No Preference Mode
Assume the Source I high-voltage switch (SW-I) is closed and Source II high-voltage switch is open. With the SOURCE PREFERENCE and RETURN MODE switch (S4) in NO PREF-NP (Terminal 4 of S4 connect- ed), loss of Source I voltage on one or more phases will open the Source I high-voltage switch (SW-I) as described in the Automatic Transfer, Preferred to Alternate section of this discussion.
Upon restoration of Source I voltage, R2 is re-ener- gized. However, due to the positioning of decks G and H of S4, neither timer can be energized since both the N.C. contacts 1-7 of R2, and 9-3 of R6 are open (both relays are energized).
The S control is now in a quiescent state with SW-II closed and SW-I open. This condition will continue until either Source II is lost or a change is made in the control settings. If Source II is lost, delay in transfer to Source I will be timed by TM-2.
Preferred Source II Mode
With the SOURCE PREFERENCE and MODE switch (S4) in either PREF II-P (Terminal 6 of S4 connected), or PREF II-NP (Terminal 5 of S4 connected) the description of operation is similar to the “Automatic Transfer, Preferred to Alternate” and “Return Transfer, Parallel Transition” or “Return Transfer, Non-Paralleled Transition” as previously described except that Source II is the preferred source (controlled by SW-II) and Source I is the alternate source (controlled by SW-I).
Control Mode Switch, S5
If S5 is placed in the center-off TEST position, there is no circuit to either the close or trip coils of either high-voltage transfer switch. This position of S5 is used to check sensing circuitry, timers, and the latching relay without affecting the status of the high-voltage switches.
If S5 is placed in the HOLD ON ALTERNATE position, return transfer will not occur after preferred source voltage is restored. Assume the S3 is in AUTO, S4 is in PREF l-P, and the S control is in the quiescent state with Source I high voltage (SWI) closed and Source II high- voltage switch (SW-II) open. Upon loss of Source I, R2 will again initiate a transfer of the latching relay R1 as previously described, followed by the opening of SW-I and the closing of SW-2. The S control is now in a quiescent state in which SW-2 will remain closed and SW-I will remain open even when Source I power is restored. When Source I is reenergized, R1 will transfer back to the latch position and close its contact 9-6. However, because deck L of S4 is open, power cannot be provided to the trip coil of SW-II or the close coil of SW-I.
Manual Control
When the OPERATION SELECTOR switch (S3) is placed in MANUAL, it connects the MANUAL OPER. SOURCE I switch (S1) and the MANUAL OPER. SOURCE II switch (S2) to the transfer bus. Power can then be supplied to either the close or trip coils of either SW-I or SW-II. Contacts 3-7 and 2-6 of S3 are opened in the MANUAL position so that opening of one high-voltage transfer switch does not cause automatic closing of the other. In the manual mode of operation, it is possible to have both high-voltage switches open, either switch closed, or both switches closed.
Indicating Lamps
The LAMP TEST switch (S6) is provided for checking the various incandescent indicators on the front panel of the S control. In the closed position, all the lamps will be energized through a diode network to check their condi- tion.
In the open position, the diode network isolates the lamps from the test switch so that it has no effect on normal circuit operation.
