Contactor auxiliary starting device for electric induction furnace

Abstract

The utility model relates to the technical field of medium-frequency induction heating technology metal smelting, and particularly discloses a contactor auxiliary starting device for an electric induction furnace, which comprises a rectifying circuit, a switch follow current circuit, a vacuum contactor control circuit, a starting feedback voltage detection circuit and a running state indication circuit, the input end of the rectifying circuit is electrically connected to a workshop power supply grid, and the rectifying circuit is electrically connected with the switch follow current circuit; the vacuum contactor control circuit is powered by a workshop control power supply VCC1, and the vacuum contactor control circuit is electrically connected with the switch follow current circuit; and the starting feedback voltage detection circuit is electrically connected with the vacuum contactor control circuit and is in signal connection with the post-stage circuit. According to the invention, the conduction time of the fly-wheel diode can be delayed when the electric induction furnace is started, so that the resonant load can obtain enough excitation energy at the initial stage of oscillation establishment, and after oscillation is stable, the fly-wheel diode plays a role again, so that the influence on oscillation establishment caused by premature conduction of the fly-wheel diode is avoided.

Description

Technical Field

[0001] This application relates to the technical field of medium-frequency induction heating technology, and in particular to a contactor-assisted starting device for an induction furnace. Background Technology

[0002] Induction furnaces are important industrial heating equipment. Their electrical components mainly consist of a frequency converter and a resonant load. The electrical system of an induction furnace typically uses a zero-voltage soft start. During operation, the frequency converter outputs a single-phase AC intermediate frequency voltage of a specific frequency to excite the resonant load, causing it to oscillate. Subsequently, the frequency converter locks onto and tracks the feedback oscillation signal, continuously outputting an intermediate frequency voltage of the same frequency to compensate for the energy consumed during the resonant load's oscillation process, maintaining stable operation and ensuring the normal operation of the induction furnace.

[0003] In existing technology, the rectifier circuit of the frequency converter power supply connected to the workshop power grid typically has a freewheeling diode connected in parallel on the rectifier bridge. When the induction furnace suddenly fails and stops, the freewheeling diode provides a discharge path, protecting the induction furnace. However, during circuit startup, the freewheeling diode reduces the excitation energy of the frequency converter power supply to the resonant load, which can easily prevent the resonant load from establishing oscillation, meaning the induction furnace cannot start normally.

[0004] Regarding the aforementioned technologies, how to delay the conduction time of the freewheeling diode so that the resonant load can obtain sufficient excitation energy in the early stage of oscillation establishment, and the freewheeling diode can play its role after the oscillation stabilizes, thus avoiding the freewheeling diode from conducting too early and affecting the establishment of oscillation, has become an urgent problem to be solved. Utility Model Content

[0005] In order to delay the conduction time of the freewheeling diode when the induction furnace is started, so that the resonant load can obtain sufficient excitation energy in the early stage of oscillation establishment, and the freewheeling diode can play its role after the oscillation stabilizes, thus avoiding the freewheeling diode from conducting too early and affecting the establishment of oscillation, this application provides a contactor auxiliary starting device for an induction furnace.

[0006] This application provides a contactor-assisted starting device for an induction furnace, which adopts the following technical solution:

[0007] A contactor-assisted starting device for an induction furnace, comprising:

[0008] A rectifier circuit, wherein the input terminal of the rectifier circuit is electrically connected to the workshop power grid, and the two output terminals of the rectifier circuit are defined as positive terminal D and negative terminal E, respectively;

[0009] A switching freewheeling circuit, wherein the switching freewheeling circuit is electrically connected between the positive terminal D and the negative terminal E;

[0010] A vacuum contactor control circuit, which is powered by the workshop control power supply VCC1, and is electrically connected to the switch freewheeling circuit;

[0011] A startup feedback voltage detection circuit is established, which is electrically connected to the vacuum contactor control circuit and is signal-connected to the subsequent circuit.

