Basler Electric BE1-51/27C - Manual (Page 18)

12 9137200998 Rev E
Power Supply
Operating power for the relay circuitry is supplied by a wide range, electrically isolated, low-burden power
supply. Power supply operating power is not polarity sensitive. The front panel power LED and power
supply status output indicate when the power supply is operating. Power supply specifications are listed in
the Specifications chapter.
Current Sensing
All relay models (except three-phase-and-neutral units) have two sensing ranges for each phase. Each
high/low sensing range has its own set of input terminal connections.
•
Five ampere CTs have: LOW (0.5 A to 4.0 A) and HIGH (1.5 A to 12.0 A).
•
One ampere CTs have: LOW (0.1 A to 0.8 A) and HIGH (0.3 A to 2.4 A).
Three-phase-and-neutral sensing units, however, have one of four possible combinations of input sensing
ranges with one range for neutral and one range for the phases.
•
Five ampere CTs have: 0.5 A to 4.0 A and 1.5 A to 12.0 A.
•
One ampere CTs have: 0.1 A to 0.8 A and 0.3 A to 2.4 A.
Tap Select and Tap Cal
Front panel TAP selectors and TAP CAL controls are provided for selection and precise adjustment of
the phase and neutral (if provided) time overcurrent pickup points. The front panel TAP selectors, ten-
position BCD weighted rotary switches, select the desired current sensing pickup point, while the front
panel TAP CAL controls provide precise adjustment between the selected setting and the next lower
setting.
Voltage Sensing
Input voltage for each phase to be monitored is applied to the voltage sensing circuits. Each voltage
sensing circuit consists of an input transformer, rectifier, and filter Analog voltages from the voltage
sensing circuits are applied to the multiplexor. Note that neutral is not monitored for voltage.
Multiplexor
The multiplexor sequentially switches a voltage representing each of the sensed input currents to the
analog-to-digital converter and level detector.
Analog-To-Digital Converter and Level Detector
When the voltage representing the actual sensed inputs meets or exceeds the selected pickup point, this
circuit converts the level to a corresponding binary number and applies it to a time trip comparator and
scaler circuit and to a counter for calculation of the required time delay.
Time Trip Comparator and Scaler
This circuit accepts both the binary number representing the detected current level and the desired time
delay characteristic selected by the front panel TIME DIAL, then computes the required time delay before
the timed output relay will be energized. Time delay characteristics are shown in the curves located in the
Time Overcurrent Characteristic Curves chapter. If extended timing range options 2-D or 2-E is present,
the time delay characteristic curves are modified so that the time delay is approximately 5.7 times the
derived value.
Time delay computations are updated continuously so that changes in the overcurrent condition are
monitored and result in a corresponding change in the time delay. A software counter begins counting
when the initial binary number is received from the analog-to-digital converter and level detector. The
counter measures the elapsed time of the overcurrent condition, and resets if the current decreases
below the pickup point. This continuously increasing binary number is then passed to the comparator.
Functional Description BE1-51/27C