Overview of Electrode Regulation System Electric Arc Furnace Technology

The electric arc furnace is the core smelting equipment in short-process steelmaking, melting scrap steel through a high-temperature electric arc generated between three-phase electrodes and the furnace charge. The electrode regulation system, as the "intelligent hub" of the EAF, has the core task of dynamically adjusting the electrode position to maintain stable arc length and arc power, thereby ensuring efficient, energy-saving, and stable operation of the smelting process and protecting critical equipment.

Modern electrode regulation system generally adopt closed-loop control systems based on programmable logic controllers (PLCs) or dedicated controllers, executed by hydraulic or fully electric drive mechanisms. The system monitors the secondary voltage and arc current (i.e., arc resistance) in real time and automatically adjusts the electrode lifting accordingly. Currently, this system is developing towards intelligence, high precision, and synergistic optimization with the entire smelting process.

Detailed Explanation of Electrode Regulation System Electric Arc Furnace

1. Characteristics of Electric Furnaces Electrode Regulation Systems 

Modern EAF electrode regulation integrates automatic detection and closed-loop control functions. Its core feature is its ability to monitor and intelligently respond to complex furnace condition changes in real time. Specifically, the system possesses automatic identification capability for the conductivity of the furnace charge. That is, when the electrode descends to touch unmelted, non-conductive furnace charge (scrap steel), it can quickly determine this based on detection signals and automatically adjust the descent strategy to prevent mechanical damage or short circuits to the electrode.

The main hardware of this system includes:

• Control Unit: 

Centered on a programmable logic controller (PLC) or dedicated controller, responsible for signal processing, logic judgment, and control command output.

• Detection Unit: 

The key component is a pressure sensor. Its oil pressure probe is precisely installed at the pressure measurement point of the outlet oil circuit of the proportional valve or servo valve to monitor the oil pressure changes of the drive system in real time. The sensor's electrical signal output terminal is directly connected to the PLC control system, forming a feedback loop.

• Actuation Unit: 

Mainly includes a proportional valve (or servo valve), hydraulic cylinder, oil pipes, and electrode lifting mechanism. The control signal output from the PLC drives the proportional valve, adjusting the flow and direction of hydraulic oil to the hydraulic cylinder, thereby precisely controlling the lifting speed and position of the electrode. The electrode is rigidly connected to the piston rod of the hydraulic cylinder via a mechanical connector.

2. System Core Objectives & Importance

Objectives:

Under rapidly changing furnace conditions such as charge collapse, melting, and stirring, the arc current or arc resistance is stabilized near the set value by rapidly raising and lowering the electrodes.

Importance:

• Maximize energy efficiency: A stable arc means optimal input power, which can shorten melting time and significantly reduce power consumption per ton of steel.

• Ensure grid friendliness: Smooth current fluctuations, effectively suppress voltage flicker, and reduce interference to the public power grid.

• Protect equipment: Prevent electrodes from breaking due to mechanical collisions or current surges, reduce excessive erosion of the furnace lining by the arc, and extend equipment life.

• Improve production efficiency: Make the smelting process more controllable and uniform, thereby improving production rhythm and steel quality. [1]

3. Main Components of the System

A typical electrode adjustment system of electric furnaces consists of the following 3 components:

3.1 Detection Components

• Electrical quantity detection: Real-time detection of the secondary voltage and secondary current of the three phases. This is the most critical input signal of the control system. 

• Source/Principle: Acquired through current transformers and voltage transformers. Early systems mainly relied on these electrical signals. [2] 

3.2 Controller (Brain) 

• Function: Based on the deviation between the detected signal and the set value, it uses specific control algorithms (such as PID, adaptive, fuzzy logic, etc.) to calculate and output the command and speed signal for electrode lifting and lowering. 

• Technological Evolution: It has evolved from early analog amplifiers and magnetic amplifiers to modern digital controllers with PLCs and dedicated microprocessors as the core, and gradually incorporates intelligent control algorithms. [2] 

3.3 Actuator (Hands and Feet) 

• Hydraulic System: The current mainstream method. The controller outputs electrical signals to drive electro-hydraulic servo valves or proportional valves, adjusting the flow and pressure of the hydraulic cylinder, thereby driving the electrode lifting and lowering with high thrust and fast response. 

• All-Electric Drive System: An emerging solution. It uses high-power servo motors and high-precision ball screws/gear racks to directly drive the electrode. Its advantages are maintenance-free, no risk of hydraulic oil leakage, higher positioning accuracy, and better compliance with green factory requirements. 

4. Evolution of Core Control Strategies & Algorithms

Control algorithms are the decisive factor in system performance, and their development history is as follows:

4.1 Classical PID Control

• Principle: Based on the deviation of arc current (or impedance), linear operations of proportional (P), integral (I), and derivative (D) are performed. Due to its simple structure and high reliability, it is still the control basis of many systems.

• Limitations: The electric arc furnace is a complex object with strong nonlinearity, time-varying characteristics, and three-phase coupling. It is difficult for PID with fixed parameters to maintain the best control effect throughout the entire process cycle, including arc initiation, well penetration, and melting. [3]

4.2 Adaptive Control

• Principle: The control system can identify changes in key process parameters such as arc resistance online in real time and automatically adjust the parameters or structure of the controller itself to adapt to different smelting conditions and improve the overall control quality. 

(B.R. Copeland and T.R. Jenkins, among others, discussed the application of adaptive control in improving the stability of electric arc furnaces in detail in their papers from the 1980s and 1990s.)

4.3 Modern Integrated Optimization Strategies

• Multi-objective Coordinated Optimization: Modern advanced systems not only pursue arc stability but also incorporate multiple objectives such as power factor optimization, flicker suppression, three-phase power balance, and electrode consumption minimization into a unified optimization framework.

• Integration with Advanced Process Control (APC): Electrode regulation, as a key execution sub-module, is integrated into the whole-furnace APC system. Based on intelligent models and global optimization algorithms, the optimal power curve is dynamically set to achieve optimal economic efficiency throughout the smelting process.

The electric arc furnace electrode regulation system is a complex industrial system that deeply integrates detection technology, advanced control theory, and highly dynamic actuators. Its development has evolved from initial constant current regulation to a key core technology centered on intelligent control algorithms, guaranteed by highly reliable actuators, and oriented towards multi-objective coordinated optimization throughout the entire process. The performance of this system directly determines the efficiency, cost, quality, and impact on the power grid of EAF electric furnaces smelting. Its an indispensable core link for the intelligent and green upgrading of modern electric arc furnaces.

References:

[1] Wang Zhaomin, Liu Xiaohe. Electric Arc Furnace Steelmaking Equipment and its Automation [M]. Metallurgical Industry Press, 2010.

[2] Yu Yong, Tang Haiyan, Li Jing. Advances in Modern Electric Arc Furnace Steelmaking Technology [J]. Iron and Steel, 2019, 54(1): 1-10.

[3] Li Chongjian, Li Yaohua. Intelligent Control Technology of High-Power Electric Arc Furnace [J]. China Metallurgy, 2008, 18(12): 1-5.