System and method for controlling power across multiple electrodes in a furnace

Abstract

A method and system for stabilizing energy consumption in multiple loads, or in single multi-phase loads. The method and system also compensates for unbalance in multi-phase loads. A central controller monitors variable reactances in the loads and identifies situations of power and/or current fluctuation and/or unbalance. It determines appropriate corrective action by the other loads/phases to compensate for the power and/or current change or unbalance due to the problematic load, and it issues control signals instructing variable reactor controllers associated with the other loads to adjust accordingly. The method and system may by applied to electric arc furnace installations. An electrode position controller may be used in place of, or in conjunction with, the variable reactance control system to take corrective action to address power and/or current changes or unbalances. The system and method may be employed to maintain a predetermined level of unbalance in the system.

1 . A method of controlling a multi-phase electric furnace, each phase being coupled to a multi-phase power supply through an associated variable reactor and having a set-point, the method comprising the steps of: 
 monitoring an operating characteristic and a value of the variable reactor for each phase;    determining whether the operating characteristic of at least one of the phases deviates from the respective set-point; and    adjusting the values of the variable reactors when it is determined that the operating characteristic of the at least one of the phases deviates from the respective set-point, based on the operating characteristics of all phases.    
   
   
       2 . The method of  claim 1 , wherein the set-point comprises a power set-point and wherein the operating characteristic comprises power consumption.  
   
   
       3 . The method of  claim 2 , wherein the step of determining includes calculating a difference between the power set-point for the at least one phase and the power consumption for the at least one phase, and includes selecting adjusted values based upon the difference.  
   
   
       4 . The method of  claim 1 , wherein the set-point comprises a current set-point and wherein the operating characteristic comprises current draw.  
   
   
       5 . The method of  claim 1 , wherein at least one of the set-points for one of the phases differs from another of the set-points for another of the phases.  
   
   
       6 . The method of  claim 1 , wherein the operating characteristic is an impedance characteristic.  
   
   
       7 . The method of  claim 1 , wherein the multi-phase electric furnace is a three-phase electric arc furnace.  
   
   
       8 . The method of  claim 2 , further comprising: determining that one of the phases has experienced a decrease in power consumption for which adjustment of the variable reactor associated with that phase cannot fully compensate; and adjusting the power consumption of the respective other phases to achieve a total power across all phases that is closer to a total power set-point than would be achievable without adjustment of the power consumption of the other phases.  
   
   
       9 . The method of  claim 8 , wherein the adjusting power consumption comprises at least one of: adjusting the variable reactors of the respective other phases; and adjusting an electrode position of at least one electrode coupled to the respective other phases.  
   
   
       10 . The method of  claim 1 , wherein the adjusting is performed to substantially maintain an overall set-point of the electric furnace.  
   
   
       11 . The method of  claim 10 , wherein the overall set-point comprises at least one of: a current set-point; and a power set-point.  
   
   
       12 . The method of  claim 10 , whereby productivity loss due to partial or total loss of power to the electric furnace is mitigated by maintenance of the overall set-point.  
   
   
       13 . The method of  claim 1 , wherein the multi-phase electric furnace comprises one electrode coupled to each phase.  
   
   
       14 . The method of  claim 1 , wherein the multi-phase electric furnace comprises a pair of electrodes coupled to each phase.  
   
   
       15 . The method of  claim 14 , wherein the multi-phase power supply is a three-phase power supply and the multi-phase electric furnace comprises six electrodes coupled as electrode pairs to each of the three phases.  
   
   
       16 . A control system for controlling unbalance of a multi-phase electric furnace, each phase being coupled to a power supply, the control system comprising: 
 a variable reactor associated with each of the phases, each variable reactor being coupled between its associated load and the power supply; and    a controller coupled to each variable reactor, the controller including an unbalance determination component for monitoring an operating characteristic of each phase and for determining an unbalance value for the multi-phase electric furnace, and a reactance adjustment component responsive to the unbalance determination component for controlling the variable reactors based upon the operating characteristics on all phases to maintain a predetermined degree of unbalance.    
   
   
       17 . The control system of  claim 16 , wherein the operating characteristic includes impedance, power draw or current draw.  
   
   
       18 . The control system of  claim 16 , wherein the multi-phase electric furnace is a three-phase electric arc furnace.  
   
   
       19 . The control system of  claim 16 , wherein a transformer is provided on each phase intermediate the power supply and a load supplied by that phase, and wherein the variable reactor of each phase is positioned intermediate the transformer and the power supply.  
   
