ABB RARIC User manual

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RARIC
Shaft current protection
• Sensitive protection for bearings of large rotating machines
• Operates for shaft currents larger than 0,3 - 0,8 A AC, depend-
ing on the diameter of the shaft
• Fundamental or third harmonic operating principle
• AC or DC powered, galvanically isolated
• Shaft current transformer with test winding
• Can be applied to shafts with diameters up to 2960 mm
• Settable time delay
• Trip relay with heavy duty contacts and indicating flag
• Test switch
Features
User’s guide
1MRK 502 001-UEN
Revision: A
Issued January 2003
Data subject to change
without notice

1MRK 502 001-UEN
Page 2 RARIC
Shaft current protection
Contents Page
1 APPLICATION........................................................................... 3
2DESIGN........................................................................................ 4
2.1 The RARIC protection ..................................................... 4
2.2 The ILDD shaft current transformer.............................. 5
3 MODE OF OPERATION........................................................... 6
4 RECEIVING, STORAGE AND INSTALLATION................. 8
4.1 Receiving............................................................................ 8
4.2 Storage................................................................................ 8
4.3 Installation......................................................................... 8
5 SETTING, TESTING AND COMMISSIONING.................... 9
5.1 Setting................................................................................. 9
5.2 Testing and commissioning.............................................. 9
5.2.1 Injection test............................................................ 9
5.2.2 Primary test............................................................. 9
6 MAINTENANCE ........................................................................ 9
7 TECHNICAL DATA ................................................................ 10
8DIAGRAMS............................................................................... 12
9 DIMENSION ILDD .................................................................. 15
10 MOUNTING ............................................................................. 16

RARIC
Shaft current protection 1MRK 502 001-UEN
Page 3
An emf is induced in the shaft of the generators due to the magnetic dis-
similarities in the armature field. The emf normally contains a large
amount of harmonics. Both the wave-shape and the magnitude of the
induced voltage depend on the type and size of the machine and they also
vary with the loading.
Normally, the induced voltage will be in the range 0.5 to 2 volts for turbo-
generators and 10 to 30 volts for hydro-generators.
To prevent the rotor from being electrically charged, the shaft of the turbo-
generators is usually grounded via a slip-ring on the prime mover side. For
hydro-generators, the water in the turbine provides a connection to
ground. If the bearing pedestal at the other side of the rotor is grounded,
the induced voltage will be impressed across the thin oil-film of the bear-
ing. Due to the low impedance of the loop formed by the shaft, the bearing
and the ground structure, a breakdown of the oil-film insulation may give
rise to a heavy current which leads to destruction of the bearing.
Consequently, the bearing pedestal furthest from the prime mover is usu-
ally insulated from ground and the insulation should be supervised by a
suitable protection. Severe damage on the bearings is not expected to
occur if the shaft current is less than one ampere.
Shaft current protection RARIC with a special current transformer ILDD
is used to detect currents that can damage the bearings of a generator. The
relay can be used for generators with shaft diameter up to 2960 mm.
Min operate current is 0.3 to 0.8 ampere, depending on the diameter of the
shaft.
The RARIC protection is available in two versions:
Version 1 has a linear frequency characteristic and operates on the funda-
mental and harmonic components in the shaft current.
Version 2 has a damping filter for the fundamental frequency and operates
on the harmonics in the shaft current. This version is used when the shaft
current transformer is exposed to a large fundamental frequency leakage
flux.
1
APPLICATION

1MRK 502 001-UEN
Page 4 RARIC
Shaft current protection
The RARIC protection is built up of a test switch, terminal bases, plug-in
modules and connection parts of type COMBIFLEX. The test switch and
the terminal bases are screwed to two apparatus bars. The plug-in modules
are inserted and screwed to the terminal bases. All internal connections are
made on the rear of the terminal bases with COMBIFLEX socket leads.
Leads with a 10 A COMBIFLEX socket at one end are used for external
connections to the relay bases and leads with 20 A socket are used for con-
nections to the test switch.
Fig. 1 shows the components of the RARIC protection and the connec-
tions to the measuring and test windings of the ILDD shaft-current trans-
former. The numbers below refer to the numbering of the components in
Fig. 1.
1. Test switch RTXP 18
When a test handle RTXH 18 is inserted into the test switch, the trip
and alarm circuits are opened. A relay test apparatus can be con-
nected to terminals 3B and 4B on the test handle to inject current into
the test winding A - B.
2. Damping filter RXTFB 4 (only for RARIC, Version 2)
contains capacitors, reactors and resistors. One parallel resonance
and one series resonance circuit in the filter gives the frequency char-
acteristic shown in Fig. 4.
3. Overcurrent relay RXIK1
is the measuring unit of RARIC. The operating value of RXIK 1 is
steplessly settable 0.5 - 2 mA. The current input circuit has an resist-
ance of 82 ohms and contains an RC circuit to suppress high fre-
quency disturbance signals. The output circuit contains an impulse
holding function which ensures operation also when intermittent
input current signals are received.
4. Time relay RXKL 1
is a static relay with scale 30 ms to 99 h. The setting determines the
delay of the trip signal.
5. Auxiliary relay RXME 18
has heavy-duty contacts which can be used in signal and tripping cir-
cuits. The relay is fitted with a red flag to indicate operation.
The flag is manually reset by means of a resetting knob in the cover.
6. Power supply unit RXTUB 2
is an AC/DC converter which contains a transformer, full-wave recti-
fier and smoothing capacitors. The unit supplies auxiliary voltage to
the relays in RARIC.
The output DC voltage is 24 volts (± 12 V).
RARIC is also available with a DC/DC converter RXTUG 22H for
DC auxiliary voltage supply.
2 DESIGN
2.1 The RARIC protection

RARIC
Shaft current protection 1MRK 502 001-UEN
Page 5
Fig. 1 Basic circuit for RARIC.
The ILDD shaft-current transformer is of special design with high quality
core steel, where the number of secondary turns and the core cross-sec-
tional area are optimized to the diameter of the transformer to get the low-
est possible primary operate current when connected to the RXIK 1 relay.
The measuring and the test windings are covered with cotton tape and then
embedded in a circular shaped U-profile for mechanical protection and
magnetic screening. The profile with the core and the windings is then
embedded in resin.
The transformer is split up in two parts for sizes with inner diameter up to
and including 2 000 mm. For larger diameters, the transformer is split up
in four parts. When the parts are jointed, the steel sheets of the core are
interleaved with an overlap of about 30 mm.
The measuring winding, with 400 - 800 turns depending on the diameter
of the transformer, is evenly distributed on the parts of the core. When the
transformer parts are mounted together, the parts of the measuring wind-
ing must be connected to the terminals S, see Fig. 2. The pilot-wires to the
RARIC protection are connected to terminals S1 -S2, see Fig. 2.
The test winding has four turns and is connected to terminals marked
A and B.
ALARM
TRIP 17A
16A
1
-
+++
0
100V
110V
220V
18A
2A 1A
1:
9A
10A 11A 12A
5
3
6
4
+ 0 -
2
3A3B
4A4B
S1
S2
B
A
1
Ι
Ι
Ι
502001
-5
2.2 The ILDD shaft current transformer