Active harmonic filter

Active Harmonic Filter: Operation, application and benefits for your installation

In modern electrical installations, energy efficiency is the standard, but this brings an invisible challenge: harmonic pollution. An Active Harmonic Filter (AHF) is the most effective, dynamic solution to neutralise this pollution, prevent failures and extend the life of your equipment.

Where passive filters often fail in variable conditions, an active filter offers real-time correction of the current form. This page tells you exactly how this technology works, why it is essential for your operational reliability and how to determine whether you need an AHF.

For whom is an Active Harmonic Filter relevant?

The use of an Active Harmonic Filter is rarely a luxury, but often a technical necessity in environments with many power electronics. It is specifically relevant for:

• Installation managers in industry: where variable speed drives (VSDs) drive motors and production processes must run continuously.
• Technical Managers in data centres: where servers and UPS systems create a non-linear load and failure has disastrous financial consequences.
• Facility Managers in hospitals and utilities: because of the large amount of LED lighting, climate control and lifts that generate harmonic currents.
• Engineers in the maritime sector: On board ships, the network is island mode, which means that pollution directly affects propulsion and navigation.

Why is reducing harmonics crucial?

Ignoring harmonic contamination is a risk to the continuity of your operations. The impact can be divided into three main categories: safety, cost and compliance.

1. Preventing physical damage and fire risk

Harmonic currents generate additional heat. Since harmonics often have higher frequencies (e.g. the 5th harmonic is 250Hz, the 7th is 350Hz), losses occur due to the skin effect in cables and eddy currents in transformers.

• Neutral conductors: The 3rd harmonic (and multiples thereof) accumulate in the neutral conductor, which can lead to overheating and fire, even if phase currents are within standards.
• Transformers: These degrade faster and can get so hot that oil or insulation is affected.

2. Reliability and efficiency

Contaminated voltage leads to "inexplicable" failures. Think of electronics jamming, PLCs giving error messages or circuit breakers tripping with no apparent overload. An Active Harmonic Filter increases the Power Factor, making more efficient use of your existing transformer and infrastructure. There is less "blind current" and pollution, so more room for useful power.

3. Meeting standards (Compliance)

Grid operators are imposing increasingly stringent requirements on the quality of the power you purchase as well as feed in (e.g. the Grid Code). In addition, manufacturers of sensitive equipment often require the voltage to comply with standards such as EN 50160 or IEC 61000-2-4. Without an active filter, you risk warranty claims being rejected because the supply voltage was out of specification.

What causes harmonic contamination?

The irony of the energy transition is that the devices that help us save energy are also the biggest sources of pollution. Plants used to consist mainly of linear loads (light bulbs, direct switched motors). Today, devices with power electronics dominate .

The most common sources are:

• Variable speed drives (VSDs): Used to efficiently control pumps and fans. The rectifier bridge in these controllers chops up the current.
• LED lighting: The drivers in LED luminaires are non-linear. While one bulb does little, thousands of bulbs in a greenhouse or office building create enormous pollution.
• EV Chargers: The internal inverters of electric cars and chargers generate harmonic currents during charging.
• Solar photovoltaic panels (PV inverters): Although they provide energy, inverters can inject harmonics into the grid, especially at lower loads.

Nuance: There is no need to avoid these devices. They are essential for sustainability. The key is to manage the impact of these equipment with proper filtering.

Common mistakes when selecting filters

Implementing Power Quality solutions is specialist work. We regularly see in practice that investments do not deliver the desired results due to the following mistakes:

• Placement in the wrong place: Placing a filter centrally (at the main switch) is often more economical, but sometimes decentralised (at the source) is technically better to avoid cable losses internally.
• Wrong sizing: Looking only at the transformer's rated power, instead of the actual pollution profile.
• Forgotten power transformers (CTs): An active filter needs the right current transformers in the right place to "see" what is happening. Incorrect placement renders the filter useless.
• No consideration for environment: An AHF is power electronics and needs cooling. Placement in a too hot, dusty room without filtration leads to failure of the filter itself.
• Thinking that "meeting the standard" is enough: Sometimes equipment already experiences failures within the norm limits. A generic solution then does not work; customisation is required.

When do you need HyTEPS' expertise?

You can solve some basic problems yourself, but with Power Quality, things quickly become complex. Call in a specialist if:

• You face frequent outages of expensive production equipment with no apparent cause.
• You are planning a significant expansion with LED, EV chargers or heat pumps.
• Grid operator threatens disconnection or fines due to grid pollution.
• You doubt the measurements of your own fixed energy meters (they often do not measure accurately enough in the high frequency spectrum).
• There is an 'island mode' situation (generators/emergency power), where stability is especially critical.