30
TB MRI3-ITE(R) 12.00 E
6.4.4
Example of a test circuit with earth fault directional feature
Figure 6.1:
Test circuit
For testing
MRI3-ITER
relays with earth fault directional
feature, current and voltage sources are required, with
one of the two sources having to be equipped with a
phase shifter.
Fig. 6.2 shows an example of a test circuit with vari-
able current and voltage sources. First, the parameters
IE> and IE>> must be set to "EXIT" in order to prevent
possible tripping. For the purpose of testing the direc-
tional feature, a test voltage equal to the rated voltage
is applied to terminals A2/A5. The parameter "Volt-
age transformer connection for residual voltage meas-
uring" (refer to 5.3.4) must be adjusted to "3Pha".
The appropriate measuring value is selected via the
<SELECT/RESET> key. The display must indicate 1/3
of the rated voltage (
±
0.5% Un). Now a current of
0.4 x I
N
is injected (terminals B1/B2). The display
must now indicate a value of 0.40 (
±
3%).
Finally, using the phase shifter, it must be checked
whether the setting of the testing equipment coincides
with the indication on the display (
±
3
o
).
By using an RMS-metering instrument, a greater devia-
tion may be observed if the test current contains har-
monics. Because the
MRI3-ITER
relay measures only
the fundamental component of the input signals, the
harmonics will be rejected by the internal DFFT-digital
filter. Whereas the RMS-metering instrument measures
the RMS-value of the input signals.
