Direction Test of the Earth Quantities for Directional Earth-Fault
Functions
Overview
If only calculated earth fault protection is used in the device and only calculated residual voltage 3V0, testing
as above for direction test of the phase quantities (Current and Voltage Connection) is sufficient to ensure that
the direction is correct, no additional directional test is required.
If earth current is measured such as for measured earth fault protection elements, or the residual voltage is
directly measured such as with a 3V0 voltage configuration, the correct polarity of the earth current and the
earth voltage path must be checked in addition to the phase checks.
!
DANGER
Live system parts! Capacitive coupled voltages on dead parts!
Noncompliance with the following measures can lead to death, serious physical injury, or consider-
able material damage.
²
Primary measures may be performed only on dead and earthed system parts.
Directional Testing for Solid or Resistive-Earthed Systems
Primary Test
The primary test is used for the evaluation of the correct polarity of the transformer connections for the defini-
tive determination of the earth fault direction.
To generate a zero-sequence voltage V
0
, the e-n winding of 1 phase in the voltage-transformer set (for
example, phase A) is bypassed, see
. If no connection on the e–n windings of the voltage trans-
former is provided, the corresponding phase is disconnected on the secondary side, see
. Only the
current of the transformer in the phase of which the voltage is missing is transferred via the current circuit. If
the line carries resistive-inductive load, the protection is subject to the same conditions as those existing
during a earth fault in line direction.
For directional testing, the relay instruments show the direction of the applied current for the measured earth
input as well as the calculated earth current. This should be used to check current polarity. The forward/
reverse boundary of current direction for the instruments is defined by the parameters for 67N, 67G and 67GS
protection elements.
If a wrong direction is logged, 1 of the following conditions may have occurred:
•
The direction of the load flow is from the line towards the busbar.
•
The ground-current connection is incorrect.
•
The voltage connection is incorrect.
•
The device directional settings are incorrect.
9.5
Functional Tests
9.5 Direction Test of the Earth Quantities for Directional Earth-Fault Functions
410
Reyrolle 7SR5, Transformer Protection Device, Device Manual
C53000-G7040-C015-1, Edition 11.2019