IEC 60676 pdf download – Industrial electroheating equipment — Test methods for direct arc furnaces

IEC 60676 pdf download – Industrial electroheating equipment — Test methods for direct arc furnaces
5.3 Measurement of the speed of electrode motion
The measurement is made with manual control of the moving system of the electrodes in two directions. NOTE The measurement may be made by another method, for example, using electric signal control. The measurement of the speed of motion is carried out separately on each electrode and then on all three together by means of a stop-watch (or electronic time-base control), noting the distance covered by the electrode arm relative to its fixed support. 5.4 Check of the rated capacity of the furnace The furnace, lined according to the manufacturer’s requirements, is charged with material, the quality of which is agreed between manufacturer and user so as to obtain a quantity of liquid metal equal to the rated capacity.
The charge is melted, refined and slagged according to a procedure agreed between manufacturer and user. The volume of slag shall conform with that required. The total quantity of liquid metal, which is tapped when completely emptying the furnace, should not be less than the rated capacity of the furnace. For furnaces with bottom tapping, the adequate quantity of molten metal should be left in the furnace as “hot heel” before the next charge.
5.5 Carrying out a short-circuit test during normal operation (not applicable for d.c. direct arc furnaces)
5.5.1 General To obtain the values of the resistance and reactance of the high-current line and asymmetry factor on the primary side, the measurements are performed on the primary side of the transformer and the results are converted to the secondary-based value.
5.5.2 Determination of resistance and reactance of the high-current line The measurements are made during the phase short circuits during normal operation under sinusoidal voltage at the primary side.
The furnace currents, voltages and power losses are determined after melt-down and/or after superheating. Possible test circuits are shown in figure 1 and in figure 2. A suitable alternative method may be used by mutual agreement between manufacturer and user.
NOTE 1 The current circuit of meters, and the equipment apparatus connected to the current transformers in the circuits of which are also inserted meters used for the short-circuit test, can be shunted before the test when the load of the current transformers is exceeded. During the test, the clamps of the active furnace electrodes are placed at the same height, preferably as low as possible. The accuracy of the measuring instruments used may not be lower than Class 0,5 (wattmeters should be calibrated at low power factor).
NOTE 2 Care should be taken to reduce the magnetic flux in the transformer core to avoid saturation.
NOTE 3 In case of saturable reactors special provisions should be taken. The arc furnace reactance and resistance values are significant only for sinusoidal currents.
5.5.3 Treatment of vector groups other than Dd 0 (delta/delta without phase shift) The furnace equipment shall allow the measurements of the secondary currents with relevant instruments. Since Rogowski coils are frequently used to measure the LV currents, these shall be equipped with an integrator unit and an amplifier, which delivers a correct phase shift signal. Hence, during the measurements, the LV signals are available and can support the HV measurements. Adaptation transformers represent an alternative possibility to image the HV values to the LV side. These are to adapt the vector group as well as the transformer tap. In both cases, the measured LV values can be used for calculations.
5.5.4 Test procedure Before the test, the arc furnace transformer shall be switched to suitably low tapping (reactor inserted, when installed) to ensure that the furnace current under the three-phase operational short-circuit conditions are as close as possible to the rated secondary current of the furnace. The electrodes shall then be lowered to dip their ends into the liquid metal to a depth allowing for a complete short circuit (usually to half or to two-thirds of the electrode diameter), and fixed.