ATS Meeting the 10 sec rule in health care environments
ATS Meeting the 10 sec rule in health care environments
Forgive me if this has been discussed before. I couldn't find it in a search.
I am in a healthcare setting and we are required to transfer power within 10 seconds which is tested monthly and documented. We can't always meet that due to our closed transition switches. Is there any exceptions to the 10 second rule that would allow for the syncing of the two power sources during testing? We could open normal power and will meet the time. However, there are many instances where it is not practical to do so.
When we go over, the timing is generally around 11-18 seconds. Any assistance would be appreciated. Thank you
First of all, the problem you are experiencing has nothing to do with you having closed transition switches. Whether closed transition (make-before-break) or open transition (break-before-make) design, ATS's employ a feature called an in-phase monitor which is nothing more than a sync check circuit to only allow transfer when both sources are within a certain sync threshold (usually within 10 electrical degrees.) This occurs when the test is performed from the test switch on the controller, what we call a hot bus - hot-bus test. or during a re-transfer after a power failure.
From what you are describing, when you test from the test switch you cannot meet the 10 sec requirement. This indicate that there is an unusually long sync time before transfer. We find the most common reason for this is that the genset frequency is set either too close or too far away from the utility: 60.00HZ. GE-Zenith recommends a setting of 60.10HZ. We like to see it set at 60.20HZ to allow for speed drift.
When you test by opening the normal source breaker (which no hospital likes to do, but simulates a real power failure) you meet the 10 second rule. In this type of test, we call a dead bus - hot bus test, your closed transition ATS reverts to a delayed transition ATS with a faster transfer time since there is no sync time in the equation.
I would recommend calling in your genset vendor to adjust the frequency to 60.20HZ for a faster sync time. Most younger techs aren't aware of this and are prone to setting it dead on 60.00HZ. The other problem is that most gensets come from the factory set at 60.00HZ and either requires a laptop program to make changes or the tech ordering and installing an accessory panel to correct the problem as in the case of Kohler.
I have attached files from 2 previous jobs that may also help to explain the situation. Good luck.
