52
TB MRI(K)3-C 03.02 E
6.4.1 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 In
= 5A, for example, a secondary current injection of 1A
should be indicated on the display with about 0.2 (0.2
x In). 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. Compare the displayed current value with
the reading of the ammeter. The deviation must not ex-
ceed 3% or 1% In. By using an RMS-metering instru-
ment, a greater deviation may be observed if the test
current contains harmonics. Because the
MRI(K)3-C
re-
lay measures only the fundamental component of the in-
put signals, the harmonics will be rejected by the inter-
nal DFFT-digital filter. Whereas the RMS-metering instru-
ment measures the RMS-value of the input signals.
6.4.2 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 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 activated.
Read the operating current indicated by the ammeter.
The deviation must not exceed 3% of the set operating
value or 1% In.
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 cur-
rent measuring
±
3% of measuring value.
6.4.3 Checking the relay operating time
"For this test the AR function should be deactivated. The
number of automatic reclosing attempts "SHOT" should
be set to "EXIT".
To check the relay operating time, a timer must be con-
nected to the trip output relay contact. The timer should
be started simultaneously with the current injection in the
current input circuit and stopped by the trip relay con-
tact. Set the current to a value corresponding to twice
the operating value and inject the current instantane-
ously. The operating time measured by the timer should
have a deviation of less than 3% of the set value or
±
10
ms (DEFT). Accuracy for inverse time characteristics refer
to IEC 255-3.
Repeat the test on the other phases or with the inverse
time characteristics in the similar manner.
In case of inverse time characteristics the injected current
should be selected according to the characteristic curve,
e.g. two times I
S
. The tripping time may be red from the
characteristic curve diagram or calculated with the
equations given under "technical data".
Please observe that during the secondary injection test
the test current must be very stable, not deviating more
than 1%. Otherwise the test results may be wrong.
6.4.4 Checking the high set element
of the relay
Set a current above the set operating value of I>>. If re-
quired an alarm relay can be tripped if in this moment if
it is assigned to this function. Check the tripping time of
the high set element according to chapter 6.4.3.
Check the accuracy of the operating current setting by
gradually increasing the injected current until the I>>
element picks up. Read the current value from the amme-
ter and compare it with the desired setting.
Repeat the entire test on other phases and earth current
input circuits in the same manner.
Note !
Where test currents >4 x I
N
are used, the thermal with-
stand capability of the current paths has to be consid-
ered (see technical data, chapter 7.1).
