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3-3
Protection Functions
Start and Trip Signals
Every protection stage has two internal binary output signals: start
and trip. The start signal is issued when a fault has been detected.
The trip signal is issued after the configured operation delay unless
the fault disappears before the end of the delay time.
Output Matrix
Using the output matrix the user connects the internal start and trip
signals to the output relays and indicators. For more details see
Chapter 6.
Blocking
Any protection function, except arc protection, can be blocked with
internal and external signals using the block matrix (Chapter 5).
Internal signals are for example logic outputs and start and trip
signals from other stages and external signals are for example digital
and virtual inputs.
Some protection stages have also inbuilt blocking functions. For
example under-frequency protection has inbuilt under-voltage
blocking to avoid tripping when the voltage is off.
When a protection stage is blocked, it won't pick-up in case of a fault
condition is detected. If blocking is activated during the operation
delay, the delay counting is frozen until the blocking goes off or the
pick-up reason, i.e. the fault condition, disappears. If the stage is
already tripping, the blocking has no effect.
Retardation Time
Retardation time is the time a protection relay needs to notice that a
fault has been cleared during the operation time delay. This parameter
is important when grading the operation time delay settings between
relays.
RetardationTime
t
FAULT
t
< 50 ms
RET
DELAY SETTING > t
+ t
FAULT
RET
TRIP CONTACTS
Figure 3.1 – Retardation Time
857-UM001A-EN-P – July 2009
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