What Is the Function of the Isolating Switch in an Electric Arc Furnace?
The isolating switch in an electric arc furnace (EAF) is a three-phase knife-type high-voltage switch used to disconnect the power supply during equipment maintenance. It is characterized by a clearly visible disconnection point but lacks an arc-extinguishing chamber like a load switch.
As such, the isolating switch must not be operated under load, since doing so may generate arcs between the blades and contacts, potentially melting the switch and causing phase-to-phase or phase-to-ground short circuits.
To ensure safe operation, the isolating switch should only be operated under the following conditions:
- In a vacuum environment
- Inside an oil-insulated circuit breaker
- In a protective gas atmosphere
Standard procedure: close the isolating switch before powering on; during maintenance, open the circuit breaker first, then disconnect the isolating switch.
What Is the Function of the Circuit Breaker in an Electric Arc Furnace?
The circuit breaker acts as a switch between the secondary side of the furnace transformer and the short network load. Its structure is relatively simple, and it is typically either:
- A vacuum circuit breaker
- An oil-insulated arc-extinguishing circuit breaker
During smelting operations, the typical sequence is:
- Close the isolating switch;
- Then close the circuit breaker to start power delivery;
- For maintenance, open the circuit breaker first, then the isolating switch.
The circuit breaker ensures safe and controlled energization and de-energization of the furnace, playing a crucial role in the operational sequence.
What Is the Function of the Reactor in an Electric Arc Furnace?
The reactor (or inductor) serves to stabilize the system and limit short-circuit currents, and its role differs slightly between AC and DC arc furnaces.
In AC Arc Furnaces:
The AC reactor is a three-phase iron-core coil connected in series with the high-voltage winding of the transformer. Its core remains unsaturated even under short-circuit conditions. Main functions include:
- Stabilizing the arc
- Limiting the short-circuit current to protect equipment
AC reactors can be built into the transformer or installed as separate units.
In DC Arc Furnaces:
The DC reactor plays an even more important role, with two key functions:
- Limiting the rate of rise of short-circuit currentduring arc initiation or scrap collapse, helping rectifiers react quickly, preventing overcurrent, and ensuring proper operation of protective fuses;
- Smoothing arc current fluctuations, thereby reducing disturbances and feedback to the power supply system, enhancing overall system stability.
