Manual MRI3 GB
Woodward
DOK-TD-MRI3 Rev.A
53
6.5 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 MRI3 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 MRI3 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 MRI3 relay with directional feature, the
active and reactive parts of the measured currents may be checked and the actual 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 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 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 MRI3, this interval can be substantially longer.
This is because:
The MRI3 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 MRI3 relays enable supervision the relay functions
during
service.
The combined TRIP test function of the MRI3 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.