Specifications

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Doc. no.
Model
Apparatus
Scale
Page No
1SDH000460R0002
L5439
to guarantee correct operation of the relay on the supply side.
13.2.9.3.1 Start-up threshold “I”
The start-up function can be selected.
The function can be enabled from the menu on the protection “I” page.
The function behaves in exactly the same way as the protection “S” (see par. 13.2.9.9.2).
13.2.9.4. Protection “MCR” against closing on short-circuit
The MCR function is used to protect the system against closing.
If activated (the protection can be enabled/disabled), it operates only in the presence of Vaux or PR120/V, and with Protection
“I” disabled.
The MCR function has the same functional characteristics as protection “I” (it uses the same control or trip algorithm), and starts
operation only when the CB closes, with a time window of 0 to 40…500ms (settable by the user), after which it is deactivated.
The time window and threshold settings are set by the user.
This function can be activated through a hand-held PR010/T unit with the ABB SD-Testbus2 communication softwares or through
a remote system via a system bus.
Protection “S” protects against short circuits.
13.2.9.5. Protection “G”
This protection can be disabled; it can be of the fixed time (t=k) or inverse time (t=k/I
2
); type; in the latter case, the trip time is
given by the expression:
Max
,
2
I
2
t
4
where I=I
f
/I
4
, I
f
is the fault current and I
4
is the protection threshold.
NB: Time expressed in seconds.
WARNING: It is possible to disable the trip control of the protection (“Enable Trip: Off”).
For the whole duration of the earth fault, circuit-breaker opening does not take place, but only the alarm condition
is signaled (“Alarm” LED lit and alarm message).
The PR122/P unit can provide two different types of earth fault protection as an alternative:
Internal protection G
This is provided inside the relay by vectorially summing the phase and neutral currents. The fault current is defined by the fol-
lowing formula:
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. This operating mode is enabled by default.
N.B.: it can be used also with CS for an external neutral.
Protection G with external toroid “Source Ground Return”
Also called “Source Ground return”, this can be carried out when there is the need to check operation of a machine (transformer,
generator or motor etc.) which has star-configured windings.
The protection is assured by physically positioning an external toroid on the cable connected from the star center of the machine
to the earthing connection point.
The induced current on the winding of the toroid is proportional to the fault current which, in this case, only transits in the above-
mentioned toroid.
To work in this mode, “Ground protection” must be selected on the Circuit-breaker Settings menu.
WARNING: The external toroid must be connected to the PR122/P by means of a corded shielded two-wire cable
(see note A in par. 11.2.2) with a length not exceeding 15m.
The shield must be earthed both on the circuit-breaker side and on the toroid side.
It is indispensable for the star center to be connected openly to earth and for it not to be used as a neutral conductor too (as in
the TNC system), making a protection according to the TT system.
The minimum allowable threshold for the Gext protection is 0.1 x In (where In is the rated current of the homopolar toroidal
transformer; the In settings available are 100, 250, 400, 800A), both for curve t=K both for I
2
t=K for release with 2.05 sw version.
13.2.9.5.1 Start-up threshold “G”
The start-up function can be selected in the case where the curve with fixed time is selected.
The function can be enabled and disabled on the protection “G” page.
The function behaves in exactly the same way as the protection “S” (see par. 13.2.9.2.2).
13.2.9.5.2 Zone selectivity “G”
The zone selectivity function can be enabled providing the fixed time curve is selected, and function is assured only if auxiliary
voltage is provided.
Zone selectivity “G” can be active at the same time as zone selectivity “S”.
The behavior and wiring of the function are identical to those indicated for zone selectivity “S” (see par. 13.2.9.2.3).
13.2.9.6. 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. Range: 2 … 90% by 1% steps.
The percentage of unbalance is therefore calculated