Method of operation
7SV512
V1
39
C53000---G1176---C91
4.5.4 Monitoring functions
The device incorporates comprehensive monitoring
functions which cover both hardware and software;
furthermore, the measured values are continuously
checked for plausibility so that the current trans-
former circuits are also included in the monitoring
system.
4.5.4.1 Hardware monitoring
Because of the high safety demand for the breaker
failure protection, a special hardware trip release
module is incorporated in 7SV512. This is described
in conjunction with the breaker failure protection
function in Section 4.2.7. In addition, the general
monitoring functions of numerical protection and
automation relays are present:
The complete hardware is monitored for faults and
inadmissible functions, from the measured value in-
puts to the output relays. In detail this is accom-
plished by monitoring:
--- Auxiliary and reference voltages
The processor monitors the offset and reference
voltage of the ADC (analog/digital converter). The
protection is blocked as soon as impermissible
deviations occur. Permanent faults are annun-
ciated.
Failure or switch-off of the auxiliary voltage auto-
matically puts the system out of operation; this
status is indicated by a fail-safe contact. Transient
dips in supply voltage of less than 50 ms will not
disturb the function of the relay.
--- Measured value acquisition
The complete chain, from the input transformers
up to and including the analog/digital converters
are monitored by the plausibility check of the
measured values.
In the current path, there are four input conver-
ters; the digitized sum of the outputs of these
must always be zero. A fault in the current path is
recognized when
|i
L1
+ i
L2
+ i
L3
+ k
I
x i
E
|
²
SUM.Ithres x
I
N
+ SUM.Fact.
I
x
I
max
An adjustable factor k
I
(parameter Ie/Iph) can be
set to correct the different ratios of phase and
earth current transformers (e.g. summation trans-
former). If the residual earth current is derived
from the current transformer starpoint, k
I
= 1.
SUM.
I
thres and SUM.Fact.
I
are setting parame-
ters (refer to Section 6.3.6). The component
SUM.Fact.
I
x
I
max
takes into account permissible
current proportional transformation errors in the
input converters which may particularly occur un-
der conditions of high short circuit currents (Fig-
ure 4.20).
Note:
Current sum monitoring can operate prop-
erly only when the residual current of the pro-
tected object is fed to the I
E
input of the relay.
I
max
I
N
I
F
I
N
I
F
= Fault current
SUM.
I
thres
Slope:
SUM.Fact.
I
Figure 4.20 Current sum monitoring (current
plausibility check)
--- Command output channels:
The command relays for tripping are controlled by
two command and one additional release chan-
nels. As long as no pick-up condition exists, the
central processor makes a cyclic check of these
command output channel for availability, by excit-
ing each channel one after the other and check-
ing for change in the output signal level. Change
of the feed-back signal to low level indicates a
fault in one of the control channels or in the relay
coil. Such a condition leads automatically to
alarm and blocking of the command output. In ad-
dition, a trip release module as described in Sec-
tion 4.2.7 is effective for trip relays K1 and K2.
--- Memory modules:
The memory modules are periodically checked
for fault by:
D
Writing a data bit pattern for the working
memory (RAM) and reading it,
www
. ElectricalPartManuals
. com
