Circuit Breaker Thermal Trip Calibration via Bidirectional Deformation

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Solution Overview

Problem

Existing thermal trip apparatuses in circuit interrupters face challenges in calibration due to manufacturing variations, leading to unacceptably high rejection rates of circuit breakers that are over-deformed during the calibration process, as the deformation is irreversible without substantial reworking.

Innovation Solution

A calibration machine employing a tool with an elongated shank and engagement elements that can deform the support in opposite directions to adjust the thermal trip setting, allowing for calibration in either direction and reversing over-deformation, thereby enabling precise calibration of the thermal trip apparatus.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If inelastic deformation is applied to calibrate the thermal trip apparatus, then the thermal trip setting can be adjusted, but the deformation cannot be reversed without substantial reworking leading to high rejection rates

Engineering Contradiction:

Improvethermal trip setting accuracyVSAvoidcalibration reversibility

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent applies the inversion principle by enabling the support to be deformed in opposite directions. Instead of allowing deformation in only one direction (which makes over-deformation irreversible), the support is designed with geometry that permits deformation in both directions, allowing calibration adjustments to be reversed if over-deformation occurs, thereby reducing rejection rates while maintaining calibration precision

Inventive Principle:

Principle #13The other way round (Inversion)

2Measurement precision

If the frame is deformed beyond the calibration point, then calibration is achieved, but the deformation cannot be reversed requiring substantial reworking and discarding of circuit breakers

Engineering Contradiction:

Improvecalibration setting accuracyVSAvoidcircuit breaker waste

Core Design Contradiction:

Measurement precisionVSLoss of substance

Solution Approach 1:

The support structure is designed to allow deformation in opposite directions, enabling reversal of calibration adjustments. This prevents permanent over-deformation and eliminates the need to discard circuit breakers that exceed calibration specifications, thereby reducing material waste while maintaining precise calibration control

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent incorporates a geometric design in the support that anticipates potential over-deformation and provides built-in capacity for reversal. By designing the support geometry beforehand to accommodate bidirectional deformation, the system prevents calibration errors from becoming permanent defects requiring product disposal

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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

This solution allows for efficient and reversible calibration of the thermal trip apparatus, reducing the need for reworking and discarding circuit breakers, making the manufacturing process less expensive by minimizing waste and ensuring accurate thermal trip settings.

Implementation Method 1

a bimetal element that becomes heated in a persistent overcurrent condition

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

a bimetal element that becomes heated in a persistent overcurrent condition and accordingly trips the circuit breaker

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 3

deforming the support by applying one of a compressive force and a tensile force to the shank

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Implementation Method 4

The engagement elements can deform the support in opposite directions to either increase or decrease the thermal trip setting

Methodology Applied

Scientific EffectPlastic deformation: Plasticity

Data Source

PatentUS8531256B2Tool and calibration machine for calibrating a thermal trip apparatus of a circuit interrupter, and improved method

Publication Date: 2013.09.10 EATON INTELLIGENT POWER LTD

AI summary

An improved calibration machine for calibrating a thermal trip apparatus of a circuit interrupter employs a tool having an elongated shank and a pair of engagement elements. The engagement elements are engageable with a support that carried a bimetal element. The engagement elements can deform the support in opposite directions to either increase or decrease the thermal trip setting of the thermal trip apparatus. If the support is over-deformed in one direction, it can be deformed in an opposite direction to enable a circuit interrupter whose thermal trip apparatus has been deformed beyond a desired target thermal calibration setting to be deformed in an opposite direction to reach the desired target thermal calibration setting.