Under normal conditions; two sources should be adequate for reliable operation of the critical load. In some cases however, both sources of a dual cord distribution system may become unavailable due to a catastrophic infrastructure mishap.
A tri-source STS will have a third source, mains or generator, from some independent distribution scheme available as a source to power the load.
In a given system, normally, the dual cord infrastructure is supported by UPS (Uninterruptible Power supplies), and in almost all cases this should provide adequate protection against equipment failures and cascading failures due to aspects of single point failures. In this case it would be most usual for the third alternate source to be mains. Mains power is resilient enough and has the capacity to clear downstream faults in the case where all else fails will support the critical load infrastructure.
How the Tri-Source STS works
For normal operation the critical loads will be provided by either Source 1 or Source 2 and the third source (Source 3) will be available as a back-up. When Source 1 or 2 (or both) become available the load will be returned to the setting of the preferred source. Source 3 failing has no effect on the critical load and does not change the state of the Static Transfer Switch. If no priority is set then the load continues to be supplied by the source that was last requested (either Source 1, 2 or 3) and can then be manually transferred to any desired supply source by the operator when they are available.
Basic STS operation remains the same. All transfers are break-before make in both directions, (break is so small it is not seen by the critical load).
Static Power is currently developing this tri-source single phase configuration in their iSTS Model B2. The Model B2 has a Hot Socket Replaceable Power Module and maintenance bypass switch. The Model B2 in this configuration can be rated for 32 or 63 Amperes and switches both active and neutral conductors.
The Model B2 is a two part design; comprising a segregated fixed termination module incorporating a 3 position Maintenance Bypass Switch and a removable hot-socket power module. Terminals at the rear of the fixed portion (incorporating the maintenance bypass switch) enable connection of input and output cables of up to 16mm2, providing flexible connection to your PDU or load distribution infrastructure.
Static Power | Rack Mount & Static Transfer Switches
Over the last 16 years Static Power pty ltd in Australia under the banner of iSTS has been manufacturing a comprehensive range of mature fully Solid State “Static Transfer Switches”.
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