6.2 Self-supervision
The protection relay's extensive self-supervision system continuously supervises the
relay’s software, hardware and certain external circuits. It handles the run-time fault
situation and informs the user about a fault via the LHMI, the relay's main unit
power module Ready LED and through the communication channels. The target
of the self-supervision is to safeguard the relay’s reliability by increasing both
dependability and security. The dependability can be described as the relay’s ability
to operate when required. The security can be described as the relay scheme’s
ability to refrain from operating when not required. The dependability is increased
by letting the system operators know about the problem, giving them a chance
to take the necessary actions as soon as possible. The security is increased by
preventing the relay from making false decisions, such as issuing false control
commands.
There are two types of fault indications.
• Internal faults
• Warnings
Warnings are indications of less severe situations which can also be caused by
external reasons, for example, in case the RTD sensor measurement circuit is not
complete.
On the LHMI, the self-supervision status is available as an advanced page under
Relay Status page. The self-supervision status is indicated with Internal Fault,
Warning and All OK LEDs. In normal operation, All OK LED is lit. The self-supervision
also controls the status of IRF output relay. The IRF output relay is energized under
normal conditions and de-energized under internal fault conditions.
Figure 87: Relay self-supervision status on local HMI
On the WHMI, the self-supervision status is available under Device menu. The top
right LED indicates the relay status.
1MRS759118 D
Troubleshooting
REX640
Operation Manual
89
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