Selective Network Protection via Voltage Deviation Monitoring

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Solution Overview

Problem

Existing electrical energy supply systems face challenges in selectively isolating limited network areas from electrical faults, particularly with energy sources having low overcurrent capability, leading to ineffective protection and potential damage to unaffected parts of the network.

Innovation Solution

A protective device is implemented, comprising load protection stages with measuring devices for phase current and voltage, switching devices to disconnect from the energy source when limits are exceeded, and a central control stage for comparing load and source voltages to selectively isolate affected network branches, ensuring targeted protection of energy sources and loads.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional overcurrent protection devices are used with energy sources having low overcurrent capability, then the energy source can be protected against overcurrent, but the protection is ineffective because the overcurrent capability is insufficient to trigger conventional protection devices

Engineering Contradiction:

Improveprotection effectivenessVSAvoidcompatibility with low overcurrent capability sources

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent changes the protection parameter from overcurrent-based triggering to voltage deviation-based triggering. The central control stage compares load voltage with source voltage and detects faults when the deviation exceeds a predetermined threshold, enabling effective protection for energy sources with low overcurrent capability that cannot trigger conventional overcurrent protection devices

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the mechanical/electromagnetic triggering mechanism of conventional protection devices with an electronic control system. The central control stage uses electronic voltage comparison and digital control to activate switching devices, providing more precise and adaptable protection that can respond to the specific characteristics of low overcurrent capability energy sources

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If selective intervention is implemented to isolate only affected network areas, then the operational state of the rest of the network is maintained, but the device complexity increases due to multiple protection stages and control mechanisms

Engineering Contradiction:

Improvenetwork availabilityVSAvoidnumber of protection stages

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent divides the protection system into multiple hierarchical stages: load protection stages at individual load locations and a central control stage at the energy source. This segmentation allows selective isolation of faulted network branches while maintaining operation of healthy branches, achieving localised protection without requiring complete network shutdown

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The central control stage continuously monitors voltage parameters from all network branches and uses feedback control to selectively activate switching devices only in branches where voltage deviation exceeds the threshold. This feedback mechanism enables intelligent selective intervention that maintains network availability while avoiding unnecessary protection actions

Inventive Principle:

Principle #23Feedback

3Reliability

If voltage comparison is used to detect faults in network branches, then faults can be accurately identified and isolated, but the measurement precision requirements increase for voltage detection

Engineering Contradiction:

Improvefault detection accuracyVSAvoidvoltage measurement accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent introduces an intermediary threshold value that represents the maximum acceptable voltage deviation. The central control stage compares the measured voltage deviation against this predetermined threshold rather than requiring absolute precision. This intermediary threshold provides a practical decision boundary that achieves reliable fault detection while accommodating normal measurement variations and line impedance effects

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentEP3148028A1Device for protecting an electric power supply device and electrical energy supply device with such a protective device

Publication Date: 2017.03.29 HELMUT SCHMIDT UNIV UNIV DER BUND

AI summary

A protective device (100, 300, 400) for at least one energy source (102), in particular with low overcurrent capability, an energy transmission device (103, 303, 403) with at least one network line (104, 105, 106, 304, 404) and an electrical power supply device (101, 301, 401) comprising at least one connected load (107) on each network line, which selectively protects limited components of the energy transmission device and the energy source, includes for each network line a load protection stage (108, 109, 110, 308) to which the at least one load is connected, a source protection stage (111) for disconnecting the energy source in case of undervoltage or overvoltage at the energy source, and in each load protection stage a measuring device (150, 151, 350, 351) for detecting a line current (IL, IL1, IL2, IL3) and a load voltage (UL,UL1,UL2,UL3) and a switching device (153,353) for disconnecting the network string from the power source,when the phase current exceeds a predefinable limit, and a central control stage (112,312) for comparing the load voltage with a source voltage (UQ) for each network phase and for selectively disconnecting those network phases in which a predetermined deviation occurs between the load voltage and the source voltage.