open/closed transition switching

[stagedad]

Our regional electric utility will only allow Open Transition switching when they supply a customer who has a double-ended substation. This seems perfectly logical to me, and in fact I am not aware of any scenarios where a Closed Transition arrangement would might be preferred.

After the manufacture and installation of our new main sercvice (using a double-ended 4160 Volt substation), and half-way thru the start-up testing, the manufacturer now states that the set-up of the GE SR750 relays they have used on all of the breakers, including the Main,Tie, and other Main, will not prevent closed transtion.

Help? Does this make any sense to anyone out there?

 

[dpc]

Firstly, open transition implies a temporary loss of power. this is often unacceptable so closed transition is sometimes used to avoid any interruption of power. Closed transitions are fairly common, but have problems related to high fault currents and sometimes synchronizing/phase shifts issues.

Secondly, the SR750 is basically a feeder protection relay providing overload and short circuit protection (plus a bunch of other features). It can be programmed to provide some automatic and manual transfer logic, but I would never expect a manufacturer to program an overcurrent relay to prevent closed transition unless this requirement was explicitly specified when the equipment was purchased.

To reliably prevent closed transition, the mains and tie should be electrically interlocked, via breaker auxiliary switches, or preferably mechanically interlocked via a Kirk Key interlock system, or both.

So it all makes sense to me. What seems to be missing is the translation of the utility's requirement into a engineering specification.