R10 User Manual

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PRISMIC R10ELECTRONIC ROTOR EARTH

FAULT MONITOR(INFRA RED TYPE)

HANDBOOK9592007-00

REVISION D

DATEFEBRUARY 2001

Back



Electronic Rotor Earth Fault Monitor Infra-Red Type

This handbook, in addition to the information relating to the specification,installation and commissioning of the units, includes information for basic fault finding,with technical descriptions, circuit diagrams and parts lists of various plug-in modules.

IssueFebruary 2001

Technical Handbook No 88 Rev D



List of Contents

Chapter Title

1 Introduction

2 Description

3 Specification3a Earth Fault Detection Sensitivity3b Output Relay Rating3c Receiver Auxiliary Supply3d Transmitter Supply (Rotor Voltage)3e Temperature3f Low Exciter Field Voltage Inhibit

3g Loss of Auxiliary Supply3h Distance Between IR Detector and Receiver 3i Test Facility3j Indication of Circuit Conditions3k Transmitter Centrifugal Force Limit3l Transmitter Weight

4. Commissioning4a Meggering4b Check installation4c Receiver 4d Commissioning Tests4e Functional Check

5. Fault Finding5a Fault Finding Table5b Static Testing5c Static Testing with Transmitter and Aerial on Bench

6 Installation6a Aerial Cable

7 Periodic Testing and Maintenance

8 List of Drawing Numbers

9 List of Part Numbers



1 Introduction

General practice in Brushless Generators is for the rotor field circuit to be fully isolated such that a single earth

fault does not cause adverse operating conditions. However, a second earth fault requires the immediateshutdown of the set.

To avoid this occurrence it has been the practice in the past to detect a single rotor earth fault by use of brushes and sensitive earth fault current relays and to take the machine out of service for investigation andrepair of the fault at the earliest opportunity.

The Brush Rotor Earth Fault Monitor dispenses with the need for brushes by using fully static techniques todetect a single rotor earth fault on the shaft and transmit the information to a stationary receiver, thereby givingenhanced reliability and reduced maintenance costs.



2 Description

(Fig 1 shows the basic system).

The transmitter has 3 electrical connections to the rotor; to earth, rotor positive (F1) and rotor negative (F2).The rotor voltage provides the power supply for the unit, from which it generates its own isolated dc source thatis used as the earth fault detection supply. The negative of this isolated source is tied to ground, the positive tothe rotor negative (F2). During healthy conditions the current flowing from the isolated dc source is negligibleand the transmitter produces a high frequency signal that is detected by the receiver aerial and the receiver indicates no fault.

Any earth fault on the rotating assembly either on the armature or the rotor winding will cause a current to flowfrom the dc source. This current is detected and used to remove the transmitted high frequency signal. Byremoving the signal the detection system becomes 'fail-to-safe' in that a loss of transmitted signal is detectedas an earth fault condition.

The transmitted signal is sensed by an aerial and fed, via screened cable and amplifier, into a 'phase lockedloop' within the receiver. This device locks onto the transmitted signal and serves to decode the pulse signal aswell as filter out any background noise caused by external sources. The decoded signal is used to hold off theoutput alarm relay after an amplification and time delay stage. In the event of an earth fault condition the alarmrelay becomes energized after a short time delay (incorporated to suppress 'nuisance' alarms) thereby givingexternal indication of the fault condition.

The auxiliary supply required by the receiver for its power supplies is normally provided by the AVR excitationsource (usually a PMG*). During run up on AVR over flux control or during normal off load transients, theavailable rotor voltage may be too low to ensure correct transmitter operation. To overcome this a circuit isincorporated in the receiver to inhibit output relay energisation on either low exciter field voltage or low auxiliaryac supply voltage. A time delay stage within this circuit allows for the rotor voltage to build up prior to giving apermissive output.

*PMG - Permanent Magnet Generator



3 Specification

3a Earth Fault Detection SensitivityThe fault resistance detected by the unit depends on the position of the fault and the rotor voltage.

The system is least sensitive when the fault is present on the negative of the field and in this case the

sensitivity is approximately 12kΩ.

On a machine with a full load rotor voltage of 200V, the sensitivity to a fault on the positive of the field

would be approximately 157kΩ.

