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RU-2804344-C2 - POWER SOURCE FOR ARC FURNACE WITH RESONANCE CIRCUIT

RU2804344C2RU 2804344 C2RU2804344 C2RU 2804344C2RU-2804344-C2

Abstract

FIELD: electrical engineering. SUBSTANCE: invention is related in particular to a power supply system for an electric arc furnace, a method and a controller for controlling the power supply system. The power supply system (12) for the electric arc furnace (10) contains an AC input (20) connected to the electrical network (22), and an AC output (24) for powering at least one current electrode (14) of the arc furnace (10); a resonant circuit (46a, 46b, 46c) connected between the AC input (20) and the AC output (24). The resonant circuit (46a, 46b, 46c) includes a controllable bypass switch (60) for connecting and disconnecting a circuit input (56) and a circuit output (58) in the resonant circuit (46a, 46b, 46c) and a capacitor (64) and a main induction coil (66) connected in parallel with the bypass switch (60). EFFECT: increased efficiency of the arc furnace power source 15 cl, 6 dwg

Inventors

  • STEIMER, Peter Karl

Dates

Publication Date
20230928
Application Date
20200508
Priority Date
20190627

Claims (20)

  1. 1. Power supply system (12) for an electric arc furnace (10), wherein the power supply system (12) contains:
  2. AC input (20), connected to the electrical network (22), and AC output (24) for powering at least one current electrode (14) of the arc furnace (10);
  3. a resonant circuit (46a, 46b, 46c) connected between the AC input (20) and the AC output (24);
  4. wherein the resonant circuit (46a, 46b, 46c) comprises a controlled bypass switch (60) for connecting and disconnecting the circuit input (56) and the circuit output (58) in the resonant circuit (46a, 46b, 46c);
  5. wherein the resonant circuit (46a, 46b, 46c) comprises a capacitor (64) and a main induction coil (66) connected in parallel with the bypass switch (60);
  6. wherein the power supply system (12) includes a controller (54) for controlling the bypass switch (60) such that a ring current is generated in the resonant circuit (46a, 46b, 46c) when the bypass switch (60) is closed, which reduces the current through the system ( 12) power supply.
  7. 2. Power supply system (12) according to claim 1,
  8. wherein an additional induction coil (62) is connected in series with a bypass switch (60) between the circuit input (56) and the circuit output (58).
  9. 3. Power supply system (12) according to claim 2,
  10. wherein the additional induction coil (62) is connected in parallel with the capacitor (64) and the main induction coil (66); and/or
  11. wherein the capacitor (64) and the main induction coil (66) are connected in series.
  12. 4. Power supply system (12) according to paragraph 2 or 3,
  13. wherein the main induction coil (66) has a higher inductance compared to the additional induction coil (62).
  14. 5. Power supply system (12) according to one of the previous paragraphs,
  15. wherein the bypass switch (60) consists of semiconductor switches (68); and/or
  16. wherein the bypass switch (60) is a two-way switch.
  17. 6. Power supply system (12) according to one of the previous paragraphs,
  18. wherein the bypass switch (60) contains two back-to-back semiconductor switches (68); and/or
  19. wherein the bypass switch (60) contains two back-to-back thyristors (68).
  20. 7. Power supply system (12) according to one of the previous paragraphs, additionally containing:

Description

Field of technology to which the invention relates The invention relates to the field of arc furnaces. In particular, the invention relates to a power supply system for an electric arc furnace, a method and a controller for controlling the power supply system, as well as an arc furnace with such a power supply system. State of the art Electric arc furnaces are often directly connected to alternating current (AC) power via a transformer. It may then be difficult to limit electrode current during operation, which may limit electrode use and productivity. Additionally, the transformer may then require an expensive on-load tap changer system, which is frequently used, and the arc furnace may generate ripple on the AC line. Therefore, an additional static adjustable compensator may be necessary to mitigate pulsation problems. EP 0 589 544 B1 and US 6 603 795 B2 show an arc furnace power supply which is adapted to limit electrode current using series-connected back-to-back thyristors with or without a parallel induction coil. In this way, the performance of the arc furnace can be improved. However, by limiting the current, the internal resistance of the electric arc furnace may be increased more than necessary, which may reduce the efficiency of the electric arc furnace. US 6 274 851 B1 shows a power supply for an arc furnace that contains a semiconductor switch in each of the phases. A damper circuit with a capacitor and an inductor is connected in parallel with the switch. EP 0 429 774 A1 shows an arc furnace power supply with a two-way semiconductor switch connected in parallel to an induction coil which is connected to the power supply phase. US 2012/314728 A1 shows an arc furnace power supply with two-way semiconductor switches connected in series with an induction coil which is connected to a phase of the power supply. WO 2016/191861 A1 describes a control system for an arc furnace power supply that is adapted to regulate pulsation. Shown is a two-way solid state switch that is connected in series and parallel with induction coils connected to the power supply phase. Description of the invention The object of the invention is to provide an arc furnace power source with adjustable electrode current and high efficiency. This problem is solved by means of the subject matter of the invention from the independent claims. Additional exemplary embodiments will be apparent from the dependent claims and the following description. The first aspect of the invention relates to a power supply system for an electric arc furnace. An electric arc furnace can be a device that is adapted to melt or remelt metallic materials using an electric arc that is created through an electric current. The electric current is generated by a power supply system that can be connected between the average AC power supply and the electrodes of the arc furnace. The power supply system may also include a transformer that converts the medium AC input voltage into a low AC output voltage that is supplied to the electrodes. Medium voltage can be a voltage between 1 kV and 20 kV. Low voltage can be voltage below 1 kV. It should be noted that the current through the electrodes can be higher than 1000 A. The power supply system may be a multiphase system, having several, for example three, phases. The input voltage may be a three-phase voltage, for example, with a frequency of 50 or 60 Hz. According to an embodiment of the invention, the power supply system includes an AC input, which may include one or more phases connected to the electrical network, and an AC output, which may include one or more phases for powering at least one electrode of the arc furnace. The AC input can contain three phases. Also, the AC output can contain three phases. According to an embodiment of the invention, the power supply system includes a resonant circuit connecting an AC input and an AC output, wherein the resonant circuit includes a controllable bypass switch for connecting and disconnecting an input of the circuit and an output of the circuit in the resonant circuit. The resonant circuit may include a capacitor and a main induction coil connected in parallel with a bypass switch. The capacitor and the main induction coil may be connected in series and/or may be connected between a circuit input and a circuit output. The resonant circuit may be connected to the AC input phase and/or to the AC output phase. According to an embodiment of the invention, the power supply system includes a controller for controlling the bypass switch such that a ring current is generated in the resonant circuit when the bypass switch is closed, which reduces the current through the power supply system. By controlling the bypass switch, the current through the resonant circuit can be adjusted; when the bypass switch is open, the current through the resonant circuit can only flow from the input of the circuit through the capacitor and main induction coil to the output of the circuit and v