Introduction to Voltage Sag

Voltage sag, often referred to as voltage dip, is a common phenomenon in high-power applications. It is characterized by a brief decrease in voltage magnitude in the electrical power system, typically lasting from a few milliseconds to a few seconds. Understanding what causes voltage sag is crucial for engineers and plant managers as it can affect the performance and reliability of electrical equipment, leading to increased maintenance costs and downtime.

Causes of Voltage Sag

Heavy Load Start-Up: One of the most prevalent causes of voltage sag is the sudden start-up of heavy electrical loads, such as motors and compressors. When these devices switch on, they draw a significant amount of current to overcome inertia and achieve operational speed. This high demand for current can lead to a temporary drop in voltage levels within the electrical system.

Short Circuits: Short circuits in the electrical network can lead to a sudden and dramatic decrease in voltage. When a short circuit occurs, the path of least resistance is formed, causing an excessive amount of current to flow. This sudden surge in current can cause voltage levels to drop significantly until the short circuit is cleared.

Transformer Energization: When transformers are energized, they can draw a substantial inrush current, leading to voltage sag. This occurs because transformers need a large initial current to magnetize their core. The inrush current can temporarily reduce voltage levels across the network, affecting other connected equipment.

Fault Conditions: Faults within the electrical network, such as line-to-ground faults or line-to-line faults, can also result in voltage sag. These faults cause large currents to flow, which can subsequently lead to a drop in voltage. Clearing these fault conditions often requires protective devices like circuit breakers to intervene.

Impact of Voltage Sag on Equipment

Voltage sag can have detrimental effects on sensitive equipment, such as computers, industrial controls, and other electronic devices. These devices often rely on stable voltage levels to function correctly, and a sudden dip can lead to malfunctions or shutdowns. Motors and drives may experience reduced torque or stalling, which can disrupt industrial processes and lead to potential damage.

Mitigation Strategies

Implementing preventive measures can help mitigate the effects of voltage sag in high-power applications. Some strategies include:

Voltage Regulators: Installing voltage regulators can help maintain consistent voltage levels. These devices automatically adjust the voltage to ensure it remains within the desired range, minimizing the impact of voltage sag.

Uninterruptible Power Supplies (UPS): UPS systems can provide temporary power during voltage sag, helping to maintain operation of critical equipment without interruption. They are particularly useful for sensitive devices that cannot tolerate voltage fluctuations.

Network Design: Designing a robust electrical network with proper distribution and load management can also minimize voltage sag risks. This includes using appropriately sized conductors, transformers, and balancing load distribution across phases.

Conclusion

Voltage sag is a significant concern in high-power applications due to its potential impact on equipment performance and reliability. Understanding its causes, such as heavy load start-up, short circuits, transformer energization, and fault conditions, is essential for implementing effective mitigation strategies. By adopting measures like voltage regulators, UPS systems, and careful network design, industries can minimize the risks associated with voltage sag and ensure the smooth operation of their electrical systems.