reduced by moisture adsorbed into an insulator between a coil and an earth provided at the outside of the furnace, preventing flowing of a relatively large current through the coil.SOLUTION: When an intermittent switch (6) is always made on and an isolating switch (7) is always made off, till a resistance value obtained by a current detected by a current detection part (9) and a voltage detected by a voltage detection part (10) is made higher than a threshold, the intermittent switch (6) is made on-off, further, the isolating switch (7) is always made on, thereafter, the intermittent switch (6) is always made on and the isolating switch (7) is always made off, the above operation is repeated, and, when the resistance value is higher than the threshold, an alternating current is made to flow through a coil (L).SELECTED DRAWING: Figure 1

Description

本発明は、誘導炉及び誘導炉の運転方法に関する。 The present invention relates to an induction furnace and a method of operating the induction furnace.

誘導炉として、炉の外側に設けられるコイルに交流電流を流すことで生じる磁界により炉の内側の金属を加熱させて金属を溶解させるものがある。 As an induction furnace, there is one that heats the metal inside the furnace by a magnetic field generated by passing an alternating current through a coil provided on the outside of the furnace to melt the metal.

上記誘導炉では、コイルとアースとの間の絶縁体に吸着される水分により絶縁体の抵抗値が低下していると、コイルに流れる電流が増加してコイルが発熱し、コイルが劣化するという懸念がある。 In the above induction furnace, if the resistance value of the insulator is lowered due to the moisture adsorbed on the insulator between the coil and the ground, the current flowing through the coil increases, the coil generates heat, and the coil deteriorates. There are concerns.

そこで、他の誘導炉として、コイルの近傍に設けられる温度センサにより検出される温度が保護温度を超えると、コイルに流れる電流を低減させて、コイルの劣化を抑制するものがある。関連する技術として、特許文献１がある。 Therefore, as another induction furnace, when the temperature detected by the temperature sensor provided in the vicinity of the coil exceeds the protection temperature, the current flowing through the coil is reduced to suppress the deterioration of the coil. Patent Document 1 is a related technique.

特開２００９−２８９５４５号公報Japanese Unexamined Patent Publication No. 2009-289545

しかしながら、上記他の誘導炉では、絶縁体に吸着される水分により絶縁体の抵抗値が低下しているとき、誘導炉の運転が開始されてから温度センサにより検出される温度が保護温度を超えるまでの間において、コイルに比較的大きな電流が流れてコイルが劣化してしまうという懸念がある。 However, in the above other induction coil, when the resistance value of the insulator is lowered due to the moisture adsorbed on the insulator, the temperature detected by the temperature sensor after the operation of the induction coil is started exceeds the protection temperature. In the meantime, there is a concern that a relatively large current will flow through the coil and the coil will deteriorate.

そこで、本発明の一側面に係る目的は、コイルとアースとの間の絶縁体に吸着される水分により絶縁体の抵抗値が低下していても、コイルに比較的大きな電流が流れないようにすることである。 Therefore, an object according to one aspect of the present invention is to prevent a relatively large current from flowing through the coil even if the resistance value of the insulator is lowered by the moisture adsorbed by the insulator between the coil and the ground. It is to be.

本発明に係る一つの形態である誘導炉は、炉の外側に設けられるコイルに交流電流が流れることにより炉の内側に磁界が発生する誘導炉であって、コイルの一方端子と電源の正極端子との間に接続される間欠スイッチと、コイルの他方端子と電源の負極端子との間に接続される遮断スイッチと、コイルに流れる電流を検出する電流検出部と、電源の電圧を検出する電圧検出部と、間欠スイッチ及び遮断スイッチのそれぞれの動作を制御する制御部とを備える。 The induction furnace according to the present invention is an induction furnace in which an alternating current flows through a coil provided on the outside of the furnace to generate a magnetic field inside the coil, and one terminal of the coil and a positive terminal of the power supply are generated. An intermittent switch connected between the two, a cutoff switch connected between the other terminal of the coil and the negative terminal of the power supply, a current detector that detects the current flowing through the coil, and a voltage that detects the voltage of the power supply. It includes a detection unit and a control unit that controls the operation of the intermittent switch and the cutoff switch.

制御部は、間欠スイッチが常時オンしているとともに遮断スイッチが常時オフしているときに電流検出部により検出される電流と電圧検出部により検出される電圧とにより求められる抵抗値が閾値より大きくなるまで、間欠スイッチをオン、オフさせるとともに遮断スイッチを常時オンさせた後、間欠スイッチを常時オンさせるとともに遮断スイッチを常時オフさせることを繰り返し、抵抗値が閾値より大きくなると、コイルに交流電流を流す。なお、間欠スイッチがオンすると、間欠スイッチが導通し、間欠スイッチがオフすると、間欠スイッチが遮断する。また、遮断スイッチがオンすると、遮断スイッチが導通し、遮断スイッチがオフすると、遮断スイッチが遮断する。 In the control unit, the resistance value obtained by the current detected by the current detection unit and the voltage detected by the voltage detection unit when the intermittent switch is always on and the cutoff switch is always off is larger than the threshold value. The intermittent switch is turned on and off and the cutoff switch is always turned on, and then the intermittent switch is always turned on and the cutoff switch is turned off repeatedly. When the resistance value becomes larger than the threshold value, an alternating current is applied to the coil. Shed. When the intermittent switch is turned on, the intermittent switch is electrically connected, and when the intermittent switch is turned off, the intermittent switch is shut off. Further, when the cutoff switch is turned on, the cutoff switch is conducted, and when the cutoff switch is turned off, the cutoff switch is cut off.

また、本発明に係る一つの形態である誘導炉の運転方法は、炉の外側に設けられるコイルの一方端子と電源の正極端子との間に接続される間欠スイッチと、コイルの他方端子と電源の負極端子との間に接続される遮断スイッチと、コイルに流れる電流を検出する電流検出部と、電源の電圧を検出する電圧検出部とを備える誘導炉の運転方法であって、間欠スイッチが常時オンしているとともに遮断スイッチが常時オフしているときに電流検出部により検出される電流と電圧検出部により検出される電圧とにより求められる抵抗値が閾値より大きくなるまで、間欠スイッチをオン、オフさせるとともに遮断スイッチを常時オンさせた後、間欠スイッチを常時オンさせるとともに遮断スイッチを常時オフさせることを繰り返し、抵抗値が閾値より大きくなると、コイルに交流電流を流して炉の内側に磁界を発生させる。 Further, the method of operating the induction furnace, which is one embodiment of the present invention, includes an intermittent switch connected between one terminal of the coil provided outside the furnace and the positive terminal of the power supply, and the other terminal of the coil and the power supply. An intermittent switch is an operation method of an induction furnace including a cutoff switch connected between the negative terminal and a current detection unit for detecting the current flowing through the coil, and a voltage detection unit for detecting the voltage of the power supply. The intermittent switch is turned on until the resistance value obtained by the current detected by the current detector and the voltage detected by the voltage detector becomes larger than the threshold value when the cutoff switch is always on and the cutoff switch is always off. After turning off and always turning on the cutoff switch, the intermittent switch is always turned on and the cutoff switch is always off repeatedly. When the resistance value becomes larger than the threshold value, an AC current is passed through the coil to create a magnetic field inside the furnace. To generate.

本発明によれば、炉の外側に設けられるコイルとアースとの間の絶縁体に吸着される水分により絶縁体の抵抗値が低下していても、コイルに比較的大きな電流が流れないようにすることができる。 According to the present invention, even if the resistance value of the insulator is lowered due to the moisture adsorbed on the insulator between the coil provided on the outside of the furnace and the ground, a relatively large current does not flow through the coil. can do.

実施形態の誘導炉の一例を示す図である。It is a figure which shows an example of the induction furnace of embodiment. 制御部の動作の一例を示すフローチャートである。It is a flowchart which shows an example of the operation of a control part. 間欠スイッチの制御信号、遮断スイッチの制御信号、コイルにかかる電圧、及びコイルに流れる電流の一例を示すタイミングチャートである。It is a timing chart which shows an example of the control signal of an intermittent switch, the control signal of a cutoff switch, the voltage applied to a coil, and the current flowing through a coil. パルス電圧モードの実施回数の増加に伴う絶縁体の抵抗値の上昇の一例及び時間経過に伴う絶縁体の抵抗値の低下傾向の一例を示す図である。It is a figure which shows an example of the increase in the resistance value of an insulator as the number of times of execution of a pulse voltage mode increases, and an example of the tendency of the resistance value of an insulator decrease with the passage of time. 実施形態の誘導炉の変形例を示す図である。It is a figure which shows the modification of the induction furnace of embodiment.

図１は、実施形態の誘導炉の一例を示す図である。 FIG. 1 is a diagram showing an example of an induction furnace of the embodiment.

