L2275
Emax UL
38/132
Doc. N°
Mod.
RH0109002
Apparatus
Scale
Page N°
Area 1
RELAY 1a
RELAY 1b
ZSO
ZSO
1a
1b
RELAY 1
ZSI
1
ZSO
1
Area 2
Area n
○
○
○
○
RELAY 2
ZSI
2
ZSO
2
RELAY 0
ZSI
0
RELAY n
ZSI
n
ZSO
n
○
○
○
○
13.7.1.1
Thermal memory “L”
It is possible to enable the thermal memory function for cable protection. This is based on the “tL” parameter defined as the trip time of the curve
(t1) at 1.25xI1.
The trip time of the release is certainly 100% of the one selected after which a time of tL has passed from the last overload or from the last trip.
Otherwise the trip time will be reduced depending on the overload which has take place and on the time which has passed.
The PR112 is fitted with two instruments to make this thermal memory. The first only works when the release is supplied (it remembers overloads
which did not last long enough to cause intervention of the release), whereas the second works even when the release is not
supplied (it reduces any trip times when there is immediate reclosing).
It is the PR112 release which automatically decides which of the two to use according to the various different situations.
13.7.2
Protection “S”
The protection, which can be disabled, can be either with fixed time (t = k) or with inverse time. In the latter case, the trip time is given by the expression
where
I
f
is the fault current and
I
2
the protection threshold.
13.7.2.1
Thermal memory “S”
It is possible to enab le the thermal memory function for cable protection when the inverse time curve is selected. This is based on the
parameter “tS” defined as the trip time of the curve (t2) selected at 1.5xIn. The other character istics are the same as those for thermal
memor y “L”.
13.7.2.2
Zone selectivity “S”
By means of the keyboard, it is possible to enable or disable the zone selectivity function “S”.
This is done by connecting together all the zone selectivity outputs (ZSO) of the releases belonging to the same zone and taking this signal
to the zone selectivity input (ZSI) of the release immediately to the supply side.
If the cabling oper ation has been done correctly, all the zone selectivity inputs of the last circuit-breakers in the chain and all the outputs of the
circuit-breakers at the head of each chain must be empty.
The zone selectivity function allows the fault area to be isolated, only isolating the installation at the level closet to the fault, keeping the rest
of the installation operative.
This means that a fault on the load side of “Relay 1a” will be isolated by the latter without “Relay 1” and “Relay 0” intervening. A fault just to the
load side of “Relay 1” will be isolated by the latter without “Relay 0” intervening, guaranteeing that Areas 2…n remain active.
Cabling of zone selectivity “S” is alternative to the one for “G” and operation is only guaranteed when there is an auxiliary voltage.
The ZSI signal can be connected up to 20 units in parallel (to the relative ZSO signal).
The ZSO unit can be connected to a maximum of 3 ZSI relays on the supply side in the selectivity chain.
13.7.3 Protection “I”
The protection, which can be disabled, is made with intentional delay nil.
The maximum length of the cabling for zone selectivity, between two units, is 300 meters.
Use corded shielded two-wire cab le (see note A to par. 11.2.2).
The shield must only be earthed on the circuit-breaker of the supply side relay (ZSI side).
13.7.4
Protection G
It is possible to disable the trip control of function G (Trip: Off).
For the whole duration of the earth fault, circuit-breaker opening does not take place, but only the alarm conditions is
signalled (Emergency LED lit and alarm message).
The PR112 unit is able to provide two different types of protection against earth fault.
13.7.4.1 Protection G with internal toroidal transformer
The first is carried out by means of passage of all the secondary currents (coming from the CTs) to the inside of a toroidal transformer
(contained in the unit itself) which induces a current proportional to the fault current of the primary circuit on its secondary winding.
The fault current is defined by the following formula:
(Vectorial sum of all the phase currents and neutral)
In the case when the circuit does not have any fault, the module of the sum of these currents is always 0, vice versa the value of the fault
current will always take on a larger value depending on the size of the fault.
To wor k in this mode, it is necessary set Tor.selec.:Int.
for
( )
2
2
2
,
100
max
t
I
t
f
⋅
2
I
I
f
>
Ig I
I
I
In
= + + +
1
2
3
NB: Time expressed in seconds.
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