[0012] By adopting the above technical solution, when the frequency converter output gradually increases from zero voltage, and the resonant load receives a low excitation intermediate frequency voltage, the resonant load will not oscillate, and the start-up feedback voltage detection circuit will not receive the oscillation voltage of the resonant load. At this time, the vacuum contactor control circuit is turned on, the rectifier circuit is turned off, and the energy of the excitation resonant load output from the workshop power grid will not be consumed by the rectifier circuit, but will be entirely loaded onto the resonant load. At this time, the resonant load of the induction furnace can easily establish an oscillation circuit, and the induction furnace completes normal startup. After the induction furnace starts, the start-up feedback voltage detection circuit obtains the oscillation voltage signal, the vacuum contactor control circuit is turned off, and the rectifier circuit is turned on, providing protection for the operation of the workshop power grid. This circuit can delay the conduction time of the freewheeling diode when the induction furnace starts, allowing the resonant load to obtain sufficient excitation energy in the early stage of oscillation establishment. After the oscillation stabilizes, the freewheeling diode will then play its role, avoiding the freewheeling diode from turning on too early and affecting the establishment of oscillation.

[0013] Preferably, the rectifier circuit includes a silicon controlled rectifier (SCR) group, which is powered by the workshop power grid, and the two output terminals of the SCR group are simultaneously electrically connected to the positive terminal D and the negative terminal E.

[0014] By adopting the above technical solution, the thyristor rectifier group converts the AC power output from the workshop power grid into DC power.

[0015] Preferably, the thyristor rectifier group includes thyristor SCR1, thyristor SCR2, thyristor SCR3, thyristor SCR4, thyristor SCR5, and thyristor SCR6. The cathodes of thyristor SCR4, SCR6, and SCR2 are electrically connected to phases A, B, and C of the workshop power grid, respectively. The anodes of thyristor SCR4 and SCR6 are... The anodes of the SCR2 are electrically connected to the negative electrode E; the anodes of the SCR1, SCR3, and SCR5 are electrically connected to phases A, B, and C of the workshop power grid, respectively; the cathodes of the SCR1, SCR3, and SCR5 are electrically connected to the positive electrode D; and the switching freewheeling circuit is electrically connected between the positive electrode D and the negative electrode E.

[0016] By adopting the above technical solution, the silicon controlled rectifiers SCR1-SCR6 form a three-phase full-wave rectifier bridge, which provides a stable DC voltage for the induction furnace system. The DC voltage is obtained between the positive terminal D and the negative terminal E.

[0017] Preferably, the switching freewheeling circuit includes a main contact K1 and a freewheeling diode D7. One end of the main contact K1 is electrically connected to the positive terminal of the freewheeling diode D7, and the other end of the main contact K1 is electrically connected to the negative terminal E. The negative terminal of the freewheeling diode D7 is electrically connected to the positive terminal D. The main contact K1 is electrically connected to the vacuum contactor control circuit.

[0018] By adopting the above technical solution, during the startup phase of the induction furnace, the vacuum contactor control circuit changes the main contact K1 from a normally closed state to an open state. When the main contact K1 is open, the freewheeling diode D7 branch is cut off, and the switch freewheeling circuit does not work. After the induction furnace has started up, the vacuum contactor control circuit restores the main contact K1 to a normally closed state. When the main contact K1 is closed, the freewheeling diode D7 branch is connected. The freewheeling diode D7 can protect the induction furnace in the event of a sudden malfunction and shutdown.

[0019] Preferably, the rectifier circuit further includes multiple RC snubber circuits, with each of the two ends of the SCR1, the two ends of the SCR2, the two ends of the SCR3, the two ends of the SCR4, the two ends of the SCR5, the two ends of the SCR6, and the two ends of the freewheeling diode D7 connected in parallel with one of the RC snubber circuits.

[0020] By adopting the above technical solution, the RC absorption circuit can effectively suppress the overvoltage and spike pulses generated by each thyristor rectifier and freewheeling diode during the switching process, thereby protecting the circuit.

[0021] Preferably, the RC snubber circuit includes a resistor R and a capacitor C connected in series.

