Maintenance and Repair
292
7SS52 V4 Manual
C53000-G1176-C182-3
8.2 Fault Analysis
Disturbances of digital protection devices are in most cases caused by component
failures. Practical experience also shows that environmental conditions may in few
cases initiate failure alarm. Such environmental conditions can be e.g. short
electromagnetic interference beyond the values guaranteed by the manufacturer.
If the protection system or its components are continuously disturbed, the green LED
(RUN) goes out, the red LED (ERROR) lights up and the "Device operative / healthy"
(FNo. 51/BU) alarm relay drops off. In the event of a continuous disturbance, the pro-
tection system or its components are blocked to avoid overfunction. In the event of a
failure in one bay unit or in the transmission link between one bay unit and the central
unit, the availability of the intact system can be ensured by setting the parameter
BLOCKING MODE (6305/CU) to zone/phase.
The disturbance can be caused by:
• Failures in the central unit
(Failure or defect in the auxiliary voltage supply, module failure)
• Failures in one of the connected bay units
(interruption of the power supply, defective measuring circuit, module failure)
• Interruption of the communication link to one of the bay units
(defective transmission or reception modules, interrupted FO link, increased
number of transmission errors)
The protection system provides the following diagnostic information to support the
user in a systematic analysis of the causes for the disturbance:
• Central unit
− operational event buffer
− fault event buffer
− operational events marshalled to LEDs
− LED indications on the modules
• Bay unit
− operational events marshalled to LEDs
− operational event buffer
8.2.1 Evaluation of Operational Events
The central unit's operational events provide first hand information about the cause of
a registered device failure.
 If operational events which have been marshalled to LEDs are missing, you should
interrogate immediately the operational event buffer in the central unit. You will get
there information about:
− auxiliary voltage failure
− pick-up of the differential current supervision
− errors in the measured value supervision of the bay units and
− failure detection by the cyclic test
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