図１に示す誘導炉１は、インバータ回路２と、切替スイッチ３（第１の切替スイッチ）と、切替スイッチ４（第２の切替スイッチ）と、コイルＬと、炉５と、間欠スイッチ６と、遮断スイッチ７と、ローパスフィルタ８と、電流検出部９と、電圧検出部１０と、記憶部１１と、制御部１２とを備える。 The induction furnace 1 shown in FIG. 1 includes an inverter circuit 2, a changeover switch 3 (first changeover switch), a changeover switch 4 (second changeover switch), a coil L, a furnace 5, and an intermittent switch 6. , A cutoff switch 7, a low-pass filter 8, a current detection unit 9, a voltage detection unit 10, a storage unit 11, and a control unit 12.

インバータ回路２は、誘導炉１の運転中において、電源Ｐから流れる直流電流を交流電流に変換して炉５の外側に設けられるコイルＬに流す。コイルＬに交流電流が流れると、炉５の内部に発生する磁界により炉５の内部の金属が発熱し、その金属が溶解する。なお、電源Ｐは、系統電源、整流回路、及び平滑コンデンサなどを備え、系統電源から流れる交流電流を整流回路により整流するとともに平滑コンデンサにより平滑することで直流電流に変換し、その直流電流をインバータ回路２に出力するように構成してもよい。 During the operation of the induction furnace 1, the inverter circuit 2 converts the direct current flowing from the power source P into an alternating current and flows it through the coil L provided outside the furnace 5. When an alternating current flows through the coil L, the metal inside the furnace 5 generates heat due to the magnetic field generated inside the furnace 5, and the metal melts. The power supply P includes a system power supply, a rectifier circuit, a smoothing capacitor, and the like. The AC current flowing from the system power supply is rectified by the rectifier circuit and smoothed by the smoothing capacitor to convert it into a direct current, and the direct current is converted into an inverter. It may be configured to output to the circuit 2.

すなわち、インバータ回路２は、ＩＧＢＴ（Insulated Gate Bipolar Transistor）などのスイッチング素子ＳＷ１〜ＳＷ４を備える。スイッチング素子ＳＷ１のコレクタ端子はスイッチング素子ＳＷ３のコレクタ端子と接続され、インバータ回路２の一方の入力端子ＩＮ＋を介して切替スイッチ３に接続されている。スイッチング素子ＳＷ２のエミッタ端子はスイッチング素子ＳＷ４のエミッタ端子に接続され、インバータ回路２の他方の入力端子ＩＮ−を介して切替スイッチ４に接続されている。スイッチング素子ＳＷ１のエミッタ端子はスイッチング素子ＳＷ２のコレクタ端子と接続され、インバータ回路２の一方の出力端子ＯＵＴ１を介してコイルＬの一方端子に接続されている。スイッチング素子ＳＷ３のエミッタ端子はスイッチング素子ＳＷ４のコレクタ端子と接続され、インバータ回路２の他方の出力端子ＯＵＴ２を介してコイルＬの他方端子に接続されている。 That is, the inverter circuit 2 includes switching elements SW1 to SW4 such as an IGBT (Insulated Gate Bipolar Transistor). The collector terminal of the switching element SW1 is connected to the collector terminal of the switching element SW3, and is connected to the changeover switch 3 via one input terminal IN + of the inverter circuit 2. The emitter terminal of the switching element SW2 is connected to the emitter terminal of the switching element SW4, and is connected to the changeover switch 4 via the other input terminal IN− of the inverter circuit 2. The emitter terminal of the switching element SW1 is connected to the collector terminal of the switching element SW2, and is connected to one terminal of the coil L via one output terminal OUT1 of the inverter circuit 2. The emitter terminal of the switching element SW3 is connected to the collector terminal of the switching element SW4, and is connected to the other terminal of the coil L via the other output terminal OUT2 of the inverter circuit 2.

また、インバータ回路２の入力端子ＩＮ＋が切替スイッチ３を介して電源Ｐの正極端子に電気的に接続され、インバータ回路２の入力端子ＩＮ−が切替スイッチ４を介して電源Ｐの負極端子に電気的に接続されているとき、スイッチング素子ＳＷ１、ＳＷ４がオンするとともにスイッチング素子ＳＷ２、ＳＷ３がオフすると、電源Ｐの正極端子から切替スイッチ３、スイッチング素子ＳＷ１、コイルＬ、スイッチング素子ＳＷ４、及び切替スイッチ４を介して電源Ｐの負極端子に電流が流れる。また、スイッチング素子ＳＷ１、ＳＷ４がオフするとともにスイッチング素子ＳＷ２、ＳＷ３がオンすると、電源Ｐの正極端子から切替スイッチ３、スイッチング素子ＳＷ３、コイルＬ、スイッチング素子ＳＷ２、及び切替スイッチ４を介して電源Ｐの負極端子に電流が流れる。すなわち、スイッチング素子ＳＷ１、ＳＷ４とスイッチング素子ＳＷ２、ＳＷ３とが交互にオン、オフすると、コイルＬに交流電流が流れる。 Further, the input terminal IN + of the inverter circuit 2 is electrically connected to the positive terminal of the power supply P via the changeover switch 3, and the input terminal IN− of the inverter circuit 2 is electrically connected to the negative terminal of the power supply P via the changeover switch 4. When the switching elements SW1 and SW4 are turned on and the switching elements SW2 and SW3 are turned off, the changeover switch 3, the switching element SW1, the coil L, the switching element SW4, and the changeover switch are connected from the positive terminal of the power supply P. A current flows through the negative terminal of the power supply P via 4. When the switching elements SW1 and SW4 are turned off and the switching elements SW2 and SW3 are turned on, the power supply P is transmitted from the positive electrode terminal of the power supply P via the changeover switch 3, the switching element SW3, the coil L, the switching element SW2, and the changeover switch 4. Current flows through the negative electrode terminal of. That is, when the switching elements SW1 and SW4 and the switching elements SW2 and SW3 are alternately turned on and off, an alternating current flows through the coil L.

間欠スイッチ６は、ＩＧＢＴやＭＯＳＦＥＴ（Metal Oxide Semiconductor Field Effect Transistor）などの半導体リレーまたは電磁式リレーにより構成される。間欠スイッチ６の一方端子は切替スイッチ３に接続され、間欠スイッチ６の他方端子はローパスフィルタ８を介してコイルＬの一方端子に接続されている。なお、間欠スイッチ６がオンすると、間欠スイッチ６が導通し、切替スイッチ３とローパスフィルタ８とが電気的に接続される。また、間欠スイッチ６がオフすると、間欠スイッチ６が遮断し、切替スイッチ３とローパスフィルタ８とが電気的に接続されなくなる。 The intermittent switch 6 is composed of a semiconductor relay such as an IGBT or a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or an electromagnetic relay. One terminal of the intermittent switch 6 is connected to the changeover switch 3, and the other terminal of the intermittent switch 6 is connected to one terminal of the coil L via a low-pass filter 8. When the intermittent switch 6 is turned on, the intermittent switch 6 is electrically connected, and the changeover switch 3 and the low-pass filter 8 are electrically connected. Further, when the intermittent switch 6 is turned off, the intermittent switch 6 is cut off, and the changeover switch 3 and the low-pass filter 8 are not electrically connected.

遮断スイッチ７は、ＩＧＢＴやＭＯＳＦＥＴなどの半導体リレーまたは電磁式リレーにより構成される。遮断スイッチ７の一方端子は切替スイッチ４に接続され、遮断スイッチ７の他方端子はコイルＬの他方端子に接続されている。なお、遮断スイッチ７がオンすると、遮断スイッチ７が導通し、切替スイッチ４とコイルＬの他方端子とが電気的に接続される。また、遮断スイッチ７がオフすると、遮断スイッチ７が遮断し、切替スイッチ４とコイルＬの他方端子とが電気的に接続されなくなる。 The cutoff switch 7 is composed of a semiconductor relay such as an IGBT or MOSFET or an electromagnetic relay. One terminal of the cutoff switch 7 is connected to the changeover switch 4, and the other terminal of the cutoff switch 7 is connected to the other terminal of the coil L. When the cutoff switch 7 is turned on, the cutoff switch 7 becomes conductive, and the changeover switch 4 and the other terminal of the coil L are electrically connected. Further, when the cutoff switch 7 is turned off, the cutoff switch 7 is cut off, and the changeover switch 4 and the other terminal of the coil L are not electrically connected.

