TD_MRI1-IU_05.04_GB
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6.4.2
Example of test circuit for
MRI1-IU
relays without directional feature
For testing
MRI1-IU
relays current and voltage input
signals are required. Figure 6.1 shows an example of
a test circuit connected to the
MRI1-IU
relay under test.
For testing relays with voltage controlled feature, three
phase voltages from a variable voltage source should
be applied to the relay with a V-connection as shown
in the diagram.
The three phase voltage should be adjustable within
the effective operating range of the undervoltage ele-
ment and have a phase relationship apart from 120°.
The current inputs could be single or three phase.
Figure 6.1:
Test curcuit
6.4.3
Checking the input circuits and
measured
values
Apply three phase rated voltage (e.g. 100 V phase to
phase) to the voltage input circuits (terminals A3, A5,
A7) and inject a current, which is less than the relay
pickup current set values, in phase 1 (terminals B3-B4),
and check the measured current on the display by
pressing the push button <SELECT/RESET>. For a re-
lay with rated current In = 5A, for example, a secon-
dary current injection of 1A should be indicated on the
display with about 0.2 (0.2 x In). The voltage will be
indicated on the display in volts. The current can be
also injected into the other current input circuits (Phase
2: terminals B5-B6, Phase 3: terminals B7-B8).
Compare the displayed current and voltage value with
the reading of the ammeter and voltmeter. The devia-
tion must not exceed 3%. By using an RMS-metering
instrument, a greater deviation may be observed if the
test current contains harmonics. Because the
MRI1-IU
relay measures only the fundamental component of the
input signals, the harmonics will be rejected by the in-
ternal DFFT-digital filter. Whereas the RMS-metering in-
strument measures the RMS-value of the input signals.
Summary of Contents for HighTECH Line MRI1IU
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