[0022] By adopting the above technical solution, when the rectifier circuit is running, the resistor R is used to dissipate overvoltage energy, and the capacitor C is used to absorb spike pulses, protecting the silicon controlled rectifiers SCR1-SCR6 and the freewheeling diode D7 from overvoltage damage.

[0023] Preferably, the vacuum contactor control circuit includes a voltage relay switch K3, a vacuum contactor coil KM, and an auxiliary start knob K2. One end of the voltage relay switch K3 is electrically connected to one end of the auxiliary start knob K2, and the other end of the voltage relay switch K3 is electrically connected to one end of the vacuum contactor coil KM. The other end of the vacuum contactor coil KM is electrically connected to the neutral wire N1 of the workshop control power supply VCC1. The other end of the auxiliary start knob K2 is connected to the live wire L1 of the workshop control power supply VCC1. The vacuum contactor coil KM is electrically connected to the main contact K1.

[0024] By adopting the above technical solution, when the auxiliary start knob K2 is turned on, the voltage relay coil is energized, and the voltage relay switch K3 is closed. The current will flow through the live wire L1, the auxiliary start knob K2, and the voltage relay switch K3 into the vacuum contactor coil KM, and then through the neutral wire N1 to form a circuit, energizing the vacuum contactor coil and generating a magnetic field. This, in turn, controls the main contacts of the vacuum contactor to change from the normally closed state to the open state, realizing the conduction of the vacuum contactor control circuit. When the voltage relay coil is not energized, the voltage relay switch K3 is opened, and the main contacts K1 return to the closed state, realizing the disconnection of the vacuum contactor control circuit. This realizes the control of the vacuum contactor control circuit by the voltage relay coil, and further controls the on / off of the switching freewheeling circuit.

[0025] Preferably, the start-up feedback voltage detection circuit includes a voltage relay coil KU and an intermediate frequency transformer T. The primary side of the intermediate frequency transformer T is connected to the signal of the subsequent circuit, and the secondary side of the intermediate frequency transformer T is electrically connected to both ends of the voltage relay coil KU. The voltage relay coil KU is electrically connected to the voltage relay switch K3, and the signal output terminal is used to output intermediate frequency AC power.

[0026] By adopting the above technical solution, the intermediate frequency transformer T transforms the signal to provide the working voltage for the voltage relay coil KU; the voltage relay coil is set to be less than a certain voltage value, and the voltage relay switch changes from a normally open point to a closed point, thus realizing the control of the voltage relay switch by the voltage relay coil.

[0027] Preferably, it further includes an operating status indication circuit, which includes an auxiliary start indicator LED and an auxiliary contact K4. One end of the auxiliary contact K4 is electrically connected to the live wire L2 of the mains power, and the other end of the auxiliary contact K4 is electrically connected to one end of the auxiliary start indicator LED, and the other end of the auxiliary start indicator LED is electrically connected to the neutral wire N2 of the mains power. The auxiliary contact K4 and the main contact K1 operate synchronously.

[0028] By adopting the above technical solution, when the auxiliary contact K4 is closed and the auxiliary start indicator LED is lit, the operating status indicator circuit is in the ON state; when the auxiliary contact K4 is open and the auxiliary start indicator LED is off, the operating status indicator circuit is in the OFF state. During the induction furnace start-up phase, the vacuum contactor control circuit changes the main contact K1 from the normally closed state to the open state. At this time, the auxiliary contact K4 will also open. After the induction furnace starts up, the vacuum contactor control circuit returns the main contact K1 to the normally closed state. At this time, the auxiliary contact K4 will also close, keeping in sync with the action of the main contact K1, thereby controlling the on / off state of the auxiliary start indicator LED and reflecting the operating status of the circuit.

