Voltage surge, often called voltage swell in technical jargon, is a temporary increase in voltage in your electrical installation. Although voltage dips (sags) are more common, swells are potentially much more damaging. A dip often leads to downtime; a boost leads to direct physical damage to components, insulation faults and irreparable failure of sensitive equipment.
For plant managers and technical managers in industry, data centres and the medical sector, it is crucial to not only recognise, but proactively prevent this phenomenon. Whereas a dip often originates externally, the cause of a swell frequently lies within the in-house installation or at the transfer point.
What is it: A temporary increase in RMS voltage (>110%) for several periods of time up to one minute.
Hazard: Direct damage to power supplies, printed circuit boards, variable speed drives and motor insulation.
Cause: Often the sudden switching off of large loads, switching on or off capacitor banks or a fault in the feeding network.
Action: Measuring is knowing. Analyse Power Quality data to determine whether the cause is internal or external.
This article is written for professionals responsible for the operational reliability and safety of electrical installations:
According to international standards (such as EN 50160 and IEC 61000-4-30), we speak of a voltage boost when the effective value (RMS) of the voltage rises above 110% of the rated voltage, with a duration ranging from 10 milliseconds (half a period at 50Hz) to 1 minute. Does the increase last longer than one minute? Then we speak of a structural overvoltage(overvoltage), which is another phenomenon.
Imagine a water main through which water flows at a constant pressure. If you suddenly turn off a large tap while the water is flowing at full speed, the pressure builds enormously immediately behind the tap because the water cannot release its kinetic energy.
In an electrical installation, something similar happens. If a heavy load (e.g. a large motor or furnace) is suddenly switched off, the energy in the network has nowhere to go. The result is a sudden rise in voltage on the busbar systems, which spreads through the installation like a wave and puts pressure on connected equipment.
The impact of voltage surge is often underestimated because the event is brief. However, the energy content of a swell can be devastating. Where a dip creates a 'shortage', a swell creates an 'overdose' of energy that components have to absorb.
Nuance: Much modern equipment is robust, but the cumulative impact of regular swells is often the cause of what is wrongly called "natural wear and tear".
Because a swell is often brief (milliseconds to seconds), you rarely see it on an analogue voltmeter. You will recognise the phenomenon by its effects and patterns in your installation:
1. Switching off large loads
This is the most common internal cause. According to Ohm's Law, a current through the impedance of the cables and transformer creates a voltage drop. When a large current consumer (large motor, heating element) suddenly drops, this voltage drop abruptly disappears. As a result, the voltage on the bus bar temporarily rises to near or above the no-load voltage.
This is a more complex phenomenon. In a three-phase grid, when a short circuit occurs between one phase and earth, the voltage on that particular phase will collapse(dip). However, in grids that are not effectively earthed (such as IT grids or grids with high impedance earthing), the voltage on the two healthy phases may actually rise dramatically relative to earth.
Switching on a capacitor bank for reactive current compensation can resonate with the inductance of the transformer. This often causes an oscillating transient that can turn into a momentary voltage boost.
When a large part of the load in a neighbourhood or industrial estate is down (for example, after a power failure elsewhere), while a lot of solar photovoltaic (PV) power is being generated locally, the voltage can rise quickly before the solar inverters can adjust or switch off.
Solving Power Quality issues requires a structured approach. There is no "one size fits all" plug you plug in. The solution depends on the source.
Without data, you are sailing blind. A Power Quality analysis (with IEC 61000-4-30 Class A compliant equipment) is necessary to establish:
HyTEPS engineers analyse this data to find the root cause. Is it the capacitor bank? The transformer tap stand? Or an external grid fault?
Confusion with transients: A swell is not the same as a spike (spike/transient). A transient lasts microseconds, a swell milliseconds to seconds. Protection against transients (SPDs) will not help against a swell; rather, the SPD will burn due to the excessive energy content of a swell.
Blinded by average voltage: Multimeters often measure an average over time. A swell of 200ms is completely missed, but is long enough to crash your PLC. You need a meter with cycle-by-cycle recording.
Symptom management: replacing a faulty power supply without investigating the cause. If the swell keeps coming back, keep replacing components.
Focus purely on dips: Many UPS systems are built to handle dips (battery operation). Not all UPS systems cope well with an input voltage that is too high, and then switch off themselves for protection.
Underestimating grid reactions: Thinking that the grid operator always delivers a perfect 230V/400V. In the energy transition, grid voltage fluctuates more strongly than before.
Do you suspect voltage drift? Follow these steps:
Not every dip requires external help. However, in the following situations, it is advisable to speak to an engineer from HyTEPS:
Solving voltage problems yourself is possible in simple installations. However, in complex environments, specialist knowledge is required. Engage our engineers when:
Delve further into voltage and power quality:
Voltage Dip (Voltage Sag): The counterpart of swell, often caused by inrush currents.
Harmonic pollution: distortion of the sine wave form due to non-linear loads.
Transients: Very short-lived high-frequency voltage spikes.
EN 50160: The standard for the quality of voltage in the public grid.
Power Quality Measurement: How we map your installation.
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 keep guessing about the cause of failures. Our engineers will help you with a clear diagnosis and a solution that works.
HyTEPS
Beemdstraat 3
5653 MA Eindhoven
