Magnetometer-Based Motor Protection Relay Interface

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Solution Overview

Problem

Conventional current transformers (CTs) used in motor protection relays are unreliable at frequencies below 15 Hz due to saturation, and alternative solutions like Rogowski coils have poor phase response and frequency magnitude errors, while shunt resistors lack galvanic isolation.

Innovation Solution

Magnetometer-based current and voltage sensors, such as Hall effect sensors, are used to measure magnetic fields generated by currents and voltages, with signal conversion circuits including burden resistors and amplifiers to generate inputs for motor protection relays, providing reliable sensing across a range of frequencies.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional current transformers (CTs) are used for current sensing, then galvanic isolation is provided, but measurement precision deteriorates at frequencies below 15 Hz due to saturation

Engineering Contradiction:

Improvecurrent sensing reliabilityVSAvoidcurrent measurement accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent replaces conventional current transformers (electromagnetic induction-based mechanical system) with Hall effect sensors (solid-state electronic system). This substitution eliminates the saturation problem inherent in CTs at low frequencies while maintaining galvanic isolation through the magnetic field coupling mechanism. The Hall effect sensor directly measures the magnetic field generated by current without relying on transformer core properties.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the sensing mechanism from electromagnetic induction (CT) to Hall effect sensing. This parameter change in the physical principle enables accurate current measurement across a wide frequency range including very low frequencies (down to 1.5 Hz), while maintaining galvanic isolation through magnetic field coupling.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If Rogowski coil CTs are used to improve low frequency performance, then measurement precision improves, but phase response and frequency magnitude accuracy deteriorate

Engineering Contradiction:

Improvelow frequency current measurementVSAvoidphase response accuracy

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent replaces Rogowski coil CTs with closed-loop Hall effect sensors. This substitution provides accurate phase response because the Hall effect sensor directly measures the magnetic field without the integration and differentiation operations required by Rogowski coils, which can introduce phase errors. The closed-loop design ensures linear response across the frequency range.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If shunt resistors are used for current sensing, then measurement precision improves, but galvanic isolation is lost

Engineering Contradiction:

Improvecurrent measurement accuracyVSAvoidgalvanic isolation

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent uses magnetic field coupling as an intermediary between the high-voltage current-carrying conductor and the low-voltage sensing circuit. The Hall effect sensor detects the magnetic field generated by the current without direct electrical contact, providing both accurate measurement and galvanic isolation. This intermediary magnetic field approach combines the benefits of both shunt resistors (accuracy) and CTs (isolation).

Inventive Principle:

Principle #24Intermediary (Mediator)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The magnetometer-based sensors and signal conversion circuits enable accurate current and voltage sensing, overcoming the limitations of conventional CTs at low frequencies and providing galvanic isolation, thus enhancing the reliability of motor protection relays.

Implementation Method 1

The current sensor or the voltage sensor may include a closed-loop Hall effect sensor

Methodology Applied

Scientific EffectHall effect: Hall Effect

Implementation Method 2

a magnetometer-based voltage sensor configured to sense a magnetic field generated in response to a voltage of the at least one conductor

Methodology Applied

Scientific EffectMagnetic field sensing: Magnetic Field

Data Source

PatentUS11677230B2Motor protection relay interface using magnetometer-based sensors

Publication Date: 2023.06.13 EATON INTELLIGENT POWER LTD

AI summary

An apparatus includes a magnetometer-based current sensor (e.g., a Hall-effect or fluxgate-based current sensor) configured to sense a magnetic field generated by a current in at least one conductor connecting a motor drive output to a motor and to responsively produce a first current sense signal and a magnetometer-based voltage sensor (e.g., a Hall-effect or fluxgate-based voltage sensor) configured to sense a magnetic field generated in response to a voltage of the at least one conductor and to responsively produce a first voltage sense signal. The apparatus further includes a signal conversion circuit configured to receive the first current sense signal and the first voltage sense signal and to generate a second current sense input and a second voltage sense input for provision to a current sense input and a voltage sense input, respectively, of a motor protection relay that protects the motor.