Time-Domain Directional Relay for IBR Fault Direction Detection

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Solution Overview

Problem

Existing directional relays in power grids fail to reliably determine current direction in systems with inverter-based resources due to unique fault characteristics, leading to misoperation and compromised system protection, especially with high penetration of renewable energy sources.

Innovation Solution

A source-agnostic time-domain directional relay that uses instantaneous voltage and current measurements without converting to phasors, employing the sign of the derivative of the voltage-to-current ratio to determine fault direction, immune to decaying DC offsets and pre-fault currents, and operable at low sampling rates for integration into existing numerical relays.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If phasor-based directional relay methods are used, then the relay can determine current direction in traditional power systems, but it fails to reliably determine current direction in the presence of inverter-based resources

Engineering Contradiction:

Improvecurrent direction determination reliabilityVSAvoidadaptability to inverter-based resources

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent changes the domain parameter from phasor domain to time-domain, using instantaneous values of voltage and current instead of phasors. This parameter change makes the relay immune to decaying DC offsets and pre-fault currents that plague phasor-based methods, enabling reliable operation with inverter-based resources while maintaining compatibility with traditional systems

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Instead of converting time-domain samples to phasors and then determining direction (traditional approach), the patent inverts the process by directly using time-domain instantaneous values to determine current direction through the sign of the derivative of voltage-to-current ratio, eliminating the need for polarization and making the method source-agnostic

Inventive Principle:

Principle #13The other way round (Inversion)

2Measurement precision

If polarization mechanisms are used in directional relays, then current direction can be determined in phasor domain, but the method becomes sensitive to decaying DC offsets and pre-fault currents

Engineering Contradiction:

Improvecurrent direction measurement accuracyVSAvoidsensitivity to decaying DC offsets and pre-fault currents

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent extracts and eliminates the polarization mechanism from the directional relay, using only the sign of the derivative of the voltage-to-current ratio in the time domain. This extraction removes the sensitivity to decaying DC offsets and pre-fault currents that inherently plague phasor-based polarization methods, while maintaining accurate current direction determination

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent substitutes the mechanical/phased-based polarization system with a purely time-domain mathematical approach using instantaneous values and derivatives. This substitution replaces the vulnerable phasor conversion and polarization mechanisms with a robust time-domain method that is immune to DC offsets and pre-fault conditions

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If high sampling rates are used to improve directional relay accuracy, then measurement precision improves, but implementation complexity increases in existing numerical relays

Engineering Contradiction:

Improvedirectional measurement accuracyVSAvoidimplementation complexity in existing relays

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent uses a moderate sampling rate of 24 samples per cycle, which is sufficient for the time-domain method but lower than what would be required for high-precision phasor-based methods. This partial action approach achieves adequate measurement precision while significantly reducing implementation complexity in existing numerical relays, making the solution practical and deployable

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS20250277826A1Source-agnostic time-domain directional relay for power grid

Publication Date: 2025.09.04 CLEMSON UNIVERSITY

AI summary

The disclosure deals with system and methodology subject matter for source-agnostic time-domain directional relays for power grid applications, including system and methodology subject matter for Inverter based resources (IBRs) which are instrumental in facilitating the integration of renewable energy resources and storage into the power grid. IBRs exhibit unique fault characteristics significantly different from synchronous generators (SGs), dictated by their proprietary controls, posing challenges for the reliable operation of directional relays designed in phasor domain. This disclosure relates to a source-agnostic directional relay formulated in time domain, thus making any polarization unnecessary. It is immune to decaying dc offset and pre-fault currents, and applicable to transmission and distribution feeders with up to 100% IBR penetration. Its performance is superior to a numerical commercial relay in a hardware in the loop setup, and its chosen sampling rate of 24 or more samples per cycle (spc) makes it readily implementable in commercial numerical relays.