Voltage Transformer Overcurrent Protection Relay Fuse

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Solution Overview

Problem

Voltage transformers face challenges in protecting against overcurrents without damaging the control logic when connected to high voltage primary windings, and existing solutions complicate manufacturing and increase costs.

Innovation Solution

A voltage transformer design incorporating a relay with a coil in series with the primary windings and normally open contacts that short circuit a fuse when thrown, along with a second fuse in parallel with the relay coil to minimize voltage drop and a resistor in series to limit short circuit current, ensuring accurate voltage transformation and protection without interfering with the secondary windings.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a low impedance fuse is provided for high overcurrents, then short circuit protection is improved, but the interrupting value becomes too high causing a region of overcurrents that cannot be interrupted

Engineering Contradiction:

Improveshort circuit protectionVSAvoidinterrupting capability range

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The protection system is segmented into two independent fuse levels: a first fuse for high overcurrents/short circuits and a second fuse for lower overcurrents. This segmentation allows each fuse to be optimized for its specific current range, resolving the contradiction between protecting against high overcurrents and maintaining interrupting capability for lower overcurrents.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The voltage transformer acts as an intermediary element between the primary and secondary circuits. By placing fuses on the secondary side rather than the primary side, the system gains the ability to protect against overcurrents with appropriate interrupting values while maintaining protection effectiveness.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If control logic is connected to primary windings for overcurrent protection, then protection function is improved, but the control logic is damaged by high voltage

Engineering Contradiction:

Improveovercurrent protection functionVSAvoidhigh voltage damage to control logic

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The voltage transformer serves as an intermediary that electrically isolates the control logic from the high voltage primary windings. The control logic operates on the low voltage secondary side while still being able to detect and respond to overcurrent conditions through the transformed voltage signal, thus protecting the control logic from high voltage damage.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces direct electrical connection-based protection with electromagnetic induction-based protection. Instead of connecting control logic directly to primary windings, the system uses the voltage transformer's electromagnetic coupling to transfer protection signals from the primary to secondary side, eliminating the need for direct high voltage connections.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If control logic is added for overcurrent protection, then protection capability is improved, but manufacturing complexity and costs increase

Engineering Contradiction:

Improveovercurrent protection capabilityVSAvoidmanufacturing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The voltage transformer provides self-service protection through its inherent electromagnetic transformation properties. The transformer naturally steps down high voltage to low voltage, and by placing simple fuse protection on the secondary side, the system achieves overcurrent protection without requiring complex control logic, microprocessors, or additional sensing circuits.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent uses inexpensive, simple fuse elements as the primary protection mechanism rather than expensive, complex electronic control systems. Fuses are disposable protective devices that provide reliable overcurrent protection through a simple, well-understood physical mechanism, reducing manufacturing complexity and cost.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 solution effectively prevents damage from overcurrents by blowing the fuse at lower currents, maintaining accuracy and reducing manufacturing complexity and costs by isolating the control logic and minimizing voltage drop across the relay coil.

Implementation Method 1

a body with primary windings and secondary windings coupled to each other by electromagnetic induction

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS11251604B2Voltage transformer

Publication Date: 2022.02.15 EATON INTELLIGENT POWER LTD

AI summary

A voltage transformer includes: a body with primary windings and secondary windings coupled to each other by electromagnetic induction; a measuring device electrically connected to the secondary windings via a first fuse; and a relay having a coil and at least one pole with normally open contacts, the at least one pole being configured to be thrown by an energizing of the coil. The coil is arranged in series with the primary windings. The at least one pole with normally open contacts is arranged between the secondary windings via the first fuse in order to short circuit the first fuse when the at least one pole is thrown.