TB MRIK3 12.00 E
31
6.4.2
Example of test circuit for
MRIK3
relays
For testing
MRIK3
relays only current input signals are
required. Figure 6.1 shows a simple example of a sin-
gle phase test circuit with adjustable current energizing
the
MRIK3
relay under test.
Note!
Care must be taken that the correct functions are as-
signed to the output relays (refer to 5.7). In this exam-
ple, relay 1 is assigned to the tripping function and re-
lay 4 to the auto reclosing function.
Figure 6.1: Test curcuit
6.4.3
Checking the input circuits and
measured values
Inject a current, which is less than the relay pickup cur-
rent set values, in phase 1 (terminals B3-B4), and check
the measured current on the display by pressing the
push button <SELECT>. For a relay with rated current I
N
= 5A, for example, a secondary current injection of 1A
should be indicated on the display with about 0.2 (0.2
x I
N
). When parameter Iprim = „sek“ is set, the indica-
tion is 0.2 x In and at „5“ the indication is 1.00 [A].
The current can be also injected into the other current
input circuits (Phase 2: terminals B5-B6, Phase 3: termi-
nals B7-B8 and the earth current input). Compare the
displayed current value with the reading of the amme-
ter. The deviation must not exceed 3% of the measuring
value or 1% I
N
. By using an RMS-metering instrument, a
greater deviation may be observed if the test current
contains harmonics. Because the
MRIK3
relay measures
only the fundamental component of the input signals, the
harmonics will be rejected by the internal DFFT-digital fil-
ter. Whereas the RMS-metering instrument measures the
RMS-value of the input signals.
6.4.4
Checking the operating and
resetting values of the relay
Inject a current which is less than the relay set values in
phase 1 of the relay
MRIK3
and gradually increase the
current until the relay starts, i.e. at the moment when the
LED I> and L1 light up or the alarm output relay I> is ac-
tivated. Read the operating current indicated by the
ammeter. The deviation (
MRIK3
) must not exceed 3% of
the set operating value or 1% I
N
.
Furthermore, gradually decrease the current until the re-
lay resets, i.e. the alarm output relay I> is disengaged.
Check that the resetting current is smaller than 0.97
times the operating current.
Repeat the test on phase 2, phase 3 and earth current
input circuits in the same manner. (Accuracy of earth
current measuring
±
3% of measuring value).
