Key Things to Consider When Buying Active Harmonic Filters

In today's industrial and commercial environments, “Harmonic Distortion” — a byproduct of non-linear loads like variable frequency drives and UPS devices — is a primary cause of poor power quality.

This distortion leads to a range of operational issues — including:

• Overheating transformers and cables
• Malfunctioning sensitive equipment
• Higher energy bills
• Premature component failure

This is where “Active Harmonic Filters (AHFs)” come into play as a crucial solution.

They actively:

• Suppress harmonics.
• Correct power factor.
• Minimise system losses to restore electrical stability.

This guide provides you with a practical checklist that outlines the essential things to consider when buying AHFs.

How to Choose an Active Harmonic Filter?

Choosing an AHF involves assessing your system’s harmonic levels, load profile, and compensation needs. The right filter should match current rating, voltage, and performance requirements while allowing room for future expansion.

Consider the following:

• Required harmonic compensation
• Current and voltage rating
• Load type (stable/variable)
• THD limits and power factor needs
• Space, budget, and future capacity margin

So, what are the requirements for an active harmonic filter?

An AHF requires appropriate system compatibility, correct installation conditions, and proper monitoring to function effectively. It must match the site’s voltage, harmonic profile, and performance goals for THDi and PF correction.

Key requirements include:

• Parallel connection to the load
• Correct voltage and frequency rating
• Adequate compensation capacity
• Proper CT placement and direction
• Configuration matching system conditions

With these basics covered, the next step is to assess your facility’s actual harmonic profile for accurate filter sizing.

Assess Your Facility’s Unique Harmonic Profile

Harmonic distortion varies uniquely from one facility to another.

Therefore, conducting a thorough harmonic analysis or audit is the essential first step before purchasing an AHF. This assessment:

• Reveals your facility's specific harmonic profile — a critical baseline for any solution.
• Details the primary non-linear loads.
• Measures the total harmonic distortion (THD) at key points.
• Identifies the dominant harmonic orders.

This data-driven understanding is crucial for accurately sizing and configuring your AHF.

• Neglecting this analysis can lead to either suboptimal performance from an undersized unit or wasteful overinvestment in an oversized one.

Moreover, the analysis determines whether selective harmonic compensation is needed.

With this foundational data in hand, you can confidently proceed to evaluate the filter's technical specifications and internal architecture.

Also Read: Why Choose Active Harmonic Filters Over Passive Harmonic Filters?

Evaluate the Core Performance and Technical Specifications

Beyond the high-level specifications, one of the most vital things to consider when buying active harmonic filters is the internal inverter topology.

• Most modern AHFs may use a 3-level NPC inverter topology, which offers distinct benefits over the conventional 2-level inverter topology.

This leads to:

• Lower losses
• Higher efficiency
• An extended component lifetime
• Reduction in Total Cost of Ownership (TCO)

However, as topologies vary across manufacturers, it is important to verify this feature in the vendor's datasheet.

When your facility has dynamic loads like welding machines or cranes, you must evaluate the AHF's response time to ensure swift harmonic mitigation. The harmonic compensation capacity isn't fixed — it degrades at higher harmonic orders, a factor known as “derating”.

• Derating values differ from one manufacturer to another.

However, a derating curve alone cannot demonstrate the filter's true capability; the di/dt capacity remains an important indicator of real dynamic compensating performance — especially in rapidly fluctuating load environments.

Furthermore, to prevent electromagnetic interference, the AHF must be fitted with a properly designed EMC filter.

The next logical step is to assess the AHF's physical design and how it will integrate into your facility's infrastructure.

Consider the Physical Characteristics and System Integration

Most suppliers offer several installation alternatives: wall mount, cubicle type, or loose modules that can be installed inside existing cubicles.

• Your choice will depend on the available physical footprint, while a cubicle-type installation often provides a greater IP rating.

Beyond the immediate fit, scalability and modularity are key things to consider when buying AHFs, as a modular design allows for future expansion.

• This approach enables you to add filtering capacity as your facility's loads grow — ensuring you don't have to replace the entire system.

Furthermore, assess the AHF's capacity for system integration with other power quality equipment.

