Siemens SIPROTEC 4 7UT6 Series Manual Download

Page: 111 / 684

Differential Current Monitoring

Whereas a high sensitivity of the differential protection is normally required for transformers, reactors, and
rotating machines in order to detect even small fault currents, high fault currents are expected in case of faults
on a busbar or a short line so that a higher pickup threshold (above rated current) is conceded here. This
allows for a continuous monitoring of the differential currents on a low level. A small differential current in the
range of operational currents indicates a fault in the secondary circuit of the current transformers.
This monitor operates phase-selectively. When, during normal load conditions, a differential current is
detected in the order of the load current of a feeder, this indicates a missing secondary current, i.e. a fault in
the secondary current leads (short-circuit or open-circuit). This condition is annunciated with time delay. The
differential protection is blocked in the associated phase at the same time.

Feeder Current Guard

With busbars and short lines, a release of the trip command can be set if a threshold is exceeded by one of the
incoming currents. The three phase currents at each measuring location of the protected object are monitored
for over-shooting of a set value. Trip command is allowed only when at least one of these currents exceeds a
certain (settable) threshold.

Single-phase Differential Protection for Busbars

Dependent on the ordered model, 7UT6x provides 7, 9, or 12 current inputs of equal design. This allows for a
single-phase differential current busbar protection for up to 7 or 9 or 12 feeders.
There are two connection possibilities:

•

One 7UT6x is used for each phase. Each phase of all busbar feeders is connected to one phase dedicated
device 7UT6x.

•

The three phase currents of each feeder are summarised into a single-phase summation current. These
currents are fed to one device per feeder.

Phase Dedicated Connection

For each of the phases, a 7UT6x is used in case of single-phase connection. The fault current sensitivity is
equal for all types of fault. 7UT612 is suited for a busbar with up to 7, 7UT613 and 7UT633 are suited for a
busbar with up to 9, 7UT635 for up to 12 feeders.
The differential protection feature of the 7UT6x refers all currents to the rated current of the protective object.
Therefore, a common rated current must be defined for the entire busbar even if the feeder CTs have different
rated currents. This common rated current has been set in address 371

I PRIMARY OP.

. It is the maximum

of the rated currents of all feeders set in the device in the data of the protected object. Measured value
matching in the device is thus limited to current quantity factors. No external matching devices are necessary
even if the feeders and/or the current transformer sets at the ends of the protected zone have different
primary currents.

Siemens SIPROTEC 4 7UT6 Series, Manual

Search results

Summary of Contents for SIPROTEC 4 7UT6 Series

Reviews:

Related manuals for SIPROTEC 4 7UT6 Series

Brands by name

Popular brands