ローパスフィルタ８は、抵抗やコンデンサなどにより構成され、後述するパルス電圧モード実施時に間欠スイッチ６からローパスフィルタ８に流れる電流を平滑してコイルＬに出力する。なお、パルス電圧モード実施時に間欠スイッチ６からローパスフィルタ８に流れる電流を平滑する必要がない場合、ローパスフィルタ８を省略してもよい。このように構成する場合、間欠スイッチ６の他方端子はコイルＬの一方端子に直接接続される。 The low-pass filter 8 is composed of a resistor, a capacitor, or the like, and smoothes the current flowing from the intermittent switch 6 to the low-pass filter 8 when the pulse voltage mode described later is executed and outputs the current to the coil L. If it is not necessary to smooth the current flowing from the intermittent switch 6 to the low-pass filter 8 when the pulse voltage mode is executed, the low-pass filter 8 may be omitted. In this configuration, the other terminal of the intermittent switch 6 is directly connected to one terminal of the coil L.

電流検出部９は、ホール素子やシャント抵抗などにより構成され、コイルＬに流れる電流を検出し、その検出した電流を制御部１２に送る。なお、電流検出部９の接続箇所は特に限定されない。 The current detection unit 9 is composed of a Hall element, a shunt resistor, or the like, detects a current flowing through the coil L, and sends the detected current to the control unit 12. The connection location of the current detection unit 9 is not particularly limited.

電圧検出部１０は、分圧抵抗やオペアンプなどにより構成され、電源Ｐの電圧を検出し、その検出した電圧を制御部１２に送る。なお、電圧検出部１０の接続箇所は特に限定されない。 The voltage detection unit 10 is composed of a voltage dividing resistor, an operational amplifier, or the like, detects the voltage of the power supply P, and sends the detected voltage to the control unit 12. The connection point of the voltage detection unit 10 is not particularly limited.

記憶部１１は、ＲＡＭ（Random Access Memory）またはＲＯＭ（Read Only Memory）などにより構成され、コイルＬとアースとの間の絶縁体ＲＬの抵抗値を記憶する。 The storage unit 11 is composed of a RAM (Random Access Memory), a ROM (Read Only Memory), or the like, and stores the resistance value of the insulator RL between the coil L and the ground.

制御部１２は、ＣＰＵ（Central Processing Unit）やプログラマブルなデバイス（ＦＰＧＡ（Field Programmable Gate Array）やＰＬＤ（Programmable Logic Device））などにより構成される。制御部１２は、誘導炉１の運転前において、切替スイッチ３、切替スイッチ４、間欠スイッチ６、及び遮断スイッチ７のそれぞれの動作を制御することによりコイルＬに定格電流に相当する直流電流を流す。コイルＬに直流電流が流れると、コイルＬの抵抗成分により生じる熱（銅損）により絶縁体ＲＬに吸着している水分が蒸発し、絶縁体ＲＬの抵抗値が上昇する。また、制御部１２は、誘導炉１の運転中において、切替スイッチ３、４及びスイッチング素子ＳＷ１〜ＳＷ４の動作を制御することによりコイルＬに交流電流を流して炉５の内側に磁界を発生させる。炉５の内側に磁界が発生すると、炉５の内側の金属により生じる熱により絶縁体ＲＬに吸着している水分が蒸発し、絶縁体ＲＬの抵抗値が上昇する。これにより、誘導炉１の運転前や誘導炉１の運転中において、電源ＰからコイルＬ及び絶縁体ＲＬを介してアースに流れる電流を抑えることができるため、コイルＬに流れる全体の電流がコイルＬの定格電流を超えることを抑えることができ、コイルＬが劣化することを抑制することができる。 The control unit 12 is composed of a CPU (Central Processing Unit), a programmable device (FPGA (Field Programmable Gate Array), PLD (Programmable Logic Device), and the like. Before the operation of the induction furnace 1, the control unit 12 controls the operations of the changeover switch 3, the changeover switch 4, the intermittent switch 6, and the cutoff switch 7 to allow a DC current corresponding to the rated current to flow through the coil L. .. When a direct current flows through the coil L, the water adsorbed on the insulator RL evaporates due to the heat (copper loss) generated by the resistance component of the coil L, and the resistance value of the insulator RL rises. Further, the control unit 12 controls the operations of the changeover switches 3 and 4 and the switching elements SW1 to SW4 during the operation of the induction furnace 1 to cause an alternating current to flow through the coil L to generate a magnetic field inside the furnace 5. .. When a magnetic field is generated inside the furnace 5, the water adsorbed on the insulator RL evaporates due to the heat generated by the metal inside the furnace 5, and the resistance value of the insulator RL rises. As a result, the current flowing from the power supply P to the ground via the coil L and the insulator RL can be suppressed before the operation of the induction furnace 1 or during the operation of the induction furnace 1, so that the entire current flowing through the coil L is the coil. It is possible to suppress exceeding the rated current of L, and it is possible to suppress deterioration of the coil L.

図２は、制御部１２の動作の一例を示すフローチャートである。図３（ａ）は、間欠スイッチ６のオン、オフを制御する制御信号Ｓ１の一例を示すタイミングチャートである。図３（ｂ）は、遮断スイッチ７のオン、オフを制御する制御信号Ｓ２の一例を示すタイミングチャートである。図３（ｃ）は、コイルＬにかかる電圧の一例を示すタイミングチャートである。図３（ｄ）は、コイルＬに流れる電流の一例を示すタイミングチャートである。なお、図３（ａ）に示す２次元座標の横軸は時間を示し、縦軸は制御信号Ｓ１の大きさ（電圧）を示している。また、図３（ｂ）に示す２次元座標の横軸は時間を示し、縦軸は制御信号Ｓ２の大きさ（電圧）を示している。また、図３（ｃ）に示す２次元座標の横軸は時間を示し、縦軸は電圧を示している。また、図３（ｄ）に示す２次元座標の横軸は時間を示し、縦軸は電流を示している。図３（ａ）〜図３（ｄ）に示す横軸の時間は互いに一致しているものとする。 FIG. 2 is a flowchart showing an example of the operation of the control unit 12. FIG. 3A is a timing chart showing an example of the control signal S1 that controls the on / off of the intermittent switch 6. FIG. 3B is a timing chart showing an example of the control signal S2 that controls the on / off of the cutoff switch 7. FIG. 3C is a timing chart showing an example of the voltage applied to the coil L. FIG. 3D is a timing chart showing an example of the current flowing through the coil L. The horizontal axis of the two-dimensional coordinates shown in FIG. 3A indicates time, and the vertical axis indicates the magnitude (voltage) of the control signal S1. Further, the horizontal axis of the two-dimensional coordinates shown in FIG. 3B indicates time, and the vertical axis indicates the magnitude (voltage) of the control signal S2. Further, the horizontal axis of the two-dimensional coordinates shown in FIG. 3C indicates time, and the vertical axis indicates voltage. Further, the horizontal axis of the two-dimensional coordinates shown in FIG. 3D indicates time, and the vertical axis indicates current. It is assumed that the times on the horizontal axes shown in FIGS. 3 (a) to 3 (d) coincide with each other.

まず、制御部１２は、ユーザによる運転開始ボタンの操作などにより誘導炉１の運転開始指示が入力されると、パルス電圧モードを実施する（ステップＳ１１）。制御部１２は、パルス電圧モードを実施する一定時間Ｔ１において、間欠スイッチ６の一方端子が切替スイッチ３を介して電源Ｐの正極端子に接続され、遮断スイッチ７の一方端子が切替スイッチ４を介して電源Ｐの負極端子に接続されるように切替スイッチ３、４の動作を制御する。また、制御部１２は、図３（ａ）及び図３（ｂ）に示すように、一定時間Ｔ１において、制御信号Ｓ１の電圧をハイレベルとローレベルに交互に切り替えるとともに、制御信号Ｓ２の電圧を常時ハイレベルにする。これにより、一定時間Ｔ１において、間欠スイッチ６が繰り返しオン、オフし、遮断スイッチ７が常時オンする。言い換えると、一定時間Ｔ１において、間欠スイッチ６が導通と遮断を繰り返し、遮断スイッチ７が常時導通する。すると、図３（ｃ）及び図３（ｄ）に示すように、一定時間Ｔ１において、コイルＬに直流電圧がかかり、コイルＬに直流電流が流れる。これにより、一定時間Ｔ１において、コイルＬの抵抗成分により生じる熱の温度が上昇していく。なお、一定時間Ｔ１において、コイルＬに流れる直流電流がコイルＬの定格電流以下になるように制御信号Ｓ１のデューティ比が設定されているものとする。 First, the control unit 12 executes the pulse voltage mode when the operation start instruction of the induction furnace 1 is input by the operation of the operation start button by the user (step S11). In the control unit 12, one terminal of the intermittent switch 6 is connected to the positive electrode terminal of the power supply P via the changeover switch 3 and one terminal of the cutoff switch 7 is connected to the positive electrode terminal of the power supply P via the changeover switch 4 in T1 for a certain period of time when the pulse voltage mode is executed. The operation of the changeover switches 3 and 4 is controlled so as to be connected to the negative electrode terminal of the power supply P. Further, as shown in FIGS. 3A and 3B, the control unit 12 alternately switches the voltage of the control signal S1 between a high level and a low level at T1 for a certain period of time, and the voltage of the control signal S2. Is always at a high level. As a result, at T1 for a certain period of time, the intermittent switch 6 is repeatedly turned on and off, and the cutoff switch 7 is always turned on. In other words, at T1 for a certain period of time, the intermittent switch 6 repeatedly conducts and shuts off, and the cutoff switch 7 constantly conducts. Then, as shown in FIGS. 3 (c) and 3 (d), a direct current voltage is applied to the coil L at T1 for a certain period of time, and a direct current flows through the coil L. As a result, the temperature of the heat generated by the resistance component of the coil L rises at T1 for a certain period of time. It is assumed that the duty ratio of the control signal S1 is set so that the direct current flowing through the coil L becomes equal to or less than the rated current of the coil L at T1 for a certain period of time.

