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The fault block accessory is mounted in the upper right
corner of the back panel of the control, Figure 18. Controls
and instructions for operating the accessory are located
on the front panel above the input fuses, Figure 19.
General Description
In response to fault current above preselected phase or
ground levels, the accessory is activated and latched to
disable both high-voltage switches. Thus a load-side fault
followed by loss of potential will result in partial load
transfer opening the connected source but not closing
the faulted load into the alternate feeder.
The accessory must be manually reset at the control
panel to restore service to the load. If activation of the
fault block accessory is due to a temporary fault (pre-
ferred source voltage is restored before the transfer delay
timer runs out), line current of 5 Amps, or more, flowing
through the high-voltage switch will automatically reset
the accessory in approximately 10 to 15 seconds.
To prevent the fault block accessory from being activated
due to inrush current that may occur as a result of the
backup opening and closing, an inrush restraint feature is
built into the accessory logic. Upon loss of the preferred
source voltage, the inrush restraint operates to increase
the phase fault actuating level by a predetermined multi-
ple for a predetermined time after voltage is restored.
Simultaneously, ground fault current detection is blocked
completely for the same time interval. When the time runs
out, both the phase and ground current actuating levels
return to their normal values.
To operate the fault block accessory, the Source I and
Source II high-voltage switches must be equipped with
1000:1 ratio current transformers to monitor the magni-
tude of the line current and an auxiliary “a” contact. The
bushing current transformers and associated wiring are
provided as a factory-installed accessory to the high-volt-
age switch.
Accessory Settings
The selected phase and ground fault
actuating levels should be greater
than any peak load phase current or
zero-sequence (ground) current, but
less than the trip setting of the back-
up protective device. A general rec-
ommendation is to set the phase
and ground actuating levels to
approximately 80% of the phase and
ground trip levels of the backup.
The phase fault current minimum
actuating level is determined by a
plug-in circuit card, Figure 20.
Cards are available for 80, 112,
160, 224, 320 and 448 Amp actuat-
ing levels. The ground fault current
minimum actuating level is deter-
mined by a resistor cartridge that
clips on to the phase card.
Cartridges are available for 10, 14,
20, 28, 40, 56, 80, 112, 160, 224,
320 and 448 Amp actuating levels.
Type S Automatic Load-Transfer Control Installation, Operation, and Maintenance Instructions
28
Figure 19.
Fault block accessory controls and operating instructions plate.
020077KM
INSTRUCTION LABEL
Provides instructions
for resetting the
fault block accessory.
RESET SWITCH (S7)
Reactivates the S control
after a fault block operation.
FAULT BLOCK
OPERATED SWITCH
Indicates that the fault block
accessory has operated.
FAULT BLOCK ACCESSORY
(Applicable to VR, VLR, VRV, TSC, CS, and PST-6 switchgear.)
Figure 18.
Fault block accessory mounted in upper-right corner of the back panel.
ACTUATING LEVEL PRINTED
CIRCUIT CARD (FIGURE 18)
TERMINAL BLOCK FOR
EXTERNAL CONNECTIONS
RAISED FAULT LEVEL
DURATION TIMER
020080KM