Application; Measuring Principle; Design - ABB REC 561 User Manual

ABB Network Partner AB
Version 1.0-00
October 1996
Function:

1 Application

2 Measuring principle

3 Design

Loss of power system voltage
Optional
The tripping of a circuit breaker at prolonged loss-of-voltage is normally
used in automatic restoration systems to facilitate the system restoration
following a major blackout. All three-phase voltages are checked to initi-
ate a trip and an alarm when all phase voltages have been low for more
than seven seconds.
The voltage measuring elements continuously measure the three phase-to-
phase and three phase-to-earth voltages and compare them with the set
operating values. Fourier's recursive filter filters the measured-voltage
signals, and a separate trip counter prevents a too high overreaching of the
measuring elements.
The logical values of the following signals will be equal to logical 1, if
one of the measured voltages decreases under the pre-set value:
• UCHL1< corresponds to voltages UL1L2, UL3L1, and UL1N
• UCHL2< corresponds to voltages UL2L3, UL1L2, and UL2N
• UCHL3< corresponds to voltages UL3L1, UL2L3, and UL3N
The measurement of different analog signals occurs in different signal
processors within the REx 5xx terminals. Timing and logical processing
occurs in the control processor.
Figure 1 shows a simplified block diagram for the loss-of-power system
voltage function. Digital signal processors perform a check of all three
measured voltages and their combinations. If all of them are low for more
than seven seconds, the LOV--TRIP signal changes to a logical one for
150 ms. After this, the logic remains blocked until normal voltage condi-
tions are established on the line for at least three seconds.
The LOV--VTSU connectable signal can block the loss-of-power system
voltage logic. It is normally necessary to configure it to the output signal
of FUSE-VTSU, the fuse failure supervision function.
The logic also remains blocked for at least three seconds after the circuit
breaker has been closed so it is necessary to connect the NC contact of the
circuit breaker to one of the binary inputs, and configure it to the LOV--
BC.
The logic also gets blocked if only one or two-phase voltages remain low
for more than 10 seconds.
1MRK 580 153-XEN
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