次に、制御部１２は、一定時間Ｔ２が経過するまで待機する（ステップＳ１２：Ｎｏ）。制御部１２は、一定時間Ｔ２において、間欠スイッチ６の一方端子が切替スイッチ３を介して電源Ｐの正極端子に接続され、遮断スイッチ７の一方端子が切替スイッチ４を介して電源Ｐの負極端子に接続されるように切替スイッチ３、４の動作を制御する。また、制御部１２は、図３（ａ）及び図３（ｂ）に示すように、一定時間Ｔ２において、制御信号Ｓ１の電圧を常時ローレベルにするとともに、制御信号Ｓ２の電圧を常時ローレベルにする。これにより、一定時間Ｔ２において、間欠スイッチ６及び遮断スイッチ７が常時オフする。言い換えると、一定時間Ｔ２において、間欠スイッチ６及び遮断スイッチ７が常時遮断する。これにより、一定時間Ｔ２において、コイルＬの熱の温度上昇により絶縁体ＲＬに吸着されている水分を蒸発させることができる。なお、ステップＳ１１において、絶縁体ＲＬに吸着されている水分を十分に蒸発させることができる場合、一定時間Ｔ２待機せず、ステップＳ１１からステップＳ１３に移行してもよい。 Next, the control unit 12 waits until T2 elapses for a certain period of time (step S12: No). In the control unit 12, at T2 for a certain period of time, one terminal of the intermittent switch 6 is connected to the positive electrode terminal of the power supply P via the changeover switch 3, and one terminal of the cutoff switch 7 is connected to the negative electrode terminal of the power supply P via the changeover switch 4. The operation of the changeover switches 3 and 4 is controlled so as to be connected to. Further, as shown in FIGS. 3A and 3B, the control unit 12 always lowers the voltage of the control signal S1 and always lowers the voltage of the control signal S2 at T2 for a certain period of time. To. As a result, the intermittent switch 6 and the cutoff switch 7 are always turned off at T2 for a certain period of time. In other words, at T2 for a certain period of time, the intermittent switch 6 and the cutoff switch 7 are always shut off. As a result, at T2 for a certain period of time, the water adsorbed on the insulator RL can be evaporated by the temperature rise of the heat of the coil L. If the water adsorbed on the insulator RL can be sufficiently evaporated in step S11, the process may shift from step S11 to step S13 without waiting for T2 for a certain period of time.

次に、制御部１２は、一定時間Ｔ２が経過すると（ステップＳ１２：Ｙｅｓ）、直流電圧モードを実施する（ステップＳ１３）。制御部１２は、直流電圧モードを実施する一定時間Ｔ３において、間欠スイッチ６の一方端子が切替スイッチ３を介して電源Ｐの正極端子に接続され、遮断スイッチ７の一方端子が切替スイッチ４を介して電源Ｐの負極端子に接続されるように切替スイッチ３、４の動作を制御する。また、制御部１２は、図３（ａ）及び図３（ｂ）に示すように、一定時間Ｔ３において、制御信号Ｓ１の電圧を常時ハイレベルにするとともに、制御信号Ｓ２の電圧を常時ローレベルにする。これにより、一定時間Ｔ３において、間欠スイッチ６が常時オンし、遮断スイッチ７が常時オフする。言い換えると、一定時間Ｔ３において、間欠スイッチ６が常時導通し、遮断スイッチ７が常時遮断する。すると、図３（ｃ）及び図３（ｄ）に示すように、一定時間Ｔ３において、コイルＬに直流電圧がかかり、コイルＬに直流電流が流れる。また、制御部１２は、一定時間Ｔ３において、電圧検出部１０により検出される電圧を電流検出部９により検出される電流で除算することにより、その結果を絶縁体ＲＬの抵抗値として測定する。 Next, when T2 elapses for a certain period of time (step S12: Yes), the control unit 12 executes the DC voltage mode (step S13). In the control unit 12, one terminal of the intermittent switch 6 is connected to the positive electrode terminal of the power supply P via the changeover switch 3 and one terminal of the cutoff switch 7 is connected to the positive electrode terminal of the power supply P via the changeover switch 4 at T3 for a certain period of time when the DC voltage mode is executed. The operation of the changeover switches 3 and 4 is controlled so as to be connected to the negative electrode terminal of the power supply P. Further, as shown in FIGS. 3A and 3B, the control unit 12 always keeps the voltage of the control signal S1 at a high level and always keeps the voltage of the control signal S2 at a low level at T3 for a certain period of time. To. As a result, at T3 for a certain period of time, the intermittent switch 6 is always on and the cutoff switch 7 is always off. In other words, at T3 for a certain period of time, the intermittent switch 6 is always conductive and the cutoff switch 7 is always shut off. Then, as shown in FIGS. 3 (c) and 3 (d), a direct current voltage is applied to the coil L at T3 for a certain period of time, and a direct current flows through the coil L. Further, the control unit 12 divides the voltage detected by the voltage detection unit 10 by the current detected by the current detection unit 9 at T3 for a certain period of time, and measures the result as the resistance value of the insulator RL.

次に、制御部１２は、絶縁体ＲＬの抵抗値が閾値以下である場合（ステップＳ１４：Ｎｏ）、すなわち、電源ＰからコイルＬ及び絶縁体ＲＬを介してアースに電流が流れ易くなっている場合、ステップＳ１１〜Ｓ１３の処理を再度実施して、絶縁体ＲＬに吸着されている水分を蒸発させて絶縁体ＲＬの抵抗値をさらに上昇させる。ここで、図４（ａ）は、パルス電圧モードの実施回数の増加に伴う絶縁体ＲＬの抵抗値の上昇の一例を示す図である。なお、図４（ａ）に示す２次元座標の横軸は誘導炉１の起動前におけるパルス電圧モードの実行回数を示し、縦軸は絶縁体ＲＬの抵抗値を示している。図４（ａ）に示す例では、誘導炉１の起動前において、３回目のパルス電圧モードの実施後、絶縁体ＲＬの抵抗値がまだ閾値以下であり、４回目のパルス電圧モードの実施後、絶縁体ＲＬの抵抗値が閾値より大きくなっている。 Next, in the control unit 12, when the resistance value of the insulator RL is equal to or less than the threshold value (step S14: No), that is, a current easily flows from the power supply P to the ground via the coil L and the insulator RL. In this case, the treatments of steps S11 to S13 are carried out again to evaporate the water adsorbed on the insulator RL and further increase the resistance value of the insulator RL. Here, FIG. 4A is a diagram showing an example of an increase in the resistance value of the insulator RL as the number of times the pulse voltage mode is executed increases. The horizontal axis of the two-dimensional coordinates shown in FIG. 4A shows the number of times the pulse voltage mode is executed before the induction furnace 1 is started, and the vertical axis shows the resistance value of the insulator RL. In the example shown in FIG. 4A, the resistance value of the insulator RL is still below the threshold value after the third pulse voltage mode is executed before the induction furnace 1 is started, and after the fourth pulse voltage mode is executed. , The resistance value of the insulator RL is larger than the threshold value.

