Chances are, you have experienced a faulty Automatic Transfer Switch, know someone who has, or will at some point in the future. Here is how the story goes: The facility loses utility power. The generator starts, the uninterruptible power supply goes to UPS battery, and everything is working flawlessly. The generator should sync to the uninterruptible power supply in 10-15 seconds, and since you recently performed a proactive replacement of your previous set of 4-year-old UPS batteries, you should have a solid 15 minutes of buffer time. But for some reason, after a full minute, the uninterruptible power supply is still running on UPS batteries and the generator is not syncing. Your confidence is wavering.
Wait, Why is the ATS still in Utility mode? You have found the culprit! Now you begin to recall your Nationwide Power service provider asking you to test the automatic transfer switch so they can verify proper operation. You also recall declining their request, cringing at the possibility that the automatic transfer switch won’t work, and that you did not want to take that chance at that moment.
Now, a real scenario is here, and the automatic transfer switch is not working! It has not been serviced since, well, the facility was first put on-line. Now those mechanical contacts that have not been inspected won’t change state. The automatic transfer switch is even making a weird clattering noise.
Someone call the Nationwide Power emergency line ASAP! We need this to transfer now!
I need to let IT and the facility folks know they must start a controlled shutdown of all the equipment, severs, etc. before we have a load loss!
The UPS beeps: “Shutdown Imminent”.
Why is the automatic transfer switch not working? Maybe if I manually… too late! Load loss has occurred. The uninterruptible power supply has shutdown on Low DC / DC Under-Voltage.
Conclusion: All of this could have been avoided. To your credit, you did have the uninterruptible power supply properly serviced and maintained, up to and including a new UPS battery, fresh capacitors and fans – everything! You also ensured the generator was properly serviced and checked regularly, up to and including new oil, oil filters, air filters, topped-off with fuel – everything!
If only the automatic transfer switch would receive as much attention in our industry as those other ‘obvious’ pieces of the critical power system, this scenario would not be as common as it is. Often, performing a real test of the automatic transfer switch does equate to an actual power transfer of the facility, and most facilities do not want to schedule such a test, or take the chance it may not work. By not testing the automatic transfer switch in a controlled environment, however, you are taking a risk of failure during the worst possible time. Test your automatic transfer switch in a controlled and planned environment to improve the likelihood your automatic transfer switch will work properly in an emergency.
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