TS 880 TRANSFER SWITCH
PM064 REV8 10/01/25 14 Thomson Technology
Closed Transition Operation Sequence Diagram
(Normal Power Failure & Return Sequence)
The following operating sequences and time delays are associated with closed
transition type transfer switches which momentarily parallel two sources of supply for
less than 100 milliseconds. For closed transition type transfer switches, which utilize
extended parallel operation for soft-loading operating sequences, refer to separate
instruction manual.
1. Transfer Control Switch (Open/Closed Transition): A two position selector switch
is provided on the front of the transfer switch for operator section of desired
operation. The 2 positions are as follows:
§ OPEN TRANSITION: The transfer switch will operate in a “break-
before-make” open transition sequence during load transfers. A
programmed neutral delay period will occur during the transfer
sequence to ensure voltage decays on the load bus before load is
re-applied. The two sources will not be paralleled at any time
during operation in this mode.
§ CLOSED TRANSITION: When both sources of supply are
available, the transfer switch will operate in a “make-before-break”
closed transition sequence during load transfers. Note: If only
one source of supply is available during an initiated transfer
sequence, the control system will automatically revert to an open
transition transfer sequence.
2. Synchronizing Protection: To ensure both sources are in synchronism prior to
initiating a closed transition transfer sequence, a sync check relay is used
(Device 25). The synch check relay is door mounted and proved a LED light
Synchroscope to monitor phase angle of the two sources. The synch check relay
will block a closed transition transfer sequence until both sources phase angle
and voltages are within programmed limits. The synch check relay settings are
field programmable (+-5 to 20 Deg Phase Angle (rw) and 1-10% voltage
difference (rU) and they must be set at time of final equipment commissioning
for desired values. The factory settings are as follows:
To Next Page
Loading...
