SAG Compensator: the definitive solution for voltage dips

Are you experiencing production stoppages, failing PLCs or jammed variable speed drives even though the main voltage is not completely lost? Chances are that voltage dips ( voltage sags) are the cause. In modern, state-of-the-art installations, these short voltage drops are disastrous for continuity.

A SAG Compensator (or Active Voltage Conditioner) corrects these dips in real time. Unlike a conventional UPS, this system often does not use batteries, but advanced power electronics to maintain voltage. The result: your critical processes keep running even when the grid fluctuates.

In brief: what you need to know about SAG Compensation

Short on time? Here are the key points you need to know:

The problem: Short voltage drops (dips) cause sensitive electronics to shut down or reset, leading to costly downtime.

The cause: often external (short circuit elsewhere in the grid, thunderstorms) or internal (switching on heavy motors).

The solution: A SAG Compensator injects extra voltage at lightning speed to restore the sine wave form.

The difference: Whereas a UPS uses batteries for complete failure, a SAG Compensator is optimised for dips: more efficient, compact and low-maintenance.

For whom is this technology crucial?

This technology is indispensable in environments where fault tolerance is zero and restart times lead to major financial losses.

Technical Managers & Maintenance Managers: who are looking for the "root cause" of unexplained failures and want to reduce the maintenance costs of leaden UPS systems.
Installation managers (IV): Who are responsible for NEN 3140 and the safety of systems that must not fail (such as emergency lighting or process monitoring).
Production managers: In the process industry (Food, Chemicals, Pharma) where one dip makes an entire batch unusable.
Engineering Consultants: who advise on new construction of data centres, hospitals or high-tech production facilities.

What is a SAG Compensator?

A SAG Compensator, also known as an Active Voltage Conditioner (AVC), is a piece of power electronics placed in series between the power grid and your critical load.

You can compare it to the active suspension of a car. When you drive over a pothole (the stress dip), the suspension immediately pushes the wheel down so that the body (your installation) remains stable and straight.

The system continuously measures the input voltage. As soon as it drops below a set threshold (e.g. 90% of nominal voltage), the compensator "injects" the missing voltage within milliseconds. This happens so quickly (often <3 milliseconds) that connected equipment such as relays, PLCs and robotics do not notice any disturbance.

Why is protection against dips necessary?

The quality of our electricity supply is under pressure due to the energy transition. Although complete power outages (blackouts) are rare in the Netherlands and Belgium, voltage dips occur daily. For modern electronics, a dip is often just as fatal as a blackout.

The consequences are often greater than first thought:

Direct production loss: A machine stopping in a continuous process (e.g. extrusion or pasteurisation) often means that semi-finished products have to be thrown away.
Long restart times: Resetting, cleaning and resynchronising a production line can take hours.
Equipment damage: Frequent switching moments and abrupt stops cause mechanical wear and thermal stress in electronic components.
Data corruption: In data centres or automated warehouses, a dip can lead to loss of transaction data or synchronisation errors in databases.

Nuance: Many companies think their energy supplier is responsible for a perfect sine wave. The reality is that the grid operator works according to the EN 50160 standard. This standard allows considerable margins in voltage variations. A dip is often "compliant with the standard", but disastrous for your process.

What causes voltage dips?

Voltage dips are often force majeure. They occur due to physical laws in the power grid. We distinguish two main categories:

1. External causes (from the grid) This is the most common cause.

Short circuit elsewhere: If a short circuit occurs at a neighbouring company or in a substation, this temporarily "pulls down" the voltage in the entire region until protection intervenes.
Weather effects: Thunderstorms striking high-voltage lines or heavy wind gusts that cause cables to slam together.
Switching operations: Switching of large transformers by the grid operator.

2. Internal causes (within your installation)

Starting up heavy motors: A large motor demands 6 to 10 times its rated current (starting current) at start-up. This causes a temporary voltage drop on the internal cabling.
Short circuit in subgroups: A short circuit in a non-critical group can briefly dip the voltage on the main busbar, causing critical groups to fail as well.

What can you do: UPS or SAG Compensator?

When companies experience outages, they often traditionally turn to an Uninterruptible Power Supply (UPS). While a UPS is useful, for voltage dips only, it is often an expensive and inefficient choice. A SAG Compensator is specifically designed for this problem.

Below are the main differences for a technical consideration:

1. Maintenance and Batteries

UPS: Relies on batteries. These need to be replaced every 3-5 years, require a conditioned room (air conditioning) and pose fire risks.
SAG Compensator: often operates battery-free (extracts residual energy from the grid) or with supercapacitors. This means: no chemical waste, no air conditioning needed and a lifespan of >15 years without major maintenance.

2. Efficiency (Yield)

UPS: Since all power passes through the inverter continuously (double conversion), there is always energy loss (typically 4-8%).
SAG Compensator: is in "standby" or eco mode as long as the voltage is right. This makes the efficiency extremely high (>98-99%). This saves significantly on operational energy costs (OPEX).

3. Footprint

UPS: Large, heavy, often requiring extra space for battery racks.
SAG Compensator: Compact, often fits into existing technical rooms.

When to choose what?

Need protection against complete power outages lasting minutes or hours? Choose a UPS (possibly with emergency generator).
Do you have a stable grid but suffer from short dips that disrupt processes? Choose a SAG Compensator. This is the most economically and technically correct solution in Western Europe in 90% of cases.

Common mistakes in voltage problems

In practice, our engineers often see investment in solutions that do not eliminate the problem.

Symptom management: replacing PLCs or weighting fuses without addressing the cause (the dip).
Wrong sizing: Choosing an expansion joint based on average power instead of peak power (inrush currents).
Blindly relying on the grid operator: Thinking that the grid operator will solve the dip. The grid operator is often not obliged to do so within the applicable standards.
Focus on blackouts: investing in heavy emergency power generators that only start up after 10 seconds. For sensitive electronics, the damage is long done by then (failure after 20 milliseconds).
Forgetting harmonics: Some low-cost voltage regulators cause harmonic contamination themselves. High-quality SAG Compensators filter or are neutral.

Roadmap: From dip to stable voltage

Want to structurally get rid of voltage dips? Follow these steps for a solid approach.

Inventory: Keep a logbook. When do machines fail? Is there a correlation with weather, switching times or neighbours?
Measurement (Crucial): Have a Power Quality measurement carried out. Without data, it is guesswork. Professional measurement equipment is used to determine how deep the dips are, how long they last and how often they occur.
ITIC curve analysis: lay measurement results alongside the ITIC curve (formerly CBEMA). This shows whether your dips fall into the "danger zone" for electronics.
Selection Solution: Based on the data, determine whether a UPS or SAG Compensator is needed and what the required power is.
Implementation & Validation: Install the solution and perform another measurement to verify operation.

When is specialist help needed?

Selecting the right voltage compensation is complex engineering work. Engage a specialist if:

The cause of the outage is unclear (is it a dip, a harmonic disturbance or a transient?).
The focus is on large capacities (>100 kVA) where standard solutions do not suffice.
There is a complex load (high regenerative energy, varying load).
You want independent advice on the best technical solution, independent of a specific brand of hardware.

At HyTEPS, we first analyse the installation with measurements and simulations. We do not sell a "box", but guarantee to solve the problem.