   
       20 . The control system of  claim 16 , wherein a transformer is provided on each phase intermediate the power supply and a load supplied by that phase, and wherein the variable reactor of each phase is positioned intermediate the transformer and the load.  
   
   
       21 . The control system of  claim 16 , wherein the multi-phase electric furnace comprises one electrode coupled to each phase.  
   
   
       22 . The control system of  claim 16 , wherein the multi-phase electric furnace comprises a pair of electrodes coupled to each phase.  
   
   
       23 . The control system of  claim 22 , wherein the multi-phase power supply is a three-phase power supply and the multi-phase electric furnace comprises six electrodes coupled as electrode pairs to each of the three phases.  
   
   
       24 . The control system of  claim 16 , wherein the controller is a central controller and further comprising a reactor controller associated with each phase and responsive to the central controller to control each variable reactor.  
   
   
       25 . The control system of  claim 24 , further comprising an electrode position controller associated with each phase for controlling an electrode position of an electrode coupled to each phase.  
   
   
       26 . The control system of  claim 25 , wherein the central controller is configured: to determine that one of the phases has experienced a decrease in power consumption for which adjustment of the variable reactor associated with that phase cannot fully compensate; and to adjust the power consumption of the respective other phases to achieve a total power across all phases that is closer to a total power set-point than would be achievable without adjustment of the power consumption of the other phases.  
   
   
       27 . The control system of  claim 26 , wherein the central controller is configured to adjust power consumption by at least one of: adjusting the variable reactors of the respective other phases; and adjusting an electrode position of at least one electrode coupled to the respective other phases.  
   
   
       28 . The control system of  claim 16 , wherein each variable reactor comprises a power switch.  
   
   
       29 . The control system of  claim 28 , wherein the power switch comprises thyristors.  
   
   
       30 . The control system of  claim 28 , wherein the variable reactor comprises at least one of: an inductor in parallel with the power switch; and an inductor in series with the power switch.  
   
   
       31 . A method of controlling a multi-phase electric furnace, each phase being coupled to a power supply through an associated variable reactor, the method comprising the steps of: 
 monitoring an operating characteristic of each phase;    determining an unbalance value for the multi-phase electric furnace load; and    controlling the variable reactors based on the unbalance value and the operating characteristics on all phases to maintain a predetermined degree of unbalance.    
   
   
       32 . The method of  claim 31 , wherein the operating characteristic includes impedance, power draw or current draw.  
   
   
       33 . The method of  claim 31 , wherein the multi-phase electric furnace is a three-phase electric arc furnace.  
   
   
       34 . The method of  claim 31 , further comprising: determining that one of the phases has experienced a decrease in power consumption for which adjustment of the variable reactor associated with that phase cannot fully compensate; and adjusting the power consumption of the respective other phases to achieve a total power across all phases that is closer to a total power set-point than would be achievable without adjustment of the power consumption of the other phases.  
   
   
       35 . The method of  claim 34 , wherein the adjusting power consumption comprises at least one of: adjusting the variable reactors of the respective other phases; and adjusting an electrode position of at least one electrode coupled to the respective other phases.  
   
   
       36 . The method of  claim 31 , wherein the controlling is further performed to substantially maintain an overall set-point of the electric furnace.  
   
   
       37 . The method of  claim 36 , wherein the overall set-point comprises at least one of: a current set-point; and a power set-point.  
   
   
       38 . The method of  claim 36 , whereby productivity loss due to partial or total loss of power to the electric furnace is mitigated by maintenance of the overall set-point.  
   
   
       39 . The method of  claim 31 , wherein the multi-phase electric furnace comprises one electrode coupled to each phase.  
   
   
       40 . The method of  claim 31 , wherein the multi-phase electric furnace comprises a pair of electrodes coupled to each phase.  
   
   
       41 . The method of  claim 40 , wherein the multi-phase power supply is a three-phase power supply and the multi-phase electric furnace comprises six electrodes coupled as electrode pairs to each of the three phases.  
   
   
       42 . A control system for controlling a multi-phase electric furnace, each phase being coupled to a power supply, the control system comprising: 
 a variable reactor associated with each of the phases, each variable reactor being coupled between an associated load and the power supply; and    control means coupled to each variable reactor, the control means including a monitoring component for monitoring an operating characteristic of each phase, and a reactance adjustment component responsive to the monitoring component for controlling the variable reactors based upon the operating characteristics on all phases to maintain a predetermined set-point on each phase.    
   
   
       43 . The control system of  claim 42 , wherein the set-point comprises a power set-point.  
   
   
       44 . The control system of  claim 42 , wherein the set-point comprises a current set-point.  
   
