RARIC
Shaft current protection
1MRK 502 001-UEN
Page 9
The setting of the overcurrent relay RXIK 1 is suitably decided after
checking the magnitude of the stray current to the relay when the genera-
tor is running at load. In case of induced stray currents, a setting 50%
higher than the setting which gives unwanted operation is recommended.
The time delay set on time relay RXKL 1 should with margin override the
time delay of the phase short-circuit back-up impedance or overcurrent
protection. A normal setting is 3 s.
Set the overcurrent relay and the time relay according to the above. Insert
the RTXH 18 test handle into the RTXP 18 test switch.The primary oper-
ating current of the protection is tested by injecting current of rated fre-
quency into test winding A - B of the shaft current transformer from test
terminals 3B - 4B on the handle. The test winding has four turns, hence
the primary operate shaft current is four times the injected operate current.
Observe that for RARIC Version 2, rated frequency is 150 or 180 Hz. For
this version, the relay shall not operate at lowest setting when 3 V rated
frequency voltage is applied to relay terminals 107:231 - 241, (see Fig. 4).
Without altering the settings, interchange the leads to the test terminals
and check the operate value. It can be different from the earlier measured
value. Both values should be recorded for comparison at future tests.
Set the injection current to 2 times the operate value and check the time
delay.
Connect a brush via a test lead to an ammeter and then further to ground
via a series connected adjustable resistor, 0 - 30 ohms. When the machine
is running, press the brush against the shaft near the insulated bearing and
reduce the resistance until the relay operates. Record the operate current.
Check the external connections for the trip and alarm signals.
Under normal conditions RARIC requires no special maintenance.
The covers should be installed in place and the hole for the current setting
knob should be blanked off with a plastic plug.
Maintenance testing at regular intervals, say every second years, should be
made. The testing is suitably made by injection of current to the test wind-
ing, since this also checks the ILDD transformer and the wiring up to the
protection.
5 SETTING, TESTING AND COMMISSIONING
5.1 Setting
5.2 Testing and commissioning
5.2.1 Injection test
5.2.2 Primary test
6 MAINTENANCE