• Some AHFs support integration with detuned capacitor banks or APFC panels, creating a Hybrid Var Compensator (HVC) — but this capability varies between vendors, so confirm compatibility during the evaluation stage.

Finally, while AHFs can be connected to medium-voltage systems using a step-up transformer, be aware that this can reduce compensation performance due to increased impedance.

The next step is to evaluate how you will monitor and manage the AHF's daily performance.

Review the Usability and Smart Monitoring Features

In the age of Industry 4.0, remote monitoring and intelligent diagnostics are no longer optional but essential for AHFs, as they play a crucial role in enhancing operational efficiency.

• Your chosen filter should include an intuitive Human-Machine Interface (HMI) — such as a graphical LCD touchscreen that displays key data like voltage and current waveforms for easy on-site control.

This on-site capability must be supported by remote monitoring, integral to smart grid functionality.

• Look for systems that offer access via web-based interfaces, Ethernet, or Modbus protocols — allowing you to manage the filter from any location.

By utilising these smart features, you can:

• Log events.
• Monitor multiple units.
• Perform remote analysis.

This supports proactive maintenance and minimises production disruptions.

Enter commissioning software: it is vital for a streamlined installation process and represents a significant value-add.

• Ensure the software performs automated routines — including self-checks for voltage and CT phase order, CT polarity verification, self-diagnosis, and self-calibration.

These functions drastically shorten commissioning time and prevent errors, therefore reducing system costs and dependency on external support.

This focus on usability and smart features directly contributes to the filter's financial justification, which we will explore next.

Calculate the True Cost and Return on Investment

When building a business case for investment in an AHF, don't focus solely on the initial purchase price — instead, evaluate the TCO and Return on Investment (ROI).

TCO stands for the comprehensive cost over the asset's life — including:

• The purchase price
• Installation
• Maintenance
• The filter’s own operating losses (typically a small percentage depending on the design)
• Expected lifespan

Investing in a high-quality AHF saves energy losses, eliminates equipment downtime, avoids penalty fees, and prolongs asset life — with these cost savings flowing directly into your ROI.

• Begin by documenting the current power factor penalties from your utility bills; in many installations, facilities recover AHF investment through reduced penalties — often within a 2–5 year range, depending on load profile and utility tariff structure.
• Then, estimate the annual costs from harmonic-related equipment failures; case in point, even a single unplanned motor drive failure can justify the AHF investment by highlighting the financial impact of downtime.

For a balanced calculation, factor in the AHF's own energy consumption, noting that the exact consumption varies with topology and load conditions.

For the investment to be secure, it needs protection from a comprehensive warranty; only then can you truly mitigate long-term financial risk by comparing terms beyond the standard 1–2 years.

With these financial and operational benefits in mind, the next step is to verify the manufacturer’s reputation and the level of long-term support available.

Verify Manufacturer Reputation and Long-Term Support

As you finalise your selection, remember the manufacturer is not merely a supplier but a long-term partner — crucial for your facility's operational reliability.

Reputable manufacturers provide comprehensive support, covering:

• Pre-sale technical advice
• Application engineering
• Post-sale services — like commissioning, operator training, and emergency assistance

For instance, ask: “Does the vendor provide application engineering support — such as harmonic studies — before purchase?”

• This single service can prevent the costly mistake of improper sizing — saving you from significant financial losses.

Furthermore, verify the emergency service response times in your region and assess the depth of operator training provided to minimise errors.

You must also scrutinise the warranty terms and inquire about Annual Maintenance Contracts (AMCs) to protect your investment long-term. Additionally, require references from facilities with similar load profiles to validate the supplier's expertise and performance claims.

This thorough due diligence ensures expert support is always available — safeguarding your investment throughout the lifecycle of the AHF.

Making a Future-Proof Power Quality Investment

Ultimately, a carefully chosen AHF delivers:

• Significant cost savings
• Improved system reliability
• Optimal outcomes
• A strong ROI
• Protection against future operational and compliance risks

Ready to ensure reliable power quality? At Nantech Power Systems Pvt. Ltd — one of the leading UPS manufacturers in Chennai — we provide the right AHF for your power system. Connect with us today to schedule your power solution consultation!