the phases can be individually checked but for a Y-d or D-y transformer the current for each phase of the
differential protection is supplied from more than 1 phase and testing is more complex.
Primary Tests
i
i
NOTE
Be aware that a trip results in case of incorrect connections.
Before the transformer is energized from a high voltage supply it is necessary to ensure that a backup protec-
tion is in service on the supply side first, for example, overcurrent protection such that a trip will result if a
short circuit fault is present during initial energization and the differential protection has been configured or
connected incorrectly such that the fault is not detected by the 87T element. The trip circuits of other protec-
tion equipment, for example, Buchholz protection, must also remain active.
The configuration and connections of the 87T element can be tested by the application of 3-phase low voltage
supply to 1 winding with a 3-phase short circuit applied to the other windings in turn.
Repeat the current tests in the case of protected objects with more than 2 measuring points. All sides of the
protected object must be included at least once in the current flow test. You do not have to check every
possible current path. Applying the test current to the lower voltage winding will provide higher current which
is easier to measure and interpret. When a side has more than measuring point, you must include each at least
once in the test. The remaining open circuit measuring points carry no current.
If other 3-phase protected objects are present, these are checked separately in accordance with their topology.
The test setup varies, depending on the use case.
!
DANGER
Dead components hazardous due to capacitive coupling of other system parts!
Failure to comply with the safety notes, can result in death, severe injury or considerable material
damage.
²
Primary tests may be performed only on dead and earthed system parts!
Performance of Current Tests
Before you begin with the first current test, check the polarity setting for the measuring points and compare
them to the actual current connections.
For the commissioning tests, a flowing current of at least 2 % of the device's rated current per phase is neces-
sary.
i
i
NOTE
These tests cannot replace a visual check of the correct current transformer connections. Completed checks
of the system connections are therefore a prerequisite.
The 7SR5 device makes operational measured values for operation and restraint currents available for inspec-
tion in the
Instruments
screens. With these operational measured values, quick commissioning without
external instrumentation is possible.
Check the phase sequence of the currents at the first winding input.
Check the residual current during balanced 3 phase tests. A significant measured value can indicate incorrect
polarity of a single phase current transformer compared to the other 2 phases.
Check the phase sequence of the currents at the second winding input and compare to the phase angles of
the 3 phases to those of the first winding. Repeat for the third winding if applicable. Relay currents should be
equal and in opposite phase direction. Line currents should be different by the angle appropriate to the
Vector Group
.
Functional Tests
9.8 Configuration Tests for Transformer Differential Protection
416
Reyrolle 7SR5, Transformer Protection Device, Device Manual
C53000-G7040-C015-1, Edition 11.2019
