Test · IEEE 95-2002

RSO Test — Repetitive Surge Oscillograph for Generator Rotors

Non-destructive diagnostic test for inter-turn shorts in synchronous generator rotor field windings. The RSO test injects repetitive impulse pulses and compares the response between symmetrical winding ends — detecting early faults before catastrophic failure, with no full rotor disassembly.

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Repetitive Surge Oscillograph

IEEE 95-2002CFE LAPEM W4200-12ISO 9001:2015

Technical definition

What is the RSO test

RSO (Repetitive Surge Oscillograph) is a non-destructive diagnostic technique that simultaneously injects a repetitive high-voltage impulse pulse at both ends of the rotor field winding. When the rotor is healthy, the two waveforms (one from each end) reflect symmetrically on the oscilloscope. When an inter-turn short is present, the waveforms become unbalanced — the location and depth of the short are identified by analyzing the asymmetry. It is the only industrial technique that diagnoses inter-turn shorts on a fully assembled rotor.

Reference standard: IEEE 95-2002 (testing of synchronous machines) and IEEE Std 115
Calibrated equipment traceable to national standards
Repetitive impulse pulses of 1 to 4 kV with microsecond duration
Comparative analysis between both ends of the rotor field winding
Digital documentation with captured waveforms and side-by-side comparisons
No rotor disassembly required — onsite or in-workshop diagnostic

Operational opportunity

When the RSO test is recommended

RSO is not a commissioning test — it is a predictive diagnostic and post-rewind acceptance test. It is recommended at these operational opportunities:

Major overhaul of generator or turbogenerator (every 4 to 6 years or per operating hours)
After rotor field rewind — acceptance validation
Before commissioning a new or reinstalled generator
When a rotor short is suspected (abnormal vibration, overheating, voltage unbalance)
As part of an annual or biennial predictive maintenance program
After a severe electrical event (short-circuit, lightning strike, excitation system failure)

Client value

What the RSO test detects

The RSO test is the only industrial technique that diagnoses inter-turn shorts in the rotor field winding with the rotor mounted and without disassembly. What it detects:

Full shorts between adjacent turns (turn-to-turn)

Partial or incipient shorts — valuable for predictive maintenance

Insulation degraded by overheating or thermal aging

Approximate location of the defect (connection end, phase side)

Comparison between current state and historical rotor baseline

Deliverables

What we deliver at the end of the test

Each test is delivered with a signed documentation package under IEEE 95-2002 and ISO 9001:2015. Full traceability by work-order number and signature of the responsible engineer.

1Signed test protocol under IEEE 95-2002 with documented methodology
2Oscilloscope waveform captures in digital and PDF format
3Comparative symmetry analysis with technical interpretation
4Diagnosis: rotor passed / rotor with observation / rotor with fault
5Recommended action: continue operation, predictive monitoring, or major intervention
6ISO 9001:2015 traceability with work-order number and responsible engineer's signature

Typical case

Predictive diagnostic on a cogeneration plant turbogenerator

IEEE 95

Applicable standard

Adjacent outages

Documented

Technical diagnosis

Major maintenance program on a turbogenerator at a private industrial cogeneration plant. RSO was applied to the rotor field during a scheduled outage window. The test detected incipient asymmetry in one zone of the winding — the recommendation was quarterly monitoring. Unnecessary major intervention was avoided and the repair was scheduled for the next operating window, with the documented report delivered for engineering and operations records.

FAQ

Frequently asked questions — RSO test

Preguntas que recibimos con frecuencia. ¿No encuentras la tuya? Escríbenos a ventas@temisa.mx.

Is full rotor disassembly required for the RSO test?

No. The RSO test is applied with the rotor in place and electrical connections accessible from the slip rings or field terminals. It does not require complete rotor disassembly, which makes it ideal for major maintenance windows where downtime is tight.

How is the RSO test different from a surge comparison test?

Surge comparison is typically used on stator coils (phase-to-phase). RSO is specifically designed for the rotor field winding — it injects pulses at both ends and compares the response. The two tests are complementary, not substitutes.

Can you apply RSO to large turbogenerators?

Yes. We apply RSO to cogeneration, combined-cycle and thermal-plant turbogenerators up to 350 MW under CFE LAPEM W4200-12. We coordinate the test during major maintenance windows with the grid operator when applicable.

Does the RSO test damage the rotor or the insulation?

No. RSO uses low-energy pulses with microsecond duration, well below the level that would damage healthy insulation. The test is non-destructive by design and is routinely applied in public and private generation fleets.

How long does a complete RSO test take?

Between 4 and 8 hours onsite for setup, execution, data capture and initial interpretation. The documented protocol is delivered within 5 to 7 business days after the test with complete technical analysis.

What happens if the RSO test detects a short?

We document the finding with technical evidence and discuss options with the client: predictive monitoring if the short is incipient, or rewind intervention if the fault justifies it. The client decides with data in hand, not blindly.

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