Slow voltage variations are structural deviations from the rated voltage (usually 230V or 400V) that persist for longer than a few minutes. Unlike short voltage dips, which are immediately visible through flashing lights or breakdowns, prolonged undervoltage or overvoltage cause invisible wear, overheating of motors and unexplained failures in sensitive equipment.
In the ideal world, the sinusoidal alternating voltage is constant. In practice, voltage fluctuates continuously due to load variations and renewable energy generation. When these variations go beyond the legal or technical limits (as defined in EN50160), the operational reliability of your installation is at risk. As a specialist in Power Quality, HyTEPS helps you analyse the cause and stabilise the voltage.
The phenomenon: A long-term deviation (higher or lower) from the rated voltage, often caused by heavy loads, long cables or decentralised generation (solar/wind).
The risk: Undervoltage leads to overheating of motors (due to higher current consumption) and failure of control systems. Overvoltage drastically shortens the lifetime of electronics and lighting.
The standard: According to EN50160, the voltage should not deviate by more than 10% during 95% of the week. However, for critical processes, this margin is often too wide.
The solution: always start with a Power Quality measurement to determine whether the problem lies internally (your installation) or externally (the grid operator).
This article is written for Installation Managers, Technical Managers and Engineers in environments where electricity availability is directly linked to operational results. Think of:
Utility with a lot of PV: Where feed-in provides local voltage boost.
Industry & Manufacturing: Where electric motors, pumps and conveyors run continuously.
Data centres: where UPS systems trigger unnecessarily when voltage deviations occur, leading to battery wear.
Healthcare (Hospitals): Where sensitive medical imaging equipment (MRI/CT) requires tight voltage tolerances.
Technically, we speak of slow voltage variations when the effective value (RMS) of the voltage deviates from the nominal voltage (Un) for an extended period (standard 10 minutes).
A simple comparison: Imagine voltage as the water pressure in your shower.
In electrical terms:
Nuance: Do not confuse this with transient overvoltages (spikes caused by lightning or switching) or voltage dips (short interruptions). Slow variations are about the 'steady state' condition of your installation.
Many plant managers trust that equipment will "keep on doing it". This is often true, but at what cost?
1. Undervoltage and motors (The hidden cost) Many industrial loads are 'constant power' loads. If the voltage (U) drops, the current (I) must increase to deliver the same power (P) (P = U x I).
2. Overvoltage and electronics Modern LED lighting and switching power supplies are sensitive. Prolonged overvoltage overloads capacitors and semiconductors.
3. Process failure Control systems (PLCs) and protection relays have undervoltage protection. If the voltage drops too far, the machine shuts down to protect itself.
Do you recognise any of the following signs? Then chances are you are dealing with voltage variations.
To solve the problem, we need to know where it comes from.
The system operator (DSO) provides voltage, but its quality varies depending on your location in the network.
Often the cause lies within their own gates.
Have you found that voltage variations are disrupting your process? Here are the possible interventions.
1. Adjust tap settings transformer Do you have your own medium-voltage transformer? Often, the primary winding can be adjusted via a 'tap changer'. This increases or decreases the secondary voltage structurally.
2. Optimise cabling Reduce voltage drop by weighting cables or shortening cable runs.
3. Active Voltage Conditioning (AVC) An AVC is a system that continuously monitors voltage and corrects it at lightning speed. When there is a dip, the system adds energy; when there is a peak, it regulates back.
4. Reactive power compensation (Capacitor bank) By reducing reactive power (power factor improvement), the current through the cables decreases and with it the voltage drop.
Harmonics: How pollution from non-linear loads threatens your installation.
Voltage dips: All about short interruptions.
EN50160: The standard explained.
Power Factor: Blinding power and efficiency.
Grid Analysis: How we measure and report.
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.
Don't wait for motors to fail or production to stop. With a temporary measurement or continuous monitoring, our engineers can precisely identify whether slow voltage variations pose a risk to your installation.
HyTEPS
Beemdstraat 3
5653 MA Eindhoven
