Ahmet Merev

VTT Technical Research Centre of Finland | vtt · National Metrology Institute MIKES

The calibration of digital recorders has special significance for the traceability of high voltage impulse measuring systems to the national or international references. Lightning impulse (LI) and switching impulse (SI) calibrators are the main important devices for this purpose. In a calibration of a digital recorder, the deviations of the peak va...

Composite voltage test according to IEC 60060-1:2010 is a test method where impulse high voltage is applied simultaneously with alternative voltage (AC) or direct voltage (DC) to the same terminal of the test object.. The equipment used in the DC and AC high-voltage grids has some special test procedures to be fulfilled under not only DC, AC, and l...

Besides the typical test voltages like DC, AC, lightning impulse (LI) and switching impulse (SI), combined and composed test voltages are of increasing interest. Combined test voltage is typical for disconnector tests where on both sides of the open contacts AC and impulse voltage will be applied. The elements between the two voltage sources and th...

A very Low Frequency (VLF) high voltage measuring system including the resistive high-voltage divider has been designed, developed, and implemented from DC to 1 Hz up to 120 kV. The divider consists of three modules stacked on top of each other. The characterization of the VLF high voltage measuring system has been performed by the calibration of t...

Modern commercial PD calibrators often have their lowest charge level as 0.1 pC. However, now National Metrology Institutes (NMIs) provide traceable calibration services for apparent charge starting from 0.5 pC upwards and the relative uncertainty at this level is typically 20 %. The main problem with the widely used numerical calibration method pr...

Surface tracking on organic solid insulators is one of the main reasons for failure in high voltage (HV) systems. Due to various factors, such as humidity, pollution, ice load, increase in local voltage, etc., it is hard to make an estimation about the life of an insulator. For many years Weibull statistics have been widely used and accepted as a s...

To ensure long-term stability, it is very important to prequalify capacitors used in high-precision voltage dividers. This paper analyzes how film and foil capacitors change due to charge and discharge cycles under different test conditions. The presented experiments aimed at simulating the electric stress associated with high voltage tests in a la...

As part of the production of equipment for high voltage electricity grids, high voltage tests are performed to verify that the equipment can withstand the operational voltage stresses. Such ‘withstand tests’ are performed using combined and com-posite waves, where lightning impulse (LI) or switching impulse (SI) waves are superimposed on AC or DC.B...

Society’s increasing demand for electrical energy, along with the increased integration of remote renewable generation has driven transmission levels to ever higher voltages in order to maintain (or improve) grid efficiency. Consequently, high voltage testing and monitoring beyond voltage levels covered by presently available metrology infrastructu...

As part of the production of equipment for high voltage electricity grids, high voltage tests are performed to verify that the equipment can withstand the operational voltage stresses. Such ‘withstand tests’ are performed using combined and composite waves, where lightning impulse (LI) or switching impulse (SI) waves are superimposed on AC or DC. T...

Partial discharge (PD) detection is based on the measurement of apparent charge originated from PD in test sample. Since the measurement system configuration affects the PD measuring system response, a PD reference calibrator is the most important part of measuring system for the determination of scale factor in measurement system. In this paper, t...

2012 yılında yapımı gerçekleştirilen referans yüksek doğru gerilim bölücüsü, dirençsel elemanlardan oluşan geleneksel tipte bir gerilim bölücüsü olmayıp yapısında şönt tipi gerilim referansları bulunmaktadır. UME-20 adı verilen gerilim bölücüsünün, belirsizlik hesaplamalarında gerilim referanslarının oluşturduğu modüllerin sıcaklık katsayısı, ölçüm...

This paper describes the design and performance of a modular wideband high-voltage dc (HVDC) reference divider with a ratio uncertainty of less than 0.005% at 1000 kV. The divider has a maximum nominal voltage of 1000 kV when five 200-kV modules are stacked on top of each other. The divider is used for traceable calibration of HVDC measuring system...

In this paper, a 20-kV voltage reference based on shunt type bandgap references has been built and characterized. Compared with earlier designs based on temperature compensated Zener diodes, the main advantages of the new design are much lower uncertainty and dynamic impedance, combined with lower cost. The temperature coefficient of shunt referenc...

Portable DC high voltage (HV) measuring system up to 40 kV has been designed and built with DC HV probe and AC/DC voltmeter developed at TUBITAK UME (The Scientific and Technological Research Council of Turkey). The structure and construction of the HV probe and DC voltmeter for evaluating their performance are described. The comparison measurement...

