In order to maintain high levels of system availability within warships, many circuits are arranged with dual sources of supply. One source is generally designated the preferred or normal source. The second source functions as a back up or alternative. Should the preferred source fail or drop out of acceptable power limits, a transfer switch will automatically switch the supply to the alternative source. Traditionally this switching has been done by electromechanical devices with a switching time of 50 - 100 msec. On modern warships, many systems are computer controlled and switching times of this duration are unacceptable. As a result the computer systems are supported by an uninterruptible power supply unit with battery back up. The introduction of the Static Automatic Bus Transfer (SABT), Solid State, Three Phase Transfer Switch having a transfer time better than 4 msec overcomes this and allows for the elimination of the UPS units and associated battery banks. This paper describes the technology and operation of the SABT and identifies how it can be used in a warship application, using the UK Royal Navy T45 Destroyer as an example. The recent UK proving trials are also described and the results presented.
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