Fault sensing current: Approximately 1.5mATime delay on operation: 1s

3b Output Relay Rating

200VA or 100W (Non Inductive) maximum 5A or 250V

3c Receiver Auxiliary Supply

110V, 220V, 264V, or 400V, ±25% - 50Hz to 500Hz, Burden 6VA

3d Transmitter Supply (Rotor Voltage

Maximum Continuous Voltage - 200V dcMaximum 10 second overload voltage - 500V dcMinimum guaranteed operating voltage - 30V dc

3e Temperature

Receiver Operating -25°C to +85°C Aerial and Transmitter Operating -25°C to +70°C

Storage -40°C to +100°C

3f Low Exciter Field Voltage Inhibit

Adjustment of the exciter field voltage inhibit is from 3.0V to 25V. Unless the field exceeds this voltage theoutput alarm is inhibited. On build up of exciter field voltage above the preset level there is a time delay of 3 to 4 seconds before the inhibit is released.

If the exciter field voltage falls below the preset level the inhibit will be applied instantaneously.

The maximum continuous exciter field voltage at this input is 400V dc.

3g Loss of Auxiliary Supply

The output relay will be inhibited when the supply falls below 75% of the nominal transformer tap rating.

3h Distance Between IR Detector and Receiver

Screened cable capacitance must not exceed 0.1µF total per core to screen. Resistance not to exceed

10Ω per core.

3i Test Facility

Operation of an external test push-button when the machine is running and excited will simulate an earthfault and produce an alarm signal.



3j Indication of Circuit Conditions

LED1 ON - Low Auxiliary supply inhibit is released.

LED2 ON - Low Exciter field voltage inhibit is released.

LED3 ON - Earth fault condition.

LED4 ON - Auxiliary supply is present.

3k Transmitter Centrifugal Force Limit

The transmitter is suitable for mounting on the shaft at a radius of up to 115mm for a continuous speed of 3,600rpm. The unit is suitable for an overspeed 4,800rpm for 5 minutes duration.

The transmitter may be mounted at a larger radius provided the speed is reduced accordingly.

3l Transmitter Weight

The weight of the transmitter is 710g ±25g.



4 Commissioning

(For location of controls, adjustments, test points and indications, see Fig 2)

4a MeggeringDisconnect the transmitter unit from the rotor before meggering rotor to earth to avoid false Megger reading and damage to the transmitter.

4b Check installation

(1) On Machine

Confirm that the unit has been installed in accordance with the instructions given in Chapter 6.

Pay particular attention to the position of the aerial in relation to the transmitter, also to the polarity of the rotor connections to the transmitter.

Ensure that the transparent windows on the transmitter and aerial are clean.

(2) Wiring Between Aerial and Receiver Check that three core screened cable has been used and that the screen is connected to earth at theaerial (terminal 3).

4c Receiver

(1) SupplyEnsure that the receiver is connected on the correct voltage terminal and that the handbag links arein correct position according to the following table (see Fig 2 for link location):

Nominal Supply Voltage Terminals Link Arrangement110V ± 25% 11 & 12 Fit LK1 Omit LK2,3,4

220V ± 25% 10 & 12 Fit LK2 Omit LK1,3,4

264V ± 25% 9 & 12 Fit LK2,4 Omit LK1,3

400V ± 25% 9 & 12 Fit LK2,3 Omit LK1,4

(2) Operating FrequencySelect the unit for the infra red transmitter frequency by setting switches 1 to 4 on and switches 5 to8 off. (See Fig 2)

4d Commissioning Tests

(1) Run the set up to rated speed with auto excitation selected using the AVR overflux limiter to allowthe voltage to build up gradually. If the overflux limiter is not included in the AVR switch on excitationat rated speed.

(2) Check supply present LED4 is illuminated

(3) Set up the supply inhibit circuit by adjusting RV1 so that the dc voltage on TP4 with respect to TP1 is1.3 times the voltage measured across TP5 and TP1 (approximately 6V).Check that the supply inhibit released, LED1 is illuminated.



(4) Set up the exciter field voltage inhibit circuit as follows

Rotate RV2 fully anticlockwise and check that LED2 is on.Rotate RV2 slowly clockwise until LED2 is turned off, then anticlockwise approximately 20 degrees.

If LED2 remains on, leave RV2 fully clockwise.

(5) Check that no alarm signal is given and protection operated LED3 is off

(6) Suppress excitation and again check that no alarm signal is given, check that LED2 is off

(7) Apply excitation and check that no alarm signal is given as the excitation builds up. Operate the testpushbutton and check that an alarm is given after approximately 1 second.

Release the test button and check that the alarm is cancelled.

(8) Optimise the receiver tuning as follows:Connect a Fluke dc voltmeter (10V range) between Tp13 +ve and TP1.With the machine running and the transmitted signal being received, adjust RV3 so that the voltmeter indicates a minimum reading.

