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Doc N°
Mod.
Apparatus
Scale
Page No
1SDH000587R0002
3.6.2. Protection L
Protection L is the only protection that cannot be disabled since it provides self-protection against circuit-breaker overloads. 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 tripping time is calculated in relation to the value of If:
- For fault currents If
≤
12ln, the tripping time of the protection is given by the expression: t(s)=
. If the calculated value is
less than 1 second, the real tripping time is forced to 1 second (t(s)= 1s.).
- For fault currents If >12ln, the tripping time is always t(s)= 1s.
Standard trip curve according to IEC 60255-1
5
1
3 types of curve settings can be made and are defined by standard IEC60255-1
5
1 as A, B and C.
The protection trip time, with inverse time, is given by the expression:
( )
b
I
k
t
•
−
=
1
α
where
1
I
I
I
f
=
NOTES:
- t(s):
envisaged tripping time
-
I
f
:
fault current; given in [In] (example: 0.7In)
-
I
1
, t
1
:
protection L parameters set by the user, given in [In] and [s]
-
-a
, k
:
parameters suggested by standard IEC60255-1
5
1, which vary with the type of gradient selected (e.g. for type B
gradients:
a-
= 1 and
k
= 13.5)
- b:
parameter included to increase the number of curves with the same slope. This parameter is automatically calcu-
lated by setting parameter t1 (required tripping time with If= 3xI1).
Protection L has 3 operating conditions established by the fault current level I
f
and by the setting of the protection itself I
1
:
I
f
≤
0.9 xI
1
No alarm, all settings possible. No time delay in progress.
0.9 xI
1
< I
f
< (1.05...1.2) xI
1
Prealarm L signal, all settings possible. No opening time delay in progress.
(1.05...1.2) xI
1
≤
I
f
Alarm L signal, no setting possible. Opening time delay in progress.
WARNING: the protection L threshold entry range ensures that:
-
the protection release does not set to the alarm status for current values of less than 1.05 xI
1
;
-
the protection release will set to the alarm status for current values exceeding 1.2 xI
1.
3.6.2.1.
Thermal memory L
The thermal memory function can be enabled for cable protection. It is based on the “
τ
L” parameter, defined as the tripping time
of the curve (t1) selected at 1.25xI1. The function can be activated via PR010/T or Ekip Connect.
The tripping time of the protection release will certainly be 100% of the selected value after time
τ
L has elapsed since the last
overload or the last trip, otherwise the tripping time will be reduced in relation to the overload that has occurred or the time that
has elapsed.
PR332/P and PR333/P have two instruments for processing the thermal memory. The first only operates when the protection
release is energized (it also records overloads that have not lasted long enough to trip the CB), while the second operates even
when the protection release is not energized, reducing any trip times in the case of immediate reclosing and activating the mo-
ment the circuit-breaker trips.
It is the protection release that decides which of the two to use, depending on the situation in question.
WARNING: t
he thermal memory function is enabled by default in the UL version.
In the IEC version, it can only be activated if the curve is the standard type
(t=k/I2).
3.6.3. 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.
The tripping time with inverse time curve is given by the expression: t(s)=
. If the calculated value is less than t
2
, the
real tripping time is forced to t
2
(t(s)= t
2
.)
NOTES:
t(s):
envisaged tripping time
I
f
:
fault current; given in [In] (example: 1.4In)
I
2
, t
2
:
protection S parameters set by the user, given in [In] and [s]
3.6.3.1.
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.
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