WHY PLCs AND DRIVES ARE AMONG THE MOST SENSITIVE LOADS TO VOLTAGE SAGS
Modern production infrastructure relies on increasingly advanced automation logic. In 2023, the Italian Artificial Intelligence market reached €760 million, with 61% of spending directed precisely at projects supporting business processes. The effectiveness of these investments in automation depends closely on the reliability of field hardware.
Programmable logic controllers (PLCs) and inverters (drives) operate with microprocessors and power electronic components designed to function within tight electrical tolerances. A variation in supply voltage outside these parameters causes an immediate shutdown or reset of the control logic. The internal capacitors of electronic circuits discharge within fractions of a second, preventing the system from maintaining its operational state. This sensitivity makes industrial electronics the weak link in the production chain when faced with instabilities in the external electrical network.
WHAT VOLTAGE SAGS ARE AND WHY THEY CAUSE LINE STOPPAGES
A voltage sag consists of a sudden reduction in supply voltage (typically between 10% and 90% of the nominal value) lasting between 10 milliseconds and 1 minute. It is not a total blackout. Energy continues to flow, but at a level insufficient to keep contactors and power electronics active.
The causes may lie in events external to the plant (faults on the transmission network, lightning strikes) or internal ones (starting of large motors). When the voltage waveform drops below the tolerance threshold, the safety components of the systems interpret the anomaly as a fault and cut the power supply for self-protection. The immediate result is a halt in production.
Driver: OEE (Overall Equipment Effectiveness)
Impact: An increase in plant availability of up to 15% per year through the elimination of micro-stoppages and manual recovery procedures following electrical anomalies.
HOW VOLTAGE SAGS MANIFEST ON PLCs AND DRIVES
The effect of a network anomaly varies depending on the machine architecture, but follows recurring patterns on operating components.
PLC RESET OR LOSS OF CONTROL LOGIC
The PLC power supply loses the ability to deliver the correct direct current voltage (typically 24V DC) to the CPU. The processor halts or performs an unexpected restart. Variables in volatile memory are reset and the system loses track of the exact phase the production cycle was in.
DRIVE SHUTDOWN OR UNEXPECTED FAULT
Motor drives constantly monitor the internal DC bus voltage. If the external supply decreases, the bus voltage drops rapidly. The inverter enters an alarm state (often reported as an Undervoltage Fault) and removes torque from the motor. The mechanical axis stops uncontrollably through inertia.
LINE STOPPAGE REQUIRING MANUAL RESET
Emergency circuits and run contactors de-energise due to insufficient electromotive force in the coils. The entire electrical panel undergoes a shutdown. Restarting requires physical intervention from an operator to reset alarms, re-arm protections, and initiate the machine homing sequence.
PRODUCTION WASTE AND LOSS OF SYNCHRONISATION
An uncontrolled stoppage causes material damage. In hot-working processes (extrusion, moulding), material solidifies in the moulds. In CNC machines, the tool stops on the workpiece, compromising it. Conveyor belts lose pace and synchronisation with pick-and-place robots.
SPORADIC EVENTS THAT ARE DIFFICULT TO DIAGNOSE
Voltage sags last fractions of a second. Standard multimeters do not have the sampling frequency required to record them. Operating personnel therefore find themselves facing stopped machines with generic alarms, erroneously attributing the malfunction to non-existent software or mechanical faults.
WHAT OPERATIONAL CONSEQUENCES THEY CAN HAVE ON INDUSTRIAL PROCESSES
Electrical instability translates into cascading inefficiencies across the entire company organisational model. A single event lasting a few milliseconds triggers a domino effect that takes hours to be absorbed by the value chain.
