Cl aims

1. A method for measuring the electric quantities of an AC electric-arc furnace, especially for measuring electrode-related active powers, c h a r a c t e r i z e d in that at adjacent time instants there are performed a plurality of successive current and voltage measurements at various energy distributions of a furnace and the measurement results are used to determine at the desired frequencies such estimates for electrode-related quantities, such as impedances, voltages or powers, which consistently explain the electrode currents of a furnace in relation to the total power, or its components, supplied to the furnace.

2 . A method as set f orth in cl aim 1 , c h a r a c t e r i z e d by

- measuring the electrode currents directly, or

alternatively the transformer secondary currents either in primary, intermediate or secondary and reducing them to electrode currents;

- measuring the furnace transformer voltages either in primary, intermediate or secondary and, if necessary, performing also a current measurement in such a location that the total power supplied into a furnace is

calculable;

- calculating on the basis of current and voltage

measurements the power supplied into a furnace or one component of such power, possibly taking into account dissipations in the furnace transformer and secondary wiring;

- making a plurality of successive measurements, in which the measured currents and power fluctuate;

- recording the results obtained from a plurality of successive measurements as various equations, wherein one side of the equation includes a power or a power component calculated on the basis of current and voltage measurements and the other side includes a sum of electrode-related measurement results and impedances or electrode-related powers or power components calculated thereby; and

- processing said various equations as a group of

equations or a matrix equation, from which are solved electrode-related impedances or their components, used for determining the active power supplied through each electrode.

3 . A method as set forth in claim 1 , c h a r a c t e r i z e d by

- measuring the electrode currents directly or

alternatively the transformer secondary currents either in primary, intermediate or secondary and reducing them to electrode currents;

- measuring the furnace transformer voltages either in primary, intermediate or secondary and, if necessary, also performing the current measurement from such a location that the total power supplied into a furnace is calculable;

- using the results of current and voltage measurements to calculate the power or one of its components supplied into a furnace, possibly taking into account the

dissipations in a furnace transformer and secondary wiring;

- performing a plurality of successive measurements, in which said currents and power fluctuate; and

- using an estimating method or an adaptive model which consistently explains the variation of the total furnace power or that of its components in relation to the variation of electrode currents and which is thus used for determining the electrode-related impedances or their components, the active power supplied through each electrode being determined thereby.

4. A method as set forth in any of claims 1...3, c h a r a c t e r i z e d in that the electrode-related powers supplied into a furnace are in a per se known manner divided in power components dissipated on the one hand in a conduction phenomenon and on the other hand in an electric arc.

5. A method as set forth in any of claims 1...4, c h a r a c t e r i z e d in that the estimates for electroderelated quantities can be calculated or modeled as r.m.s. or power values which include all frequencies, or at each frequency separately or as a combination of desired frequencies.

6. A method as set forth in any of claims 1...5, c h a r a c t e r i z e d in that the estimates for electroderelated reactive powers can be calculated or modeled as reactive and distortion powers.

7. A method as set forth in any of claims 1...6, c h a r a c t e r i z e d in that the estimates for electroderelated quantities are calculated from a plurality of successive results obtained as solutions to groups of equations or matrix equations or provided by an estimation method or an adaptive model by using non-linear filtering or hybrid median filtering or standard median filtering.

8. A method as set forth in any of claims 1...6, c h a r a c t e r i z e d in that the estimates for electroderelated quantities are calculated from a plurality of successive results obtained as solutions to groups of equations or matrix equations or provided by an estimation method or an adaptive model by using the selection of measurement data (i.e., the input data for estimation or modeling) and linear or non-linear filtering or hybrid median filtering or standard median filtering.

9. A method as set forth in any of claims 1...8, c h a r a c t e r i z e d in that the furnace electrodes are coupled to a polyphase power supply and the neutral power connection is coupled to a furnace shell or to serve as an electrode as such or is totally uncoupled and that the virtual star-point voltages or their components are calculated at various instants either as r.m.s. values or separately at desired frequencies.

10. A method as set forth in any of claims 1...9,

c h a r a c t e r i z e d in that the results of said current and voltage measurements are used for calculating the active and reactive power supplied through all phases of a furnace at successive instants, i.e., separately at each phase angle of a system voltage cycle.