Cooper Lighting S260-75-1 - Manual (Page 4)

Description of Operation
The Type S control is designed for use primarily with Kyle
Type VR, VLR, VRV, TSC, and C three-phase, load-break
switches in automatic load-transfer schemes. In a typical
scheme, service to a critical load is normally supplied from
a preferred source. It is automatically switched to an alter-
nate, standby source if the preferred source voltage is lost
for any reason for a preset period of time. Upon restora-
tion of the preferred source voltage, the load is automati-
cally switched back to the preferred source, again after a
predetermined time delay.
Typical Automatic Load-transfer
Sequence using the Type S Control
• The load is transferred to the alternate source after a
preset time delay, when the preferred source voltage
is lost and normal voltage is present on the alternate
source. Either Source I or Source II can be selected
as the preferred source by a setting on the SOURCE
PREFERENCE Switch, S4.
• The load is transferred back to the preferred source—
after another preset time delay—when normal volt-
age is restored to the preferred source. The return
transfer (from Source II to Source I) can be either
non-parallel (alternate-source switch opens before
preferred-source switch closes) or parallel (preferred-
source switch closes before alternate-source switch
opens). With parallel return the second interruption is
eliminated; however, both sources must be in syn-
chronism. The return transfer mode is selected by a
setting on the SOURCE PREFERENCE switch, S4.
Variations in the Operation
of the Type S Control
• No-Preference Operation. When either source is
acceptable for continuous critical load supply. Upon
loss of Source I voltage—and after a preset time
delay—the load is automatically transferred to Source
II, provided normal voltage is present on Source II.
However, the load is not transferred back to Source I
when voltage is restored, but remains on Source II
until such time as Source II voltage is lost. Then an
automatic nonparallel transfer to Source I is per-
formed. (Accomplished by setting SOURCE PREF-
ERENCE switch, S4, to NO PREF position.)
• Hold on Alternate Source. When placed to the
HOLD ON ALTERNATE position, the S control will not
automatically return to the preferred feeder. If the pre-
ferred feeder is energized, the S control can be man-
ually transferred to the preferred feeder by momen-
tarily moving S3 to the NORMAL position.
• Manual Operation of the S control. The Source I and
Source II high-voltage switches can be opened and
closed independently to effect manual transfer from
one source to the other. (Accomplished by setting
OPERATION SELECTOR switch, S3, to MANUAL and
operating MANUAL OPER. SOURCE I (S1) and MAN-
UAL OPER. SOURCE II (S2) switches as required.)
In addition, a factory-installed fault block accessory will
Block Transfer if loss of voltage is due to a fault on the
load side of the high-voltage switches. When preferred
source voltage is lost (due to the opening of the backup
protective device)—and after the preset time delay—the
preferred source switch will open and the fault block
accessory will disable the S control to prevent closing
either high-voltage switch into the fault. The S control
must be manually reset before service to the load can be
restored. The fault block option is a factory-installed
accessory. The accessory is activated by over-current
signals supplied by load-sensing current transformers
built into special factory-modified Type VR, VLR, VRV,
TSC, and CS high-voltage switches. It is also compatible
with the PST-6 switchgear. The PST-9 switchgear does
not require fault block.
Time Delay Selection
The time delay setting for preferred to alternate source
transfer must be long enough to allow discrimination
between permanent loss of voltage and temporary loss of
voltage due to transient effects or reclosing intervals of
backup protective reclosers or breakers. The time-delay
required to override reclosing intervals is difficult to deter-
mine since voltage may be subnormal during the retard-
ed timing operations of the backup device due to the
presence of the fault. It is recommended that the time
delay before transfer from preferred to alternate source is
set to exceed the maximum cumulative time to lockout of
the backup protective device. This approach assures that
the transfer switch will not interrupt the current of a fault
occurring on the load side of the switch.
The time delay for return from alternate to preferred source
upon restoration of preferred source voltage should be set
for an interval long enough to assure that service on the
preferred source has been permanently restored.
When the control is programmed to operate in the “no-
preference” mode, there are no preferred or alternate
sources. Time delay intervals for transfer from Source I to
Source II are governed by the left-hand Preferred to
Alternate timer and for transfer from Source II to Source
I by the right-hand Alternate to Preferred Timer. Settings
of the two timers may be different because of difference
in backup protection on the two sources.
Type S Automatic Load-Transfer Control Installation, Operation, and Maintenance Instructions
4
IMPORTANT: If Control Mode Switch S3 is placed in
the “AUTO” position, the S-control will place the high-
voltage transfer switches into the configuration that is
currently selected by the Source Preference Switch
S4. This may result in an unintended transfer. Make
sure the desired state of the high-voltage transfer
switches match the setting of S4 before returning S3 to
the “AUTO” position.