| Impact Category | Operational Consequence | Business Implication |
| Direct costs | Scrap material, broken tools, labour downtime. | Increased unit cost of production and erosion of job margins. |
| Indirect costs | Delivery delays, contractual penalties, extended set-up times. | Loss of reliability with the end customer and supply chain misalignment. |
| Component wear | Multiple forced restarts, thermal stress on electronics. | Increased maintenance budget and reduced useful service life of the plant. |
HOW TO DETERMINE WHETHER A LINE STOPPAGE IS CAUSED BY A VOLTAGE SAG
Accurate diagnosis requires the installation of Power Quality Analysers compliant with standard EN 50160, positioned at the point of energy delivery or directly upstream of the line’s electrical panel. These instruments record the waveform at high frequency and save the event profile. Cross-referencing the timestamp from the analyser log with the time the PLC recorded the Undervoltage error provides technical certainty that the stoppage derives from the electrical network and not from the automation system itself.
HOW TO PREVENT LINE STOPPAGES CAUSED BY VOLTAGE SAGS
Electrical continuity requires a targeted design approach, moving beyond empirical attempts based on the simple replacement of control components.
ANALYSING THE PHENOMENON BEFORE INTERVENING
Acquiring network data over an extended period (Power Quality audit) makes it possible to quantify the magnitude, duration, and frequency of voltage sags. Without an accurate profile of the disturbance, there is a risk of unnecessary oversizing or ineffective undersizing of the protective equipment.
MAPPING SENSITIVE LOADS
Within an entire production plant, not all loads require the same level of energy stability. Lighting systems or unregulated motors can tolerate slight fluctuations. It is essential to electrically separate the power supply for servers, PLCs, drives, and sensors, concentrating protection exclusively on the logical nodes of the plant.
CHOOSING THE RIGHT COMPENSATION TECHNOLOGY
Based on the power drawn by sensitive loads and the statistical depth of recorded voltage sags, the appropriate industrial equipment is selected. Solutions exist to compensate for drops of up to 50% of the nominal value or to supply energy during brief total interruptions.
INTEGRATING PREVENTION INTO THE PLANT STRATEGY
Company policies must include compensation systems within the scheduled maintenance plan. This ensures that the protective asset maintains its declared performance over the long term, guaranteeing a fast and measurable return on investment (ROI).
WHEN A VOLTAGE STABILISER IS NOT ENOUGH AND A VOLTAGE SAG COMPENSATOR IS REQUIRED
A recurring technical mistake is to use electromechanical voltage stabilisers to mitigate voltage sags. A stabiliser is designed to correct slow, steady voltage drift throughout the course of the day. Its mechanical reaction time is measured in tenths of a second or seconds.
A voltage sag manifests and disappears in 20–50 milliseconds. In that time, the PLC has already shut down before the stabiliser has begun to move its contacts to raise the voltage. The use of a high-speed electronic compensator is therefore essential. These devices use inverters and capacitive components to inject the missing energy in less than 3 milliseconds, rendering the anomaly invisible to the downstream electronics.
ORTEA NEXT SOLUTIONS FOR PROTECTING PLCs, DRIVES, AND AUTOMATED LINES
Technical procurement procedures today evaluate devices in an increasingly digital manner. In 2024, 75% of B2B buyers preferred to purchase or analyse technical solutions online independently. During this analysis phase, the response specifications offered by power quality technologies prove decisive for design choices. Ortea Next’s specialist approach, backed by entirely Made in Italy manufacturing, provides a precise engineering response to every type of electrical vulnerability.
OXYGEN FOR VOLTAGE SAGS
The Oxygen series is an industrial-grade voltage sag compensator. It intervenes in less than 3 milliseconds and can compensate for drops of up to 50% of the nominal value for up to one minute. The use of supercapacitors, in place of traditional batteries, eliminates the periodic maintenance costs of accumulators, improving plant reliability in demanding environments.
OXYGEN ZERO FOR MICRO-INTERRUPTIONS
Some networks experience total outages lasting tenths of a second (micro-interruptions). The Oxygen Zero system covers complete voltage loss by delivering full power until supply is restored, operating with a response time of less than 5 milliseconds. This solution ensures absolute continuity for field buses, logic controllers, and highly electromagnetic-sensitive applications, such as data centres and continuous-cycle production processes.
