Transmission Voltage Levels Research Articles

A Test System for Transmission Expansion Planning Studies

This paper introduces a 17-bus 500 kV test system intended for transmission expansion planning (TEP) studies. The overhead lines used in the system are based on an actual 500 kV transmission line geometry. Although several test systems have been developed for various forms of power system analysis, few are specifically tailored for TEP studies at the transmission voltage level, as opposed to the distribution voltage level. Current test systems for TEP studies are limited to single loading conditions only for normal operating conditions, and the majority of these systems are intertwined with issues related to the energy market or devised specifically for integrating new generations and loads into the existing power systems. However, ensuring a test system satisfies both voltage drop and line loading criteria during both normal and all single contingency operations is crucial in TEP studies, and addressing these issues under contingency conditions poses notable challenges. Moreover, practical TEP scenarios involve varied loadings, including peak load and dominant loading (60% of peak load) scenarios, while the existing test systems are configured solely for single loading conditions. To address these technical gaps, this paper introduces the 17-bus test system operating at a transmission voltage level of 500 kV, meeting technical requirements under normal and all single contingency operations for both peak load and dominant load scenarios. Detailed specifications of the proposed test system and load flow analysis at both normal and contingency conditions for different loading conditions are presented. This test system serves as an invaluable resource for TEP studies.

Analysis of the optimum allocation of BESS for contingency support

The development of energy storage technologies is considered a key issue to increase the flexibility of future power systems and to achieve high penetration levels of renewable generation. In recent years, battery-based storage has attracted great interest due to the cost reduction of lithium-ion batteries. In addition, the modularity of batteries makes possible to develop not only grid-scale energy storage facilities connected at transmission voltage levels but also smaller distributed energy storage systems connected at distribution voltage levels. However, it must be taken into account that the size and services provided by batteries depend on their location in the power system. In this paper, a methodology to determine the optimal location of battery based electrical energy storage systems for contingency support is presented. The methodology has been applied to a Spanish power system to evaluate the effect of batteries on contingency support when installed either in the transmission network or in the distribution network.

Research on damage characteristics and microscopic appearance of ReBCO tapes after DC overcurrent

With the expansion of the power grid, the use of DC transmission technology is becoming increasingly prevalent. This has led to higher transmission voltage levels, which in turn have brought to the fore the issue of large short-circuit currents. The existing circuit limiter’s performance is insufficient to meet the growing demand. Superconducting fault current limiter, which based on ReBCO tapes, is considered to be the solution to the problem of large short-circuit current. However, the failure mode of ReBCO tapes under DC overcurrent remains to be studied. In the superconducting state, the current flows mainly through the superconducting layer. Therefore, it is necessary to investigate the overcurrent characteristics of the superconducting layer after overcurrent. In this work, the damage characteristics and microscopic appearance of ReBCO tapes after overcurrent were investigated. The magnetic field distribution characteristics and the microscopic appearance of the superconducting layers of ReBCO tapes with different degrees of critical current recession were investigated, and the chemical elements of the superconducting layers were analyzed. The results show that large-area pits were found on superconducting layer after overcurrent, the element types and mass proportions did not change. Overcurrent affects the superconductivity of the tape mainly by changing the physical structure of the superconducting layer.

Influence of Water Content on the Dielectric Characteristics of LN2-Impregnated PPLP for HTS Power Cables

High-Temperature Superconducting (HTS) power cables operate at low, medium, and high voltage levels for electrical power transmission. Polypropylene Laminated Paper (PPLP) is wrapped helically around the HTS layer and it is impregnated with Liquid Nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) to form a composite dielectric layer. During the installation and maintenance process of HTS cables, any leak of moisture in the cryostat will lead to immediate ice formation. Once the cable warms up, the ice will melt into water, which will be absorbed by the PPLP Kraft paper layer and is similar to the PPLP paper soaked with water. When the moist PPLP is cooled with LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> it will form ice and forms a composite material during operation. The objective of this paper is to investigate the influence of water content on the breakdown strength, relative permittivity (ϵ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ) and dielectric losses of LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> impregnated PPLP samples for different number of layers. Considering the worst-case scenario of moist samples, wet PPLP samples were tested for breakdown strength and dielectric properties at Room Temperature (RT) and LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> temperature and was compared with dry PPLP samples. Two different experimental setups were developed to measure the breakdown strength and dielectric properties respectively for stacked PPLP layers. The wet and dry samples were tested for the AC V-I characteristics, the effect of PPLP stack thickness on dielectric strength, statistical analysis using two parameter Weibull distribution and computation of relative permittivity and loss factor from capacitance measurement.

