The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
Under continuous application of high electrical stresses, the insulation system of an underground power cable is subjected to long-term degradation that can eventually cause premature breakdown of the cable. This is as a result of electronic charges being injected into the dielectric material when intense electric field is applied. These charges will then interact with polymer molecules; causing even...
This paper presents work that was carried out to investigate the effect that asymmetrical ageing of composite insulators, including ethylene-propylene rubbers (EPDM) and silicone rubbers (SiR), has on water dripping behaviour and subsequent electrical performance. Surface features and hydrophobicity measurements of 132 kV EPDM and 400 kV SiR service aged insulators from coastal environments are examined...
Sheath voltages limiters (SVL's - see Fig.1) are used to protect the sheath sectionalising insulators of joints or terminations for specially bonded cable systems. Their purpose is to minimize the transient voltage that is produced across the sectionalising insulator during switching surges or lightning strikes and to reduce the risk of them flashing-over. These SVL's are normally located within link-boxes...
Diagnostic tests such as insulation resistance, polarization index, dissipation factor, capacitance and partial discharge can be useful to diagnose the condition of the stator winding insulation, and identify many problems that could lead to insulation failure. Many years of experience, however, has shown these quantities by themselves cannot predict the remaining life of a winding. However, asset...
A stator ground fault occurred in a hydrogen cooled synchronous condenser rated 300 MVA. This was as a result of a small metallic object that had been left in the rotor during an overhaul. The object had entered the air gap and damaged the end arms of three stator bars, one of which failed. The OEM patched the three stators bars. A series of off-line electrical tests were performed to assess the adequacy...
The paper presents the behavior of ultrasound induced cavitation voids and bubbles in mineral insulating oils with different aging properties. At suitable values of signal amplitude and frequency many of cavitation bubbles were observed. Collapsing bubbles were responsible for broadband noise included in acoustic emission signal spectra. To represent the cavitation intensity a cavitation indicator...
In times when personal safety and the security of electrical power supply become more and more important, the usage of alternative insulation fluids is demanded in large power transformers. The minimizing of fire loads is another significant reason for new liquids. Different companies are offering such alternative insulation liquids which are already used in distribution transformers. On the other...
In this paper, we investigate the influence of nanofiller material and its concentration on dielectric properties of epoxy-based composite systems. A comparative study is performed between the unfilled base epoxy, the systems containing one type of nanoparticles (silicon dioxide, aluminum oxide or aluminum nitride) and composites containing a combination of two different fillers inside the host polymer.
Return Voltage Measurements are an efficient tool to measure the dielectric properties of an insulating system and thus to characterize the degradation of cellulose-oil insulations. They are widely used for the diagnosis of power cables. As a consequence of misinterpretations of the results in the past, the use Return Voltage Measurements for power transformers has been reduced. Nevertheless - performing...
Additive tree-retardant crosslinked polyethylene (TR-XLPE) has been utilized as medium-voltage power cable insulation for over 25 years, and has been recognized for excellent performance in retention of breakdown strength in both accelerated aging and field-service conditions. Now, an improved TR-XLPE insulation has been developed which will enhance the longevity and reliability of medium-voltage...
The paper discusses the temperature profile along the stress grading and the conductive armor layers on the endwinding of a 13.8 kV motor coil when energized by repetitive fast pulse voltages such as pulse width modulated (PWM) voltages. The effect of the pulse rise time in the temperature profile at the end portion of the motor bar is also measured experimentally. The thermal stress due to two equivalent...
This paper presents the design and experimental testing of an induction coil as a magnetic field sensor with other measurement devices. The results show that the induction coil functioned as expected, giving a high sensitivity to magnetic fields at 50 Hz. Such fields emitted from power cables can be detected not only in a laboratory environment but also on a pavement.
The range of problems in high voltage and materials engineering which can be addressed through mathematical and numerical modeling has expanded with the reduction in the price of computing power. Presently, very complex transient nonlinear finite element problems can be solved in both 2D and 3D. In addition, density functional theory (DFT), the most useful implementation of computational quantum mechanics,...
Many underground power cable users are faced with aging fluid-filled transmission cables that have exceeded their design life of 30-40 years. Major and possibly costly decisions have to be made whether to replace or to continue to use the existing cable system. This paper presents a condition assessment strategy focused on fluid-filled cables that involves a combination of visual observations through...
The mineral mica has found application in the mainwall insulation of high-voltage electric rotating machines for over a century, and remains intrinsic to achieving high machine reliability and lifetimes. This paper retraces the historical development of micaceous mainwall insulation, and examines the materials and construction of modern mica tapes in detail. In this context, we provide examples of...
Until recently, power plant operators have had very limited options for on-line monitoring of the health of motor and generator rotors, particularly those with brushless excitation systems. Degradation of field winding insulation can lead to ground faults or shorted turns, with little or no warning. Moreover, the capability to monitor local hot spot temperatures on rotor windings in service has not...
This paper is a step forward to investigate the thermal effect of underground cables. It is to experiment the circumstances that affects the real cable and to find out what are the most effecting factors heats up and causes thermal stress in the cable. This paper will give brief information about the underground cables. In addition, it will talk about the soil effects. Finally, it discusses the whole...
This paper deals with the partial discharge behavior of epoxy resin filled with hollow glass microspheres. The resulting material, called syntactic foam, is a new composite insulation material which combines advantages of solid and gaseous dielectrics. Specimens of syntactic foam are stressed with uniform AC field stress and the partial discharge activity is simultaneously measured. After the electrical...
Based on the laboratory test carried out on 351m 10kV XLPE power cable in which there are some typical PD defects, the method of OWTS for detecting PD in XLPE cable and its accessories was introduced. The time domain characters of the OWTS signal is researched in order to distinguish the PD signal from the disturbance. The PD spectrum of q-m was analyzed. The way to locate the PD point was also introduced...
Measurement of partial discharge (PD) has been used to assess the condition of insulating material used in electric power equipment. Analysis of the electromagnetic (EM) waves emitted from PD is useful from the viewpoint of noncontact diagnosis because PD emits wideband EM waves. The EM waves emitted from PD in insulating materials were numerically visualized using the constrained interpolation profile...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.