Voltage Dips & Interruption (VDI)

Voltage dips and interruptions are important tests conducted in the realm of electromagnetic compatibility (EMC) to evaluate how electrical and electronic equipment responds to variations in the power supply. These tests are critical for ensuring the reliability and stability of equipment under real-world conditions where power supply disturbances might occur.

​1. Voltage Dips

A voltage dip (or sag) is a short-duration decrease in RMS voltage level, typically lasting from a fraction of a second to a few seconds. Voltage dips can be caused by events such as short circuits, motor starting, or high inrush currents when large loads are turned on.

​Purpose of the Voltage Dip Test:

The purpose of this test is to determine how a device under test (DUT) behaves when subjected to brief reductions in supply voltage. The equipment should continue to operate correctly or fail in a predictable manner, allowing it to recover automatically once normal voltage levels are restored.

​Voltage Dip Test Procedure

• Test Levels: The voltage dip is usually expressed as a percentage of the nominal voltage. Common test levels include 10%, 30%, 40%, 50%, 70%, and 100% voltage reduction.

• Duration: The dip is applied for a specified duration, often ranging from 10 milliseconds to several seconds, depending on the test standard and the nature of the equipment being tested.

• Phases: The test may be performed on single-phase or three-phase systems, depending on the equipment's operating environment.

• Evaluation: The DUT's performance is monitored to observe any malfunctions, resets, or unexpected behaviour. For instance, critical equipment might be expected to ride through the dip without any noticeable disruption.
   

2. Voltage Interruption

A voltage interruption is a more severe event than a dip, where the voltage supply is completely cut off for a brief period. This can occur due to faults, protection system operations, or maintenance activities.

​Purpose of the Voltage Interruption Test:

The interruption test aims to assess how a DUT handles a complete loss of voltage and whether it can recover gracefully when the power is restored.

​Voltage Interruption Test Procedure

• Duration: The interruption typically lasts for a period ranging from a few milliseconds to a few seconds. Common durations include 10 ms, 20 ms, 200 ms, and 1 second.

• Recovery: After the interruption, the DUT is monitored to check if it returns to normal operation automatically or requires manual intervention.

• Evaluation: The performance criteria are based on the DUT's intended function. For example, some devices may be allowed to temporarily stop functioning but must resume normal operation without manual intervention once power is restored.
   

Standards and Guidelines

Several international standards specify the requirements for voltage dip and interruption tests:

• IEC 61000-4-11: For equipment connected to low-voltage networks.

• IEC 61000-4-29: For DC-powered equipment.

These standards define the levels, durations, and procedures for conducting voltage dips and interruptions to ensure consistent testing across different equipment and industries.

Key Points to Consider

• Critical Equipment: For life-support systems or critical industrial processes, even a brief voltage dip or interruption can have significant consequences. Such equipment typically has stringent requirements for ride-through capability.

• Power Conditioning: Devices like uninterruptible power supplies (UPS), voltage regulators, and surge protectors are often tested to ensure they can provide stable power during dips and interruptions.

• Product Certification: Manufacturers often need to pass these tests as part of the certification process for selling products in certain markets, especially for products used in sensitive applications.
   

In summary, voltage dip and interruption tests are crucial for determining the robustness and reliability of electrical and electronic devices under fluctuating power conditions.