[0029] In summary, this application includes at least one of the following beneficial technical effects:

[0030] 1. When the VCC output of the frequency converter gradually increases from zero volts, the resonant load will not oscillate when it receives a low excitation intermediate frequency voltage. At this time, since the start-up feedback voltage detection circuit does not receive the oscillation voltage from the resonant load, the vacuum contactor control circuit will be in the ON state, while the rectifier circuit cannot be energized. This ensures that the energy output by the frequency converter VCC to excite the resonant load for startup is not consumed by the switching freewheeling circuit, but is entirely loaded onto the resonant load, allowing the resonant load of the induction furnace to easily establish an oscillation circuit and successfully complete normal startup. When the induction furnace has finished starting, the start-up feedback voltage detection circuit obtains the oscillation voltage signal, and the vacuum contactor control circuit immediately switches to the OFF state, while the rectifier circuit is energized, thus providing protection for the operation of the workshop power grid. This design can delay the conduction time of the freewheeling diode during the startup phase of the induction furnace, allowing the resonant load to obtain sufficient excitation energy in the early stage of oscillation establishment. After the oscillation stabilizes, the freewheeling diode then plays its role, avoiding premature conduction of the freewheeling diode and affecting the establishment of oscillation.

[0031] 2. When the auxiliary start knob K2 is turned on, the voltage relay coil is energized, and the voltage relay switch K3 is closed. Current then flows through the live wire L1, the auxiliary start knob K2, and the voltage relay switch K3 into the vacuum contactor coil KM, and then through the neutral wire N1 to form a circuit. This energizes the vacuum contactor coil and generates a magnetic field, which in turn controls the main contacts of the vacuum contactor to change from a normally closed state to an open state, thus enabling the vacuum contactor control circuit to conduct. When the voltage relay coil is not energized, the voltage relay switch K3 is opened, and the main contacts K1 return to a closed state, thus enabling the vacuum contactor control circuit to be cut off. This achieves the control of the vacuum contactor control circuit by the voltage relay coil, further controlling the on / off state of the switching freewheeling circuit.

[0032] 3. The intermediate frequency transformer T transforms the signal to provide the working voltage for the voltage relay coil KU; the voltage relay coil is set to be below a certain voltage value, and the voltage relay switch changes from a normally open point to a closed point, realizing the control of the voltage relay switch by the voltage relay coil. Attached Figure Description

[0033] Figure 1 The circuit diagram of this application.

[0034] Reference numerals in the attached diagram: 1. Rectifier circuit; 2. Switching freewheeling circuit; 3. Vacuum contactor control circuit; 4. Start-up feedback voltage detection circuit; 5. Operating status indicator circuit; 6. RC snubber circuit. Detailed Implementation

[0035] The following is in conjunction with the appendix Figure 1 This application will be described in further detail.

[0036] A variable frequency power supply (VCC) is a power device that converts alternating current (AC) into medium-frequency AC power of a specific frequency and voltage, used to provide power to induction furnaces. During normal operation of the induction furnace, the VCC outputs a single-phase AC medium-frequency voltage of a specific frequency to excite the resonant load, causing it to oscillate. This oscillation process generates medium-frequency AC power as feedback. The VCC then outputs three-phase AC power to the rectifier circuit through the workshop's power grid.

[0037] This application discloses a contactor-assisted starting device for an induction furnace.

[0038] Reference Figure 1A contactor-assisted starting device for an induction furnace includes a rectifier circuit 1, a vacuum contactor control circuit 3, a switching freewheeling circuit 2, and a starting feedback voltage detection circuit 4. The input terminal of the rectifier circuit 1 is electrically connected to the voltage output terminal of the workshop power grid, and the two output terminals of the rectifier circuit 1 are defined as positive D and negative E, respectively. The switching freewheeling circuit 2 is electrically connected between the positive D and negative E. The vacuum contactor control circuit 3 is powered by the mains power. The vacuum contactor control circuit 3 is electrically connected to the switching freewheeling circuit 2. The starting feedback voltage detection circuit 4 is electrically connected to the vacuum contactor control circuit 3 and is signal-connected to the subsequent circuit.

