You expand your electrical installation with frequency-controlled drives, charging stations or PV systems. Or you experience unexplained faults where fuses trip and capacitor banks fail. In both cases, there is a good chance that harmonic contamination in your grid is colliding with the grid impedance present. The result? Resonance.
An electrical installation is never static. Every metre of cable and every transformer affects impedance. Without insight into this frequency-dependent resistance, you are sailing blind when making adjustments. An impedance scan (or grid impedance measurement) gives you the hard data needed to guarantee operational reliability. HyTEPS analyses the complex interaction between capacitance and inductance in your grid, so you know exactly where the danger zones lie.
What: A measurement or simulation that maps the resistance of your network over a wide frequency spectrum.
Risk: Without this understanding, harmonics can cause dangerous voltage buildup (resonance).
Result: A clear report with resonance points and advice for filters or adjustments.
Action: Necessary in case of expansions or misunderstood component failure.
To understand what an impedance scan is, we must first look at the definition of impedance. Basically, this is the total resistance a current experiences in your installation. However, in Power Quality terms, we are not only looking at the resistance at 50 Hz (the fundamental frequency), but at the behaviour of your network over a broad spectrum, for example up to the 50th harmonic (2500 Hz).
An impedance scan plots the course of this resistance in graph form. Your installation consists of inductive components (transformers, motors, long cables) and capacitive components (long cables, capacitors, EMC filters). These components react differently to different frequencies:
At specific frequencies, the two can conflict or reinforce each other. The impedance scan visualises these interactions. It is in fact an 'X-ray' of the electrical properties of your network, regardless of the current that is currently flowing. It tells you how your installation will react when harmonic currents are introduced.
A voltage dip or voltage sag is technically defined in the European standard EN 50160. We speak of a dip when the voltage suddenly drops to a value between 90% and 1% of the agreed nominal voltage, followed by a rapid recovery to normal levels.
The main purpose of an impedance scan is to identify resonance points. Resonance occurs when the inductive reactance (XL) and capacitive reactance (XC) of your network are equal to each other at a certain frequency. At that intersection, a so-called parallel resonance occurs.
With parallel resonance, the mains impedance for that particular frequency is extremely high. If there is a device in your installation (such as an LED driver or frequency converter) that happens to generate harmonic currents at exactly that frequency, the current has nowhere to go. According to Ohm's Law (U = I x Z), a small current (I) at a very high impedance (Z) creates a huge voltage swing (U).
The consequences of undetected resonance:
An impedance scan prevents you from being surprised by these physical laws. It enables you to take proactive measures, instead of repairing damage afterwards.
At HyTEPS, we approach the impedance of your network in two ways, depending on the phase of your project (existing or new construction).
1. Physical Measurement (Online Measurement) In existing situations, our engineers place sophisticated measurement equipment at strategic points, often at the main distribution board or specific sub-distributions. We not only measure the voltage and current present, but also analyse the response of the grid to switching actions or inject specific signals. This gives an up-to-date picture of the current situation. We validate whether the theoretical models match reality.
2. Simulation and Modelling Often, measurement alone is not enough. After all, you want to know what happens after you have installed that new production line. That is why we rebuild your installation in specialist simulation software (such as Vision or specific Power Quality tools). In this, we enter the parameters of:
In this model, we perform a 'frequency sweep'. The software calculates the impedance for each frequency (e.g. 50Hz to 2500Hz). This produces a graph with peaks (parallel resonance) and troughs (series resonance). By virtually adding your new equipment, we immediately see whether dangerous shifts occur in the resonance points.
An impedance scan is not a standard maintenance job, but a specialist diagnosis. There are specific moments in the life cycle of an installation when this analysis is crucial for operational reliability.
Typical situations for plant managers and engineers:
Context: A major manufacturer in the plastics industry replaced conventional motors with energy-efficient variable speed drives. At the same time, production capacity was expanded.
Problem: Random production lines were failing on a weekly basis. The main machine did not trip, but local controls crashed. In addition, the chokes of the existing capacitor bank were burning up. The house installer could not find a direct cause; currents were nominally within limits.
Approach: HyTEPS conducted a grid analysis and impedance simulation. The scan showed that the new inverters were producing harmonics around 350 Hz (7th harmonic). The impedance curve of the grid showed a high peak (parallel resonance) exactly at that frequency, caused by the combination of the transformer and the undivided capacitors.
Result: By replacing the capacitor bank with a 'detuned' (doused) variant, the resonance point was shifted to a safe frequency (189 Hz). The harmonic currents were no longer amplified. The breakdown stopped immediately and production has been running fault-free ever since.
In practice, our engineers regularly see that risks are underestimated or wrong assumptions are made.
Want to make sure your installation is free of dangerous resonances? Follow this roadmap.
Not every dip requires external help. However, in the following situations, it is advisable to speak to an engineer from HyTEPS:
Our engineers look beyond just the meter; we analyse the complete electrical context of your installation, from transformer to end-user.
Deepen your knowledge with these related topics:
Harmonics: How pollution from non-linear loads threatens your installation.
Transients: About short, destructive voltage spikes.
Flicker: On rapid voltage variations and annoying light flicker.
Power Quality Measurement: How we map the health of your installation.
Don't gamble on the operational reliability of your plant. Whether you are expanding or struggling with vague faults, an impedance scan will provide the definitive answer. Our engineers are ready to review your network. Discuss your situation with HyTEPS today.
HyTEPS
Beemdstraat 3
5653 MA Eindhoven
