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3-2
Protection Functions
General Features of
Protection Stages
857-UM001A-EN-P – July 2009
Setting Groups
Most stages have two setting groups. Changing between setting
groups can be controlled manually or using any of the digital inputs,
virtual inputs, virtual outputs or LED indicator signals. By using
virtual I/O the active setting group can be controlled using the local
panel mimic display, any communication protocol or using the
inbuilt programmable logic functions.
Forcing Start or Trip Condition for Testing
The status of a protection stage can be one of the followings:
•
The stage is not detecting any fault.
Ok = '–'
•
The stage is detecting a fault but blocked by some
Blocked
reason.
•
The stage is counting the operation delay.
Start
•
The stage has tripped and the fault is still on.
Trip
The blocking reason may be an active signal via the block matrix
from other stages, the programmable logic or any digital input.
Some stages also have inbuilt blocking logic. For example an under
frequency stage is blocked if voltage is too low. For more details
about block matrix, see Chapter 5.
Forcing Start or Trip Condition for Testing Purposes
There is a "Force flag" parameter which, when activated, allows
forcing the status of any protection stage to be "start" or "trip" for a
half second. By using this forcing feature any current or voltage
injection to the relay is not necessary to check the output matrix
configuration, to check the wiring from the output relays to the
circuit breaker and also to check that communication protocols are
correctly transferring event information to a SCADA system.
After testing the force flag will automatically reset 5-minute after the
last local panel push button activity.
The force flag also enables forcing of the output relays and forcing
the optional mA outputs.
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