L2275
Emax UL
69/132
Doc. N°
Mod.
RH0109002
Apparatus
Scale
Page N°
15.2.6.5
Protection “G”
The protection, which can be disabled, can be with fixed time ( t = k ) or inverse time. In the latter case, the trip time is given by the expression
(
)
4
2
4
,
2
max
t
I
I
f
where
I
f
is the fault current and I
4
the protection threshold.
NB: Time expressed in seconds.
It is possible to disable the trip control of the protection (“Trip: Off”).
For the whole duration of the ground fault the power circuit breaker will not be opened, but only the alarm condition will
be signaled (“emergency” LED lit and alarm message).
The PR113 unit is able to provide two different types of ground fault protection:
$
Internal protection G
This is carried out inside the trip unit by vectorially summing the phase and neutral currents. The fault current is defined by the following formula
NE
G
I
I
I
I
I
+
+
+
=
3
2
1
In the case when the circuit does not show any fault, the module of the sum of these currents is always nil, vice versa the value of the fault current
will take on an increasingly large value depending on the size of the fault.
It is necessary to set “Tor.selec.: Int.” to work in this mode.
$
Protection G with external toroidal transformer “Source Ground Return”
Also called “Source Ground return”, this can be carried out when there is the need to check operation of a machine (transformerù or generator
or motor etc.) which has star configured windings.
The protection is carried out by physically positioning an external toroidal transformer on the cable connected from the star center of the machine
to the earthing connection point.
The induced current on to the winding of the toroid is proportional to the fault current which, in this case, only transits in the above-mentioned toroid.
It is necessary to set “Tor.selec.Ext.” to work in this mode.
The external toroid must be connected to the PR113 by means of a corded shielded two-wire cable (see note A to par. 11.2.2)
with a length not exceeding 15m.
The shield must be grounded both on the power circuit breaker side and on the toroid side.
It is indispensable for the star center to be connected openly to earth and for the same not to be used as a neutral conductor as well (as in the
TNC system), making a protection according to the TT system. The nominal values of the current sensors available are given in par. 15.4.2.1.
In single-phase self-supply, protection “G” is only active if the primary current is higher than 0.4xIn. When the value of the phase current
is above 4xIn , function “G” excludes itself since, in this case, it is the other protections which intervene as the fault is considered
a phase fault.
In accordance with the Nec standard, the maximum settable threshold is limited.
15.2.6.5.1 Start-up threshold “G”
It is possible to select the start-up function in the case where the curve with fixed time is selected.
The function is disabled by selecting ‘——-’ at the “Startup” parameter on the protection “G” page.
The behavior of the function is identical to the one described for protection “S” (see par.15.2.6.2.2).
15.2.6.5.2 Zone selectivity “G”
It is possible to enable the function of zone selectivity in the case when the curve with fixed time is selected and there is an auxiliary power supply.
The cabling and enabling of zone selectivity “G” is an alternative to the “D” one and operation is only guaranteed when there is auxiliary voltage.
Zone selectivity “G” can be active at the same time as zone selectivity “S” since the inputs and the outputs are independent (ZSI=K51/GZin and
ZSO=K51/Gzout).
The behavior and cabling of the function are identical to those indicated for zone selectivity “S” (see par.15.2.6.2.3).
15.2.6.6 Protection against phase unbalance “U”
The protection with fixed time, which can be excluded, trips in the case when, for a time greater than or the same as the time t6 set, an unbalance
is determined between two or more phases higher than the set threshold I6.
The percentage of unbalance is therefore calculated
100
.
%
max
min
max
⋅
−
=
I
I
I
Sbil
where I
max
is the maximum and I
min
the minimum phase current.
It is possible to disable the trip control of the protection (“Protection Trip: Off”).
In that case, for the whole duration of the unbalance the power circuit breaker will not be opened, but only the condition
will be signaled by means of the “warning” LED lit up and a warning message.
When the value of the phase current is above a 6xIn , function “U” excludes itself since in this case it is the other protections
which intervene since the fault is considered a phase fault.
The protection is not enabled for maximum phase current values lower than 0.3xIn.
