Siemens SIPROTEC 7UT613 series Manual page 298

2 Functions
298
The disconnection ends when the binary input is deactivated. This requires, once
again, that no current is flowing at the moment the disconnection is ended.
One can evade the condition that the disconnection mode can only be started or
ended when no current is flowing via the measuring location. If you wish to start and
end the disconnection mode even in case of current flow, you have to activate — to-
gether with the corresponding binary input („>disconnect Mx") — the input
„>disconn. I>=0" (30361). This can be done by means of a logical CFC-combi-
nation.
The effectiveness of the disconnection is stored in the device's NV RAM and saved
against auxiliary voltage failure, i.e. the last information about the disconnection state
is maintained when the power supply of the device fails. When the power supply re-
turns, the state of the binary input(s) for disconnection is checked against the stored
information. Only when they match will the protection functions become active again.
Inconsistencies are indicated as an alarm „Fail.Disconnect" (FNo 30145), and
the life contact of the relay remains open. The device cannot operate again until the
state of the binary input(s) has been adapted to the stored information.
The effect of the disconnection is that the currents from the disconnected measuring
location — as far as they are assigned to a side of the main protected object — are
set to zero for those protection functions that are assigned to this side. Currents arriv-
ing from the system after disconnecting the measuring location are not effective here.
The currents from 1-phase auxiliary measuring inputs allocated to the isolated mea-
suring input stay valid. Currents remain valid for those protection functions which are
not assigned to a side.
No protection functions are blocked. The differential protection continues to work with
the remaining available measured values. In the above example, the transformer can
still operate through measuring location M1, with the differential protection remaining
fully effective.
Overcurrent protection functions assigned to a side continue to work without the
current from the disconnected measuring location.
Overcurrent protection functions which are assigned exclusively to the disconnected
measuring location (i.e. not via a side definition) are supplied with the currents of the
disconnected measuring location, i.e. continue to operate with these currents. If nec-
essary, they must be blocked by the information about disconnection (either by corre-
sponding assignment in the matrix of binary inputs or by user defined logical combi-
nation by means of CFC).
The restricted earth fault protection, too, does not receive any more currents from the
isolated measuring location. If it is assigned to a side with two or more measuring lo-
cations, it can continue to work with the currents from the remaining measuring loca-
tion(s). If the isolated measuring location is the only 3-phase source for the restricted
earth fault protection, the starpoint current stays effective. This means that the restrict-
ed earth fault protection will trip immediately if the starpoint current exceeds the pickup
threshold. Such a current must be a fault current in the protected object: it cannot
come from the power system, which is in fact isolated from the protected object.
7UT613/63x Manual
C53000-G1176-C160-2