Woodward
Manual MRI3-ITER GB
42
DOK-TD-MRI3 ITERE Rev.A
6.4.4 Example of a test circuit with earth fault directional feature
Figure 6.2: 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 variable current and voltage sources. First, the
parameters IE> and IE>> must be set to "EXIT" in order to prevent possible tripping. For the pur-
pose of testing the directional feature, a test voltage equal to the rated voltage is applied to termin-
als A2/A5. The parameter "Voltage transformer connection for residual voltage measuring" (refer to
5.3.4) must be adjusted to "3Pha".
The appropriate measuring value is selected via the <SELECT/RESET> key. The display must in-
dicate 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°).
By using an RMS-metering instrument, a greater deviation may be observed if the test current
contains harmonics. 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.
