The Role of Static Transfer Switches – How fast do They Switch?

Static Transfer Switches – How fast do They Switch, In the event of a power loss?

Power Continuity installations switch seamlessly via STS to the UPS & Generator supplies without any break, to avoid any disruption or loss to your site; virtually instantaneous.

No Break Power Protection. True Power Continuity.

For true resilience, though, there needs to be at least TWO GRID supplies feeding your Data Centre as a bare minimum and preferably these A & B feeds are from two separate ring mains. This is where a Power Continuity Static Transfer Switch (STS) comes into play.

The STS automatically selects the best & most stable available power from either of the two or more available sources, and rapidly switches over; as and when required, simultaneously. Should the STS sense any aberration in the mains supply it will switch. Your supply may not even go onto UPS and yet the STS can sense micro distortions and switch; afterwards switch back to the preferred source. This can happen many times or hardly any. It’s automatic.

How quickly will a Power Continuity STS respond?

It depends on the model of STS you choose.

Power Continuity Static Switches usually respond within around 3 to 5 milliseconds (thousandths of a second) – in fact, so fast that your equipment will not even notice or be affected by the change of power source from Source A to B feed or vice versa.

How is this achieved?

By the use of silicon-controlled rectifiers (SCRs) which, having no reliance on moving parts, allowing the transfer to be made extremely super fast, in fact Power Continuity STS are the most reliable in the industry.

As static switches are so vital to Data Centre resilience, what can go wrong?

  • The Static Switch needs to be regularly maintained as part of a service contract.
  • There must be at least TWO power sources available to allow the switch to take place
  • If the second source is not available during a power aberration then the static switch has no alternative source to turn to, hence the supported load would drop.
  • Your Data Centre must have records proving that the servers & racks have at least the minimum industry standard of hold times built in – as at 2018 that is 20 milliseconds.
  • Ensure that the available power sources have NO phase shift and the correct phase rotation. That needs to be verified, during every maintenance, with written records, to ensure nothing has changed.
  • Keep the LV breakers serviced & upgraded. Failure would remove an alternative source
  • Human intervention – STS are automatic so do NOT require human intervention during normal operation. LEAVE ALONE and DON”T touch. STS engineers only to set up.
  • Switching happens in the blink of an eye. This is normal operation. DON”T panic
  • Static Switching – Must have reliable and robust sources from at least TWO distinct supplies
  • In conditions where the A feed source and the B Feed source are not in alignment the static switches will still operate although NOT as fast as they are designed to switch.In fact disparity between the A & B Feeds will cause the Static Switches to switch between primary and secondary power spruces much more frequently.

What are the most common issues?

A common issue is that the servers and racks that are being powered by the Static Switches have not been maintained.
For example an internal UPS within the rack could be actually ‘dead’.
A rack mount ATS has never been tested, hence when called upon; it fails.
Worst still, no one in the Data Centre has reliably checked that each rack actually has two sources of power.
Therefore, guess work assumes that all racks are dual fed, hence when the static switches operate, some racks inevitably fall over as the two feeds are found to be from a single source.

Other issues that need to be considered and resolved

If the priority source or either of the sources are out of limits, transfer will be effected only after it has remained stable and within limits for a preset switch; but NOTE: Synchronization, transfer will only take place when the phase difference between the two sources is established by the intelligence with each Static Switch.

Should your site develops issues that cause the Static Switch to have to ‘think’ longer before making the switch, then it will take many more milliseconds before the switch takes place and may even caused multiple switching, in rapid succession.

To allow the Static Switch to operate correctly:

  1. Ensure that your site has, reliable and tested A& B feed supplies.
  2. Ensure that your site has NO phase shift or Phase Rotation issues.
  3. Ensure that the site transformers feeding the site are separate A & B feed transformers
  4. Ensure that the site is  NEVER feed the site from one single ring main.
  5. Lastly regularly TEST to ensure nothing has been actioned on your incoming power supplies that could jeopardise the functionality of your Static Switches.
  6. Ensure Any maintenance/changes/upgrades/faults etc. MUST be noted and placed on up dated drawings.
  7. Finally – Be in control of your site- Take the governance and ownership. Maintenance Records and a robust reliable schedule.

PowerContinuity engineers are experienced in installing Power Continuity Static Transfer Switches as part of our complete power protection package.

For more information of Static Switches- Call Power Continuity on 0845 0558455

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