Fault Direction Indicator Using Current Phase Accumulation

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Solution Overview

Problem

Existing directional overcurrent relays in power distribution systems face challenges in accurately determining fault direction, especially for close-in faults, and are costly due to the need for voltage measurements, which become unreliable when faults occur near the relay.

Innovation Solution

A method and device that measure time-dependent currents on an AC transmission line, calculate phase differences between pre-fault and post-fault current values, and accumulate these differences to determine fault direction without requiring voltage measurements, allowing for accurate fault direction indication even in close-in faults and reducing costs by eliminating the need for voltage sensors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If voltage measurement is used for fault direction determination, then measurement precision is improved, but device complexity and cost increase

Engineering Contradiction:

Improvefault direction determination accuracyVSAvoidmeasurement equipment requirements

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent extracts the voltage measurement component from the fault direction determination system, achieving accurate fault direction identification using only current measurements. By removing the voltage sensor requirement and relying solely on current phasor analysis, the system reduces device complexity and cost while maintaining measurement precision through alternative computational methods

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The current measurement system is enhanced to perform multiple functions: it simultaneously provides both protection operation triggering and fault direction determination. By making the current measurement system universal, the patent eliminates the need for separate voltage measurement equipment, thereby reducing device complexity while maintaining accurate fault analysis capabilities

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Measurement precision

If voltage measurement is used for fault direction determination, then measurement precision is improved, but cost increases

Engineering Contradiction:

Improvefault direction determination accuracyVSAvoidsystem cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent removes the voltage measurement component from the system, achieving cost reduction by eliminating expensive voltage sensors and associated hardware. The extraction principle allows the system to maintain measurement precision through current-only analysis methods while significantly reducing manufacturing costs

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent employs a cost-effective approach by using only current measurement equipment, which is cheaper and more readily available than voltage measurement systems. This substitution with less expensive components achieves the same functional outcome at lower cost

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Ease of operation

If reference voltage phasor is used for close-in fault detection, then fault direction determination is provided, but reliability deteriorates

Engineering Contradiction:

Improvefault direction indicationVSAvoidclose-in fault detection accuracy

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

Instead of using reference voltage phasor as the basis for fault direction determination, the patent inverts the approach by using current phasor as the primary reference. This inversion allows the system to reliably detect close-in faults by comparing post-fault current phasor angle changes against pre-fault current characteristics, eliminating the reliability issues associated with voltage measurement during close-in faults

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the measurement parameter from voltage to current, fundamentally altering the basis for fault direction determination. By monitoring current phasor angle changes rather than voltage phasor relationships, the system achieves reliable close-in fault detection without the reliability deterioration that occurs when reference voltage becomes unavailable or inaccurate during near-relay faults

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9250282B2Fault parameter indicator device and related methods

Publication Date: 2016.02.02 ABB (SCHWEIZ) AG

AI summary

A method of determining a fault parameter of a fault on an AC transmission line 10 of a power distribution system 1 relative to a measurement location 12 of the transmission line 10 comprising: measuring a time-dependent current of the transmission line 10 at the measurement location 12; transmitting a current signal indicative of the measured current to a decision logic section 36, the current signal comprising a plurality of pre-fault current values and a plurality of post-fault current values; determining, by the decision logic section 36, a plurality of phase difference values indicative of respective phase differences between respective pre-fault current values and respective post-fault current values; accumulating the plurality of phase difference values into an accumulated phase difference parameter; obtaining the fault parameter by comparing the accumulated phase difference parameter to a threshold value; and outputting the determined fault parameter.