一方、制御部１２は、絶縁体ＲＬの抵抗値が閾値より大きい場合（ステップＳ１４：Ｙｅｓ）、すなわち、電源ＰからコイルＬ及び絶縁体ＲＬを介してアースに電流が流れ難くなっている場合、誘導炉１の運転を開始する（ステップＳ１５）。制御部１２は、誘導炉１の運転中において、インバータ回路２の入力端子ＩＮ＋が切替スイッチ３を介して電源Ｐの正極端子に接続され、インバータ回路２の入力端子ＩＮ−が切替スイッチ４を介して電源Ｐの負極端子に接続されるように切替スイッチ３、４の動作を制御する。また、制御部１２は、誘導炉１の運転中において、スイッチング素子ＳＷ１、ＳＷ４をオンさせるとともにスイッチング素子ＳＷ２、ＳＷ３をオフさせた後、スイッチング素子ＳＷ１、ＳＷ４をオフさせるとともにスイッチング素子ＳＷ２、ＳＷ３をオンさせることを繰り返してコイルＬに交流電流を流す。 On the other hand, when the resistance value of the insulator RL is larger than the threshold value (step S14: Yes), that is, when it is difficult for the current to flow from the power supply P to the ground via the coil L and the insulator RL, the control unit 12 has a control unit 12. The operation of the induction furnace 1 is started (step S15). In the control unit 12, during the operation of the induction furnace 1, the input terminal IN + of the inverter circuit 2 is connected to the positive electrode terminal of the power supply P via the changeover switch 3, and the input terminal IN− of the inverter circuit 2 is connected via the changeover switch 4. The operation of the changeover switches 3 and 4 is controlled so as to be connected to the negative electrode terminal of the power supply P. Further, during the operation of the induction furnace 1, the control unit 12 turns on the switching elements SW1 and SW4 and turns off the switching elements SW2 and SW3, then turns off the switching elements SW1 and SW4 and turns on the switching elements SW2 and SW3. An alternating current is passed through the coil L by repeating turning it on.

なお、制御部１２は、絶縁体ＲＬの抵抗値が閾値より大きい場合（ステップＳ１４：Ｙｅｓ）、ステップＳ１５において、誘導炉１の起動毎に求めた複数の抵抗値の低下傾向により絶縁体ＲＬの残りの寿命を推定するように構成してもよい。ここで、図４（ｂ）は、時間経過に伴う絶縁体ＲＬの抵抗値の低下傾向の一例を示す図である。なお、図４（ｂ）に示す２次元座標の横軸は時間を示し、縦軸は抵抗値を示し、図４（ｂ）に示す各点は、誘導炉１の起動毎に記憶部１１に記憶された絶縁体ＲＬの抵抗値を示している。なお、記憶部１１に記憶される抵抗値は、例えば、絶縁体ＲＬの抵抗値が閾値以下である場合に最後に求められる抵抗値とする。制御部１２は、図４（ｂ）に示すように、一定期間において、記憶部１１に記憶される複数の抵抗値のうち、各所定時刻にそれぞれ対応する最低抵抗値（図４（ｂ）に示す時刻ｔ１〜ｔ６にそれぞれ対応する最低抵抗値ｒ１〜ｒ６）を用いて近似直線を求め、その近似直線と閾値との交点に対応する時刻と、現在の時刻との差を、絶縁体ＲＬの残りの寿命とする。なお、図４（ｂ）に示す閾値は、図４（ａ）に示す閾値と互いに同じ値でもよいし、互いに異なる値でもよい。 When the resistance value of the insulator RL is larger than the threshold value (step S14: Yes), the control unit 12 determines that the resistance value of the insulator RL is decreasing due to the decreasing tendency of the plurality of resistance values obtained for each start of the induction furnace 1 in step S15. It may be configured to estimate the remaining life. Here, FIG. 4B is a diagram showing an example of a tendency for the resistance value of the insulator RL to decrease with the passage of time. The horizontal axis of the two-dimensional coordinates shown in FIG. 4 (b) indicates the time, the vertical axis indicates the resistance value, and each point shown in FIG. 4 (b) is stored in the storage unit 11 each time the induction furnace 1 is started. The resistance value of the stored insulator RL is shown. The resistance value stored in the storage unit 11 is, for example, the resistance value finally obtained when the resistance value of the insulator RL is equal to or less than the threshold value. As shown in FIG. 4B, the control unit 12 has the lowest resistance value (in FIG. 4B) corresponding to each predetermined time among the plurality of resistance values stored in the storage unit 11 in a certain period of time. An approximate straight line is obtained using the minimum resistance values r1 to r6) corresponding to the indicated times t1 to t6, respectively, and the difference between the time corresponding to the intersection of the approximate straight line and the threshold value and the current time is determined by the insulator RL. Remaining life. The threshold value shown in FIG. 4B may be the same value as the threshold value shown in FIG. 4A, or may be different from each other.

このように、実施形態の誘導炉１では、間欠スイッチ６が常時オンしているとともに遮断スイッチ７が常時オフしているときに電流検出部９により検出される電流と電圧検出部１０により検出される電圧とにより求められる抵抗値が閾値より大きくなるまで、間欠スイッチ６をオン、オフさせるとともに遮断スイッチ７を常時オンさせた後、間欠スイッチ６を常時オンさせるとともに遮断スイッチ７を常時オフさせることを繰り返し、抵抗値が閾値より大きくなると、誘導炉１の運転を開始している。これにより、誘導炉１の運転前において、コイルＬとアースとの間の絶縁体ＲＬに吸着している水分を蒸発させて絶縁体ＲＬの抵抗値を上昇させた後、誘導炉１の運転を開始させることができる。すなわち、誘導炉１の起動直前に、直流電流によるコイルＬの自己発熱で絶縁体ＲＬに吸着している水分を蒸発させて、その後、直流電圧と直流電流とにより求められる抵抗値により絶縁体ＲＬの絶縁性を評価し、絶縁体ＲＬの絶縁性を担保してから誘導炉１を起動させている。そのため、誘導炉１の運転中において、電源ＰからコイルＬ及び絶縁体ＲＬを介してアースに流れる電流を抑えることができるため、コイルＬに流れる電流がコイルＬの定格電流を超えることを抑えることができ、コイルＬが劣化することを抑制することができる。すなわち、実施形態の誘導炉１によれば、絶縁体ＲＬの抵抗値が低下していても、コイルＬに比較的大きな電流が流れないようにすることができる。 As described above, in the induction furnace 1 of the embodiment, the current detected by the current detection unit 9 and the voltage detection unit 10 are detected when the intermittent switch 6 is always on and the cutoff switch 7 is always off. The intermittent switch 6 is turned on and off and the cutoff switch 7 is always turned on, and then the intermittent switch 6 is always turned on and the cutoff switch 7 is always turned off until the resistance value obtained by the voltage becomes larger than the threshold value. When the resistance value becomes larger than the threshold value, the operation of the induction furnace 1 is started. As a result, before the operation of the induction furnace 1, the water adsorbed on the insulator RL between the coil L and the ground is evaporated to increase the resistance value of the insulator RL, and then the induction furnace 1 is operated. Can be started. That is, immediately before the start of the induction furnace 1, the water adsorbed on the insulator RL is evaporated by the self-heating of the coil L due to the direct current, and then the insulator RL is determined by the resistance value obtained by the direct current and the direct current. The induction furnace 1 is started after evaluating the insulating property of the insulator RL and ensuring the insulating property of the insulator RL. Therefore, during the operation of the induction furnace 1, the current flowing from the power supply P to the ground via the coil L and the insulator RL can be suppressed, so that the current flowing through the coil L can be suppressed from exceeding the rated current of the coil L. It is possible to prevent the coil L from deteriorating. That is, according to the induction furnace 1 of the embodiment, even if the resistance value of the insulator RL is lowered, it is possible to prevent a relatively large current from flowing through the coil L.

また、実施形態の誘導炉１では、誘導炉１の運転前において、誘導炉１の運転中にコイルＬに交流電流を流すための電源Ｐを、コイルＬに直流電流を流すための電源として兼用しているため、電源Ｐの他に新たな電源を設ける必要がないため、その分製造コストを抑えることができる。 Further, in the induction furnace 1 of the embodiment, before the operation of the induction furnace 1, the power supply P for passing an alternating current through the coil L during the operation of the induction furnace 1 is also used as a power supply for passing a direct current through the coil L. Therefore, it is not necessary to provide a new power source in addition to the power source P, so that the manufacturing cost can be suppressed accordingly.

本発明は上記実施形態に限定されず、種々変更して実施することが可能である。上記実施の形態において、添付図面に図示されている構成要素の大きさや形状、機能などについては、これに限定されず、本発明の効果を発揮する範囲内で適宜変更することが可能である。その他、本発明の目的の範囲を逸脱しない限りにおいて適宜変更して実施することが可能である。 The present invention is not limited to the above embodiment, and can be implemented with various modifications. In the above embodiment, the size, shape, function, and the like of the components shown in the accompanying drawings are not limited to this, and can be appropriately changed within the range in which the effects of the present invention are exhibited. In addition, it can be appropriately modified and implemented as long as it does not deviate from the scope of the object of the present invention.

