RSO TEST   - RECURRENT SURGE OSCILLOGRAPGH TEST           

 IT IS USED TO DETECT AND LOCATE THE POSITION OF WINDING FAULTS IN A LARGE GENERATOR, ALTERNATOR ROTORS. THE TEST IS VERY SENSITIVE AND CAN DETECT EARTH FAULT, INNER TURN FAUL, AND HIGH RESISTANCE JOINTS.

THE RSO TEST IS BASED ON APPLYING 12 V PULSES BETWEEN THE ENDS OF THE ROTOR WINDINGS AND ROTOR BODY (GROUND) AND PRODUCES A GIVEN OF WAVEFORMS, WHICH ARE VIEWED AND COMPARED TO DETECT AND LOCATE ANY WINDINGS FAULT. THESE WAVEFORM PAIRS SHOULD BE IDENTICAL FOR A FAULT-FREE ROTOR WINDING.

PROCEDURE:

FIRST TURN ON THE SWITCH SR1 SIDE WHICH IS MEASURE THE WAVEFORM POSITIVE TO EARTH THEN SECOND TURN ON THE SWITCH SR2 SIDE WHICH IS MEASURE THE WAVE FORM NEGATIVE TO EARTHSIDE.

RESULT: (* RESULT VARIES FROM PLACES, THIS IS ONLY FOR KNOWLEDGE PURPOSES)

Temp: 40°C

 

No inter turn fault inside winding

 

 

 

CONNECTION DIAGRAM:

Abstract— Detection of inter turn shorts in rotor windings of high voltage turbine generators (TG) has emerged as one of the important diagnostic measures in condition monitor (CM) for uninterrupted power generation. Conventional test methods cannot identify the location of defects. Recurrent Surge Oscillograph (RSO), an off-line novel technique method has widely supported the quality of decisions of diagnosticians to locate the shorts in rotor windings.

Methodology of applying RSO technique for rotor windings is detailed. Wave patterns for possible inter turn shorts with a demo delay unit are depicted. Case study on faulty windings of TG is presented. This novel detection technique benefits the customers to avoid sudden outages.

Recurrent Surge Oscillograph (RSO) test method to effectively detect and locate inter turn shorts of rotor windings. Traditional test methods and disadvantages are narrated. Effects of inter turn shorted field windings are mentioned. Owing to the benefits of the novel approach, RSO test has been viewed as mandatory for condition assessment diagnosis (CAD) of TGs in recent years. Time Domain Reflectometry, the principle behind RSO is briefed. Waveforms of various faults are depicted by delay unit demo. Case study on 15MW TG is presented and rectification methods to isolate the fault is recommended.

TRADITIONAL DETECTION OF INTER TURN SHORTS

Assessing the condition of field winding which is hidden in rotor slots and end bells is a challenging domain. Incorrect decisions may result into power plant shut down for long time. Traditional methods to observe inter turn shorts of field

windings are

1) Open circuit (OC) and load current (LC) test

2) Ohmic resistance measurement

3) Impedance measurements in static and running condition

4) Pole and turn to turn volt drop test

5) Vibration analysis

6) Flux probe analyzer

In residual life analysis (RLA) and condition monitor (CM) diagnosis studies, above methods are being used as off-line and flux probe is recommended for on-line detection of shorts. In OC and LC tests, an increase in excitation energy for the same output voltage and load current is indication of shorts in the field winding. Vibration behavior is different. Up rise of DC current in rotor circuit will be the result if the shorts are >5%. Location of the defects are not in the per view of this performance test.

.RECURRENT SURGE OSCILLOGRAPH (RSO)

 RSO test technique is used to capture on dual channel oscilloscope, the reflected waves of the input rectangular pulse travelled in the field winding simultaneously at the two slip rings. It is a non destructive off line method to locate inter turn faults of windings. Principle of time deflection reflectometry (TDR) has been extended to visualize the inter turn short defects in TG excitation windings.

Incident pulsating wave will travel at one slip ring into the field circuit with speed of light and reaches other slip ring in a healthy field winding with no inter turn shorts and earth faults. Reflection wave will travel back from open end of the other slip ring to the input slip ring point. Both the traces are identical and the summation after inversion will be a straight line with no ripples. Healthy winding will be symmetrical electrically and travelling time of transient pulse injected at both the slip rings will be same. It results into identical reflections as shown in the fig. if superimposed a single trace is visible

Resulting reflected signals at the shorted turns due to sudden change in impedance travels back to the front end of the winding. It can be observed on duel channel oscilloscope as two different waves with kinks. A comparison between the super imposed incident and reflected waves will be used for finding out the abnormal contacts of turns.

RLC network with 10 sections with a characteristic impedance of 100 ohms is used as delay unit. Terminations of each section is for simulating the shorts and observing the wave patterns on digital oscilloscope.

Effect of inter turn shorts and earth faults are depicted in the fig.