The governance effect and precautions of medium and high voltage SVG in the metallurgical industry

The metallurgical industry is a typical "severely affected area for power quality," and it is also where SVGs can deliver the most significant benefits.

My explanation will be divided into two main parts: Governance Effects and Key Considerations.

Part 1: The Governance Effects of Medium-High Voltage SVG in the Metallurgical Industry

Production processes such as Electric Arc Furnaces (EAF), Ladle Furnaces (LF), and rolling mills (especially reciprocating mills) have load characteristics that are random, rapid, and impulsive, causing severe power quality issues for the grid. Medium-high voltage SVG, as a dynamic reactive power compensation device based on power electronics technology, with its extremely fast response time (<1ms), high control precision, and continuous bidirectional (capacitive/inductive) reactive power regulation, is the ideal solution to these problems.

The specific governance effects are manifested in the following aspects:

1. Significant Improvement of Power Factor, Avoiding Penalties and Obtaining Rebates

• Problem: Equipment like EAFs require a large amount of reactive power during the melting period, leading to a very low system power factor (can drop below 0.5), far below the requirements of power supply authorities (usually required to be above 0.9 or 0.95).

• SVG Effect: The SVG can detect the system's reactive power demand in real-time and instantly generate or absorb an equivalent amount of capacitive or inductive reactive power, stabilizing the power factor above 0.95 or even close to 1.0. This directly avoids hefty electricity bill penalties for non-compliance and, in many regions, can even qualify for rebates, resulting in a very short investment payback period.

2. Effective Suppression of Voltage Fluctuations and Flicker

• Problem: Voltage fluctuations and flicker are the most challenging and prominent power quality issues in the metallurgical industry. Instantaneous, massive reactive power impacts, such as electrode short-circuits in EAFs or rolling mills biting the steel, cause rapid changes in grid voltage, leading to light flickering and seriously affecting the normal operation of other sensitive equipment on the same line.

• SVG Effect: The SVG's extremely fast response speed allows it to "capture" each reactive power impulse and deliver the required reactive current within one power frequency cycle (or even faster), filling the reactive power gap. Thereby, it suppresses the voltage fluctuations and flicker values (e.g., Pst) at the busbar to within the limits allowed by national standards (e.g., GB/T 12326). This is something slow compensation devices like traditional TSCs (Thyristor Switched Capacitors) cannot achieve.

3. Stabilizing System Voltage, Enhancing Power Supply Reliability

• Problem: Severe voltage fluctuations can cause trips or malfunctions in sensitive equipment such as PLCs, computer systems, and drives, leading to production interruptions and significant economic losses.

• SVG Effect: By dynamically supporting the voltage at the Point of Common Coupling (PCC), the SVG acts as a "fast voltage stabilizer," providing a stable voltage environment for critical loads within the plant, significantly reducing unplanned downtime, and improving overall production continuity and efficiency.

4. Mitigation of Three-Phase Imbalance

• Problem: The operation of large single-phase loads (like EAFs) in metallurgical lines can cause severe three-phase current imbalance, increasing line and transformer losses, and even causing protection system misoperations.

• SVG Effect: Advanced SVGs have per-phase compensation capability, allowing them to independently control the reactive current output in each phase, thereby compensating for the unbalanced reactive current and effectively improving the three-phase unbalance.

5. Increased Load Capacity of Transformers and Transmission Lines

• Problem: A low power factor means significant reactive current flows through transformers and lines, occupying valuable capacity resources, causing transformers and lines to reach full load prematurely, and preventing power supply to additional loads.

• SVG Effect: The SVG provides reactive power locally, meaning reactive current no longer needs to be transmitted from the distant grid. This "frees up" the capacity of transformers and lines, allowing more capacity to be used for transmitting active power, thereby enhancing the load-bearing capacity of existing power supply facilities and delaying the investment for capacity expansion.

6. Certain Harmonic Compensation Capability (Active Filtering Function)

• Note: The primary function of a standard SVG is reactive power compensation. However, by enhancing its control algorithms and hardware overload capacity, it can compensate for some harmonics (typically 2nd to 13th order) while performing reactive power compensation. This function is often referred to as "Hybrid" or "Enhanced" SVG. For sites with particularly severe harmonic distortion, it is still recommended to use a dedicated APF in conjunction with the SVG.