   
       45 . The control system of  claim 42 , wherein the operating characteristic is an impedance characteristic, a power draw or a current draw.  
   
   
       46 . The control system of  claim 42 , wherein at least one of the set-points for one of the phases differs from another of the set-points for another of the phases.  
   
   
       47 . The control system of  claim 42 , wherein the multi-phase electric furnace is a three-phase electric arc furnace.  
   
   
       48 . The control system of  claim 42 , wherein a transformer is provided on each phase intermediate the power supply and a load supplied by that phase, and wherein the variable reactor of each phase is positioned intermediate the transformer and the power supply.  
   
   
       49 . The control system of  claim 42 , wherein a transformer is provided on each phase intermediate the power supply and a load supplied by that phase, and wherein the variable reactor of each phase is positioned intermediate the transformer and the load.  
   
   
       50 . The control system of  claim 42 , wherein the multi-phase electric furnace comprises one electrode coupled to each phase.  
   
   
       51 . The control system of  claim 42 , wherein the multi-phase electric furnace comprises a pair of electrodes coupled to each phase.  
   
   
       52 . The control system of  claim 51 , wherein the multi-phase power supply is a three-phase power supply and the multi-phase electric furnace comprises six electrodes coupled as electrode pairs to each of the three phases.  
   
   
       53 . The control system of  claim 42 , wherein the control means comprises a central controller and further comprises a reactor controller associated with each phase and responsive to the central controller to control each variable reactor.  
   
   
       54 . The control system of  claim 53 , further comprising an electrode position controller associated with each phase for controlling an electrode position of an electrode coupled to each phase.  
   
   
       55 . The control system of  claim 54 , wherein the central controller is configured: to determine that one of the phases has experienced a decrease in power consumption for which adjustment of the variable reactor associated with that phase cannot fully compensate; and to adjust the power consumption of the respective other phases to achieve a total power across all phases that is closer to a total power set-point than would be achievable without adjustment of the power consumption of the other phases.  
   
   
       56 . The control system of  claim 55 , wherein the central controller is configured to adjust power consumption by at least one of: adjusting the variable reactors of the respective other phases; and adjusting an electrode position of at least one electrode coupled to the respective other phases.  
   
   
       57 . The control system of  claim 42 , wherein each variable reactor comprises a power switch.  
   
   
       58 . The control system of  claim 57 , wherein the power switch comprises thyristors.  
   
   
       59 . The control system of  claim 57 , wherein the variable reactor comprises at least one of: an inductor in parallel with the power switch; and an inductor in series with the power switch.  
   
   
       60 . A method of controlling a multi-phase electric furnace, each phase being coupled to a power supply through an associated variable reactor, the method comprising the steps of: 
 monitoring an operating characteristic of each phase; and    controlling the variable reactors based on the operating characteristics on all phases to maintain a set-point on each phase.    
   
   
       61 . The method of  claim 60 , wherein the operating characteristic is an impedance characteristic, a power draw or a current draw.  
   
   
       62 . The method of  claim 60 , wherein the set-point includes power draw or current draw.  
   
   
       63 . The method of  claim 60 , wherein the multi-phase electric furnace is a three-phase electric arc furnace.  
   
   
       64 . The method of  claim 60 , further comprising: determining that one of the phases has experienced a decrease in power consumption for which adjustment of the variable reactor associated with that phase cannot fully compensate; and adjusting the power consumption of the respective other phases to achieve a total power across all phases that is closer to a total power set-point than would be achievable without adjustment of the power consumption of the other phases.  
   
   
       65 . The method of  claim 64 , wherein the adjusting power consumption comprises at least one of: adjusting the variable reactors of the respective other phases; and adjusting an electrode position of at least one electrode coupled to the respective other phases.  
   
   
       66 . The method of  claim 60 , wherein the controlling is further performed to substantially maintain an overall set-point of the electric furnace.  
   
   
       67 . The method of  claim 66 , wherein the overall set-point comprises at least one of: a current set-point; and a power set-point.  
   
   
       68 . The method of  claim 66 , whereby productivity loss due to partial or total loss of power to the electric furnace is mitigated by maintenance of the overall set-point.  
   
   
       69 . The method of  claim 60 , wherein the multi-phase electric furnace comprises one electrode coupled to each phase.  
   
   
       70 . The method of  claim 60 , wherein the multi-phase electric furnace comprises a pair of electrodes coupled to each phase.  
   
   
       71 . The method of  claim 70 , wherein the multi-phase power supply is a three-phase power supply and the multi-phase electric furnace comprises six electrodes coupled as electrode pairs to each of the three phases.