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

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, wherein the step of adjusting includes accessing a lookup table storing reactance values and reading the reactance values from the lookup table based on the operating characteristics of all phases.

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;
• wherein the step of monitoring includes measuring phase current and wherein the step of determining includes calculating a negative sequence current value based upon the phase current, and wherein the unbalance value comprises the negative sequence current value.

A control system for controlling unbalance in one or more three-phase loads, the three-phase loads being coupled to a three-phase power supply, the control system comprising:

• a variable reactor associated with each phase, each variable reactor being coupled between the three-phase load and an associated phase of the power supply;
• a variable reactance control system associated with each variable reactor for monitoring an operating characteristic of its associated phase and for setting a value of the respective variable reactor in response to the operating characteristic so as to maintain a set-point;
• and
• a central control system coupled to each variable reactance control system, wherein the central control system includes:
• a detection component for determining an unbalance value for the three-phase load and for determining whether the value of the variable reactor has reached a threshold value, and
• an override component responsive to the detection component for outputting a control signal to the variable reactance control systems,
• wherein the variable reactance control systems each include an interface for receiving the control signal, in response to which the variable reactance control systems adjust the variable reactors.

A method for controlling unbalance in one or more three-phase loads, each three-phase load being coupled to a three-phase power supply, each phase being coupled to the three-phase load through an associated variable reactor, each associated variable reactor being coupled to a corresponding variable reactance control system for monitoring an operating characteristic of the phase and for setting a value of the variable reactor in response to the operating characteristic so as to maintain a set-point, and wherein a central control system is coupled to the variable reactance control systems, the method comprising the steps of:

• at the central control system, calculating an unbalance value for the three-phase load;
• determining whether the unbalance value exceeds a predetermined threshold;
• outputting a control signal from the central control system to the variable reactance control systems if the unbalance value exceeds the threshold;
• and
• on at least one of the phases, adjusting the associated variable reactor in response to the control signal to reduce the unbalance value below the threshold.

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,
• 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.