Hidden Markov models are especially known for their application in handwriting, gesture recognition, part-of-speech tagging, musical score following, partial discharges and bioinformatics.
32.
Partial discharge measurement is routinely carried out to assess the condition of the insulation system of rotating machines ( motors and generators ), transformers, and gas-insulated switchgear.
33.
An automatic analysis of the reflectograms collected during the partial discharge measurement using a method referred to as time domain reflectometry ( TDR ) allows the location of insulation irregularities.
34.
Using a structure borne ultrasonic sensor on the exterior of the item under examination, internal partial discharge can be detected and located when the sensor is placed closest to the source.
35.
The inside of the porcelain bushing is often filled with oil to provide additional insulation and bushings of this construction are widely used up to 36 KV where higher partial discharges are permitted.
36.
;Discharges : Electrostatic discharge, corona discharge, Partial discharge, Avalanche breakdown, Glow discharge, Direct current discharge, Lichtenberg figure, Electrical treeing, Townsend discharge, Arc Flash Paschen's law
37.
Other methods include partial discharge ( PD ) testing, using either fixed or portable testers, and acoustic emission testing using surface-mounted transducers ( for oil equipment ) or ultrasonic detectors used in outdoor switchyards.
38.
To evaluate equipment condition, predictive maintenance utilizes nondestructive testing technologies such as infrared, acoustic ( partial discharge and airborne ultrasonic ), corona detection, vibration analysis, sound level measurements, oil analysis, and other specific online tests.
39.
A non-catastrophic failure mode in this application is due to the corona effect : the air enclosed in the winding element becomes ionized and consequently more conductive, allowing partial discharges on the metallized surface of the film, which causes local vaporization of the metallization.
40.
However, care must be observed in resin insulated bushings designs which use internally cast screens such that the benefit of electrical stress field control is not off set by increasing partial discharge caused by the difficulties of eliminating micro voids in the resin around the screens during the casting process.
