Voltage Sag Protection

Key Takeaways

• Voltage sags, also called voltage dips or voltage drops, are temporary drops in voltage below the nominal or rated voltage level for a short time.

• Voltage sag protection refers to the measures and devices used to prevent or minimize the effects of voltage sags.

• Including voltage sag protection in PCB design considerations can help make the product more reliable and robust.

Voltage sag protection: Uninterruptible power supply system with automatic voltage stabilizer

Voltage sags, also called voltage dips or voltage drops, are temporary drops in voltage below the nominal or rated voltage level for a short time. A sudden change in load, a fault in the power distribution system, or starting a big motor can cause voltage sags. Voltage sag protection refers to the measures and devices used to prevent or minimize the effects of voltage sags.

Voltage sags can damage sensitive electronic equipment, industrial processes, and other systems that require reliable power. These effects include disruptions in operations, equipment malfunctioning, data loss, and even damage to components. A voltage sag is different from a power interruption. A voltage sag happens when the voltage drops below 90% of the nominal level, while an interruption occurs when there is a complete voltage loss.

Voltage Sag Protection Measures

As seen from the chart above, voltage sag can have a wide range of negative effects on equipment and facilities. However, voltage sag protection measures can be implemented to mitigate the impact of voltage sags. Some common approaches include:

• Uninterruptible Power Supplies (UPS): UPS systems provide temporary power using batteries during voltage sags. When a voltage sag is detected, they switch to battery power instantly, providing a seamless transition and keeping connected equipment going.

• Energy Storage Systems: Energy storage solutions, such as flywheels and supercapacitors, provide short bursts of power during voltage sags to maintain system stability.

• Static Voltage Compensators (SVCs): SVCs regulate voltage levels by injecting or absorbing reactive power. As a result, they keep connected equipment's voltage stable even if the voltage sags or swells.

• Voltage Regulators: Voltage stabilizers or automatic voltage regulators can keep a constant output voltage even when the input voltage fluctuates. These devices use transformers and voltage control circuits to adjust the output voltage.

• Dynamic Voltage Restorers (DVRs): The DVR monitors the incoming voltage and injects a controlled amount of voltage when it detects a sag to restore voltage to the nominal level. It corrects voltage quickly and precisely to mitigate sags.

• Isolation Transformers: By buffering voltage fluctuations caused by sags, isolation transformers help isolate sensitive devices.

• Voltage Sag Ride-Through Capability: Some advanced electronic devices and equipment have specialized components that can handle short-term voltage drops without shutting down.

Voltage sag protection is critical in manufacturing, data centers, healthcare, and telecommunications industries. Voltage sag protection helps ensure the reliability and longevity of electrical and electronic systems. These measures can help minimize downtime and associated costs.

Voltage Sag Protection and PCB Design

PCB design can be affected by voltage sag protection measures, especially when dealing with sensitive or critical electronics. Including voltage sag protection in PCB design considerations can help make the product more reliable and robust. Here are some ways PCB designers can include voltage protection measures in their designs.

• Component Selection: Choosing components that can tolerate voltage fluctuations and rapid changes in supply voltage is essential when designing a PCB for a voltage sag-protected system. Consider using components with wide operating voltage ranges and transient voltage suppression capabilities, like TVS diodes.

• Grounding: Maintaining stable power distribution requires a solid grounding scheme. Grounding prevents ground loops, which can exacerbate voltage sags.

• Decoupling and Bypass Capacitors: You can stabilize the power supply by putting decoupling and bypass capacitors strategically across the PCB. During transient events, these capacitors can help mitigate voltage sags by providing a temporary power source.

• Isolation of Sensitive Components: Consider isolating voltage-sensitive components or sections of the PCB from areas with high current demands or potential transient voltage sources.

• Layout Considerations: PCB layout is crucial for managing power distribution and minimizing voltage fluctuations. You can mitigate the effects of voltage sags by placing power and ground planes strategically and minimizing trace impedance.

• Circuit Breakers Deployment: Circuit breakers can provide additional protection against excessive current flow during voltage sag events.

• Reverse Polarity Protection: In case of voltage polarity reversal during power supply events, reverse polarity protection can prevent component damage.

• Voltage Monitoring: By incorporating voltage monitoring circuits, you can detect voltage sags and trigger protective measures. System diagnostics and maintenance can also benefit from this information.

• UPS Integration: If the PCB is part of a larger system with an integrated UPS, you need to ensure support for UPS input and output connections and seamless voltage transitions.

• EMI/RFI Filtering: EMI and radio frequency interference (RFI) filtering reduces voltage sags caused by external disturbances on the power supply.

• Testing and Simulation: The behavior of the PCB under different voltage sag scenarios can be assessed using simulation tools. By testing how the PCB performs during voltage sag events, you can validate how effective the protection measures are.

Including voltage sag protection in PCB design requires an understanding of system requirements and constraints. When designing PCBs, you should work with experts in power electronics, PCB design, and voltage protection to address voltage-sag challenges. And you should make sure you have the right tools.

Cadence Has the Tools You Need

The best solution is to use Cadence’s PCB Design and Analysis Software and OrCAD PCB Designer, which provide complete circuit design, simulation, verification, and optimization abilities.

Leading electronics providers rely on Cadence products to optimize power, space, and energy needs for a wide variety of market applications. To learn more about our innovative solutions, talk to our team of experts or subscribe to our YouTube channel.