HVDC Fault Classification and Location Using ROCOC Current Ratios

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

In high voltage direct current (HVDC) transmission systems, particularly in multi-terminal VSC-based grids, identifying the faulty conductor and determining fault type is challenging due to electromagnetic coupling and similar electrical characteristics between pole-to-ground and pole-to-DMR faults, which complicates rapid fault clearance and poses safety hazards for repair crews.

Innovation Solution

A method involving monitoring current signals, filtering them to determine the maximum rate of change, calculating ratios of these changes, and comparing them against discrimination factors to identify faulted conductors, allowing for precise fault classification and location within a short time frame using local measurements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Extent of automation

If pole-by-pole protection schemes are used to identify faulty conductors, then fault detection can be implemented, but electromagnetic coupling between conductors causes false operations and reduces reliability

Engineering Contradiction:

Improvefault detection capabilityVSAvoidfalse operation rate

Core Design Contradiction:

Extent of automationVSReliability

Solution Approach 1:

The protection scheme is segmented into two independent stages: first stage identifies the faulty pole using ROCOC on local current measurements, and second stage identifies the specific fault type (pole-to-ground or pole-to-DMR) using the ratio index. This segmentation allows each stage to focus on specific detection tasks, reducing false operations caused by electromagnetic coupling while maintaining automated fault detection capability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The ratio index (RIG) acts as an intermediary parameter that bridges the gap between simple fault detection and accurate fault type identification. By introducing this intermediate measurement that compares current rates of change between different conductors, the system can distinguish between similar fault types (pole-to-ground vs. pole-to-DMR) that would otherwise cause false operations in conventional schemes.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If sensitive thresholds are used to improve fault detection sensitivity, then fault identification accuracy improves, but false operations increase due to electromagnetic coupling

Engineering Contradiction:

Improvefault identification accuracyVSAvoidfalse operation rate

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The invention changes the measurement parameter from simple current magnitude or single-conductor ROCOC to a ratio of ROCOC values between different conductors (RIG index). This parameter transformation makes the measurement inherently more robust to electromagnetic coupling effects, allowing sensitive threshold settings to be used without increasing false operations, as the ratio metric naturally compensates for coupled transients.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If additional filtering and modal transformation are applied to improve robustness, then false operations are reduced, but device complexity increases

Engineering Contradiction:

Improvefalse operation rateVSAvoidprotection scheme complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention extracts only the essential information needed for fault type identification by using a simple ratio of current rates of change, rather than applying complex filtering and modal transformation. This extraction approach achieves the same robustness against false operations with significantly reduced computational complexity, maintaining reliability while simplifying the protection scheme.

Inventive Principle:

Principle #2Taking out (Extraction)

4Productivity

If fault type identification is made explicit rather than implicit, then fault clearance speed improves, but measurement and detection difficulty increases

Engineering Contradiction:

Improvefault clearance speedVSAvoidfault type discrimination difficulty

Core Design Contradiction:

ProductivityVSDifficulty of detecting and measuring

Solution Approach 1:

The invention replaces complex mechanical or computational fault analysis systems with an electrical measurement-based ratio index (RIG). By substituting the need for complex fault analysis with a straightforward electrical measurement comparison, the system achieves explicit fault type identification that speeds up fault clearance while keeping the detection and measurement process relatively simple and direct.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS11971440B2Method for determining conductors involved in a fault on a power transmission line and fault location using local current measurements

Publication Date: 2024.04.30 UNIVERSITY OF MANITOBA

AI summary

A method for identifying one or more faulted conductors in a power transmission system having at least two power-transmitting conductors and a method for determining fault location each include steps of monitoring current signals which are representative of currents in the conductors at a generally common location within the power transmission system; filtering the current signals; determining a maximum rate of change of each filtered current signal within a predetermined time interval after the fault event has commenced; and calculating a ratio of a pair of the maximum rates of change of the filtered current signals. For fault classification, the ratio is compared against a discrimination factor to identify the one or more faulted conductors. For fault location, the calculated ratio is compared against the calibration data to determine the distance from the connection terminal of the faulted conductor to the fault location.