B0431
Emax X1-Tmax T7-Tmax T8
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Doc N°
Mod.
Apparatus
Scale
Page No
1SDH000587R0002
3.6.5. Directional protection D
PR333/P provides excludable directional protection against short-circuits with adjustable fixed time (t=k), active both with self-
powering and auxiliary supply.
The protection functionality is very similar to protection “S” with fixed time, with the capacity to recognize the current direction
during the fault period as well.
The direction of the current enables the determination of whether the fault is on the supply side or the load side of the circuit-
breaker. Especially in ring distribution systems, this enables the distribution stretch where the fault occurred to be identified and
isolated without interfering with the rest of the installation (using zone selectivity).
To determine the direction of the current, the value of the phase reactive powers has to be higher than 2% of the nominal phase
power
(
P
Q
≥2%∙P
nphase
).
The PR333 enables you to define the power flow in the circuit-breaker from the menu:
from high to low (Top
→
Bottom),
from low to high (Bottom
→
Top),
selectable in the menu Modules Measuring Module (PR330/V).
As a result, the currents in the circuit-breaker will be defined as “forward” or “backward” if their are in phase or out of phase with
the previously-defined power flow.
Ifault (I
f
)
Power flow set
Top
→
Bottom
Power flow set
Top
→
Bottom
Value
Direction
Trip T
Trip T
I
f
< I
7
Either
No trip
No trip
I
f
> I
7
High
→
Low
t
7FW
t
7BW
I
f
> I
7
Low
→
High
t
7BW
t
7FW
Example:
Once the power flow has been set as “Top
→
Bottom”, the direction of the figure alongside is:
CB
Z
V
I
Inductive/resistive load
positive reactive power in
→
“forward” direction;;
negative reacti ve power in
→
“backward” direction
If the trip time settings were t7FW = 200 ms and t7BW = 400 ms, the protection
release in the case illustrated alongside (fault current= forward) would have opened
the circuit-breaker after t7FW = 200 ms.
Note:
- When directional protection D is active and the direction of the power cannot be established, the protection release takes effect
by considering the shorter time between t
7fw
e t
7bw
.
- This protection works on the basis of the phase currents, not the neutral current.
3.6.5.1.
Start-up threshold D
The function behaves in exactly the same way as the protection S.
B1751
