ABB RARIC Manuel utilisateur

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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.

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

+++

100V

110V

220V

18A

10A

11A

12A

3A3B

4A4B

502001

-5

2.2 The ILDD shaft current transformer

1MRK 502 001-UEN

Page 6 RARIC

Shaft current protection

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.

Max 70

D±5

AQTrafoAB

S1S

en02000670.vsd

3 MODE OF OPERATION

RARIC

Shaft current protection 1MRK 502 001-UEN

Page 7

Fig. 3 Primary operate current at relay setting 0.5 resp. 1 mA as func-

tion of the inner diameter of ILDD.

The filter in Version 2 rejects the fundamental voltage by more than 70:1.

Fig. 4 Operate voltage of RARIC, Version 2 as function of frequency.

Rated frequency = 50 Hz.

502001

-1

0,5

0,1

0,04

(V)

30 50 100 150 500

I = 1 mA

I = 0,5 mA

f (Hz

)

502001

-2

1MRK 502 001-UEN

Page 8 RARIC

Shaft current protection

Remove the protection from the transport case and make a visual inspec-

tion for transport damages. Check that all screws are firmly tightened and

all relay elements are securely fastened.

Check on the rating plate of the relay units that the delivered relay has cor-

rect data as regards auxiliary voltage, frequency etc. Check against the list

of apparatus that all units are included.

If the relay is to be stored before installation this must be done in a dry and

dust-free place, preferably in the original transport case.

The RARIC protection can be placed in a 19" equipment frame for mount-

ing in a 19" rack in a cubicle. The relay can also be placed in a relay case

type RHGX.

On delivery, all internal connections in the protection are ready made.

External connections (dotted lines on the circuit diagrams) are made with

leads with 20 A COMBIFLEX sockets to the RTXP 18 test switch and

with 10 A sockets to the relay terminal bases.

The ILDD shaft current transformer should be mounted around the shaft at

a place where any possible current through the bearing is flowing in the

shaft. This means that it should be mounted at the rotor side of any bearing

or slip-ring. To avoid disturbances the transformer shall be mounted on the

turbine side of the machine which is free from field bars and at maximum

distance from the end of the stator winding. See Fig. 12 and Fig. 13 for

recommended mounting.

Screened cable, with twisted pairs and with the screen grounded only at

the relay side is recommended for the connections between the protection

and the shaft current transformer.

An inner diameter of the transformer 20 - 50 mm larger than the shaft

diameter is suitably selected. Large diameter of the transformer has a neg-

ative influence on the sensitivity of the protection and it also increases the

risk of stray fluxes entering the CT core.

The width of the transformer in axial direction is 38 mm for inner diame-

ters up to 2 000 mm and 42 mm for inner diameters above 2 000 mm.

An axial distance of at least 250 mm is required for assembling the trans-

former sections on the shaft.

Mounting details are not included in the delivery, since they must be

designed to suit the specific machine. Examples on mounting supports,

which can be used in most cases, are showned in Fig. 14.

4 RECEIVING, STORAGE AND INSTALLATION

4.1 Receiving

4.2 Storage

4.3 Installation

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

1MRK 502 001-UEN

Page 10 RARIC

Shaft current protection

Table 1: Basic data

Current setting range (RXIK) 0.5-2 mA, 50-60 Hz

Operate shaft current at setting

0.5 mA and transformer diameters

160-3000 mm Version 1: 0.3-0.8 A, 50-60 Hz

Version 2: 0.3-0.8 A, 150 Hz

Reset ratio > 99%

Filter characteristic, version 2 The filter rejects the fundamental by 70:1

Input impedance 80 ohm resistive

Overload capacity

shaft diameter < 700 mm

shaft diameter 700-1600 mm

shaft diameter 1610-2500 mm

shaft diameter > 2500 mm

50 A shaft current continuously and 200 A in 1 s

65 A shaft current continuously and 250 A in 1 s

75 A shaft current continuously and 300 A in 1 s

100 A shaft current continuously and 400 A in 1 s

Auxiliary rated voltage 100, 110 and 220 V, 50-60 Hz or 24-250 V DC

Power consumption from aux.voltage

AC supply

DC supply Approx. 2 VA before and 8 VA after operation

Approx. 3 W before and 7 W after operation

Time setting range (RXKL) 30 ms-99 h

Permissible ambient temperature -5 to +55 °C

Permissible range auxiliary voltage

supply 80-110 % of rated voltage

Table 2: Electromagnetic compability tests

Power frequency test (SS 436 15 03) 0,5 kV, class PL4

Fast transient test (SS 436 15 03) 4-8 kV, class PL4

1 MHz burst test (IEC 60255-22-1) 2.5 kV, class III

Table 3: Insulating tests (IEC 60255-5)

Dielectric test 2 kV, 50 Hz, 1 min

Impulse voltage test 5.0 kV, 1.2/50 µs, 0.5 J

Table 4: Contact data

Trip circuits (RXME 18)

Max system voltage within a

contact set 450 V dc, 400 V ac

Current-carrying capacity for already

closed contact 55 A for 200 ms

30 A for 1 s

6 A continuously

Making and conducting capacity,

L/R < 10 ms 30 A for 200 ms

20 A for 1 s

Breaking capacity,

max. 250 Vac, PF > 0.1 20 A

Breaking capacity, dc, L/R < 40 ms 20 A at 24 V

18 A at 48 V

3 A at 110 V

1 A at 220 V

7 TECHNICAL DATA

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