[0039] During operation, the frequency converter gradually increases its output voltage from zero. When the resonant load receives a low excitation intermediate frequency voltage, it will not oscillate. The start-up feedback voltage detection circuit 4 will not receive the oscillation voltage of the resonant load, the vacuum contactor control circuit 3 will be turned on, and the rectifier circuit 1 will not be turned on. The energy of the frequency converter VCC output to excite the resonant load will not be consumed by the rectifier circuit 1, but will be entirely loaded onto the resonant load. At this time, the resonant load of the induction furnace can easily establish an oscillation circuit, and the induction furnace completes normal startup. After the induction furnace has started, the start-up feedback voltage detection circuit 4 obtains the oscillation voltage signal, the vacuum contactor control circuit 3 will not be turned on, and the rectifier circuit 1 will be turned on, providing protection for the operation of the workshop power grid.

[0040] The rectifier circuit 1 includes a silicon controlled rectifier group. One end of the silicon controlled rectifier group is electrically connected to the output end of the workshop power grid, and the other end of the silicon controlled rectifier group is simultaneously electrically connected to the positive terminal D and the negative terminal E.

[0041] The thyristor rectifier group includes thyristor SCR1, thyristor SCR2, thyristor SCR3, thyristor SCR4, thyristor SCR5, and thyristor SCR6; the anodes of thyristor SCR1, thyristor SCR3, and thyristor SCR5 are electrically connected to phases A, B, and C of the workshop power grid; the cathode of thyristor SCR1, ... The cathodes of SCR3 and SCR5 are electrically connected to the positive terminal D; the cathodes of SCR4, SCR6 and SCR2 are electrically connected to phases A, B and C of the workshop power grid, respectively; and the anodes of SCR4, SCR6 and SCR2 are electrically connected to the negative terminal E.

[0042] The switching freewheeling circuit 2 is electrically connected between the positive terminal D and the negative terminal E. The switching freewheeling circuit 2 includes a main contact K1 and a freewheeling diode D7. One end of the main contact K1 is electrically connected to the positive terminal of the freewheeling diode D7, and the other end of the main contact K1 is electrically connected to the negative terminal E. The negative terminal of the freewheeling diode D7 is electrically connected to the positive terminal D. The main contact K1 is electrically connected to the vacuum contactor control circuit 3.

[0043] An RC snubber circuit 6 is connected in parallel across the two ends of any silicon controlled rectifier (SCR1-SCR6) and the two ends of the freewheeling diode D7. The RC snubber circuit 6 includes a resistor R and a capacitor C connected in series. The end of the resistor R away from the capacitor C is electrically connected to the cathode of any silicon controlled rectifier, and the end of the capacitor C away from the resistor R is electrically connected to the anode of the same silicon controlled rectifier. The end of the resistor R away from the capacitor C is electrically connected to the cathode of the freewheeling diode D7, and the end of the capacitor C away from the resistor R is electrically connected to the anode of the freewheeling diode D7.

[0044] The vacuum contactor control circuit 3 includes a voltage relay switch K3, a vacuum contactor coil KM, and an auxiliary start knob K2. One end of the voltage relay switch K3 is electrically connected to one end of the auxiliary start knob K2, and the other end of the voltage relay switch K3 is electrically connected to one end of the vacuum contactor coil KM. The other end of the vacuum contactor coil KM is electrically connected to the neutral wire N1 of the workshop control power supply VCC1. The other end of the auxiliary start knob K2 is connected to the live wire L1 of the workshop control power supply VCC1. The vacuum contactor coil KM is electrically connected to the main contact K.

[0045] The start-up feedback voltage detection circuit 4 includes a voltage relay coil KU and an intermediate frequency transformer T. The primary side of the intermediate frequency transformer T is connected to the signal of the subsequent circuit, and the secondary side of the intermediate frequency transformer T is electrically connected to both ends of the voltage relay coil KU. The voltage relay coil KU is electrically connected to the voltage relay switch K3.