STABILISERS AND OPTIMISERS FOR VOLTAGE EFFICIENCY
In industrial applications where the primary issue is not a rapid transition but slow supply fluctuation, the ranges of electromechanical and static stabilisers (such as the Orion, Sirius, or Odyssey series) maintain the RMS voltage at optimal values. For businesses that also aim to reduce energy costs, intelligent devices such as Enersolve or ComEC act on voltage to optimise consumption by up to 12%, combining machine protection with energy efficiency.
CASE STUDIES: EXAMPLES OF PRODUCTION LINES PROTECTED FROM SAGS AND MICRO-INTERRUPTIONS
Industrial sectors subject to intensive production rhythms represent the primary testbed for validating the ROI of Power Quality technologies.
PLASTICS AND PACKAGING SECTOR
The Italian e-commerce market reached €58.8 billion in 2024, imposing large-scale shipping volumes. This trend requires packaging machines running continuously. In a packaging plant, installing a compensator on extrusion drives prevents polymer solidification in the moulds, eliminating the three hours of machine downtime required for the mechanical cleaning of nozzles following a voltage sag.
MANUFACTURING AND AUTOMATED PROCESSING SECTOR
Global supply chain dynamics require perfect information exchange and production volumes, with the global B2B e-commerce market forecast to reach $83.5 trillion by 2032. At a sheet-metal processing plant, laser cutting systems were interrupting the optical beam due to micro-drops on the network, compromising entire sheets of premium metal. Integration of an Oxygen solution stabilised the laser bus, reducing the scrap rate by 90%.
HIGH AUTOMATION AND ROBOTICS SECTOR
Artificial Intelligence is permeating industrial plants, with 79% of companies surveyed globally implementing advanced systems in their operations. For an organisation based on collaborative robotics and machine vision, the real-time control infrastructure cannot tolerate any data packet loss. A single stoppage of the line Ethernet switch caused the robotic arms to halt. Adoption of the Oxygen Zero system ensured isolated power supply to the line servers, protecting the local cloud from any external imperfection.
CONCLUSION
Protecting industrial electronics from network disturbances represents a strategic choice for safeguarding operating margins. Relying on structured system engineering and tailored compensation technologies makes it possible to transform power quality from a plant vulnerability into an efficiency driver, guaranteeing uptime in line with the demands of the modern energy transition.
FAQ
WHAT HAPPENS TO A PLC DURING A VOLTAGE SAG?
The upstream power supply (often at 24V DC) drops below the minimum operating threshold. The PLC processor halts for self-protection or performs a forced restart, resetting the programme logic and blocking the entire machine automation sequence.
ARE DRIVES SENSITIVE TO VOLTAGE SAGS?
Yes. Drives constantly monitor the DC intermediate circuit voltage. A drop in the supply network causes the internal voltage to collapse, triggering the “Undervoltage” protection, which stops the motor to prevent irreversible damage to the power electronics.
HOW DO YOU VERIFY THAT LINE STOPPAGES ARE CAUSED BY THE ELECTRICAL NETWORK?
The use of certified Power Quality Analysers makes it possible to record the plant waveforms. In the event of a stoppage, the alarm log timestamp from the machine is cross-referenced with the analyser data to mathematically confirm the correspondence with the external electrical anomaly.
HOW DOES A STABILISER DIFFER FROM A VOLTAGE SAG COMPENSATOR?
Traditional electromechanical stabilisers require fractions of a second or even seconds to react via moving components, correcting slow drift. A voltage sag lasts only a few milliseconds; for this reason, an electronic compensator capable of injecting the required energy in less than 3 milliseconds is necessary.
WHAT IS THE TECHNICAL DIFFERENCE BETWEEN A VOLTAGE SAG AND A MICRO-INTERRUPTION?
A sag constitutes a temporary reduction in voltage value, typically greater than 10%, in which energy continues to flow but at insufficient levels. A micro-interruption, by contrast, represents a total absence of voltage (zero volts) lasting less than one minute.