Part 2: Key Considerations for Applying Medium-High Voltage SVG

Applying SVGs in the harsh operating conditions of the metallurgical industry requires careful attention to selection, installation, and maintenance. Failure to do so may not only fail to achieve the desired results but could also lead to equipment failure. Here are the crucial points to consider:

1. Preliminary Site Survey and Capacity Selection are Paramount

• Load Characteristic Analysis: Detailed power quality testing of the target load (e.g., EAF) is essential to analyze its reactive power impact, rate of change, harmonic spectrum, voltage flicker values, etc. The SVG's capacity must meet the maximum reactive power impact demand with a 15% to 20% margin.

• System Parameters: Clarify grid voltage level, short-circuit capacity, main transformer parameters, etc., to ensure the SVG can be safely integrated and function effectively.

2. Selection of Installation Point (Critical)

• Principle: "Compensate at the source of pollution," i.e., local compensation.

• Optimal Location: Should be as close as possible to the busbar of the impact load, for instance, directly connected to the busbar of the EAF or rolling mill transformer. This ensures the shortest path for reactive current flow, the most direct compensation effect, and avoids reactive power circulation within the plant's internal grid.

• Common Mistake: Installing the SVG at the main substation busbar (LV side of the main transformer) can improve the power factor for the upstream grid but significantly reduces its effectiveness in suppressing voltage fluctuations and flicker on other internal busbars.

3. Full Consideration of the Harsh Metallurgical Environment

• Cooling System Design: The core of an SVG consists of high-power devices like IGBTs, which generate significant heat. Metallurgical shops have high ambient temperatures and are filled with dust, including conductive metal dust. The SVG cabinet's cooling system (usually water-cooling) must be robust and reliable, and the cooling system requires regular maintenance to prevent device damage or derating due to overheating.

• Protection Rating: The cabinet should have a high Ingress Protection (IP) rating (e.g., IP54) to prevent conductive metal dust and corrosive gases from entering, which could cause PCB short circuits or component corrosion.

• Electromagnetic Compatibility (EMC): Electromagnetic interference is extremely severe in metallurgical environments. The SVG's control system and sampling CT/PT circuits must have comprehensive electromagnetic shielding and anti-interference measures to ensure the accuracy of control signals.

4. System Integration and Protection Coordination

• Background Harmonics: Before commissioning the SVG, the background harmonic voltage in the grid must be assessed. Excessively high background harmonic voltage distortion can cause SVG overcurrent. Installing filter branches may be necessary.

• Protection Settings: The SVG's protection settings (overcurrent, overvoltage, undervoltage, etc.) must be coordinated with the upstream circuit breakers and protection devices to avoid false trips or failure to operate.

5. Professional Operation and Maintenance

• Regular Inspection: A professional maintenance team is needed to regularly check the water cooling system pressure, level, and temperature; inspect the voltage sharing of power modules; clean filters, etc.

• Data Analysis: Modern SVGs are equipped with advanced power quality monitoring functions. Operational data should be regularly downloaded and analyzed to assess compensation effectiveness and predict potential failures.

6. Coordination with Existing Compensation Devices

• Many metallurgical plants already have compensation devices like TSC/FC. A reasonable approach is to have TSC compensate for the basic, slow-varying reactive power, while the SVG compensates for the fast, impulsive reactive power. Coordinated control of TSC + SVG through a master control unit can achieve optimal cost-effectiveness and compensation performance.

Summary

Medium-high voltage SVG is a "sharp tool" for solving the core power quality problems in the metallurgical industry. The benefits it brings—enhanced production continuity, electricity cost savings, extended equipment lifespan, and grid friendliness—far exceed its initial investment cost.

The secret to successful application lies in: accurate load analysis, scientific capacity selection, correct installation location, reliable design adapted to harsh environments, and professional post-commissioning maintenance. Only by executing all these steps correctly can the SVG truly deliver its immense value of stability, efficiency, and energy savings in the demanding "power-hungry" metallurgical industry.