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BE1-87G - Functional Description 3-3
Figure 3-3. Sensing Input Range 2 (1 Ampere),Stabilizing Reactor Impedance Characteristics
Bandpass Filters
Outputs from the relay transformers are filtered to eliminate the third harmonic and to minimize the effect of DC
offset caused by CT saturation (as may occur during synchronization or asymmetrical faults).
The output of the difference bandpass filter is applied to a full wave rectifier. The rectifier scales the differential
and applies the output to the comparator as the operating current (I
OP
) signal .
The output of the sum bandpass filter is also applied to a full wave rectifier. The scaled sum of the two inputs
represents the restraint current (I
R
). The restraint current is scaled for a 50% slope above nominal input current
(five amperes input range one and one ampere input range two).
Comparator
The comparator provides the variable percentage characteristic of the relay as follows:
When I
R
is less than nominal (five amperes input range one and one ampere input range two), the
comparator provides an output signal whenever the operate current (I
OP
) exceeds the front panel sen-
sitivity setting I (
S
).
When I
R
is greater than nominal (five amperes input range one and one ampere input range two), the
front panel sensitivity threshold is increased by adding to it a scaled value representing 1/2 of I
R
minus
nominal (five amperes input range one and one ampere input range two).
Outputs
In the three-phase model, the outputs of the comparators are OR'd so that the coil of the output relay is
energized if the current difference of any monitored phase exceeds the variable percentage limit. When the
current difference falls below 90% of the variable percentage threshold, the output relay resets.
Targets (Optional)
If the relay is equipped with targets, the target associated with the phase or phases with excessive differential
current is tripped.
Depending on the style number (TARGET Option A or B), a unit may contain either internally operated or current
operated targets. Internally operated targets are actuated in conjunction with the output relay. Current operated
targets require a minimum of 0.2 ampere in the output circuit for actuation. Both types are magnetically latching
devices and must be manually reset by use of the reset lever.
Push-To-Energize (Optional)
The unit may be equipped (Option 2-C) with a momentary pushbutton that is accessible through the front panel.
To prevent accidental operation of this switch, it is recessed behind the front panel of the relay and is actuated
by inserting a thin non-conducting rod through an access hole in the panel. When pushed, the switch operates
the output relays and internally operated targets. Current operated targets will activate if the required 0.2
ampere of minimum current is present.
Power Supply Status Output (Optional)
The power supply status output relay (Option 3-6) has normally closed (NC) output contacts. This relay is
energized upon power-up and the NC contacts open. Normal relay operating voltage maintains the power