This paper describes the design and performance of a wideband high-voltage dc (HVDC) reference divider module. The module has a nominal voltage of 200 kV, and it has been designed so that a number of modules can be stacked to extend voltages up to 1000 kV. The module, or a stack of modules, will be used for traceable calibration of HVDC measuring s...

The high-voltage DC measuring system based on bandgap voltage references has been used for high accuracy with low dynamic resistance up to 20 kV. The measuring system is stable output over a wide range of operating current and ambient temperature, and it is insensitive to effects due to leakage currents. One of the most important parameters of a re...

This paper describes design principles of a wideband HVDC reference divider. The modular divider will be used for traceable calibration of HVDC measuring systems up to 1000 kV in customers' laboratories. The first priority in the design was the accuracy of HVDC measurements. In addition the divider was designed to have wide bandwidth, both to enabl...

HVDC energy transmission is crucial for a successful uptake of renewable energy sources in the grid. A research program is described, intended to provide metrology support for the needs of HVDC energy transmission. This program will provide improvements for the present HVDC metrology infrastructure: accurate measurement of HVDC, determination of lo...

Partial discharges (PDs) can be destructive to electrical insulation as they may degrade the material in time. Consequently, studies have been made to develop efficient systems for PD measurements and monitoring. Due to the complexity of PDs as well as factors that can affect PD characteristics, the research on PD measurement is still active. In th...

The aim of this study is to investigate the effect of colemanite on dielectric properties of polymers. In this study polyester is used as the base polymer insulator. The electrical conductivity, relative permittivity and dissipation factor (tan¿) of polymers are measured as a function of colemanite concentration in polyester samples. After dielect...

A precise DC high-voltage divider was designed and constructed for use as a standard. The ratio of the divider for precise measurement must be known accurately independent of voltage and time. The changes in total resistance of a divider with voltage and time should be considered before design and construction. The divider consists of 100 wire-woun...

ZET Yüksek gerilim, ölçülen işaretin genliğinin yüksek olması nedeniyle bilinen ölçme sistemleri ile doğrudan ölçülemez. Yüksek gerilimin, değeri bilinen bir bölüm oranı ile bölünmesi ve bölünmüş alçak gerilim değerinin doğru olarak ölçülmesi gerekir. Bir yüksek gerilim ölçme sistemi, gerilim bölücü veya ölçü transformatörleri gibi dönüştürücü elem...

The lifetime of polyester resin samples has been determined with the ASTM D2303 inclined plane tracking test method (IPTTM) for different environmental effects. Most of the external factors have a unique degradation effect, hence the tracking image observed on polyester resin highly depends on these factors. The structure and topography of the trac...

Surface tracking is one of the severe degradation mechanisms observed on polymeric insulators. There are too many factors associated with the degradation process, hence it is not easy to make an estimate about the useful service life of an insulator. However it is possible to reduce the variability observed in the tracking initiation times and trac...

In this study, the effects of longitudinal compressive and tensile stress, ultraviolet (UV) radiation and wind pressure from different positions with respect to the surface of the sample under test have been investigated in detail with the ASTM D2303 Inclined Plane Tracking Test method. The structure and topography of surface tracking patterns gene...

Surface tracking is one of the major breakdown mechanisms observed on polymeric outdoor insulators. Continuous discharges on the surface of the insulator cause hot spots on certain points, which finally lead to carbonised tracking paths crossing the surface between the high voltage and earth electrodes. This paths (patterns) are greatly influenced...

Surface tracking is one of the severe degradation mechanisms observed on polymeric insulators. There are too many factors associated with the degradation process, hence it is not easy to make an estimate about the useful service life of an insulator. However it is possible to reduce the variability observed in the tracking initiation times and trac...

The ratio of resistive standard dividers used for precisely measuring DC voltages should have been known accurately and independent of voltage especially. A change in effective resistance with voltage may be due to any one or a combination of three factors. One of them is heating of the resistance wire due to power loss, second is current leakage t...

ZET Yüksek gerilim teknolojisinde; darbe yüksek gerilimler, iç (anahtarlama) ve dış (yıldırım) aşırı gerilimlerin yol açtığı zorlanmaları yüksek gerilim testlerinde temsil edebilmek, malzemelerin yüksek gerilime dayanım mekanizmaları ile ilgili temel araştırmalar yapmak ve üretilen elektromekanik ürünlerin ulusal/uluslararası standartlara uyumluluğ...