How the ATC-900 evaluates closed or in-phase transitions

The controller software will confirm that the closed transition (CT) or

in-phase transition is enabled through the setpoints. When source

1 and source 2 are both available within voltage and frequency set

point tolerances:

• If S1 and S2 setpoints (UV/OV, UF/OF) are identical, there can be

a difference in voltage and/or frequency when transition occurs.

Also, if there is a difference in setpoints, the actual voltage and/or

frequency may be identical when the transition occurs.

• It confirms that sources are within closed or in-phase transitions

set point tolerances when:

• Voltage difference for closed transition = +/- 1 to 5%,

• There is no voltage difference setpoint for in-phase. As long

as both voltages are within voltage limits, any difference is

acceptable

• Freq. difference = +/- 0 to 0.3 Hz for closed transition

• Freq. difference = +/- 0 to 3 Hz for in-phase

• Phase angle, when the number of generators = 0. the phase

angle difference is fixed at +/- 8 degrees

• Phase angle, when the number of generators = 1 or 2. the

phase angle difference is fixed at +/- 5 degrees

• The controller attempts a closed or in-phase transition until the

sync timer (adjustable from 1 to 60 min) expires.

Synchroscope data for in-phase & closed transitions