12 S&C Instruction Sheet 515-600
Operating Description
If the control has been programmed for “window return,” automatic return-of-source
transfer to the normal condition will be performed in the same manner as for an “auto-
matic return.” But return-of-source transfer is permitted to occur only if the time of day
is within the specified time “window.” The beginning of this window is the predetermined
Window Begin
setting;
●
the window length is adjustable from 1 minute to 3 hours.
If the control has been programmed for “hold return,” transfer to the normal condition
must be accomplished manually—unless alternate-source voltage becomes inadequate
and preferred-source voltage is adequate. In this case of loss of alternate-source voltage,
an automatic “open transition” loss-of-source transfer will take place.
When the return-of-source transfer occurs, the auto matic-transfer READY indicating
lamp will again light, indicating that the normal condition has been restored.
At installations using three-phase source voltage sensing, the control may be programmed
to detect phase unbal ance conditions on the source. This feature protects the loads from
any source-side open-phase condition at the same system voltage level as the Alduti-Rupter
Switches—whether caused by utility-line burn-down, broken conductors, single-phase
switching, equipment malfunctions, or single-phasing resulting from blown source-side
fuses.
■
When this feature has been programmed, the control will initiate an automatic source
transfer when each of the follow ing conditions exist:
• The signal-input phase-voltage unbalance of the source serving the load exceeds the
predetermined unbalance-detect voltage,
▲
for a period of time considered sufficient
to confirm the condition is not transient—the predetermined
Loss-Of-Source Time
setting
◆
• The signal-input phase-voltage unbalance of the standby source is less than the pre-
determined unbal ance-detection voltage
▲
• The
Overcurrent Lockout
feature, if programmed, is not “set up” to prevent an
Automatic Transfer
opera tion that would close a source interrupter switch into a
fault. See the “Overcurrent Lockout Condition” section below
Upon return of the preferred-source phase voltages to their normal, balanced state,
return to that source can be accomplished as described in the “Transfer on Return of
Source Voltage” section on page 11.
At installations where three user-furnished Fisher Pierce Series 1301 Powerflex Line Post
Current Sensors have been provided on each source, the control may be pro grammed to
include an
Overcurrent Lockout
feature. This feature prevents an automatic-transfer
operation that would close a source interrupter switch into a fault, thereby avoiding
further utility-system disturbances.
An overcurrent in excess of the predetermined
Lockout Level
setting
▼
detected as
the imbalance in the three-phase current—the summation of the currents sensed by the
individual phase current sensors of the source serving the load—will “set up” the
Lockout
feature. The LOCKOUT lamp will light.
Transfer on Unbalance
Condition
Overcurrent Lockout
Condition
●
Factory-set at 01:00 (24-hour format) .
■
The
Unbalance Detection feature should not be programmed in appli cations using three-phase voltage
sensing provided by two line-to-line connected voltage transformers per source .
▲
Factory-set at 18 Volts .
◆
Factory-set at 2 .00 seconds .
▼
Factory-set at 1200 amperes . S&C recommends customers use the factory-default setting or adjust this
value to 70% of the available neu tral fault current, whichever is lower . In some applications, the lockout level
setting is determined by the setting of user-furnished external relay ing . An adjustable overcurrent-lockout
pickup time delay is provided to prevent nuisance lockouts due to motor load backfeed into upstream faults .
Factory-set at 50 milliseconds . Adjustment range is 3 to 100 milli seconds .
