Specifications

L2234
L2778
L4681
L5179
Emax
52/161
Doc. no.
Model
Apparatus
Scale
Page No
1SDH000460R0002
L5439
13.2.8. Watchdog
The PR122/P unit provides some watchdog functions able to guarantee the proper management of relay malfunctions. These
functions are as follows:
 Watchdog for presence of Auxiliary power supply with “plug” icon displayed.
 RATING PLUG validity.
 Watchdog for proper connection of the current sensors (CS). If it is enabled, any anomalies are indicated by a special alarm
message and the “alarm” LED coming on, and the circuit-breaker opens after 1s.
 Watchdog for proper connection of the Trip Coil (TC). If it is enabled, any anomalies are indicated by a special alarm message
and the “alarm” LED coming on; if the PR120/D-M module is installed, this activates the coil opening command (YO), thus
opening the CB.
 Watchdog for protection of Hw Trip. If it is enabled, in the event of the sensors being disconnected or a Rating Plug error, a
CB opening command is given by the TC being enabled.
13.2.9. Description of the protection functions
13.2.9.1. Protection “L”
The “L” is the only protection that cannot be disabled because it is for self-protection against overloading of the relay itself. The
types of trip curves settable are divided into two groups according to the standard they refer to.
Standard trip curve according to IEC 60947-2
Only one type of curve is settable (t=k/I
2
) as defined by the IEC standard 60947-2.
The protection trip time - inverse time - is given by the expression:
where l
f
< 12ln, 1 s where l
f
> 12ln where I
f
is the fault current and I
1
the protection threshold.
NB: Time expressed in seconds.
Standard trip curve according to IEC 60255-3
There are 3 types of curves settable, defined by the IEC standard 60255-3 as A, B and C.
The protection trip time - inverse time - is given by the expression

b
I
k
t 


1

where
1
I
I
I
f

where I
f
is the fault current and I
1
the protection threshold specified by the user.
NB: Time expressed in seconds.
a and k are two parameters, suggested by the standard, which vary the type of slope selected
(e.g. for type B slope a = 1 and k = 13.5);
b is a parameter introduced by SACE to increase the number of curves with the same slope. This parameter is automatically
calculated by setting parameter t1 (required trip time at 3xI1).
13.2.9.1.1 Thermal memory “L”
The thermal memory function can be enabled for cable protection. It is based on the “L” parameter defined as the trip time of
the curve (t1) selected at 1.25xI1.
The release trip time is certainly 100% of the one selected, after an interval L has passed since the last overload or since the last
trip. Otherwise, the trip time will be reduced, depending on the overload which has occurred and on the time that has elapsed.
The PR122/P is fitted with two instruments to make up this thermal memory. The first is only effective when the release is powered
(it also records overloads that have not lasted long enough to trip the release), while the second works even when the release is
not powered, reducing any trip times in the case of an immediate reclosing and is enabled as soon as the CB is tripped.
It is the PR122/P release that automatically decides which of the two to use, according to the various situations.
NB: The thermal memory function can only be set if the type of curve selected is the standard one (t=k/I
2
) (see par. 13.2.9.1).
13.2.9.2. Protection “S”
This protection can be disabled; it can be of the fixed time (t=k) or inverse time (t=k/I
2
); in the latter case, the trip time is given
by the expression
Max
100 t
2
(I )
f
2
,t
2
where I
f
> I
2
where I
f
is the fault current and I
2
the protection threshold.
NB: Time expressed in seconds.
13.2.9.2.1 Thermal memory “S”
The thermal memory function can be enabled for cable protection in the case where the curve with inverse time is selected. This
is based on the “tS” parameter defined as the trip time of the curve (t2) selected at 1.5xI2. The other characteristics are the same
as those for thermal memory “L” (see par. 13.2.9.1.1).
13.2.9.2.2 Start-up threshold “S”
The start-up function can be selected in the case where the curve with fixed time is selected.