Analysis of Active Harmonic Filter installation in power side and load side

The choice between installing an Active Harmonic Filter (AHF) on the power side (at the Point of Common Coupling - PCC) versus the load side (at the source of harmonics) is a critical design decision with significant technical and financial implications.

Here is a detailed analysis comparing both installation strategies.

Executive Summary

• Load-Side Installation (Local Compensation): Targets specific, problematic nonlinear loads. It's like treating a disease at the infected organ. It's highly effective for the protected load, prevents harmonic propagation, and is often the most efficient solution.

• Power-Side Installation (Global Compensation): Treats the entire electrical system at its entry point. It's like purifying the blood for the whole body. It protects the utility supply and upstream equipment, simplifies management for multiple unknown harmonics, but can be less efficient and more expensive.

1. Load-Side Installation (At the Source of Harmonics)

This involves installing a dedicated AHF directly at the terminals of, or on the same distribution branch as, a specific non-linear load (e.g., a large VFD, UPS, SMPS).

Typical Loads: Large Variable Frequency Drives (VFDs), Industrial PCs, High-power Servers, Large UPS systems, Rectifiers.

Advantages:

1. High Efficiency & Targeted Compensation: The AHF compensates for harmonics right where they are generated. This prevents harmonics from ever propagating into the main distribution system, reducing losses (I²R) and voltage distortion throughout the entire wiring.

2. Prevents System Interaction: By containing harmonics at the source, it eliminates the risk of harmonic resonance between the load and the system impedance, which can cause catastrophic failures.

3. Optimal for Individual Problem Loads: Ideal when one or two large pieces of equipment are responsible for the majority of the harmonic distortion.

4. Smaller AHF Rating: Since it only compensates for the specific load it's connected to, a smaller, less expensive AHF can often be used.

5. Simplifies System Expansion: Adding a new non-linear load? Simply add another dedicated AHF to its circuit. There's no need to resize a central AHF.

Disadvantages:

1. Higher Initial Cost for Multiple Loads: If you have dozens of small, distributed non-linear loads (e.g., an office full of PCs), installing an AHF for each one is impractical and costly.

2. Installation Complexity: Requires running cables and finding space near each significant load, which can be challenging in a crowded facility.

3. Management Overhead: Multiple AHFs mean multiple units to monitor and maintain.

2. Power-Side Installation (At the Point of Common Coupling - PCC)

This involves installing a single, larger AHF at the main incoming service entrance or a key distribution panel that feeds multiple loads.

Typical Scenarios: Buildings with many distributed non-linear loads (e.g., data centers, hospitals, office towers), industrial plants with numerous small VFDs, or when the exact source of harmonics is difficult to isolate.

Advantages:

1. System-Wide Protection: A single unit compensates for the combined harmonic current from all downstream loads. It ensures the utility sees a clean sine wave, avoiding penalties and protecting upstream transformers and generators.

2. Centralized Management and Monitoring: All harmonic mitigation is handled in one location, making it easier to monitor performance and perform maintenance.

3. Future-Proofing: The central AHF can handle new harmonic loads added to the system, provided its total capacity is not exceeded.

4. Ideal for Distributed Loads: The most cost-effective solution when harmonics are generated by many small, scattered loads.

Disadvantages:

1. Potential for Lower Overall Efficiency: Harmonics from individual loads still travel through all the branch circuit wiring, causing losses and heating before they are filtered at the main panel. The AHF itself must work harder to cancel the combined distortion.

2. Larger, More Expensive AHF Required: The unit must be sized for the total possible harmonic current of all loads, which is often larger than the sum of individual load-side AHFs would be.

3. Risk of Internal Resonance: While the AHF prevents resonance with the utility grid, harmonic currents from different loads can still interact with each other and the system impedance within the facility's network.

4. Single Point of Failure: If the central AHF fails, the entire system loses harmonic protection.

Comparative Analysis Table

Hybrid Approach: The Best of Both Worlds

In many modern, complex facilities, a hybrid approach is the most technically and economically optimal solution.

Strategy:

• Install large, central AHFs at the main distribution boards to handle the bulk of the background harmonics from countless small loads and provide system-wide baseline protection.

• Install dedicated, load-side AHFs for large, specific harmonic generators (e.g., a large chiller plant with VFDs, a large UPS system, an arc furnace). This contains their large harmonic currents locally.

Benefits:

• Maximizes overall system efficiency.

• Reduces the required rating of the central AHF.

• Provides robust, defense-in-depth harmonic mitigation.

 Key Decision Factors

The choice is not merely "A or B" but a strategic decision based on your specific electrical landscape.

Choose Load-Side Installation when:

• A single or few large loads are the dominant harmonic sources.

• You need to prevent harmonic propagation and maximize energy efficiency.

• The loads are critical and require dedicated protection.

Choose Power-Side Installation when:

• Harmonics are generated by many small, distributed loads.

• Your primary goal is to protect the utility supply and avoid penalties.

• You want centralized, simple management.

Always start with a professional power quality audit. Measuring the harmonic spectrum, identifying the specific sources, and understanding the system impedance are essential steps before deciding on the optimal AHF installation strategy.