Widespread compact fluorescent lamp evaluations in 50 Hz electrical network

Rapid development in electrical technology has imposed strong challenges to modern power system. Power quality has become a great concern due to proliferation of power electronic technology in modern electrical loads. Specifically for lighting load such as compact fluorescent lamps (CFLs), one of the concerning issues is harmonics. CFL is a cost-competitive and energy efficient compared to incandescent lamp. Inevitably, CFL produces harmonics current due to nonlinearity behaviour of the electronic ballast circuit. This paper presents a study on the widespread installation of CFL lamps in electrical power network. Initially, the harmonic current characteristics of local-branded CFL was identified from laboratory measurement. Then, a simulated CFL model was developed in MATLAB/Simulink to replicate the identified characteristics. The same step was repeated for other two different brands where eventually all models were embedded into a distribution network. The results show that at low voltage level, with installation more than 50 units for each type of CFL, the harmonic voltage distortion exceeded the 8% total harmonic distortion (THD) limit as stipulated in EN50160 standard. However, at higher voltage, the amount of THD decreased to average 0.94% and further down to average 0.28% at small transmission voltage level.

OVERVIEW OF FACTORS AFFECTING THE ESTIMATION OF LIGHTNING SHIELDING PERFORMANCE OF OVERHEAD TRANSMISSION LINES

This paper examines the risk of lightning stroke to overhead transmission line. The estimation procedure for the lightning performance of overhead power lines is based on the selected lightning attachment model, available lightning parameter statistics, the transmission tower design and voltage levels, type of overvoltage and other characteristics. In this paper the overview of factors affecting the estimation of lightning shielding performance of overhead transmission lines was performed. Among the factors that can affect the estimation accuracy, one can list insufficiently accurate data on the ground flash density in the area of interest and lack of complete data on statistical distribution of lightning current magnitudes. The paper shows that the influence of wind on the increase in the horizontal exposed distance of the phase conductor is not also taken into account. In this research traditional electro-geometric model was used for estimation of lightning performance of 220 kV overhead power line. Results obtained suggest that swing of suspension insulator strings caused by strong winds may lead to increased risk of lightning shielding failure during thunderstorm. Calculation performed for 3 kA lightning current magnitude shows that at swing angle equal to –1 degree, the horizontal unprotected distance of phase conductor increases by 3.1%, that corresponds to 5.240 m uncovered width. When the swing angle is increased to –5 degree, the uncovered width is increased by 15.8% that corresponds to 5.885 m uncovered width. It is proposed that an increase in the risk of lightning shielding failure as a result of wind load can be accounted by applying an appropriate correction factor in expressions for calculation of shielding failure rate, shielding failure flashover rate, etc. Proposed correction factor should account frequency and strength of wind in the area of transmission line route and depend on transmission line voltage level and tower design. Further efforts should be focused on obtaining and justifying the numerical values ​​of this correction factor.

