Transients, often called overvoltage surges, are short-lived, violent variations in voltage or current that last shorter than a sine wave. Although they often last only microseconds, the energy content is often high enough to instantly destroy sensitive electronics or surreptitiously age them.
In practice, we see many organisations wrongly blaming transients on 'bad luck' or external factors such as lightning, while the cause often lies in their own installation. Correct diagnosis is essential for operational reliability.
What is it: A very short, fast pulse (impulsive or oscillatory) that disturbs the normal sine wave form.
The risk: Direct damage to printed circuit boards (breakdown), unexplained resets of PLCs and accelerated ageing of insulation.
The cause: External factors (lightning) are well known, but 80% arise internally from switching operations(capacitor banks, heavy motors).
The solution: high sample-rate measurement, source addressing, adequate surge protection (SPD) and filters.
Not every installation is equally sensitive to transients. The relevance increases with the presence of more power electronics and process-critical control.
In the world of Power Quality, we define a transient as a "sudden change in the state of the system". Unlike harmonics (which are continuous) or dips (which last several periods), a transient is an 'event'. It is over before you blink, but the impact is like a sledgehammer blow.
Imagine a water pipe. If you close a tap in one go, you hear a loud thump in the pipes ('water hammer'). The pressure briefly rises extremely high. Exactly this happens in electrical cables when switching large currents.
We distinguish two main types (according to IEEE 1159 and IEC standards):
Nuance: The difference with 'Voltage Swells' A common mistake is confusing a transient with a swell (voltage swell). A swell lasts relatively long (e.g. 100 milliseconds to a minute) and has a frequency of 50Hz. A transient lasts micro to milliseconds and contains frequencies from kHz to MHz. For the solution, this distinction is crucial: a voltage regulator solves a swell but is too slow for a transient.
The impact of transients is often underestimated because the damage is not always immediately visible. We see three degrees of impact within electrical installations:
To solve transients, you need to locate the source. Although lightning is the most well-known cause, most causes lie within one's own walls.
External Causes (approx. 20%):
Internal Causes (approx. 80%): Most pollution you create yourself.
Case study: A manufacturing facility was suffering from faulty power supplies of LED lighting in its office spaces. HyTEPS measurements showed that whenever the large refrigeration compressors in the hall next door switched off, a peak of 800V occurred on the low-voltage grid. The LED drivers were only specified to 500V. Cause: internal inductive kickback. Solution: damping at the source (the compressors).
The insidious thing about transients is their speed. A transient often lasts only a few microseconds (millionths of a second).
A standard multimeter or building management system often measures at an interval of seconds or minutes. For a transient, that's an eternity. You see "230V" on your screen, while in reality a peak of 600V passes hundreds of times per second.
Symptoms in practice:
How do you measure it? To capture transients, you need advanced Power Quality Analyzers that support continuous waveform recording with a very high sample rate (e.g. MHz range). HyTEPS engineers use equipment that not only measures averages, but captures every microsecond of the sine wave. This is the only way to see the shape, frequency and amplitude of the peak, which is crucial for finding the source.
Blind installation of a surge protection device (SPD) is often not enough, especially with internal, repetitive transients. We use a three-step approach:
1. Solve at the source (Elimination) If transients arise internally, try to attenuate them there.
2. Isolate the path (Impedance & Earthing) Ensure that faults cannot spread easily.
3. Protecting the victim (Mitigation) As a last resort, or for external events (lightning), apply protection.
Blaming the grid operator directly: Although many dips come from outside, the grid operator is not always liable. Standard EN 50160 only gives indicative values for dips and does not set a hard limit on the number of dips per year, as they often occur due to force majeure (weather, third parties).
Focusing only on average voltage: Many meters measure averages over 10 minutes. A dip often lasts milliseconds and is completely missed by simple meters. You need sophisticated Power Quality meters that record 'events'.
Symptom management: Replacing a fuse or resetting a machine does not solve the problem. Without diagnosis, the risk of recurrence remains.
Confusion with 'Notching': Notching (notches in the sine wave) looks like a dip, but is a repetitive phenomenon caused by thyristors in DC drives. This requires a different solution (filters) than an occasional voltage dip.
Focusing only on lightning: And forgetting that the lift motor or welding robot causes much more damage internally.
Wrong SPD selection: Placing an SPD with too low a 'clamping voltage' can cause it to wear out too quickly, or too high, thereby failing to protect equipment.
Poor earthing: The most expensive surge protector will not work if it cannot dissipate its energy to a low-impedance earth.
Measuring at the wrong time: Measuring a week when production is down gives a false sense of security. You should measure during worst-case scenarios (start-up, switchover).
Symptom management: Always replacing faulty cards without asking why they break down.
When to call in a specialist? Are you experiencing unexplained failure of controllers, frequent damage to circuit boards or are you about to commission a new production line with lots of power electronics? Don't wait for downtime to strike.
Do you suspect transients are disrupting your processes? Our engineers will be happy to help you with an installation analysis and a concrete improvement plan. Speak to an engineer to discuss your situation.
HyTEPS
Beemdstraat 3
5653 MA Eindhoven
