Application; Measuring Principle - ABB REC 561 User Manual

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

1 Application

2 Measuring principle

Fuse-failure supervision function
Optional
Different protection functions within the REx 5xx protection, control and
monitoring terminals operate on the basis of the decreased measured volt-
age in a relay point. Examples are: distance protection function, under-
voltage measuring function, and voltage check for the weak infeed logic.
These functions can operate unnecessarily if a fault occurs in the second-
ary circuits between the voltage instrument transformers and the terminal.
It is possible to use different measures to prevent such unwanted opera-
tions. Miniature circuit breakers in the voltage measuring circuits, located
as close as possible to the voltage instrument transformers, are one of
them. Separate fuse-failure measuring relays or elements within the pro-
tection and monitoring devices are another possibility. These solutions
can also be combined to get the best possible effect.
The fuse-failure supervision function as built into the REx 5xx terminals
has these possibilities; it can operate:
• Only on the basis of external binary signals from the miniature cir-
cuit breaker or from the line disconnector. The first case influences
the operation of all voltage-dependent functions while the second
one does not affect the impedance measuring functions.
• On the basis of the zero-sequence measuring quantities: a high value
of voltage 3
• On the basis of the negative-sequence measuring quantities: a high
value of voltage 3
current 3
The current and voltage measuring elements within one of the built-in
digital signal processors continuously measure the currents and voltages
in all three phases and calculate:
• The zero-sequence current 3
• The negative-sequence current 3
• The corresponding voltages, comparing them with the set values I>
and U>
Fourier's recursive filter filters the current and voltage signals, and a sep-
arate trip counter prevents high overreaching of the measuring elements.
The following signals receive logical values equal to 1, if the measured
voltage exceeds, and the measured current does not exceed the pre-set
value:
• VTF0 for the function based on zero-sequence quantities
• VTF2 for the function based on negative-sequence quantities
.
U without the presence of the residual current 3
0
.
U without the presence of the negative-sequence
2
.
I (this option is available only in some terminals).
2
.
I
0
1MRK 580 169-XEN
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I , and
2
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