Fast Distance Protection Scheme for Wind Farm Transmission Lines Considering R-L and Bergeron Models

The distributed capacitance of the line becomes larger as the scale of wind farms, the transmission voltage level, and the transmission distance increase. Hence, the error of the traditional time-domain distance protection scheme based on the R-L model, which ignores the distributed capacitance of the line, becomes unacceptable. Therefore, the error of the time-domain fault location method based on the R-L model, especially the maximum error range, is theoretically analyzed in this paper. On this basis, a novel fault location method based on the R-L and Bergeron models is proposed. Then, a fast time-domain distance protection scheme is designed. In the proposed scheme, the error in the fitting calculation is used to construct a weight matrix, and an algorithm for solving the time-domain differential equations is designed to improve the calculation speed and stability. Compared with the traditional frequency-domain distance protection scheme, the proposed scheme is independent of the power supply characteristics; thus, it is suitable for wind farm transmission lines. In addition, compared with the traditional method based on the R-L model, the proposed scheme effectively avoids the negative influence of the distributed capacitance of the line, which significantly improves the operating speed. Different types of faults are simulated by PSCAD/EMT-DC to verify the effectiveness and superiority of the proposed scheme.

Research and application of high voltage measurement technology in DC UHV preventive test

With the state’s high attention to clean energy and the requirement to reduce the loss of power grid transmission lines, DC UHV has developed rapidly in recent years. It refers to DC transmission and related technologies with voltage levels of ±800 kV (±750 kV) and above. In the power system, DC high-voltage transmission is inseparable from power equipment, but the higher the transmission voltage level, the higher the voltage of DC withstand voltage preventive test. Before the transmission of UHV DC transmission lines, if the DC voltage withstand device is 800 kV or above, the voltage withstand test shall not be carried out for the high-voltage line. The traditional direct comparison method using voltage divider cannot be used to measure the DC output voltage of DC UHV withstand voltage device on site. This paper analyzes the method of full coverage of DC UHV system in limited voltage range and the method of out of range calibration using scale factor. In order to solve the problem of voltage traceability in the DC high voltage generator, especially the voltage traceability of the field DC UHV device, when the voltage output range of the calibrated DC high voltage generator exceeds the measurement range of the standard, the standard value of the voltage calibration point beyond the range can be determined by comparison and obtained through the linearity test. The comparison with the standard shall be conducted at a voltage not lower than 20% of the rated voltage of the calibrated DC high voltage generator, and compared to the maximum voltage of the standard voltage divider. The comparison is carried out at a (a ≥ 2) voltage point. When comparing at a point, the highest voltage level is equal to the upper limit of the standard. Under a voltage point, according to the mathematical relationship between the voltage standard value of the tested device and the current flowing through the linear load resistance, the fitting function can be obtained through the linear regression method. For b (b ≥ 4) calibration points beyond the measurement range of DC standard voltage divider, the standard value can be “extrapolated” from the linear load resistance current and the fitting function Yang (2002). Through comparison and verification, the method is feasible, which is of great significance to promote the compilation of calibration specification for DC high voltage generator.

EMI radiation of power transmission lines in Malaysia

Background: There has been rising concern amongst the public regarding their home's proximity to high tension power transmission lines. The primary cause of fear is the impact of the electromagnetic interference (EMI) radiation on the nearby occupants' health. Despite the presence of national permissible limits of EMI radiation, there is still lack of information with regards to the EMI radiation of the types of power lines configuration in Malaysia. Methods: The electric and magnetic fields of several selected power transmission lines were simulated using the EMFACDC software program from the recommendation ITU-T K.90. Five types of power transmission lines available in Malaysia are considered. Results: It was found that the simulated electric and magnetic field levels at all the power lines' right of way (ROW) boundary complies with the prescribed exposure limit. However, the electromagnetic fields (EMF) level increases significantly as the separation distance is reduced from 30m. For a more conservative approach, the ROW can be set at 30m across all transmission voltage level and corridor area condition. Conclusion: It can be concluded that Malaysia's power transmission lines are within the prescribed exposure limits. To further minimize the electric and magnetic field level, it is recommended that the residential building should be built at least 30 meters away from the power transmission lines, especially for the 275kV double circuit, 275/132kV quadruple circuit, and 500kV double circuit lines.

