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Relay protection jitter time

Fiber and communications infrastructure knowledge brief Published 01 Jun 2023

Use this reference to prepare product questions for BAGYOU FIBRE. Check interfaces, capacity, protection and installation requirements against the current product documentation.

Relay protection jitter time is the variation or uncertainty in the operating time of a protective relay, influenced by mechanical, electrical, and communication factors.

Definition and Importance

Jitter time in relay protection refers to the small, random variations in the time it takes for a relay to operate after detecting a fault. This variability can affect the coordination and selectivity of protection systems, potentially causing either delayed fault clearing or unintended tripping of upstream devices, which may impact system stability and reliability.

Factors Affecting Jitter

Relay Type: Electromechanical relays have moving parts, and their operating time depends on the speed of the moving components and the controlling and deflecting forces. Variations in these forces, friction, or mechanical wear contribute to jitter. Static and numerical relays have fewer moving parts, reducing mechanical jitter, but digital processing and communication delays can introduce timing variability.

Settings and Multipliers: Time Setting Multiplier (TSM) adjusts the relay's operating time by controlling the travel distance of moving parts in electromechanical relays. Small variations in TSM or plug setting multiplier (PSM) can affect the relay's response time. Inverse time relays respond faster at higher fault currents, but the exact timing can vary slightly depending on current magnitude and network conditions.

Communication and Trip Circuits: In modern digital protection systems, Ethernet or serial communication delays can introduce jitter in the trip signal. Reduced latency and jitter in communication paths improve the reliability and speed of digital trip circuits. Auxiliary trip circuits and breaker actuation times also contribute to the total trip-circuit time, which includes the relay decision time plus any additional delays.

Measurement and Mitigation

Measurement: Jitter can be measured by repeatedly applying a fault signal and recording the variation in relay operating times. Lab testing and white-box/black-box testing of digital trip circuits are commonly used. Mitigation: Using numerical relays, minimizing mechanical components, optimizing communication paths, and proper calibration of TSM and PSM reduce jitter.

Ensuring relays are free from dirt and mechanical wear also helps maintain consistent operation.

Practical Implications

Excessive jitter can compromise selectivity, causing upstream relays to trip unnecessarily. Low jitter ensures predictable fault clearing, allowing higher line loading without risking network stability. In high-speed protection schemes, such as differential or distance protection, minimizing jitter is critical to maintain system reliability and safety.

In summary, relay protection jitter time is a key parameter in power system protection, representing the variability in relay operation due to mechanical, electrical, and communication factors. Proper relay selection, calibration, and system design are essential to minimize jitter and ensure fast, reliable fault clearing.

Relay protection jitter time - BAGYOU FIBRE NETWORKS [PDF]

Relay protection jitter time

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Technical note

This reference is intended for preliminary fiber and communications infrastructure research. Optical interface, fiber type, port or core capacity, electrical input and output, enclosure protection, cooling, installation limits and applicable standards must be verified for the specific project.

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