Closed transition operation

Closed transition is a feature that will temporarily parallel two live

sources in a make-before-break scheme when performing a transfer.

This achieves a transfer between sources with no power interrup

tion. Both sources must be synchronized in frequency, phase, and

voltage before the transfer will take place. Closed transition voltage

and frequency limits are adjustable in the system setpoints  (3 of 5)

screen. Maximum phase difference is fixed at 0.3 degrees.

The user can also disable closed transition and just use the following:

In-phase > TDN

In-phase > LVD

Also with closed transition and in-phase disabled: TDN or LVD

The user setpoints for closed transition are as follows: Disabled (closed transition not used)

Alarm on synchronization fail (will not switch and will show an alarm)

Fallback to open on synchronization fail (to in-phase, TDN, and/or LVD)

For in-phase and closed transfers, the phase difference between

sources is displayed above the ATC-900’s sync time countdown message.