Test · Field winding
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 low-voltage pulses and compares the responses from the two symmetrical winding ends — detecting early faults before catastrophic failure, with no full rotor disassembly.
Repetitive Surge Oscillograph
ISO 9001:2015Technical definition
What is the RSO test
RSO (Repetitive Surge Oscillograph) is a non-destructive diagnostic technique that injects repetitive low-voltage pulses from both ends of the rotor field winding and compares the two transient responses. 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: RSO has no IEEE standard of its own; it is run under a documented protocol and read by comparing the transient responses from the two ends of the field winding
- Calibrated equipment traceable to national standards
- Repetitive low-voltage pulses with fast rise time (reflectometry), injected from each end
- 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 with ISO 9001:2015 traceability. Full traceability by work-order number and signature of the responsible engineer.
- 1Signed test protocol 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
Illustrative example
Not a published project record.
Predictive diagnostic on a cogeneration plant turbogenerator
Pole comparison
Method
Periodic monitoring
Option evaluated
Scheduled repair
Option evaluated
On a turbogenerator at an industrial cogeneration plant, the RSO test can be applied to the rotor field during a scheduled outage window. If it detects incipient asymmetry in one zone of the winding, the usual recommendation is to confirm it with a pole-drop test, set up periodic monitoring and evaluate whether the repair can be scheduled for the next operating window instead of an immediate major intervention.
FAQ
Frequently asked questions — RSO test
Questions we often receive. Can't find yours? Email us at ventas@temisapowergen.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. 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.
Related testing
Complement the RSO diagnosis with the full electrical testing suite
Contact
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ISO 9001:2015 · IEEE / IEC