Before we talk about generator rotor testing, let’s make sure we are all on the same page in terms of understanding what a rotor does.  First, let’s start with a quick discussion of terminology.  Some OEMs such as GE refer to the rotating portion of the generator as the field.  Others, such as Siemens refer to it as the rotor.  Both are correct, but both have their limitations.  “Rotor” is convenient because it tells us that it is a rotating component.  “Field” tells us that it is a DC electromagnet with multiples of two poles.  “Rotor” and “Field” get confusing...

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Just as every bell has a unique tone when struck by a hammer, so do all generator winding components.  Every structure, in fact has its own characteristic modes of mechanical response when deformed after being struck.  While not very musical in nature, the response waveform gives the trained Technician valuable information on the integrity of the windings under test. Bump testing can be done discretely (giving specific results for each specimen struck), or as a composite modal wave shape function where some of the specific information about individual specimens gets lost in favor of getting system-level resonant response information.  The...

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Insulation Resistance and Polarization Index Testing of Generators

Megger & P.I. as it’s commonly referred to, is one of the quickest, safest, and simplest tests in the arena of generator electrical testing, but it is also one of the most useful.  It is this simplicity that often makes the test somehow seem less important than some of the “big ticket” tests such as Hi-Pot or ELCID.  Megger and PI is a very quick way to get an overall assessment of the health and cleanliness of an insulation system in just a few minutes’ time.   Sidewinders makes engineering evaluations based on the overall analysis of many tests and...

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Case Study: Repair of a Generator Stator with signs of extensive end winding vibration and degradation. ISSUE During a major inspection of a 55375 KVA Generator, signs of extreme winding vibration and resonance issues were apparent. After completing a visual inspection of the end winding support systems, the following issues were identified and documented: Extensive greasing and dusting on coil-to-coil ties, circuit ring to gunstock ties and circuit ring blocking Extensive greasing and dusting of stator bars where they exited out of the slot Broken and loose coil-to-coils ties Cracked and, in some cases, broken gunstocks Indications that circuit ring ties had...

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Sidewinders' case studies help you understand the performance, quality and value of our services. ISSUE During recent annual maintenance of a vertical hydro generator, a stator coil was damaged as the rotor was being removed by the client.   Damage to the coil was extensive, with bare copper exposed where it had been hit. Due to the utility company going through a large transition period, Sidewinders’ was unable to visually check the damage and complete electrical testing until the unit was completely reassembled—only four days away from its scheduled startup date. In cases like this, the utility company generally has several...

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