図５は、実施形態の誘導炉１の変形例を示す図である。なお、図５において、図１に示す構成と同じ構成には、同じ符号を付し、その説明を省略する。 FIG. 5 is a diagram showing a modified example of the induction furnace 1 of the embodiment. In FIG. 5, the same configurations as those shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

図５に示す誘導炉１において、図１に示す誘導炉１と異なる点は、切替スイッチ４、間欠スイッチ６、及び遮断スイッチ７を省略している点と、誘導炉１の運転中にコイルＬに交流電流を流すためのスイッチング素子ＳＷ１を間欠スイッチ６として兼用するとともに誘導炉１の運転中にコイルＬに交流電流を流すためのスイッチング素子ＳＷ４を遮断スイッチ７として兼用する点と、切替スイッチ３及びローパスフィルタ８をインバータ回路２の出力端子ＯＵＴ＋とコイルＬの一方端子との間に接続している点である。 The induction furnace 1 shown in FIG. 5 differs from the induction furnace 1 shown in FIG. 1 in that the changeover switch 4, the intermittent switch 6, and the cutoff switch 7 are omitted, and the coil L is operated during the operation of the induction furnace 1. The switching element SW1 for passing an AC current to the coil L is also used as the intermittent switch 6, and the switching element SW4 for passing the AC current to the coil L during the operation of the induction furnace 1 is also used as the cutoff switch 7. The point is that the low-pass filter 8 is connected between the output terminal OUT + of the inverter circuit 2 and one terminal of the coil L.

なお、インバータ回路２の一方の入力端子ＩＮ＋は電源Ｐの正極端子に直接接続され、インバータ回路２の他方の入力端子ＩＮ−は電源Ｐの負極端子に直接接続されている。また、スイッチング素子ＳＷ３を第１のスイッチング素子とし、スイッチング素子ＳＷ２を第２のスイッチング素子とする。すなわち、第１のスイッチング素子としてのスイッチング素子ＳＷ３の一方端子（コレクタ端子）が電源Ｐの正極端子に接続され、スイッチング素子ＳＷ３の他方端子（エミッタ端子）がコイルＬの他方端子に接続される。また、第２のスイッチング素子としてのスイッチング素子ＳＷ２の一方端子（コレクタ端子）がコイルＬの一方端子に接続され、スイッチング素子ＳＷ２の他方端子（エミッタ端子）が電源Ｐの負極端子に接続される。また、間欠スイッチ６としてのスイッチング素子ＳＷ１の一方端子（コレクタ端子）がスイッチング素子ＳＷ３の一方端子に接続され、スイッチング素子ＳＷ１の他方端子（エミッタ端子）がスイッチング素子ＳＷ２の一方端子に接続される。また、遮断スイッチ７としてのスイッチング素子ＳＷ４の一方端子（コレクタ端子）がスイッチング素子ＳＷ３の他方端子に接続され、スイッチング素子ＳＷ４の他方端子（エミッタ端子）がスイッチング素子ＳＷ２の他方端子に接続される。 One input terminal IN + of the inverter circuit 2 is directly connected to the positive electrode terminal of the power supply P, and the other input terminal IN− of the inverter circuit 2 is directly connected to the negative electrode terminal of the power supply P. Further, the switching element SW3 is used as the first switching element, and the switching element SW2 is used as the second switching element. That is, one terminal (collector terminal) of the switching element SW3 as the first switching element is connected to the positive electrode terminal of the power supply P, and the other terminal (emitter terminal) of the switching element SW3 is connected to the other terminal of the coil L. Further, one terminal (collector terminal) of the switching element SW2 as the second switching element is connected to one terminal of the coil L, and the other terminal (emitter terminal) of the switching element SW2 is connected to the negative electrode terminal of the power supply P. Further, one terminal (collector terminal) of the switching element SW1 as the intermittent switch 6 is connected to one terminal of the switching element SW3, and the other terminal (emitter terminal) of the switching element SW1 is connected to one terminal of the switching element SW2. Further, one terminal (collector terminal) of the switching element SW4 as the cutoff switch 7 is connected to the other terminal of the switching element SW3, and the other terminal (emitter terminal) of the switching element SW4 is connected to the other terminal of the switching element SW2.

まず、図５に示す制御部１２は、パルス電圧モードを実施する一定時間Ｔ１において、コイルＬの一方端子がローパスフィルタ８を介してインバータ回路２の出力端子ＯＵＴ＋（スイッチング素子ＳＷ１の他方端子）に接続されるように切替スイッチ３の動作を制御する。また、制御部１２は、一定時間Ｔ１において、スイッチング素子ＳＷ１を繰り返しオン、オフさせ、スイッチング素子ＳＷ４を常時オンさせ、スイッチング素子ＳＷ２、ＳＷ３を常時オフさせる。言い換えると、一定時間Ｔ１において、スイッチング素子ＳＷ１が導通と遮断を繰り返し、スイッチング素子ＳＷ４が常時導通し、スイッチング素子ＳＷ２、３が常時遮断する。すると、一定時間Ｔ１において、コイルＬに直流電圧がかかり、コイルＬに直流電流が流れる。これにより、一定時間Ｔ１において、コイルＬの抵抗成分により生じる熱の温度が上昇していく。なお、一定時間Ｔ１において、コイルＬに流れる直流電流がコイルＬの定格電流以下になるようにスイッチング素子ＳＷ１の制御信号のデューティ比が設定されているものとする。 First, in the control unit 12 shown in FIG. 5, one terminal of the coil L is connected to the output terminal OUT + (the other terminal of the switching element SW1) of the inverter circuit 2 via the low-pass filter 8 in T1 for a certain period of time when the pulse voltage mode is executed. The operation of the changeover switch 3 is controlled so as to be connected. Further, the control unit 12 repeatedly turns on and off the switching element SW1 at T1 for a certain period of time, always turns on the switching element SW4, and always turns off the switching elements SW2 and SW3. In other words, at T1 for a certain period of time, the switching element SW1 repeatedly conducts and shuts off, the switching element SW4 constantly conducts, and the switching elements SW2 and 3 constantly shut off. Then, at T1 for a certain period of time, a DC voltage is applied to the coil L, and a DC current flows through the coil L. As a result, the temperature of the heat generated by the resistance component of the coil L rises at T1 for a certain period of time. It is assumed that the duty ratio of the control signal of the switching element SW1 is set so that the DC current flowing through the coil L becomes equal to or less than the rated current of the coil L at T1 for a certain period of time.

次に、図５に示す制御部１２は、一定時間Ｔ２が経過するまで待機する。図５に示す制御部１２は、一定時間Ｔ２において、コイルＬの一方端子がローパスフィルタ８を介してインバータ回路２の出力端子ＯＵＴ＋（スイッチング素子ＳＷ１の他方端子）に接続されるように切替スイッチ３の動作を制御する。また、図５に示す制御部１２は、一定時間Ｔ２において、スイッチング素子ＳＷ１〜ＳＷ４を常時オフさせる。言い換えると、一定時間Ｔ２において、スイッチング素子ＳＷ１〜ＳＷ４が常時遮断する。これにより、一定時間Ｔ２において、コイルＬの熱の温度上昇によりコイルＬとアースとの間の絶縁体ＲＬに吸着されている水分を蒸発させることができる。なお、一定時間Ｔ１において、絶縁体ＲＬに吸着されている水分を十分に蒸発させることができる場合、一定時間Ｔ２待機しなくてもよい。 Next, the control unit 12 shown in FIG. 5 waits until T2 elapses for a certain period of time. The control unit 12 shown in FIG. 5 has a changeover switch 3 so that one terminal of the coil L is connected to the output terminal OUT + (the other terminal of the switching element SW1) of the inverter circuit 2 via the low-pass filter 8 at T2 for a certain period of time. Control the operation of. Further, the control unit 12 shown in FIG. 5 constantly turns off the switching elements SW1 to SW4 at T2 for a certain period of time. In other words, the switching elements SW1 to SW4 are constantly shut off at T2 for a certain period of time. As a result, at T2 for a certain period of time, the moisture adsorbed on the insulator RL between the coil L and the ground can be evaporated by the temperature rise of the heat of the coil L. If the water adsorbed on the insulator RL can be sufficiently evaporated in T1 for a certain period of time, it is not necessary to wait for T2 for a certain period of time.

