Suat Ilhan

380 kV corona ring optimization for AC voltages

This paper presents corona ring optimization for 380 kV V-insulator string composed of glass insulator units. The influence of the corona ring design parameters are examined not only with regard to 3D simulations but also laboratory tests. The purpose of the simulations is to find reasonable corona ring design parameters such as corona ring diameter, corona tube diameter and installation height on the point of effective field regulation around the critical region of the string. Indoor laboratory tests including radio interference voltage levels, corona inception voltages and ac flashover voltages are conducted on the centre phase of a full scaled tower both for experimental based corona ring design as well as verifications of the simulations. After both simulations and experimental based investigations, appropriate corona ring design parameters for the string are determined for effective field regulation, minimum interference level, ac flashover performance and economic point of view.

Effects of corona ring design upon impulse voltage withstand level of 380 kV V-strings

This study presents the influence of corona rings on impulse withstand performance of 380 kV V-insulator strings. Those strings comprising cap-and-pin type glass insulator units are one of the most common configurations in Turkish National Power Transmission System. Laboratory test setup was constructed for the centre phase of a full scaled tower. Laboratory tests are performed to investigate the lightning and switching impulse performance of the strings equipped with the existing racket type corona rings and the circular type corona rings. Withstand voltages, lower flashover probability levels, flashover routes and times to flashovers are determined under dry and wet test conditions. In addition, some 3D field simulations regarding potential and electric field distributions are also performed for the interpretation of insulator surface flashovers.

Ac and transient electric field distributions along a 380 kV V-string insulator

This paper presents the results of a study of the ac and the transient electric field distributions along a 380 kV V-string of glass cap-and-pin suspension insulators. The transmission tower, conductors and insulators are modeled in 3D, and COMSOL 4.2 is used for the finite element simulations. The insulators are modeled both for clean and for the polluted cases. The pollution layer is modeled by a wet conductive layer of 2 mm thickness on the insulator surface and the conductivity of the layer is varied between 10-8 to 1.0 S/m. The permittivity of the pollution layer is assumed to be 81. Clean, full pollution and partial pollution cases are taken into consideration. The effects of corona rings on the field distributions are also investigated by 3D simulations.

Simulations of pollution and their effects on the electrical performance of glass suspension insulators

This paper presents simulations of pollution and their effects on the electrical performance of cap-and-pin glass suspension insulators. The pollution is modeled by using a partially conductive epoxy resin with graphite powder. The effects of the pollution levels as well as their locations on the insulator surfaces are investigated for both simulation and experimental studies. The studies are conducted both for one suspension unit and a string of five insulators. The results show that at power frequency voltage, the reduction in the flashover voltage is about the same whether the upper surface or the bottom surface of the insulator is polluted. Moreover, the percentage reduction of a single unit is about the same as for a five unit string. At lightning impulse voltage, the insulator performance depends on the location of the pollution. Positive polarity impulse voltage is more critical than the negative polarity for the upper surface polluted case for one and the five unit string. For the bottom polluted case, negative polarity impulse voltage is more critical.

Corona ring optimization for V-insulator string on the point of RIV and AC flashover performance

This paper presents corona ring optimization of V-insulator string with respect to field simulations, RIV levels and AC flashover voltages. Corona ring diameter, tube diameter and installation height are considered as optimization parameters. Variations of electrical fields on the critical parts of the string are obtained by 3D simulation studies for different ring settings and optimum parameters are determined. Later, the concordance between laboratory RIV test results and calculated field values are investigated. AC flashover tests are also performed to validate the AC isolation level of the system under different ring settings.

Flashover performance of 380 kV V-strings with composite insulators under lightning and switching impulses

This study presents simulation and experimental test results regarding potential and electrical field distribution along 380 kV V-strings in Turkish national electric power transmission system which are composed of silicon-rubber insulators. A two-dimensional (Electro 2D) and a three-dimensional (Coulomb 3D) simulation programs are used for transient and electrostatic field calculations, respectively. Simulations are conducted only for clean insulators under dry conditions. The effects corona rings and types, lengths of conductors, conductor sags, protection lines, phase conductors, tower configurations and arc distances on the field distributions are analyzed. Experimental studies are conducted at Fuat Kulunk High Voltage Laboratory of Istanbul Technical University.

Numerical and experimental investigation of the effects of pollution on glass suspension-type insulators

This study presents both numerical and experimental results regarding the effects of pollution on the flashover performance of glass suspension-type insulators. The finite element method (FEM) was used for simulating polluted insulators both at power frequency and at lightning impulse voltages. Partially conductive epoxy resin with graphite powder was used for modeling pollution on the insulators, which enabled the measurement of the electrical potentials on the polluted insulators. Numerical studies demonstrated the variations in the field distributions caused by the location and severity of the pollution as well as by the type of voltage applied. The simulations, which were verified to a degree through measurement, showed that pollution conductivities greater than 10-6 S/m and 10-3 S/m alter field distributions for power frequency and lightning impulse voltages, respectively. Unlike the results obtained for partially polluted insulators, the voltage distribution was almost linear for fully polluted insulators. Experimental studies revealed that the location of the partial pollution plays an important role in flashover performance for lightning impulse voltages but has a negligible effect for power frequency voltages.

Voltage Distribution Effects of Non-Uniform Units in Suspension Strings

10 unit and 22-unit cap-and-pin type insulator strings are used in 154 kV and 380 kV Turkish national power transmission systems. Turkish national electric power transmission utility staff prefer replacing the damaged units by stronger fog-type ones to minimize the transient outages resulting because of the insulation problems at the lower and upper units in the string. However, it is obvious that such a replacement changes the voltage distribution of the string composed of identical units. This change depends on the several parameters. This study presents the simulation results of voltage distribution along a 10-unit suspension string and 22-unit suspension string. Studies were conducted for the strings composed of different types of units for different tower designs and different contamination cases under power frequency voltages and lightning impulse voltages.

Impacts of corona rings on the insulation performance of composite polymer insulator strings

Corona rings can improve the insulation performance of insulator strings because of their electric field grading property or can decrease the insulation performance due to their arc clearance reduction property. The resulting insulation performance of the string which is under the influence of those two conflicting effects depends on the corona ring parameter settings. Therefore, a detailed experimental work is required to determine the insulation performance for different types of test voltages under different ambient conditions. This paper presents the results of experimental studies regarding the effects of corona rings on the insulation performance of 380 kV non-ceramic V-insulator strings. Those effects and flashover routes were determined for lightning impulses, switching impulses and AC voltages. Corona ring diameter, corona tube diameter, and mounting height were selected as the ring design parameters. Experimental studies were performed for the strings including corona rings of different design parameters as well as for the ring free strings. Test results were discussed from discharge development physics point of view and optimal configuration was determined for the strings.

Improvement of thermal performance of 36 kV DAF-30 type bushing

Bushings are one of the most essential parts of the electrical distribution and transmission systems since they enable high currents to pass through from one medium to another and isolate the high voltages from the grounded parts. In addition to electrical and mechanical stresses, they are also subjected to thermal stresses. This study presents temperature distribution of 36 kV DAF-30 wall type bushings used in Turkish National Power Distribution System. Several experimental tests and simulations were performed to determine the critical parts as well as to improve the thermal performance of the bushing. In addition, skin effect of the bushing conductor was investigated to propose appropriate thermal solutions for the bushing.