[0046] To indicate whether auxiliary start is engaged, this application also includes an operating status indicator circuit 5. The operating status indicator circuit 5 includes an auxiliary contact K4 and an auxiliary start indicator LED. One end of the auxiliary contact K4 is electrically connected to the live wire L2 of the mains power supply, and the other end of the auxiliary contact K4 is electrically connected to one end of the auxiliary start indicator LED. The other end of the auxiliary start indicator LED is electrically connected to the neutral wire N2 of the mains power supply. The auxiliary contact K4 and the main contact K1 operate synchronously. When the auxiliary start indicator LED is lit, the operating status indicator circuit 5 is in the ON state; when the auxiliary start indicator LED is off, the operating status indicator circuit 5 is in the OFF state.

[0047] The mechanical device that links the auxiliary contact K4 with the main contact of the vacuum contactor is a structure that can precisely transmit the action of the main contact K1 to the auxiliary contact K4, ensuring that the states of the two change synchronously. Commonly used mechanisms include linkage mechanisms and cam mechanisms; this application uses a cam mechanism. Specifically, a specially shaped cam is installed inside the vacuum contactor. When the main contact K1 actuates, it drives the cam to rotate. During rotation, the cam pushes or pulls the transmission components of the auxiliary contact K4, achieving synchronous action of the auxiliary contact K4.

[0048] During operation, in the induction furnace startup phase, the vacuum contactor control circuit 3 changes the main contact K1 from the normally closed state to the open state. At this time, the auxiliary contact K4 will also open. After the induction furnace has started up, the vacuum contactor control circuit 3 returns the main contact K1 to the normally closed state. At this time, the auxiliary contact K4 will also close, keeping in line with the action of the main contact K1. This controls the on / off state of the auxiliary startup indicator LED, thereby reflecting the working status of the circuit.

[0049] The implementation principle of this application embodiment is as follows: First, the voltage relay coil KU is set to be less than a certain voltage value, then the voltage relay switch K3 changes from a normally open point to a closed point. Pressing the auxiliary start knob K2, the voltage output from the frequency converter power supply VCC starts from zero voltage. The initial output excitation intermediate frequency voltage is low, the resonant load will not oscillate, and the intermediate frequency transformer T will not obtain the oscillation voltage of the resonant load. Since the voltage relay coil KU cannot obtain the operating voltage signal, that is, the voltage signal received by the voltage relay coil KU is lower than the set voltage value, the normally open point of the voltage relay switch K3 closes, the vacuum contactor coil KM is energized, the main contact K1 changes from a normally closed state to an open state, the freewheeling diode D7 branch is cut off, the switch freewheeling circuit does not work, and at this time, the auxiliary contact K4 also opens, and the auxiliary start indicator LED does not light up. Therefore, the energy of the frequency converter power supply VCC excitation resonant load starting is not consumed by the freewheeling diode D7, but is entirely loaded onto the resonant load. At this time, the induction furnace resonant load easily establishes an oscillation circuit, and the induction furnace completes normal startup.

[0050] After the induction furnace starts up, the intermediate frequency transformer T will receive a certain oscillation voltage signal. Subsequently, the voltage received by the voltage relay coil KU reaches the set voltage value, and the voltage relay switch K3 opens. At this time, the main contact K1 returns to its normally closed state, and the branch containing the freewheeling diode D7 is connected. The freewheeling diode D7 can protect the induction furnace in the event of a sudden malfunction and shutdown. At this time, the auxiliary contact K4 will also close, and the auxiliary start indicator LED will light up. After the induction furnace starts up, the auxiliary start knob K2 can be lifted. This circuit delays the conduction time of the freewheeling diode D7, allowing the resonant load to obtain sufficient excitation energy in the initial stage of oscillation establishment. After the oscillation stabilizes, the freewheeling diode D7 then takes effect, preventing it from conducting too early and affecting the establishment of the oscillation.

