Electronic equipment is becoming increasingly sophisticated, but also more sensitive. In modern industrial environments, hospitals and data centres, electromagnetic interference (EMI) is a growing threat to continuity. Whereas harmonic contamination manifests itself in the low-frequency range, EMI problems in the high-frequency spectrum (kHz to MHz) cause unexplained failures of sensors, PLCs and communication buses.
An EMC filter (or RFI filter) is essential to suppress this high-frequency noise and comply with EMC directives. But fitting "just any filter" rarely works. It requires understanding the source, the path and the victim. This page tells you how to recognise, analyse and effectively eliminate EMC problems to ensure the operational reliability of your plant.
Short on time? Here are the key points you need to know:
The difference: EMI (Electromagnetic Interference) is the interference itself; EMC (Electromagnetic Compatibility) is the desired state in which equipment operates interference-free.
The cause: Switching power supplies and frequency converters (VFDs) are the biggest sources of high-frequency pollution.
The danger: EMI leads to communication errors, unjustified 'trips' of protective devices, drifting measured values and, in extreme cases, physical damage to bearings (EDM currents).
The solution: A correctly selected and - crucially - correctly installed EMC filter reduces emissions below standard limits (IEC/EN).
Note: A filter only works optimally with low-impedance high-frequency earthing. Incorrect mounting often renders a filter useless.
This topic is primarily relevant to professionals responsible for the reliability of electrical installations and machinery.
In sectors such as the maritime industry, the medical sector (MRI/CT scanners) and automated manufacturing, a "clean" high-frequency environment is not a luxury, but a hard requirement for operational security.
To understand the function of a filter, we must first separate the terms.
EMI (Electromagnetic Interference) is the phenomenon where electromagnetic energy (conducted or radiated) interferes with the operation of other equipment. This is the 'pollution'. Think of the high-frequency pulses generated by the lightning-fast switching of IGBTs in an inverter.
EMC (Electromagnetic Compatibility) is the ability of a device or installation to:
The operation of an EMC filter
An EMC filter (or mains filter) is a passive component, composed of coils and capacitors, that acts as a barrier. It allows the 50Hz operating current to pass through unimpeded, but blocks high-frequency currents (typically from 150 kHz to 30 MHz and above). The filter 'short-circuits' these currents to earth or reflects them back to the source, preventing them from leaking onto the grid or reaching sensitive equipment.
Comparison: Think of an EMC filter as a damper in a ventilation system. Constant airflow (50Hz current) is allowed to pass through it, but vibrations and noise (EMI) are absorbed or stopped before they reach the rest of the building (installation).
EMI problems are notorious because they often occur erratically and are difficult to reproduce. They are often dismissed as "ghost failures".
Common symptoms:
Main sources: The biggest culprits in modern installations are devices using power electronics that 'chop' the sinusoidal shape of the voltage (PWM - Pulse Width Modulation).
Nuance - Conducted vs. Radiated: EMI can travel via the cables (conducted emission) or through the air (radiated emission). Filters focus primarily on conducted interference. For radiated interference, shielding and cage structures are needed. However, poor filtering often leads to cables acting as antennas, turning conducted interference into radiated interference.
Selecting the right filter is tailor-made. A standard off-the-shelf filter will not work if the specifications do not match the source and installation.
1. Input Filters (Mains Filters / Line Filters) These are placed on the supply side of the interference source (e.g. directly in front of a frequency converter).
2. Output Filters (Load Filters / Sine Filters / dV/dt Filters) These are placed between the inverter and the motor.
3. Feedthrough filters Specifically designed to block high-frequency signals where cables enter or leave a shielded area (Faraday's cage).
Common Mode vs Differential Mode A crucial factor in filter selection is the nature of the fault.
Random emergency stops occurred at an automated packaging line in the food industry. The PLC gave a "sensor error", but the sensors were new and functional.
The effectiveness of a filter depends on its mounting. High-frequency behaviour is counterintuitive; what works for 50Hz will not work for 1MHz.
Do you suspect EMI is disrupting your installation? Follow these steps:
Delve further into the subject matter via these related pages:
Symptoms are often subtle until things go wrong. Look out for unexplained machine failures, flickering lights, cables getting hot or transformers buzzing. Also, if electronics (PLCs, drivers) fail earlier than the service life indicates, chances are that the power quality is insufficient. A Power Quality measurement provides the answer.
This is possible, provided you have a high-quality Power Quality Analyzer (according to IEC 61000-4-30 Class A) and the knowledge to interpret the data. Collecting data is easy; analysing the correlation between events, harmonics and your specific business processes requires specialist engineering knowledge. We are happy to support you in the analysis.
Not by definition. NEN-EN 50160 describes the minimum requirements for voltage at the grid operator's transfer point. However, modern equipment can be more sensitive and malfunction even if the voltage is within this standard. We therefore look beyond the standard: we look at the compatibility between your power supply and your connected load.
Peace of mind, certainty and insight. You get a clear diagnosis of the 'health' of your electrical installation. We pinpoint the cause of faults, enabling you to avoid unplanned downtime and reduce fire risks or unnecessary energy losses. You receive a concrete advisory report with practical points for improvement.
No, that is a misconception. A filter is a powerful tool, but not a panacea. Sometimes the solution lies in changing transformer settings, redistributing loads or adjusting cabling. HyTEPS always recommends a thorough analysis and simulation before we recommend hardware, to avoid unnecessary investments.
Yes, significantly. Solar panel inverters and LED lighting drivers are non-linear loads that cause harmonics and sometimes supraharmonics. This can lead to interference with other equipment or overloading of the neutral conductor. When renovating or preserving, a Power Quality check is essential to ensure operational reliability.
We call this phenomenon 'nuisance tripping'. Often the cause is not the total amount of current, but the distortion of the current (harmonics) or short peak currents that your measuring equipment misses. This contamination can extra heat up thermal protections or confuse electronic protections, causing them to switch off wrongly. A specialised measurement can find out exactly why a protection reacts.
For a reliable picture, we usually measure at least one to two weeks. This is necessary to capture a full duty cycle, including weekends and peak loads. For specific acute failures, we can also take short-term measurements or deploy 'continuous waveform recording' to capture transients.
Your installer is an expert in installation and maintenance (the 'general practitioner'). HyTEPS is the specialist (the 'Power Quality Doctor'). We have advanced measuring equipment, simulation software and in-depth knowledge of theoretical electrical engineering and regulations. We often work together with installers to solve complex puzzles that fall outside standard knowledge.
After the measurement, you receive a report with conclusions in understandable language as well as technical details. If necessary, we simulate the possible solutions in our software. So you know exactly what the effect of a measure will be in advance. We then supervise the implementation and verify the result with a follow-up measurement.
In doubt as to whether your faults are caused by EMI or another Power Quality phenomenon? Don't keep guessing. Speak to one of our engineers to discuss your situation or schedule a targeted measurement. We will help you find the cause and eliminate it once and for all.
HyTEPS
Beemdstraat 3
5653 MA Eindhoven