EMI radiation of power transmission lines in Malaysia

Background: There has been rising concern amongst the public regarding their home's proximity to high tension power transmission lines. The primary cause of fear is the impact of the electromagnetic interference (EMI) radiation on the nearby occupants' health. Despite the presence of national permissible limits of EMI radiation, there is still lack of information with regards to the EMI radiation of the types of power lines configuration in Malaysia. Methods: The electric and magnetic fields of several selected power transmission lines were simulated using the EMFACDC software program from the recommendation ITU-T K.90. Five types of power transmission lines available in Malaysia are considered. Results: It was found that the simulated electric and magnetic field levels at all the power lines' right of way (ROW) boundary complies with the prescribed exposure limit. However, the electromagnetic fields (EMF) level increases significantly as the separation distance is reduced from 30m. For a more conservative approach, the ROW can be set at 30m across all transmission voltage level and corridor area condition. Conclusion: It can be concluded that Malaysia's power transmission lines are within the prescribed exposure limits. To further minimize the electric and magnetic field level, it is recommended that the residential building should be built at least 30 meters away from the power transmission lines, especially for the 275kV double circuit, 275/132kV quadruple circuit, and 500kV double circuit lines.

EMI radiation of power transmission lines in Malaysia.

Background: There has been rising concern amongst the public regarding their home's proximity to high tension power transmission lines. The primary cause of fear is the impact of the electromagnetic interference (EMI) radiation on the nearby occupants' health. Despite the presence of national permissible limits of EMI radiation, there is still lack of information with regards to the EMI radiation of the types of power lines configuration in Malaysia. Methods: The electric and magnetic fields of several selected power transmission lines were simulated using the EMFACDC software program from the recommendation ITU-T K.90. Five types of power transmission lines available in Malaysia are considered. Results: It was found that the simulated electric and magnetic field levels at all the power lines' right of way (ROW) boundary complies with the prescribed exposure limit. However, the electromagnetic fields (EMF) level increases significantly as the separation distance is reduced from 30m. For a more conservative approach, the ROW can be set at 30m across all transmission voltage level and corridor area condition. Conclusion: It can be concluded that Malaysia's power transmission lines are within the prescribed exposure limits. To further minimize the electric and magnetic field level, it is recommended that the residential building should be built at least 30 meters away from the power transmission lines, especially for the 275kV double circuit, 275/132kV quadruple circuit, and 500kV double circuit lines.

Application of 66kV Active Intervention Grounding Arc Suppression Device

The energy supply is mainly based on electric energy at present, and power supply reliability is an important indicator for evaluating power supply services. In view of the 66kV transmission voltage level unique to Northeast my country, the neutral point of the transmission system directly affects the stable operation of the power system. First, the composition of the substation in the system and the working principle of the arc suppression device are analyzed. Secondly, when a single-phase grounding fault occurs in a 66kV neutral point ungrounded system, an active intervention grounding arc suppression device is designed. Finally, the operating characteristics of the designed grounding arc suppression device are demonstrated based on the simulation results.

Overview of Oman Power Transmission System and Protection Schemes for Effective Energy Management in Smart Grid Operations

This article presents an overview of the transmission system and protection schemes employed in the national power grid of Oman. The technical design requirements considering the percentage of allowable limits for the different transmission voltage levels in the power grid of Oman were considered based on the electrical standards and grid codes of Oman. Also, the protection and fault requirements based on relay settings and backup protection were some of the factors considered in this study. More so, the power flow, peak, and off-peak voltage profiles of the main interconnection and Dhofar transmission systems were analyzed in detail, considering projections for 2021 and 2025, respectively, for effective energy management and smart grid operations. The current protection equipment of the power grid of Oman was evaluated, and some improvement schemes were proposed considering the implementation of the new technology for smart grid operation. The continuous investment in the transmission system of the Oman power grid and the use of updated protection technology would lead to the enhancement of the performance of the Oman transmission system to reach a high-level power transmission availability.