(9) If the normal mode of operation is to run down the machine with the excitation turned on, themachine should be run down with excitation on to confirm that no earth fault alarm is given.

4e Functional Check

Having followed the preceding commissioning procedure it is desirable to check that an earth faultcondition is correctly detected. It is imperative that prior to this test it is confirmed that no rotor earth faultexists. (This should have been verified by the preceding commissioning checks).

Using a short light gauge wire (22 SWG or less) put an earth fault on the rotor between transmitter F2 studand the adjacent earth screw connection. Run the set up to speed and check that when auto excitationis selected an earth fault indication is given. Switch off excitation, shut down the set and remove the earthfault.



5 Fault FindingIf the equipment is not operating correctly ensure that it has been installed according to Chapter 6 andcommissioned according to Chapter 4.

The Fault Finding table below (part a) shows the action to be taken for various types of fault. Part b gives StaticTesting Procedures for the transmitter, aerial and receiver.

5a Fault Finding Table

Symptom Possible Cause Action/Remedy

1. Continuousindication of Fault (Alarm onand ProtectionOperated LEDon at Receiver)

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

Earth Fault present on Rotor.

Transmitter F1 & F2 connectionsreversed.

Output signal from aerial too shortduration.

Infra-red signal obscured by dirt.

Connection between Aerial andReceiver Faulty.

Test switch is set to "Test".

Receiver 'off tune'

Transmitter or aerial faulty

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

Confirm earth fault does notexist by meggering rotor asdescribed in machinehandbook. Disconnecttransmitter before meggering.

Check as described in Chapter 4, part b(1).

Check output of aerial is a burstof 20kHz with duration of atleast 2 milliseconds. If not checkinstallation is in accordance with0 or consult Factory.

Clean infrared emitters of transmitter and sensitive face of

aerial.

With machine at standstill or receiver completely isolatedcheck wiring between aerial andreceiver. Check screen of cableconnected according to Chapter 4, part b (2).

Return test switch to normalrunning position.

Retune the receiver as

described in section 4d (8)

Check as described in part b of this Chapter.



Symptom Possible Cause Action/Remedy

2. No indication of

fault duringcommissioningtest. Chapter 4,part e.

2.1

2.2

2.3

Receiver supply inhibit not

released (LED1 is off).

Exciter field voltage inhibit notreleased. (LED2 is off).

Receiver faulty

2.1

2.2

2.3

i) Check voltage on auxiliary

terminals is consistent withChapter 3, part cii) Check RV1 is set accordingto Chapter 4, part d(3).

i) Check exciter field voltageis applied to terminals5(+ve) and 15, and is atleast 2.5V dc on noload.

ii) If LED2 is off adjust RV2as described in Chapter 4, part d(4).

If supply inhibit and field inhibitreleased LEDS are on. Set thetest switch to 'Test' and an earthfault alarm should be given. If not the receiver is faulty andshould be replaced.

3. Occasional or spurious faultindication.

3.1

3.2

3.3

Exciter field voltage inhibit set toolow.

Receiver nearly 'off tune'

Aerial output signal too weak.

3.1

3.2

3.3

Set RV2 so that LED2 is turnedoff when the exciter field voltageis reduced to approximately80% of the no-load (cold) level.Run on manual control to set

this up if required.

Check/reset as necessary, see1.7 in this table.

i) Check wiring between aerialand receiver.ii) Check voltage at aerialterminals 4(+ve) and 2 isbetween 7.5 and 9.5V dc.iii) Clean aerial and transmitter infra red emitters with soft cloth.iv) If none of above successful

perform static test described inpart b.

5b Static Testing

If transmitter, aerial or receiver are suspected faulty the combination can be statically tested either on thebench or with transmitter and aerial mounted on the machine, and the receiver in situ.

Static testing with the components mounted in position on the machine is more realistic since the positionof the aerial relative to the transmitter is not changed. It may also be easier since the transmitter need notbe removed from the shaft.WARNING! When working on the transmitter ensure machine shaft will remain stationarythroughout. This may mean temporarily turning off barring gear



(1) Static Testing with Transmitter on the Shaft(a) Position the transmitter (by rotating the shaft) so that the LED emitters are facing the aerial. See

3a.

(b) Disconnect the rotor connections F1 and F2 from the transmitter terminals and connect a 30Vdc power supply rated at 50mA, positive to F1 (this is the right hand terminal when viewing fromthe end carrying the infrared emitters) and negative to F2.

