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7 - 1
Siemens AG ⋅ January 1999
Digital protection equipment has no special mainteĆ
nance requirements. All measuring and signal procesĆ
sing circuits are provided by static circuits with no
moving parts. All input modules are also static; the
output relays have protective covers.
Since the device is largely self-monitoring, hardware
and software errors are signaled automatically. This
guarantees the high availability of the protection.
Maintenance checks at short intervals are therefore
unnecessary.
The device blocks automatically when it detects hardĆ
ware errors; the relay "Protection in service" (if proĆ
grammed) drops out and signals the error with its
NCC.
Detected software errors initiate a processor reset
and restart. If such an error is not eliminated by the
restart, another restart attempt is made. The protecĆ
tion is automatically taken out of service after three
unsuccessful restart attempts. This is indicated by
the red "Fault" LED on the front panel; the signal reĆ
lay "Device ready" drops out and signals the fault
with its NCC.
The error reactions can be accessed under block 81
for error diagnostics in chronological order as operaĆ
tional events (see section 6.4.2).
Routine checking of characteristics or pick-up values
is unnecessary because these are part of the continuĆ
ously monitored firmware programs. The mainteĆ
nance intervals planned for inspection and mainteĆ
nance of the plant can be used to perform operational
tests on the protection equipment. This results from
the fact that maintenance serves above all to check
the device interfaces, i.e. the link with the system.
The following procedure is recommended:
D Read out the operational measured values (Block
84) and compare them with the actual values to
check the analog interfaces.
D Simulate a short-circuit with 4 times I
N
to check
the analog input at high currents.
Dangerous voltages may occur in all cirĆ
cuit components connected to the
power supply and the measuring and
test signals.
Tests with currents greater than 4 times
the rated device current lead to overloaĆ
ding of the input circuits and may only
be conducted for brief periods (see
Technical data, section 3.1.1). SubseĆ
quently, a break for cooling should be
made!
D The trip circuits for the circuit-breaker are checked
by tripping the circuit breaker under load. See secĆ
tion 6.7.4 for information.
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