# US 11,122,654 B2 · Flicker control for electric arc furnace

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- Number: US 11,122,654 B2
- Document ID: US11122654B2
- Status: Granted
- Kind: B2
- Application number: 15/579,796
- Filed: 2016-05-26
- Published: 2018-08-23
- Granted: 2021-09-14
- Earliest claimed: 2015-06-05
- Assignees: Hatch Ltd.
- Applicants: Hatch Ltd.
- Inventors: Dong Shen; Michael Morgan Campbell; Jason Cheung; James Wikston
- Web page: https://patentgrep.com/patent/US11122654B2

## CPC

- H05B 7/148: Automatic control of power (electrode feeding arrangements H05B7/109; automatic feeding of electrodes for spot or seam welding or cutting B23K9/12; disposition of electrodes in or on furnaces F27D11/10; control of position in general G05D3/00; regulating electric characteristics of arcs in general G05F1/02; regulating electric power in general G05F1/66)
- F27B 3/085: {Arc furnaces}
- F27B 3/28: Arrangement of controlling, monitoring, alarm or the like devices
- F27D 11/08: Heating by electric discharge, e.g. arc discharge
- F27D 19/00: Arrangements of controlling devices
- F27D 21/00: Arrangement of monitoring devices; Arrangement of safety devices
- H02J 3/1864: using reactive elements connected in series with semiconductor switches, e.g. static VAR compensators [SVC], thyristor-controlled reactors [TCR] or thyristor-switched capacitors [TSC]
- Y02P 10/25: Process efficiency
- H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- F27B: FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
- F27D: DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
- H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

It is proposed herein to employ thyristor firing angles as a fast prediction of flicker in power supply for an electric arc furnace. It is further proposed to actively modify operating variables for the electric arc furnace to maintain the flicker below a predefined threshold. Aspects of the present application use the thyristor firing angles in combination with control ranges of variable reactance devices to predict the flicker severity level generated by the electric arc furnace with thyristor-controlled variable reactance devices. Based on the predicted flicker level, at least one operating variable of the electric arc furnace may be changed, if required, to maintain flicker to acceptable limit.

## Claims

### Claim 1

A method of operating an electric arc furnace, the method comprising:
receiving indications of a plurality of operating variables of the electric arc furnace, wherein the operating variables include a flicker of a power grid supplying the electric arc furnace;
receiving indications of firing angles of a plurality of thyristor switches in a variable reactance device controlled by the plurality of thyristor switches, the variable reactance device having a control range;
predicting a power grid flicker based upon:
the received indications of the plurality of operating variables;
the received indications of the firing angles of the plurality of thyristor switches; and
the control range of the variable reactance device;
determining that the predicted power grid flicker is a power grid flicker excursion, wherein the predicted power grid flicker exceeds a predefined threshold, based on:
determining that at least one of the received indications of the firing angles of the plurality of thyristor switches is at one of: at or above a firing angle upper excursion likelihood threshold, or at or below a firing angle lower excursion likelihood threshold;
determining, upon receiving an indication of the predicted power grid flicker excursion, an adjustment to at least one operating variable among the plurality of operating variables; and
transmitting, to a controller of the at least one operating variable, instructions to adjust the at least one operating variable such that the predicted power grid flicker remains below the predefined threshold, with effect that the predicted power grid flicker excursion is avoided.

### Claim 2 (depends on 1)

The method of claim 1 wherein the plurality of operating variables comprises a plurality of operating electrical variables.

### Claim 3 (depends on 2)

The method of claim 2 wherein the plurality of operating electrical variables comprises signals that are representative of supply currents drawn by each phase of the electric arc furnace.

### Claim 4 (depends on 2)

The method of claim 2 wherein the plurality of operating electrical variables comprises signals that are representative of supply voltage at each phase of the electric arc furnace.

### Claim 5 (depends on 2)

The method of claim 2 wherein the plurality of operating electrical variables comprises signals that are representative of an electrode current drawn by each phase of the electric arc furnace.

### Claim 6 (depends on 2)

The method of claim 2 wherein the plurality of operating electrical variables comprises signals that are representative of per phase electrode voltages of the electric arc furnace.

### Claim 7 (depends on 1)

The method of claim 1 wherein the plurality of operating variables comprises a plurality of operating chemical variables.

### Claim 8 (depends on 7)

The method of claim 7 wherein the plurality of operating chemical variables comprises a burner power.

### Claim 9 (depends on 7)

The method of claim 7 wherein the plurality of operating chemical variables comprises an Oxygen flow rate.

### Claim 10 (depends on 7)

The method of claim 7 wherein the plurality of operating chemical variables comprises a Natural Gas flow rate.

### Claim 11 (depends on 7)

The method of claim 7 wherein the plurality of operating chemical variables comprises a Carbon injection flow rate.

### Claim 12 (depends on 7)

The method of claim 7 wherein the plurality of operating chemical variables comprises a Lime injection flow rate.

### Claim 13 (depends on 1)

The method of claim 1 wherein the variable reactance device comprises a static VAR compensator.

### Claim 14 (depends on 13)

The method of claim 13 wherein the static VAR compensator comprises a variable reactor.

### Claim 15 (depends on 14)

The method of claim 14 wherein the variable reactor comprises a series-connected pair of fixed inductors and the plurality of thyristor switches connected between the fixed inductors.

### Claim 16 (depends on 15)

The method of claim 15 wherein the controller comprises a reactive power stabilizer and the instructions comprise instructions to adjust firing angles for the plurality of thyristor switches.

### Claim 17 (depends on 1)

The method of claim 1 wherein the variable reactance device comprises a variable series reactor.

### Claim 18 (depends on 17)

The method of claim 17 wherein the variable series reactor comprises a variable reactor in series with a fixed reactor.

### Claim 19 (depends on 18)

The method of claim 18 wherein the variable reactor comprises a first inductor connected in parallel with a series combination of a second inductor and the plurality of thyristor switches.

### Claim 20 (depends on 19)

The method of claim 19 wherein the controller comprises a current stabilizer and the instructions comprise instructions to adjust firing angles for the plurality of thyristor switches.

### Claim 21 (depends on 1)

The method of claim 1 wherein the controller comprises a tap controller for a furnace transformer and the instructions comprise instructions to adjust the tap position of the furnace transformer.

### Claim 22 (depends on 1)

The method of claim 1 wherein the controller comprises an electrode controller and the instructions comprise instructions to adjust a position of electrodes in the electric arc furnace.

### Claim 23 (depends on 22)

The method of claim 22 wherein the instructions to adjust a position of electrodes in the electric arc furnace include an indication of a speed at which to adjust the position.