(c) Check that the supply current to the transmitter without a simulated earth fault is between 25and 35mA with a 30V supply, and that when terminal F2 is connected to the transmitter housing, the current drops to between 15mA and 22mA.

(d) Connect the receiver as shown in fig 5. It may be necessary to temporarily select differentpower supply links to suit the ac supply available for testing.

The exciter field voltage signal required at receiver terminals 15 and 5, may be obtained by linking

terminals 14 to 5, and terminals 2 to 15, after temporarily disconnecting the cable connected toterminal 5.

(e) No earth fault (LED3 should be OFF) should be given when the receiver and transmitter supplies are on. The supply present (LED4) indicator should be ON, and both inhibit releaseLED’s (LED1 and LED2) should be ON.

(f) Temporarily link transmitter terminal F1 then F2 to the transmitter casing and check that thereceiver gives earth fault indication (LED3 ON) in each case.

(g) Notes on above testsIf test (e) results in a continuous earth fault indication and LEDS 1,2 and 3 on the receiver areon, the signal at the input of the receiver (terminals 1 and 2) should be checked with an

oscilloscope.

With no earth fault the signal should comprise a continuous 20kHz waveform of amplitudeapproximately 0.7V ±0.2V (See Fig 6). Absence of this signal indicates faulty connections betweenaerial and receiver, or dirty aerial or transmitter (see table 5a) or faulty aerial or transmitter.

Note! When the machine is rotating this signal will occur in bursts with at least one burst of duration 2ms or more each revolution ie. each 16ms on a 3,600rpm machine, or each 20ms on a 3,000rpm machine.

There may be other shorter bursts due to spurious infrared and reflections in the machine and theseshould be disregarded.

With the simulated earth fault of test (f) above, the 20kHz signal should be completely removed.

(Ignore spurious pulses that may occur due to background infrared signals.) If the signal is notremoved, the transmitter is faulty.

If the signal is present at the receiver and an earth fault alarm persists, ensure the test switch is setto the normal running position (normally open) and adjust tuning as described in part 1.7 of table 5a.

If it is not possible to tune the receiver, a faulty receiver is indicated and it should be replaced.

5c Static Testing with Transmitter and Aerial on Bench

(1) Remove transmitter and aerial from the machine and connect to the receiver as shown in Fig 5. A30V 50mA dc supply should then be connected to the transmitter.



The aerial should be placed approximately 300mm from the transmitter, with its window pointingtowards the infrared emitters on the transmitter.

The rest of the static bench test is as described in part b (1), tests (c) to (g).

WARNING!

Care should be taken that stray infra red emissions does not activate fir e protection systems.



6 InstallationThe aerial and transmitter should be installed on the machine similar to the arrangement shown in Fig 3 withthe window of the aerial facing the shaft as shown.

The receiver, aerial and transmitter should be connected as shown in Fig 4.

6a Aerial Cable

Three core screened cable should be used to connect the aerial to the receiver. The screen should beconnected to terminal 3 at the aerial.

Length of cable should be such that the capacitance of each core to the screen does not exceed 0.1

microfarad and the resistance of each core does not exceed 10Ω. The current flowing in the aerial cabledoes not exceed 20mA.



7 Periodic Testing and MaintenanceIn common with other protection equipment it is recommended that correct operation is confirmed periodicallyby operation of the test pushbutton whilst the machine is running, to check that an alarm is given.

In addition the ability of the transmitter to detect an earth fault should be confirmed annually by performing thefunctional test described in Chapter 4, part e.

Also, each time the end cover is removed for other maintenance tasks, the infrared emitters of the transmitter and the infrared sensitive area of the detector should be cleaned with a soft cloth. This will be required to bedone annually in a normal machine environment and more frequently in a dirty environment.

RV1 = Low supply volts inhibit.RV2 = Field voltage inhibit.RV3 = Set frequency (infrared).RV4 = Set frequency (radio f requency).X = Test pointsLED1 = Supply inhibit released.LED2 = Field voltage inhibit released.LED3 = Protection operated.LED4 = Supply present.



8 List of Drawing Numbers

Receiver Assembly With Shroudand Pushbutton

9630910

Receiver Assembly Boxed 9630473

Transmitter Assembly 9615104

Aerial Assembly 9615037

9. List of Part Numbers

Receiver Assembly With Shroudand Pushbutton

963091001

Receiver Assembly Boxed 963047300

Transmitter Assembly 961502100

Aerial Assembly 961503700

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