Basler Electric BE1-51/27R - Manual (Page 21)

9137200999 Rev F 15
Voltage Restraint
Voltage restraint compares the binary number representing the monitored voltage with the fixed nominal
voltage limit (100 Vac for 50-hertz systems and 120 Vac for 60-hertz systems). When the voltage is
between 100 percent and 25 percent of the nominal voltage, the circuit automatically lowers the selected
time overcurrent pickup point proportionally. Instantaneous overcurrent operation, if present, is not
affected. Neutral is not monitored for voltage, nor is the neutral time overcurrent pickup point restrained.
When the voltage is above the 100 percent limit, the pickup point is restrained to 100 percent. When the
voltage is below the 25 percent limit, the pickup point remains at the 25 percent point.
For a given level of current above pickup, a lowering of the pickup point, via voltage restraint effectively
increases the multiples of current. This shifts the time delay characteristic to the right on the multiples-of-
pickup-current axis (characteristic curves) as voltage drops from 100 percent to 25 percent.
To find the effective multiple of pickup current use the formula:
V
V
I
I
M
N
t
× =
Where: M = Multiple of tap value current
I = Applied current level
I
T
= Tap value
V
N
= Nominal voltage
V = Applied voltage level
Microprocessor (Not Shown)
Some of the circuitry already discussed is part of the microprocessor and no definite lines are drawn to
separate the functions. The microprocessor compares the desired time delay (from the time trip
comparator and scaler) with the actual elapsed time from the counter. When the elapsed time reaches the
intended delay, the timed output relay is energized. During the time delay period, the front panel TIMING
indicator (i.e. pickup) associated with the detected phase is illuminated.
If targets are present, the front panel TIME FUNCTION target will be tripped, and the A, B, C, or N
ELEMENT target associated with the detected phase will be tripped. See the Controls and Indicators
chapter for the types of targets that are present (depending upon relay configuration).
If option 3 is present, an auxiliary output relay (with N.O., N.C., or SPDT contacts) is also actuated when
the timed output relay energizes.
Instantaneous Overcurrent (Options 1-1 and 1-2)
Input current levels applied to the time overcurrent circuitry are also passed to the instantaneous
overcurrent circuitry. These levels are compared to the setting of the front panel INST 1 adjust and the
front panel INST 1 (NEUTRAL) adjust (if present). If the input current level is above the setting, the output
driver energizes the instantaneous 1 output relay. If the instantaneous 2 option is present, the input level
is also compared with the setting of the front panel INST 2 adjust to energize the instantaneous 2 output
relay. Note that the current level settings for the instantaneous overcurrent element will always be from 1
to 40 times above the front panel TAP and TAP (NEUTRAL) settings of the time overcurrent element.
If target type A or B is present, the front panel INST 1 target and the front panel INST 2 targets are
tripped when their respective output relay is energized, along with the front panel A, B, C or N ELEMENT
targets (if present) associated with the detected phases. (See the Controls and Indicators chapter for the
types of targets that can be present depending upon the relay configuration.)
Timed and Instantaneous Outputs
Each output signal (representing either time overcurrent or instantaneous overcurrent) from each
monitored phase (or neutral) is applied to the respective output driver. Each output driver supplies
operating current to energize the associated output relay. Either normally open (output type E) or normally
BE1-51/27R Functional Description