次に、図５に示す制御部１２は、一定時間Ｔ２が経過すると、直流電圧モードを実施する。制御部１２は、直流電圧モードを実施する一定時間Ｔ３において、コイルＬの一方端子がローパスフィルタ８を介してインバータ回路２の出力端子ＯＵＴ＋（スイッチング素子ＳＷ１の他方端子）に接続されるように切替スイッチ３の動作を制御する。また、制御部１２は、一定時間Ｔ３において、スイッチング素子ＳＷ１を常時オンさせ、スイッチング素子ＳＷ２〜ＳＷ４を常時オフさせる。言い換えると、一定時間Ｔ３において、スイッチング素子ＳＷ１が常時導通し、スイッチング素子ＳＷ２〜ＳＷ４が常時遮断する。すると、一定時間Ｔ３において、コイルＬに直流電圧がかかり、コイルＬに直流電流が流れる。また、制御部１２は、一定時間Ｔ３において、電圧検出部１０により検出される電圧を電流検出部９により検出される電流で除算することにより、その結果を絶縁体ＲＬの抵抗値として測定する。 Next, the control unit 12 shown in FIG. 5 executes the DC voltage mode when T2 elapses for a certain period of time. The control unit 12 switches so that one terminal of the coil L is connected to the output terminal OUT + (the other terminal of the switching element SW1) of the inverter circuit 2 via the low-pass filter 8 in T3 for a certain period of time when the DC voltage mode is executed. Controls the operation of the switch 3. Further, the control unit 12 always turns on the switching element SW1 and always turns off the switching elements SW2 to SW4 at T3 for a certain period of time. In other words, at T3 for a certain period of time, the switching element SW1 is constantly conducting, and the switching elements SW2 to SW4 are constantly shut off. Then, at T3 for a certain period of time, a DC voltage is applied to the coil L, and a DC current flows through the coil L. Further, the control unit 12 divides the voltage detected by the voltage detection unit 10 by the current detected by the current detection unit 9 at T3 for a certain period of time, and measures the result as the resistance value of the insulator RL.

次に、図５に示す制御部１２は、絶縁体ＲＬの抵抗値が閾値以下である場合、パルス電圧モードや直流電圧モードを再度実行して、絶縁体ＲＬに吸着されている水分を蒸発させて絶縁体ＲＬの抵抗値をさらに上昇させる。 Next, when the resistance value of the insulator RL is equal to or less than the threshold value, the control unit 12 shown in FIG. 5 re-executes the pulse voltage mode and the DC voltage mode to evaporate the water adsorbed on the insulator RL. The resistance value of the insulator RL is further increased.

一方、図５に示す制御部１２は、絶縁体ＲＬの抵抗値が閾値より大きい場合、誘導炉１の運転を開始する。制御部１２は、誘導炉１の運転中において、コイルＬの一方端子がインバータ回路２の出力端子ＯＵＴ＋（スイッチング素子ＳＷ１の他方端子）に直接接続されるように切替スイッチ３の動作を制御する。また、制御部１２は、誘導炉１の運転中において、スイッチング素子ＳＷ１、ＳＷ４をオンさせるとともにスイッチング素子ＳＷ２、ＳＷ３をオフさせた後、スイッチング素子ＳＷ１、ＳＷ４をオフさせるとともにスイッチング素子ＳＷ２、ＳＷ３をオンさせることを繰り返してコイルＬに交流電流を流す。 On the other hand, the control unit 12 shown in FIG. 5 starts the operation of the induction furnace 1 when the resistance value of the insulator RL is larger than the threshold value. The control unit 12 controls the operation of the changeover switch 3 so that one terminal of the coil L is directly connected to the output terminal OUT + (the other terminal of the switching element SW1) of the inverter circuit 2 during the operation of the induction furnace 1. Further, during the operation of the induction furnace 1, the control unit 12 turns on the switching elements SW1 and SW4 and turns off the switching elements SW2 and SW3, then turns off the switching elements SW1 and SW4 and turns on the switching elements SW2 and SW3. An alternating current is passed through the coil L by repeating turning it on.

なお、パルス電圧モード実施時にスイッチング素子ＳＷ１から切替スイッチ３を介してローパスフィルタ８に流れる電流を平滑する必要がない場合、切替スイッチ３及びローパスフィルタ８を省略してもよい。このように構成する場合、インバータ回路２の出力端子ＯＵＴ＋はコイルＬの一方端子に直接接続される。 If it is not necessary to smooth the current flowing from the switching element SW1 to the low-pass filter 8 via the changeover switch 3 when the pulse voltage mode is executed, the changeover switch 3 and the low-pass filter 8 may be omitted. In this configuration, the output terminal OUT + of the inverter circuit 2 is directly connected to one terminal of the coil L.

このように、実施形態の誘導炉１の変形例では、スイッチング素子ＳＷ１が常時オンしているとともにスイッチング素子ＳＷ２〜ＳＷ４が常時オフしているときに電流検出部９により検出される電流と電圧検出部１０により検出される電圧とにより求められる抵抗値が閾値より大きくなるまで、スイッチング素子ＳＷ１をオン、オフさせるとともにスイッチング素子ＳＷ４を常時オンさせるとともにスイッチング素子ＳＷ２、ＳＷ３を常時オフさせた後、スイッチング素子ＳＷ１を常時オンさせるとともにスイッチング素子ＳＷ２〜ＳＷ４を常時オフさせることを繰り返し、抵抗値が閾値より大きくなると、誘導炉１の運転を開始している。これにより、誘導炉１の運転前において、コイルＬとアースとの間の絶縁体ＲＬに吸着している水分を蒸発させて絶縁体ＲＬの抵抗値を上昇させた後、誘導炉１の運転を開始させることができる。すなわち、誘導炉１の起動直前に、直流電流によるコイルＬの自己発熱で絶縁体ＲＬに吸着している水分を蒸発させて、その後、直流電圧と直流電流とにより求められる抵抗値により絶縁体ＲＬの絶縁性を評価し、絶縁体ＲＬの絶縁性を担保してから誘導炉１を起動させている。そのため、誘導炉１の運転中において、電源ＰからコイルＬ及び絶縁体ＲＬを介してアースに流れる電流を抑えることができるため、コイルＬに流れる全体の電流がコイルＬの定格電流を超えることを抑えることができ、コイルＬが劣化することを抑制することができる。すなわち、実施形態の誘導炉１の変形例によれば、絶縁体ＲＬの抵抗値が低下していても、コイルＬに比較的大きな電流が流れないようにすることができる。 As described above, in the modified example of the induction furnace 1 of the embodiment, the current and voltage detection detected by the current detection unit 9 when the switching element SW1 is always on and the switching elements SW2 to SW4 are always off. Switching element SW1 is turned on and off, switching element SW4 is always turned on, switching elements SW2 and SW3 are always turned off, and then switching is performed until the resistance value obtained by the voltage detected by the unit 10 becomes larger than the threshold value. The elements SW1 are constantly turned on and the switching elements SW2 to SW4 are constantly turned off repeatedly, and when the resistance value becomes larger than the threshold value, the operation of the induction furnace 1 is started. As a result, before the operation of the induction furnace 1, the water adsorbed on the insulator RL between the coil L and the ground is evaporated to increase the resistance value of the insulator RL, and then the induction furnace 1 is operated. Can be started. That is, immediately before the start of the induction furnace 1, the water adsorbed on the insulator RL is evaporated by the self-heating of the coil L due to the direct current, and then the insulator RL is determined by the resistance value obtained by the direct current and the direct current. The induction furnace 1 is started after evaluating the insulating property of the insulator RL and ensuring the insulating property of the insulator RL. Therefore, during the operation of the induction furnace 1, the current flowing from the power supply P to the ground via the coil L and the insulator RL can be suppressed, so that the total current flowing through the coil L exceeds the rated current of the coil L. It can be suppressed, and deterioration of the coil L can be suppressed. That is, according to the modified example of the induction furnace 1 of the embodiment, even if the resistance value of the insulator RL is lowered, it is possible to prevent a relatively large current from flowing through the coil L.

また、図５に示す誘導炉１は、図１に示す誘導炉１に比べて、切替スイッチ４、間欠スイッチ６、及び遮断スイッチ７を省略することができる分、製造コストを低減することができる。 Further, in the induction furnace 1 shown in FIG. 5, the manufacturing cost can be reduced because the changeover switch 4, the intermittent switch 6 and the cutoff switch 7 can be omitted as compared with the induction furnace 1 shown in FIG. ..

