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TVA DISCHARGE LOCATING PROBE 1

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cag

Electrical
Nov 17, 2002
1
I have an 11kv 9mw motor which has recently been visually inspected. Endwinding bracing showed signs of cracking & various pieces of packing have become loose. This machine has annual on line partial discharge testing carried out & reports submitted do not highlight problems. Before carrying out any remedial work on the stator winding I would like to confirm the stator coils are not moving in the slot & likely to cause high levels of discharge. I am told you can carry out a TVA discharge locating probe test on the machine which would highlight any discharge in the slot portion of the machine. Does anyone know where to find information on this type of test? Does anyone know if this type of test gives good results?
 
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IEEE1434 (Partial Discharge) has some info particularly on tva probe

section 6.3.1. provides general discussion of the method. Probe should be tuned around 5 Mhz.

Section 11.2 described acceptance critera. The strong point of this test as compared to other test (pd) is ability to localize the problem. As with any predictive technology most useful measurements are comparsion among sister machines or trending behavior over time. They do however give some suggested limits for slot tva probe readings; 100milliamps for asphalt based, 30 for polyester-based resin, 20 milliamps for epoxy-based resin system.
 
Suggestion: Reference:
A discharge locating probe for rotating machines
Sedding, H.G. Stone, G.C.
Ontario Hydro, Toronto, Ont.;
This paper appears in: Electrical Insulation Magazine, IEEE

Publication Date: Sep/Oct 1989
On page(s): 14-17
Volume: 5, Issue: 5
ISSN: 0883-7554
References Cited: 2
CODEN: IIMAE6

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Abstract:
The basic principles of an improved Tennessee Valley Authority (TVA) probe known as the discharge locating (DL) probe are presented. The principal features of the new device are very-high-frequency detection using a capacitive sensor and microprocessor-based signal processing. These features are intended to make the probe easier to use and less ambiguous in the interpretation of results. The coupling technique used permits significantly improved spatial resolution of the discharge source and immunity to radiated electrical interference. Details of the signal processing electronics and field experience are described
 
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