Basler BE1-50/51B-217, Instruction Manual

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3-1
SECTION 3
FUNCTIONAL DESCRIPTION
GENERAL
BE1-50/51B-217 Overcurrent Relays are microprocessor based non-directional relays that measure ac
current to provide secure and reliable instantaneous and time overcurrent protection for power systems.
FUNCTIONAL DESCRIPTION
Sensing Input
Single phase ac current from system current transformers (CT) is brought into the BE1-50/51B
Overcurrent Relay at terminals eight and nine. Refer to Figure 3-1 to follow the functional description.
The input current is applied to internal power and signal CTs.
Power Supply
Current from the power CT is rectified, filtered, and supplied to all of the internal circuitry for operating
power. A pre5 Vdc supply also serves as a reference for automatic calibration.
Instantaneous Signal
Current from the signal CT is rectified and applied to the instantaneous scaling resistors controlled by
the INST PICKUP selector switches. The analog voltage of the instantaneous input signal developed
across the scaling resistors is filtered and applied to the multiplexor (MUX).
Time Signal
Current from the signal CT is also rectified and applied to the time scaling resistors controlled by the
TIME PICKUP selector switches. The analog voltage of the time input signal is also filtered and applied
to the multiplexor.
Microprocessor
Operating power from the power supply is applied to the microprocessor supervisor circuit. When the
input current falls below an acceptable level, the supervisor circuit interrupts the microprocessor and
halts further operation. A microprocessor watchdog feature resets the microprocessor program when
the program flow is interrupted.
Information from the TIME DIAL selector switches, the TIME CURVE selector switch, and the 50/60 Hz,
INST DELAY, and RESET CHAR switches is also applied to the microprocessor. The microprocessor
uses these inputs to set the operating parameters.
When the microprocessor is ready for analog information from the multiplexor, microprocessor control
signals cause the multiplexor to route the desired input through to the output. The output is converted
from an analog value to a digital value and applied to the microprocessor.