[0051] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A contactor-assisted starting device for an induction furnace, characterized in that, The application relates to a rectifier circuit (1) whose input is electrically connected to a plant power supply network, two outputs of the rectifier circuit (1) are defined as a positive electrode D and a negative electrode E respectively, a switch flywheel circuit (2) is electrically connected between the positive electrode D and the negative electrode E, a vacuum contactor control circuit (3) is powered by a plant control power supply VCC1, the vacuum contactor control circuit (3) is electrically connected to the switch flywheel circuit (2), a starting feedback voltage detection circuit (4) is electrically connected to the vacuum contactor control circuit (3) and connected to a signal of a later-stage circuit. The rectifier circuit (1) comprises a thyristor group which is powered by the plant power supply network, and two outputs of the thyristor group are electrically connected to the positive electrode D and the negative electrode E simultaneously. The thyristor group comprises thyristors SCR1, SCR2, SCR3, SCR4, SCR5 and SCR6, cathodes of the thyristors SCR4, SCR6 and SCR2 are electrically connected to A-phase, B-phase and C-phase of the plant power supply network respectively, anodes of the thyristors SCR4, SCR6 and SCR2 are electrically connected to the negative electrode E, anodes of the thyristors SCR1, SCR3 and SCR5 are electrically connected to A-phase, B-phase and C-phase of the plant power supply network respectively, cathodes of the thyristors SCR1, SCR3 and SCR5 are electrically connected to the positive electrode D, and the switch flywheel circuit (2) is electrically connected between the positive electrode D and the negative electrode E. The switch flywheel circuit (2) comprises a main contact K1 and a flywheel diode D7, one end of the main contact K1 is electrically connected to the positive electrode of the flywheel diode D7, the other end of the main contact K1 is electrically connected to the negative electrode E, the negative electrode of the flywheel diode D7 is electrically connected to the positive electrode D, and the main contact K1 is electrically connected to the vacuum contactor control circuit (3). The rectifier circuit (1) further comprises a plurality of RC absorption circuits (6), two ends of the thyristors SCR1, SCR2, SCR3, SCR4, SCR5 and SCR6 and two ends of the flywheel diode D7 are respectively connected in parallel to one RC absorption circuit (6).

2. A contactor-assisted starting arrangement for an induction furnace as defined in claim 1, characterized in that The RC absorption circuit (6) comprises a resistor R and a capacitor C connected in series.

3. A contactor-assisted starting arrangement for an induction furnace as defined in claim 2, characterized in that ​ 4. A contactor-assisted starting arrangement for an induction furnace as defined in claim 3, characterized in that ​ 5. A contactor-assisted starting arrangement for an induction furnace as defined in claim 4, characterized in that ​ 6. A contactor-assisted starting arrangement for an induction furnace as defined in claim 5, characterized in that ​ 7. The contactor-assisted starting apparatus for an induction furnace of claim 4, wherein, The vacuum contactor control circuit (3) comprises a voltage relay switch K3, a vacuum contactor coil KM and an auxiliary starting knob K2, one end of the voltage relay switch K3 is electrically connected to one end of the auxiliary starting knob K2, and the other end of the voltage relay switch K3 is electrically connected to one end of the vacuum contactor coil KM; the other end of the vacuum contactor coil KM is electrically connected to the zero line N1 of the plant control power supply VCC1; the other end of the auxiliary starting knob K2 is connected to the live line L1 of the plant control power supply VCC1, and the vacuum contactor coil KM is electrically connected to the main contact K.

8. A contactor-assisted starting arrangement for an induction furnace as defined in claim 7, characterized in that The starting feedback voltage detection circuit (4) comprises a voltage relay coil KU and a medium-frequency transformer T, the primary side of the medium-frequency transformer T is connected with a rear-stage circuit signal, the secondary side of the medium-frequency transformer T is electrically connected to both ends of the voltage relay coil KU, and the voltage relay coil KU is electrically connected to the voltage relay switch K3.

9. The contactor-assisted starting apparatus for an induction furnace of claim 1, wherein, Further comprising a running state indication circuit (5), the running state indication circuit (5) comprises an auxiliary starting indication lamp LED and an auxiliary contact K4, one end of the auxiliary contact K4 is electrically connected to the live line L2 of the commercial power supply, the other end of the auxiliary contact K4 is electrically connected to one end of the auxiliary starting indication lamp LED, the other end of the auxiliary starting indication lamp LED is electrically connected to the zero line N2 of the commercial power supply; the auxiliary contact K4 and the main contact K1 are synchronously operated.

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