Galvanically Isolated Solid-State Switch for SIL4 Railway Switching
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Solution Overview
Problem
Electromechanical relays require regular maintenance, have moving parts that wear out, are expensive, and can arc due to mechanical contact, while existing solid-state relays are not used for vital functions.
Innovation Solution
A solid-state switch with an isolation boundary, semiconductor switches, programmable devices, and monitoring circuits that ensure galvanic isolation and self-testing to maintain safety integrity levels, eliminating mechanical wear and arcing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electromechanical relays are used for switching, then current switching function is achieved, but maintenance requirements increase and reliability decreases due to moving parts wear
Solution Approach 1:
The patent replaces electromechanical relays with solid-state semiconductor switches (MOSFETs or IGBTs) that have no moving parts. The mechanical contact system is substituted with electronic switching components controlled by gate signals, eliminating wear and maintenance while improving reliability for vital railway functions.
Solution Approach 2:
The patent introduces an isolation boundary with galvanic isolation between the control zone and power zone. This intermediary isolation barrier allows the solid-state switch to be controlled without direct electrical connection, enabling reliable operation while maintaining safety integrity levels required for vital railway equipment.
2Reliability
If electromechanical relays are used for switching, then current switching function is achieved, but arcing occurs due to mechanical contact
Solution Approach 1:
The patent eliminates mechanical contacts entirely by using solid-state semiconductor switches. The electromagnetic field control replaces physical contact closure, preventing arcing and electromagnetic interference that would otherwise be generated by mechanical contact operations in vital railway switching applications.
3Ease of repair
If solid state relays are used for switching, then maintenance needs are reduced, but safety integrity level cannot be achieved without additional isolation measures
Solution Approach 1:
The patent implements a galvanic isolation boundary as an intermediary between the low-voltage control zone and high-voltage power zone. This isolation barrier with defined safety integrity levels enables solid-state relays to achieve both reduced maintenance needs and required safety standards for vital railway functions through proper electrical separation.
Solution Approach 2:
The patent maintains the maintenance-free advantage of solid-state relays while adding electronic isolation measures (optical isolators, transformer coupling) that provide safety integrity without mechanical components, thus preserving the low-maintenance benefit while achieving required reliability levels.
4Reliability
If galvanic isolation is implemented between zones, then safety integrity is improved, but device complexity increases
Solution Approach 1:
The patent uses standardized galvanic isolation components (optical isolators, isolated DC-DC converters, transformer-coupled signal paths) as intermediaries to achieve safety integrity. These pre-engineered isolation building blocks provide required safety levels while minimizing the complexity of implementing isolation throughout the solid-state relay system.
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 solid-state switch reduces maintenance needs, assembly costs, and achieves Safety Integrity Level 4 (SIL4) without mechanical wear or arcing, ensuring reliable operation in vital railway equipment.
Implementation Method 1
the control connection comprises at least one first photovoltaic isolator for bridging the isolation boundary
Implementation Method 2
the monitoring circuit comprises at least one galvanic isolator for bridging the isolation boundary
Data Source
AI summary
A solid state switch, in particular for a railroad equipment, including: an isolation boundary, the isolation boundary galvanically isolating a first zone from a second zone; at least one switch, each switch being adapted to switch a current in the first zone between a switch input terminal and a switch output terminal; at least one relay operating signal input terminal adapted to receive an operating signal, the operating signal indicating whether to switch the at least one switch; at least two channels, each channel including: for each switch a switch module in the first zone, each switch module including a switch module input terminal, a switch module output terminal and a semiconductor switch adapted to switch the current between the switch module input terminal and the switch module output terminal; at least one programmable device in the second zone, the at least one programmable device including an input terminal.