Voltage dips

Voltage dips: The biggest invisible threat to your operational reliability

Your machines are failing, but the fuses are still intact. The lights might have blinked for a moment, but everything else seems normal. Chances are you are dealing with a voltage dip. In modern electrical installations, voltage dips account for most of the Power Quality-related costs and downtime. Where a complete power outage is obvious, a voltage dip often operates in the shadows: brief, unpredictable, but with disastrous consequences for your sensitive equipment and processes.

As an Installation Manager or Technical Manager, your job is to ensure continuity. HyTEPS helps you identify the cause of these disruptions and make your installation immune to these external or internal influences. We analyse, diagnose and solve.

For whom is understanding voltage dips crucial?

This article is specifically written for professionals responsible for the continuity and safety of critical electrical installations:

• Technical Managers & Engineering Managers: You want to minimise unplanned downtime and be accountable for the reliability of production processes.
• Installation managers (IV-ers): You must ensure that the installation complies with standards (such as EN 50160) and operates safely, without unexplained failures.
• Maintenance Managers: You look for the cause of faulty components or 'ghost faults' that confuse maintenance schedules.

This knowledge is particularly relevant in sectors where downtime is not an option, such as data centres, hospitals, the process industry and maritime environments.

Why voltage dips threaten your operations

Although harmonics and flicker are often discussed, research shows that voltage dips are responsible for the majority of costs due to poor Power Quality. The impact is often immediate and harsh:

1. Production downtime and data loss: Many modern electronics, such as variable speed drives and PLCs, have built-in protections that shut down the equipment when voltage is too low to prevent damage. The result: your process stops abruptly.
2. Damage to semi-finished products: In process industries (e.g. extrusion or chemical processes), a stop of a few milliseconds can result in the loss of an entire batch of raw materials.
3. Unnecessary costs: Consider the cost of restarting processes, loss of man-hours and the potential damage to reputation in case of supply problems.
4. Shortened service life: Although equipment sometimes continues to run, the internal power supply can be subjected to additional stress to compensate for voltage loss, leading to premature ageing.

CBEMA Curve: The tolerance limit Not every dip leads to damage. The impact is often visualised in the CBEMA curve (Computer & Business Equipment Manufacturers Association). This curve shows the relationship between the depth of the dip and its duration.

• Safe zone: Short, shallow dips through which equipment travels.
• No Interruption Zone: Equipment notices the dip, but continues to function (possibly with slight hiccups).
• Prohibited Zone: This is where damage or failure occurs.

What causes voltage dips?

The cause of a voltage drop can be either within your own installation or in the grid operator's network.

1. Causes in the external network:

• Short circuit: A short circuit elsewhere in the high-voltage or medium-voltage grid temporarily pulls down voltage in a large area until protection intervenes.
• Weather effects: Lightning strikes on overhead lines often cause severe, short-term dips (or even spikes/transients).
• Switching operations: Switching of heavy network sections by the grid operator.

2. Causes within your own plant:

• Inrush currents (Inrush currents): Starting up large motors, transformers or capacitor banks briefly requires a huge current (sometimes 10x the rated current). As the current passes through the impedance (resistance) of your cables, this current surge causes a temporary voltage drop (Ohm's Law: U = I x Z).
• Short circuit internal: A fault in a sub-distributor can cause a dip in the main distributor before the fuse melts.

Did you know? In a three-phase grid, a dip can be asymmetrical. A short circuit on one phase can cause the voltage on that phase to dip, while the other phases remain fairly stable or increase in voltage.

Common mistakes in voltage dips

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 are often caused by 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 .

When should you call in a specialist?

Not every dip requires external help. However, in the following situations, it is advisable to speak to an engineer from HyTEPS:

• You have regular outages, but your current meters show no anomalies.
• There is a dispute with the grid operator or supplier about the cause of damage.
• You are considering purchasing expensive equipment (such as a heavy-duty UPS or AVC) and want to be sure it is the right investment.
• You deal with complex installations where harmonics and dips may interact (e.g. in hospitals or data centres).

Our engineers look beyond just the meter; we analyse the complete electrical context of your installation, from transformer to end-user.