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

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

The synchroscope is a useful tool for synchronous transitions. When

the controller is waiting for synchronization for either in-phase or

closed transitions, there is a timer countdown and the display will

show the following:

Phase angle  xxx degrees          Sync timer  hh:mm:ss

The phase angle is between 0 and 365 degrees. On each closed

transition type switch, there is a parallel limit timer that either opens

the breaker or sends a close to user terminal blocks (contactor

types) that can be used to open breakers upstream if the overlap

time is greater than what was set by the user. Please check the

switch instruction booklet for more information.