General, Functional description, Sensing input – Basler Electric BE1-50/51M User Manual

Page 29: Power supply, Instantaneous signal, Time signal, Microprocessor, Power-off sensing, Outputs, Instantaneous and timed

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9252000990 Rev R

BE1-50/51M Functional Description

3-1

SECTION 3 • FUNCTIONAL DESCRIPTION

General

BE1-50/51M 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 overcurrent relay at

terminals 8 and 9. 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 relay internal circuitry for operating

power. A precision +5 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

microprocessor is active and executing code, the ACTIVE/PICKUP LED is green. When the input current

falls below an acceptable level, the supervisor circuit interrupts the microprocessor, halts further

operation, and turns OFF the ACTIVE/PICKUP LED. 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, INST DELAY

switches, and RESET CHAR switch 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.
The microprocessor performs the program operations based on the inputs and the internal software

program. When the sensed current exceeds the TIME PICKUP setting, the ACTIVE/PICKUP LED turns

from green to red. The TIME (51) contact is closed in accordance with the TIME characteristic equation. If

the sensed current exceeds the INST PICKUP setting, the INST contact (50) is closed.

Power-Off Sensing

In 200 series relays, power-off sensing circuits measure the decaying voltage to determine the length of

time that power is removed (zero current). This provides information for the integrating reset function even

when power has been entirely removed.

Outputs

System circuit breakers controlled by the output contacts can be manually tripped by applying a short

across the TIME or INST MANUAL TRIP front panel test points. Current flow in the trip circuit is indicated

by the operation of the target. The targets will not operate without adequate operating power for the relay.

Instantaneous and Timed

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