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6.4.9
Checking the external blocking and
reset
functions
The external blocking input inhibits e. g. the function of
the high set element of the phase current. To test the
blocking function apply auxiliary supply voltage to the
external blocking input of the relay (terminals E8/D8).
The time delay t
I>
should be set to EXIT for this test. In-
ject a test current which could cause a high set (I>>)
tripping. Observe that there is no trip and alarm for the
high set element.
Remove the auxiliary supply voltage from the blocking
input. Inject a test current to trip the relay (message
“TRIP” on the display). Interrupt the test current and ap-
ply auxiliary supply voltage to the external reset input
of the relay (terminals C8/D8). The display and LED
indications should be reset immediately.
6.4.10 Test of the CB failure protection
For testing the tripping time a test current of about 2
times the rated current to be injected. The timer is
started upon tripping of the relay of a protection func-
tion (I>, I>>, I
E
>, I
E
>>) and stopped as soon as the re-
lay for the CB failure protection has picked up. Mes-
sage "CBFP" is displayed. The tripping time ascer-
tained by the timer should not deviate more than 1%
or, at short trip delay, less than 10 ms from the set
tripping time.
Alternatively, the timer can be started when the aux.
voltage and the test current are injected simultane-
ously. The timer stops when the corresponding output
relay for circuit breaker failure protection trips.
In this case the previously measured tripping delay
(see section 6.4.5) has to be subtracted from the total
tripping time measured.
6.5 Primary injection test
Generally, a primary injection test could be carried out
in the similar manner as the secondary injection test
described above. With the difference that the pro-
tected power system should be, in this case, con-
nected to the installed relays under test “on line”, and
the test currents and voltages should be injected to the
relay through the current and voltage transformers with
the primary side energized. Since the cost and poten-
tial hazards are very high for such a test, primary in-
jection tests are usually limited to very important protec-
tive relays in the power system.
Because of its powerful combined indicating and
measuring functions, the
MRI1
relay may be tested in
the manner of a primary injection test without extra ex-
penditure and time consumption.
In actual service, for example, the measured current
values on the
MRI1
relay display may be compared
phase by phase with the current indications of the
ammeter of the switchboard to verify that the relay
works and measures correctly. In case of a
MRI1
relay
with directional feature, the active and reactive parts
of the measured currents may be checked and the ac-
tual power factor may be calculated and compared it
with the cos
ϕ
-meter indication on the switchboard to
verify that the relay is connected to the power system
with the correct polarity.
6.6 Maintenance
Maintenance testing is generally done on site at regu-
lar intervals. These intervals vary among users depend-
ing on many factors: e.g. the type of protective relays
employed; the importance of the primary equipment
being protected; the user's past experience with the re-
lay, etc.
For electromechanical or static relays, maintenance
testing will be performed at least once a year accord-
ing to the experiences. For digital relays like
MRI1
,
this interval can be substantially longer. This is be-
cause:
•
the
MRI1
relays are equipped with very wide self-
supervision functions, so that many faults in the relay
can be detected and signalized during service. Im-
portant: The self-supervision output relay must be
connected to a central alarm panel!
•
the combined measuring functions of
MRI1
relays
enable supervision the relay functions during service.
•
the combined TRIP test function of the
MRI1
relay al-
lows to test the relay output circuits.
A testing interval of two years for maintenance will,
therefore, be recommended.
During a maintenance test, the relay functions includ-
ing the operating values and relay tripping characteris-
tics as well as the operating times should be tested.
