Specifications

L2234
L2778
L4681
L5179
Emax
87/161
Doc. No
Model
Apparatus
Scale
Page No
1SDH000460R0002
L5439
14.2.9.3. Double S
Thanks to the new PR123/P release that enables two independent and simultaneously active protection S thresholds to be speci-
fied, selectivity can assured even in critical conditions.
This function enables a better selectivity level to be obtained than using a release without a “double S”. This function is valid for
t=K only.
14.2.9.4. Directional Protection “D”
The PR123/P unit carries out excludable directional protection against short-circuit with adjustable fixed time (t = k) active both
with self-powering and with 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 PR123 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 (PR120/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 (for the default setting, see par. 14.4.4).
In short:
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 reactive power in  “backward” direction
If the preset trip times were t
7FW
= 200 ms and t
7BW
= 400 ms, in this case the relay
would have opened the circuit-breaker after t
7FW
= 200 ms.
Note:
• With the directional protection D activated, if the direction of the power cannot be determined the relay takes effect considering shorter of the programmed times
between t
7
fw and t
7
bw.
• This protection works on the basis of the phase currents, not the neutral current.
14.2.9.4.1 Start-up threshold “D”
The function can be enabled from the menu (see description of the protection menu 14.5.2)
The function behaves in exactly the same way as the protection “S” (see par. 14.2.9.2.2).
14.2.9.4.2 (Directional) zone selectivity “D”
The Directional Zone Selectivity (SdZ D) function is particularly useful in ring and grid type systems where, in addition to the zone,
it is essential to define the direction of the power flow that powers the fault.
The SdZ D can be set as an alternative to Zone Selectivity S and G and requires an auxiliary power supply.
To define the zone and power flow, each relay has two inputs (DFin and DBin) and two outputs (Dfout and DBout), which must
be suitably connected to the other relays (see example below).
As in the SdZ S and G, the relays interact with each other, sending cutout signals via the outputs and reading them via the inputs.