Study on the effect of humidity on dielectric response and partial discharges activity of machine insulation materials

Self Cite

The study of dielectric response is a significant method to characterize the electrical properties of insulating materials and a useful tool for condition assessment of the insulation systems of rotating machines. Time and frequency domain measurements can be used to determine the dielectric response. Polarization and depolarization current measurements are usually used as a time domain measurement while in frequency domain the capacitance and dissipation factor of the samples can be measured over a broad range of frequencies.The dielectric response of machine insulation is affected by variety of parameters such as degree of aging, contamination and the environmental conditions such as temperature and humidity. In this work, time and frequency methods are used to determine the impact of humidity on the dielectric response of different insulation technologies used for stator insulation of large rotating machines. The measurements were conducted on bars and coils in laboratory conditions as a comparison base and then the dielectric response of the samples was monitored in an environmental chamber during two different humidification periods. The samples were selected to cover the most common materials and technologies used in operating rotating machines including asphalt; epoxy and polyester based insulating systems. The results showed considerable change in the dielectric response when the samples were exposed to moisture. Further studies demonstrated that the change in dielectric response is mostly attributable to the end-winding and stress-grading layer.

Section: The Epoxy-sc Barsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Impact of humidity on dielectric response of rotating machines insulation system

Soltani

David

Lamarre

2010

Self Cite

“…Drying insulation during temperature increase and then preparing a high or medium temperature can prevent adverse effects in insulation and the machine windings. For example the moisture of the insulation Epoxy-mica can be dried through preparing a medium heat whereas in an insulation made of Poly-ester this issue should be taken more serious because it is effected rapidly by humidity [47,48].…”

Section: Influence Of Humidity Variationmentioning

confidence: 99%

Influence of ambient and test conditions on insulation resistance/polarization index in hv electrical machines - a survey

Torkaman

Karimi

2015

Ambient and test conditions can affect the analysis results of the insulation system testing in high voltage (HV) electrical machines. In this context, insulation resistance (IR) and polarization index (PI) are two common techniques for winding insulation assessment in offline mode. This paper investigates the influence of main parameters that affects IR/PI tests results. Temperature, humidity, and pressure are the wellknown environmental parameters which could affect dielectric parameters of insulation such as IR and PI. On the other side, test voltage level and voltage polarities connections are two prominent factors in sampling the resistance during the test. Moreover, the insulation resistance value depends on the type of fault and its severity. The variations of insulation resistance with considering the mentioned parameters are evaluated in this paper, to study the possible correlation between IR/PI and changes in other parameters. It was found that with taking the effective parameters into account, the accurate and reliable insulation test interpretation can be achieved in HV electrical machines. A comprehensive review of literature was done and industry experts were surveyed for their ideas and experience under a research project. The main results are summarized in this paper.

“…The internal discharges also have a certain relationship with temperature which can be found in the literature [6] and [7]. In addition, the effect of RH on PD in stator windings was also studied by former researchers [8][9][10][11][12][13]. It is clear that the air can be acidic or alkaline, caused by several external factors such as the local acid rain or the alkaline chemical gas like ammonia, etc.…”

Section: Introductionmentioning

confidence: 95%

Effects of vapor with different chemical properties on corona partial discharges of stator windings

Song

Lin

et al. 2014

The effects of vapor with different chemical properties on corona partial discharges (PDs) at the junction section of the semi-conductive tape and the stress grading tape of stator windings were investigated. The phase resolved partial discharge (PRPD) patterns were collected during the experiment to obtain the characteristics of the PDs. The result has confirmed that relative humidity (RH) of the vapor with different chemical properties can cause corona discharge to change significantly. The acidic vapor can suppress corona discharge effectively. When RH exceeds 60%, the corona discharge would be hardly induced even though the voltage is boosted up to twice the operating voltage. When RH is over 80%, corona discharge will develop into phenomenon of creeping on the surface of the ground wall insulation and can hardly be collected through the capacitive coupler.