| 摘要 |
A control apparatus, for starting and operating a high-temperature electric furnace (F) for melting refractory materials, includes a three-phase power supply (Phase A, Phase B and Phase C) for supplying energy to three electrodes (E1, E2 and E3) of the furnace. lncluded in the connections between the power supply and the furnace electrodes are three input transformers (T1, T2 and T3) one for each phase. The primary of each transformer includes a tap-changer section. Connected between the power supply and the tap-changer are two current paths connected in parallel. The first current path is non-inductive. It includes at least one silicon controlled rectifier (SCR-A, SCR-B and SCR-C). This path is used after steady state conditions have developed. The second current path is highly inductive. The inductance is controlled by a continuously variable transformer (BT-A, BT-B and BT-C) commonly known as a Varac. This path is used during start-up. The combination, in series, of the tap-changer and Variac controlled inductance in a second path which is used during start-up, provides a vernier control of the voltage, and, hence, the current, applied to the furnace electrodes (E1, E2 and E3) during start-up, with the inductance providing protection against sudden current surges which would otherwise tend to blow fuses and open circuit breakers (CB1, CB2 and CB3).
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