１ 誘導炉
２ インバータ回路
３、４ 切替スイッチ
５ 炉
６ 間欠スイッチ
７ 遮断スイッチ
８ ローパスフィルタ
９ 電流検出部
１０ 電圧検出部
１１ 記憶部
１２ 制御部 1 Inverter 2 Inverter circuit 3, 4 Changeover switch 5 Furnace 6 Intermittent switch 7 Shutoff switch 8 Low-pass filter 9 Current detection unit 10 Voltage detection unit 11 Storage unit 12 Control unit

Claims (5)

炉の外側に設けられるコイルに交流電流が流れることにより前記炉の内側に磁界が発生する誘導炉であって、
前記コイルの一方端子と電源の正極端子との間に接続される間欠スイッチと、
前記コイルの他方端子と前記電源の負極端子との間に接続される遮断スイッチと、
前記コイルに流れる電流を検出する電流検出部と、
前記電源の電圧を検出する電圧検出部と、
前記間欠スイッチ及び前記遮断スイッチのそれぞれの動作を制御する制御部と、
を備え、
前記制御部は、
前記間欠スイッチが常時オンしているとともに前記遮断スイッチが常時オフしているときに前記電流検出部により検出される電流と前記電圧検出部により検出される電圧とにより求められる抵抗値が閾値より大きくなるまで、前記間欠スイッチをオン、オフさせるとともに前記遮断スイッチを常時オンさせた後、前記間欠スイッチを常時オンさせるとともに前記遮断スイッチを常時オフさせることを繰り返し、
前記抵抗値が前記閾値より大きくなると、前記コイルに交流電流を流す
ことを特徴とする誘導炉。 An induction furnace in which a magnetic field is generated inside the furnace when an alternating current flows through a coil provided outside the furnace.
An intermittent switch connected between one terminal of the coil and the positive terminal of the power supply,
A cutoff switch connected between the other terminal of the coil and the negative electrode terminal of the power supply,
A current detector that detects the current flowing through the coil,
A voltage detector that detects the voltage of the power supply and
A control unit that controls the operation of the intermittent switch and the cutoff switch, and
With
The control unit
The resistance value obtained by the current detected by the current detection unit and the voltage detected by the voltage detection unit when the intermittent switch is always on and the cutoff switch is always off is larger than the threshold value. Until then, the intermittent switch is turned on and off and the cutoff switch is always turned on, and then the intermittent switch is always turned on and the cutoff switch is always turned off.
An induction furnace characterized in that an alternating current is passed through the coil when the resistance value becomes larger than the threshold value. 請求項１に記載の誘導炉であって、
第１及び第２の切替スイッチと、
一方の入力端子が前記第１の切替スイッチに接続され、他方の入力端子が前記第２の切替スイッチに接続され、一方の出力端子が前記コイルの一方端子に接続され、他方の出力端子が前記コイルの他方端子に接続され、前記コイルに交流電流を流すインバータ回路と、
を備え、
前記間欠スイッチの一方端子が前記第１の切替スイッチに接続され、前記間欠スイッチの他方端子が前記コイルの一方端子に接続され、
前記遮断スイッチの一方端子が前記第２の切替スイッチに接続され、前記遮断スイッチの他方端子が前記コイルの他方端子に接続され、
前記制御部は、
前記抵抗値が前記閾値より大きくなるまで、前記間欠スイッチの一方端子が前記第１の切替スイッチを介して前記電源の正極端子に接続され、前記遮断スイッチの一方端子が前記第２の切替スイッチを介して前記電源の負極端子に接続されるように前記第１及び第２の切替スイッチの動作を制御し、
前記絶縁体の抵抗値が前記閾値より大きくなると、前記インバータ回路の一方の入力端子が前記第１の切替スイッチを介して前記電源の正極端子に接続され、前記インバータ回路の他方の入力端子が前記第２の切替スイッチを介して前記電源の負極端子に接続されるように前記第１及び第２の切替スイッチの動作を制御する
ことを特徴とする誘導炉。 The induction furnace according to claim 1.
The first and second changeover switches and
One input terminal is connected to the first changeover switch, the other input terminal is connected to the second changeover switch, one output terminal is connected to one terminal of the coil, and the other output terminal is said. An inverter circuit that is connected to the other terminal of the coil and allows alternating current to flow through the coil.
With
One terminal of the intermittent switch is connected to the first changeover switch, the other terminal of the intermittent switch is connected to one terminal of the coil, and the like.
One terminal of the cutoff switch is connected to the second changeover switch, the other terminal of the cutoff switch is connected to the other terminal of the coil, and the like.
The control unit
Until the resistance value becomes larger than the threshold value, one terminal of the intermittent switch is connected to the positive electrode terminal of the power supply via the first changeover switch, and one terminal of the cutoff switch connects the second changeover switch. The operation of the first and second changeover switches is controlled so as to be connected to the negative electrode terminal of the power supply via the above.
When the resistance value of the insulator becomes larger than the threshold value, one input terminal of the inverter circuit is connected to the positive electrode terminal of the power supply via the first changeover switch, and the other input terminal of the inverter circuit is connected to the positive electrode terminal of the power supply. An induction furnace characterized in that the operation of the first and second changeover switches is controlled so as to be connected to the negative electrode terminal of the power supply via the second changeover switch. 請求項１に記載の誘導炉であって、
一方端子が前記電源の正極端子に接続され、他方端子が前記コイルの他方端子に接続される第１のスイッチング素子と、
一方端子が前記コイルの一方端子に接続され、他方端子が前記電源の負極端子に接続される第２のスイッチング素子と、
を備え、
前記間欠スイッチの一方端子が前記第１のスイッチング素子の一方端子に接続され、前記間欠スイッチの他方端子が前記第２のスイッチング素子の一方端子に接続され、
前記遮断スイッチの一方端子が前記第１のスイッチング素子の他方端子に接続され、前記遮断スイッチの他方端子が前記第２のスイッチング素子の他方端子に接続され、
前記制御部は、
前記抵抗値が前記閾値より大きくなるまで、前記間欠スイッチをオン、オフさせるとともに前記遮断スイッチを常時オンさせるとともに前記第１及び第２のスイッチング素子を常時オフさせた後、前記間欠スイッチを常時オンさせるとともに前記遮断スイッチを常時オフさせるとともに前記第１及び第２のスイッチング素子を常時オフさせることを繰り返し、
前記抵抗値が前記閾値より大きくなると、前記間欠スイッチ及び前記遮断スイッチをオンさせるとともに前記第１及び第２のスイッチング素子をオフさせた後、前記間欠スイッチ及び前記遮断スイッチをオフさせるとともに前記第１及び第２のスイッチング素子をオンさせることを繰り返して前記コイルに交流電流を流す
ことを特徴とする誘導炉。 The induction furnace according to claim 1.
A first switching element in which one terminal is connected to the positive electrode terminal of the power supply and the other terminal is connected to the other terminal of the coil.
A second switching element in which one terminal is connected to one terminal of the coil and the other terminal is connected to the negative electrode terminal of the power supply.
With
One terminal of the intermittent switch is connected to one terminal of the first switching element, and the other terminal of the intermittent switch is connected to one terminal of the second switching element.
One terminal of the cutoff switch is connected to the other terminal of the first switching element, and the other terminal of the cutoff switch is connected to the other terminal of the second switching element.
The control unit
The intermittent switch is always turned on and off, the cutoff switch is always turned on, the first and second switching elements are always turned off, and then the intermittent switch is always turned on until the resistance value becomes larger than the threshold value. Repeatedly turning off the cutoff switch and constantly turning off the first and second switching elements.
When the resistance value becomes larger than the threshold value, the intermittent switch and the cutoff switch are turned on and the first and second switching elements are turned off, and then the intermittent switch and the cutoff switch are turned off and the first cutoff switch is turned off. An induction furnace characterized in that an alternating current is passed through the coil by repeatedly turning on the second switching element. 請求項１〜３の何れか１項に記載の誘導炉であって、
前記制御部は、当該誘導炉の起動毎に求めた複数の前記抵抗値の低下傾向により前記絶縁体の残りの寿命を推定する
ことを特徴とする誘導炉。 The induction furnace according to any one of claims 1 to 3.
The control unit is a induction furnace, characterized in that the remaining life of the insulator is estimated from a plurality of decreasing tendencies of the resistance values obtained each time the induction furnace is started. 炉の外側に設けられるコイルの一方端子と電源の正極端子との間に接続される間欠スイッチと、前記コイルの他方端子と前記電源の負極端子との間に接続される遮断スイッチと、前記コイルに流れる電流を検出する電流検出部と、前記電源の電圧を検出する電圧検出部とを備える誘導炉の運転方法であって、
前記間欠スイッチが常時オンしているとともに前記遮断スイッチが常時オフしているときに前記電流検出部により検出される電流と前記電圧検出部により検出される電圧とにより求められる抵抗値が閾値より大きくなるまで、前記間欠スイッチをオン、オフさせるとともに前記遮断スイッチを常時オンさせた後、前記間欠スイッチを常時オンさせるとともに前記遮断スイッチを常時オフさせることを繰り返し、
前記抵抗値が前記閾値より大きくなると、前記コイルに交流電流を流して前記炉の内側に磁界を発生させる
ことを特徴とする誘導炉の運転方法。 An intermittent switch connected between one terminal of the coil provided on the outside of the furnace and the positive electrode terminal of the power supply, a cutoff switch connected between the other terminal of the coil and the negative electrode terminal of the power supply, and the coil. It is a method of operating an induction furnace including a current detection unit that detects the current flowing through the coil and a voltage detection unit that detects the voltage of the power supply.
The resistance value obtained by the current detected by the current detection unit and the voltage detected by the voltage detection unit when the intermittent switch is always on and the cutoff switch is always off is larger than the threshold value. Until then, the intermittent switch is turned on and off and the cutoff switch is always turned on, and then the intermittent switch is always turned on and the cutoff switch is always turned off.
A method for operating an induction furnace, which comprises passing an alternating current through the coil to generate a magnetic field inside the furnace when the resistance value becomes larger than the threshold value.
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