Hybrid Transfer Switch With Relay Self-Test for Fast Power Transfer
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Solution Overview
Problem
Existing transfer switches in data centers face challenges in achieving fast and reliable switching times between power sources due to limitations in electromechanical relays, which fail to meet performance standards like the ITIC CBEMA Curve, and also struggle with in-rush currents and relay testing without additional components or interruptions.
Innovation Solution
A shared, hybrid transfer switching system using solid-state switching devices like TRIACs or anti-parallel SCR pairs in conjunction with electromechanical relays, enabling faster switching, soft-start features to mitigate in-rush currents, and integrated relay testing capabilities without additional components or power interruptions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If electromechanical relays are used for power source switching, then the device structure is simple and cost-effective, but the switching time cannot meet the ITIC CBEMA Curve performance standards (faster than 20 ms at 70% voltage, ideally less than or equal to 8 ms at 60 Hz line frequency)
Solution Approach 1:
The patent combines electromechanical relays with solid-state switching devices (TRIACs or anti-parallel SCR pairs) in a hybrid configuration. The solid-state devices are electrically connected in parallel with the relay contacts to provide fast switching capability while the relay provides robust mechanical isolation. This merging allows the system to achieve both fast switching times (meeting ITIC CBEMA Curve standards) and reliable power source isolation.
Solution Approach 2:
The patent replaces purely electromechanical relay-based switching with a hybrid system that incorporates solid-state switching devices. The solid-state TRIACs or SCR pairs can switch much faster than mechanical relays, enabling the system to meet the stringent switching time requirements of the ITIC CBEMA Curve (less than or equal to 8 ms at 60 Hz) while the electromechanical relay continues to provide reliable isolation.
2Speed
If dedicated solid-state switches are used for both first and second power sources to achieve fast transfer time, then the switching speed improves, but the number of parts increases and cost increases due to expensive isolated drive circuitry
Solution Approach 1:
The patent makes the solid-state switching device universal by configuring it to serve both power sources through a shared hybrid switching configuration. The same solid-state switch (TRIAC or SCR pair) can be selectively activated to switch either the first power source or the second power source, eliminating the need for separate dedicated solid-state switches for each source. This reduces component count and cost while maintaining fast switching capability.
Solution Approach 2:
The patent uses a single solid-state switching device that can be reconfigured or selectively activated to perform the switching function for both power sources, rather than having separate physical copies of solid-state switches for each source. This single device effectively 'copies' its switching capability to handle both sources sequentially or selectively.
3Reliability
If relay testing is performed to ensure proper operation, then reliability improves, but additional components or power interruptions are required which increase complexity and disrupt operation
Solution Approach 1:
The patent enables the relay testing function to be performed using the existing hybrid switching components (electromechanical relay and solid-state switch) without requiring additional dedicated testing components. The controller utilizes the inherent capabilities of the hybrid configuration to apply test voltages and detect relay contact status, allowing the system to self-test its own components.
Solution Approach 2:
The hybrid switching components serve dual purposes: they perform the primary power source switching function and simultaneously enable relay testing functionality. The solid-state switch and controller can be used to apply test voltages across relay contacts and detect their status, making the same components multi-functional and eliminating the need for separate testing hardware.
4Device complexity
If electromechanical relays are used for switching, then the circuit design is simple, but in-rush currents during cold starts can exceed relay contact ratings by an order of magnitude causing damage or energy hazards
Solution Approach 1:
The patent introduces the solid-state switching device as an intermediary between the power source and the load during startup. The solid-state device (TRIAC or SCR pair) can be controlled to gradually activate or limit in-rush current before the electromechanical relay fully closes its contacts. This intermediary function protects the relay contacts from excessive current stress while maintaining the simplicity of the overall circuit design.
Solution Approach 2:
The patent applies preliminary action by using the solid-state switching device to pre-limit or control the in-rush current before the electromechanical relay contacts fully engage. The controller can activate the solid-state device in a controlled manner during cold starts, preventing excessive current from reaching the relay contacts and causing damage.
Data Source
AI summary
The present disclosure relates to a shared transfer switching system with built in relay testing ability, for transferring power received by a load from a preferred AC power source to an alternate AC power source, or transferring power being received by the load from the alternate AC power source to the preferred AC power source. The system selectively controls various ones of the relays used to apply power from either the preferred or alternate power sources to the load, such that the relays are switched from open to closed states at controlled times, while voltage measurements are made at select locations between the relays. The system can identify which specific ones of a plurality of relays associated with each of the preferred and alternate power sources has properly opened and closed, and thus verify that all of the relays needed to switch between the preferred and alternate power sources are operating properly.