SEG Electronics GmbH
Manual MRG3
70
DOK-TD-MRG3, Rev. D
6.7 Checking the external blocking and reset inputs
By means of the external blocking input, it is possible to block all protective functions. To give an
example, the blocking function of the phase current high set element is described.
This can be tested by first setting the parameter for the phase current high set element (short cir-
cuit element) to „BLOC“ and then connecting the auxiliary voltage to terminals E8/D8.
The phase current low set element I> should be set to EXIT for this test. Inject a test current which
could cause a high set (I>>) tripping. Observe that there is no trip of any assigned output relay of
the high set or low 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 apply
auxiliary supply voltage to the external reset input of the relay (terminals C8/D8). The display and
LED indications should be reset immediately.
6.7.1 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 tim-
er is started upon tripping of the relay of a protection function (I>, I>>, I
E
>, I
E
>>) and stopped as
soon as the relay for the CB failure protection has picked up. Message "CBFP" is displayed and
LEDs CB + t> lights up. The tripping time ascertained 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 simultaneously. The timer stops
when the corresponding output relay for circuit breaker failure protection trips. In this case the pre-
viously measured tripping delay has to be subtracted from the total tripping time measured.
6.8 Primary injection test
Generally, a primary injection test could be carried out in the similar manner as the secondary in-
jection test described above. With the difference that the protected power system should be, in this
case, connected 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 potential hazards are very high for such a test, primary injection tests
are usually limited to very important protective relays in the power system.
Because of its powerful combined indicating and measuring functions, the MRG3 relay may be
tested in the manner of a primary injection test without extra expenditure and time consumption.
In actual service, for example, the measured current values on the MRG3 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.
6.9 Maintenance
Maintenance testing is generally done on site at regular intervals. These intervals vary among us-
ers depending 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 relay, etc.
For electromechanical or static relays, maintenance testing will be performed at least once a year
according to the experiences. For digital relays like MRG3 this interval can be substantially longer.
This is because:
The MRG3- relays are equipped with very wide self-supervision functions, so that many
faults in the relay can be detected and signalized during service. Important: The self-
supervision output relay must be connected to a central alarm panel!
The combined measuring functions of MRG3 relays enable supervision the relay functions
during service.
The combined TRIP test function of the MRG3 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 including the operating values and relay tripping
characteristics as well as the operating times should be tested.
