Transfer Switches

[js1960]

I have a very basic question about transfer swtiches. Do most/all transfer switches have a sensing mechanism that makes sure the "incoming" voltage is at the same frequency & in phase with the "running" voltage before the switch occurs? I have seen Synchroscopes which show if the running is faster or slower (or out of phase) with the incoming, but I doubt that they are used for anything more than a visual indication and maybe a way to know "what needs to be done" to the source before the switch occurs. Also, while I am on the subject, what can an operator do to correct incoming voltage if it is not at the same frequency and/or phase as the running?

Thanks in advance,

JS

 

[rbulsara]

I assume you are talking about electromechancal transfer switches (not static electronic type).

If so, then there are two basic types. "Open transition" type automatic transfer switches (ATS) are break before make type and therefore do not and need to look for synch.

The Closed Transition Type ATS do have logic built in to look for the synch with adjustable settings for both frequency and voltage to allow for inevitable differences between the two sources, but yet safe to make closed transfer.

If the sources are not withing acceptable limits, nothing can be done at the ATS beyond the maximum tolerances, but if one of the source is the generator, it can be adjsuted.