Cooper Lighting S260-75-1 - Manual (Page 29)

The actuating level multiplier for the inrush restraint fea-
ture for phase faults is set by a jumper wire connected
to a tab on the circuit card. Tabs are provided for X1, X2,
X4, X6, X8 and BLOCK settings. The duration of the
raised level is set by a knob on the top of the timer
(Figure 18). The timer is infinitely adjustable 0.1 to 5.0
seconds. No settings are required for ground inrush
since it is automatically blocked for the duration the
phase level is raised.
Operating Instructions
The FAULT BLOCK OPERATED lamp on the front panel
of the control, Figure 19, will light when the fault block
accessory is activated. To reset the accessory:
1. Move the OPERATION SELECTOR switch (S3) to
MANUAL.
2. Depress and hold the RESET switch (S7) until the
lamp goes out, (approximately 6-10 seconds) indicat-
ing the accessory has reset.
3. To restore service, return the OPERATION SELEC-
TOR switch (S3) to AUTOMATIC; the preferred
source high voltage switch will close.
OR
Operate either the MANUAL OPER. SOURCE I switch
(S1) or the MANUAL OPER. SOURCE II Switch (S2),
as applicable, to restore service manually.
Note: Instructions for operating the fault block accessory
also are printed on the front panel of the control
(Figure 19).
Theory of Operation
—Fault Block Accessory
The fault block accessory prevents automatic closure
into the alternate source when loss of preferred source
results from a fault on the load tap. The schematic dia-
gram for the fault block accessory, Figure 21, is used as
reference throughout this discussion.
Overcurrent Sensing
The output of bushing current transformers in both the
Source I and Source II high voltage switches are applied
to the fault block accessory via terminals lA, IB, IC, IN
and IX, IY, IZ, IN respectively. When the load current
through the switch exceeds the phase or ground actuat-
ing level selected, the relay contacts in the fault block
accessory (contacts 7-8 and 10-11 of relay RY1-B),
located in the closing circuits of both high voltage switch-
es, are opened. Subsequent closing of either switch is
blocked in either the automatic or manual mode of the S
control until the fault block accessory circuitry is reset.
Phase Fault Operation
Referring to the accessory schematic diagram, Figure
21, the phase currents are rectified by the diode bridges
D103 through D116. Current out of the positive side of
the bridge passes through diode D127 and divides into
two parallel circuits. One circuit consists of zener D123
and the minimum phase actuating resistor R301 to the
other side of the bridge. The other circuit consists of nor-
mally closed contact (1516) of latching relay RY1, diode
D201, and capacitor C201 to the other side of the bridge.
C201, charged by load or fault current, provides tripping
energy for RY1.
The current through R301 produces a voltage drop pro-
portional to the line current which is impressed across
the series resistor string R101, R102, and R103. A por-
tion of this voltage is applied through diode D120 to the
base of transistor Q201.
When this voltage exceeds the break-down voltage of
zener D212 and the base emitter junctions of Q201 and
Q202, Q201 will conduct causing Q204 to conduct. In
turn, Q204 provides the gating current to turn on the SCR
(Q206) to discharge capacitor C201 through the trip coil
of the latching relay RY1. Contacts 10-11 and 7-8 of RY1
(in series with the close coils of the high voltage switch-
es) open to prevent the high voltage switches from clos-
ing until the fault block circuitry is reset.
An important feature of this accessory is that a trip signal
cannot be initiated until there is sufficient charge on C201
to activate the trip coil of RY1. Transistors Q201 and
Q204, effectively in series across C201, cannot conduct
until the voltage across C201 is sufficient to break-down
zener diodes D211 and D212.
S260-75-1
29
!
SAFETY
FOR LIFE
Figure 20.
Phase fault current actuating level printed circuit card. 020078KM
PHASE CURRENT LEVEL
MULTIPLIER SETTING FOR
INRUSH CURRENT RESTRAINT.
GROUND-
ACTUATING
CURRENT
RESISTOR
CLIPS TO THE
PHASE CARD