Method and a device for compensation of the consumption of reactive power by an industrial load

• US 20030098672A1
• Filed: 01/02/2002
• Published: 05/29/2003
• Est. Priority Date: 11/28/2001
• Status: Active Grant

• Current Assignee: ABB Power Grids Switzerland AG (Hitachi, Ltd.)
• Original Assignee: ABB AB (ABB Limited)
• Inventors: Wernersson, Lennart
• Granted Patent: US 6,674,267 B2
• Time in Patent Office: Days
• US Class Current: 323/210
• CPC Class Codes: H02J 3/1821 using shunt compensators H02J3/1807, H02J3/1878 take precedence
• CPC Class Codes: H02J 3/1864 wherein the stepless control of reactive power is obtained by at least one reactive element connected in series with a semiconductor switch
• CPC Class Codes: Y02E 40/10 Flexible AC transmission systems [FACTS]
• CPC Class Codes: Y02E 40/30 Reactive power compensation

Abstract

An industrial load, preferably an electric arc furnace or a plant for rolling of metallic materials, is supplied from a three-phase electric ac network. A device for compensation of the reactive power consumption of the load comprises a first compensation device for controllable consumption of reactive power and a second compensation device for generation of reactive power, both connected to the electric power network in a parallel connection with the load. The first compensation device comprises a thyristor-controlled reactor for each of the phases of the ac network. Control equipment is supplied with measured values of sensed amplitude values for voltages and currents. The control equipment comprises means for forming a voltage mean value as the mean value of the sensed amplitude values of voltage, and means for forming, for each of the thyristor-controlled reactors, an amplitude deviation as a difference of the voltage mean value and the amplitude value associated with the thyristor-controlled reactor, and means for forming, for each of the thyristor-controlled reactors, a separate control order in dependence on the amplitude deviation for the respective thyristor-controlled reactor.

Claims

1. A method for compensation of the reactive power consumption of an industrial load, preferably an electric arc furnace or a plant for rolling of metallic materials, supplied from a three-phase electric ac network wherein a first compensation device for controllable consumption of reactive power and a second compensation device for generation of reactive power are both connected to the electric power network in a parallel connection with the load, the first compensation device comprising a thyristor-controlled reactor for each of the phases of the ac network, whereby the instantaneous consumption of reactive power by the load is determined, and a control order for phase-angle control of the thyristor-controlled reactors is formed in dependence thereon, wherein,

for each of the thyristor-controlled reactors, an amplitude value for a voltage is sensed, which voltage represents the voltage across said reactor,

a voltage mean value is formed as the mean value of said amplitude values,

for each of the thyristor-controlled reactors, an amplitude deviation is formed as a difference of the voltage mean value and the amplitude value associated with the thyristor-controlled reactor, and that

for each of the thyristor-controlled reactors, a separate control order is formed in dependence on the amplitude deviation for the respective thyristor-controlled reactor.

2. A method according to claim 1, wherein the thyristor-controlled reactors are mutually connected in a Δ

-connection.

3. A method according to any of claims 1-2, wherein the respective control order is formed in dependence also on the instantaneous consumption of active power by the load.

4. A method for compensation of the reactive power consumption of an industrial load, preferably an electric arc furnace or a plant for rolling of metallic materials, supplied from a three-phase electric ac network wherein a first compensation device for controllable consumption of reactive power and a second compensation device for generation of reactive power are both connected to the electric power network in a parallel connection with the load, the first compensation device comprising a thyristor-controlled reactor for each of the phases of the ac network, whereby total consumption of reactive power by the load and the second compensation device is determined, and a control order for phase-angle control of the thyristor-controlled reactors is formed in dependence thereon, wherein,

for each of the thyristor-controlled reactors, an amplitude value for a voltage is sensed, which voltage represents the voltage across said reactor,

a voltage mean value is formed as the mean value of said amplitude values,

for each of the thyristor-controlled reactors, an amplitude deviation is formed as a difference of the voltage mean value and the amplitude value associated with the thyristor-controlled reactor, and that

for each of the thyristor-controlled reactors, a separate control order is formed in dependence on the amplitude deviation for the respective thyristor-controlled reactor.

5. A method according to claim 4, wherein the thyristor-controlled reactors are mutually connected in a Δ

-connection.

6. A method according to any of claims 4-5, wherein the respective control order is formed in dependence also on the instantaneous consumption of active power by the load and the second compensation device.

7. A device for compensation of the reactive power consumption of an industrial load, preferably an electric arc furnace or a plant for rolling of metallic materials, supplied from a three-phase electric ac network, comprising a first compensation device for controllable consumption of reactive power and a second compensation device for generation of reactive power, both of said compensation devices being connected to the electric power network in a parallel connection with the load, the first compensation device comprising a thyristor-controlled reactor for each of the phases of the ac network, for each of the thyristor-controlled reactors voltage-measuring devices for sensing of amplitude values for a voltage which represents the voltage across the same, current-measuring devices for sensing of the respective current at the load, and control equipment which is supplied with measured values of the sensed amplitude values for voltages and currents, the control equipment comprising means for determining the instantaneous consumption of reactive power by the load, and a control device which, in dependence thereon, forms a control order for the thyristor-controlled reactors and supplies the control order thereto, wherein the control equipment comprises

means for forming a voltage mean value as the mean value of said amplitude values for voltage,

means for forming, for each of the thyristor-controlled reactors, an amplitude deviation as a difference of the voltage mean value and the amplitude value associated with the thyristor-controlled reactor, and

means for forming, for each of the thyristor-controlled reactors, a separate control order in dependence on the amplitude deviation for the respective thyristor-controlled reactor.

8. A device according to claim 7, wherein the thyristor-controlled reactors are mutually connected in a Δ

-connection.

9. A device according to any of claims 7-8, wherein the control equipment comprises means for determining the instantaneous consumption of active power by the load, and means for forming the respective control order in dependence thereon.

10. A device for compensation of the reactive power consumption of an industrial load, preferably an electric arc furnace or a plant for rolling of metallic materials, supplied from a three-phase electric ac network, comprising a first compensation device for controllable consumption of reactive power and a second compensation device for generation of reactive power, both of said compensation devices being connected to the electric power network in a parallel connection with the load, the first compensation device comprising a thyristor-controlled reactor for each of the phases of the ac network, for each of the thyristor-controlled reactors voltage-measuring devices for sensing of amplitude values for a voltage which represents the voltage across the same, current-measuring devices for sensing currents flowing to the parallel connection that is constituted by the load and the second compensation device, and control equipment which is supplied with measured values of the sensed amplitude values for voltages and currents, and that the control equipment comprises means for determining the total consumption of reactive power by the load and the second compensation device, and a control device which, in dependence thereon, forms a control order for the thyristor-controlled reactors and supplies the control order thereto, wherein the control equipment comprises

means for forming a voltage mean value as the mean value of said amplitude values for voltage,

means for forming, for each of the thyristor-controlled reactors, an amplitude deviation as a difference of the voltage mean value and the amplitude value associated with the thyristor-controlled reactor, and

means for forming, for each of the thyristor-controlled reactors, a separate control order in dependence on the amplitude deviation for the respective thyristor-controlled reactor.

11. A device according to claim 10, wherein the thyristor-controlled reactors are mutually connected in a Δ

-connection.

12. A device according to any of claims 10-11, wherein the control equipment comprises means for determining the instantaneous consumption of active power by the load and the second compensation device, and means for forming the respective control order in dependence thereon.