Mode Of Operation - ABB RARIC User Manual

1MRK 502 001-UEN
Page 6

3 MODE OF OPERATION

RARIC
Shaft current protection
38
Fig. 2 Shaft current transformer ILDD with diameter D up to 2000 mm.
The ILDD shaft current transformer encompasses the rotor shaft and func-
tions in principle like a cable current transformer. The measuring winding,
which is connected to the RARIC protection, contains from 400 up to 800
turns, depending on the diameter of the transformer. When the current in
the measuring winding exceeds the operate value of the overcurrent relay
RXIK 1, it operates and tripping is given after the delay set on time relay
RXKL 1.
If the shaft current is intermittent, for example due to intermittent break-
down of the insulation of the oil film in the bearing, pulses are fed to
RXIK 1. If these pulses exceed the operating value of the relay, and the
intervals between the pulses are shorter than 0.9 s, the contacts of the out-
put relay will be continuously closed.
The impedance of the current measuring circuit in RXIK 1 is about 80
ohms. Hence, for Version 1, the operate voltage is about 40 mV at the low-
est setting 0.5 mA of RXIK 1.
Fig. 3 shows the maximum primary operate current at 50 - 60 Hz for
RARIC, Version 1, at relay settings 0.5 and 1 mA as function of the inner
diameter of the ILDD transformer.
Fig. 4 shows the operate voltage for RARIC, Version 2, as function of the
frequency. The curves in both figures are valid for sinusiodal currents and
max. 5 ohms pilot-wire resistance between the transformer and the protec-
tion.
S
B
A
S S 1
S 2
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