Modification Effect of TiO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; Hollow Nanoparticles on Insulating Properties of Transformer Oil

With the promoting of transmission voltage level and the continuous fluctuation of operating conditions by connecting renewable energy into the power system, more stringent requirements have been placed on the operation reliability of transformers and other large electrical equipment. Transformer oil, as the main liquid insulating medium in large power equipment, the modification of its insulating performance has always been research focus in dielectric field. Studies have proved that TiO₂ nanomaterials can not only enhance the AC and positive impulse breakdown voltage of transformer oil, but also significantly improve the aging resistance of transformer oil. However, the DC breakdown voltage of transformer oil has not been greatly increased yet, and sometime even weakened. In this paper, TiO₂ hollow nanoparticles were prepared by hard template method to modify transformer oil. AC and DC breakdown voltage and dielectric permittivity of transformer oil before and after modification were measured and analyzed. The results show that the AC breakdown voltage of the transformer oil can be increased by 32.5%. DC breakdown voltage was increased first and then reduced with the increasing of nanoparticle concentration, while no obvious improvemnet was observed. Based on breakdown mechanism and permittivity of transformer oil, we think the hollow structure of the nanoparticles can significantly enlarge the interface between particle and oil, which greatly promotes the capturing capability to fast electrons and inhibit their migration in the oil, so the AC breakdown voltage are significantly increased. Under DC stress, nanoparticles can capture electrons and meanwhile migrate along fixed direction, which increased electrical conductivity of oil and resulted in lowering of DC breakdown voltage with the increase of nanoparticle concentration.

Research on the pollution performance and degradation of superhydrophobic nano-coatings for toughened glass insulators

Most of the research efforts to enhance the pollution performance of glass insulators have been focused on room temperature vulcanizing (RTV) silicone rubber coatings to cover the original hydrophilic surface of glass with a hydrophobic polymeric one. However, in recent years, advanced superhydrophobic nano-coatings, with intrinsic self-cleaning properties, have been developed as a possible alternative to silicone. This paper presents a research carried out in an outdoor test station, where one insulator string composed of nano-coated glass insulators was monitored for over two years and its performance compared with other identical insulator strings, but composed by RTV silicone-coated and non-coated glass insulators. The test station was located in a heavily polluted area of France and the insulator strings were energized at transmission voltage level to represent real operational conditions. The pollution performance and degradation were investigated through leakage current analyses and quarterly visual inspections of the superhydrophobic surface. The results showed that the superhydrophobic nano-coating was only effective when it was new and during a short period of time. Later on, it was subjected to a gradual degradation resulting in a loss of hydrophobicity until reaching a steady hydrophilic condition.

Fuzzy-Based Relaying Scheme for Transmission Line Based on Unsynchronized Voltage Measurement

ABSTRACT This study aims to develop a new relaying scheme for the complete protection of transmission line based on only voltage data. Fault detection and classification is obtained from the fundamental component of the voltage signal collected from one end of the line. Magnitudes of positive sequence component of voltage signals from both ends of the line have been considered for fault location. As only magnitude of voltage signal is used, the requirement for data synchronization can be avoided, and the error caused by current transformers (CT) is eliminated. Moreover, positive sequence components exist for all types of faults, unlike negative sequence components. Hence, all types of faults can be located. Fuzzy decision approach has been proposed to avoid computationally expensive training of expert systems. The proposed scheme has been tested for different dynamic situations in MATLAB/Simulink software. The superiority of the scheme has been established by considering coupling capacitor voltage transformer (CCVT) transient error, weak infeed condition, change of transmission voltage level and line loading.

Electromagnetic Immunity Performance of Intelligent Electronic Equipment in Smart Substation’s Electromagnetic Environment

With the gradual increasing of the transmission voltage level, the situation of interference on secondary side equipment in smart substations is becoming more serious. The authors tested the interference waveforms caused by the circuit breaker’s operation at the smart substation, which showed the severity of the electromagnetic (EM) environment. This paper takes the electronic current transformer acquisition card as an example. The influence of EM interference sources on the reliability of the acquisition card is analyzed. Then, standardized electromagnetic compatibility (EMC) immunity tests of the international electrotechnical commission (IEC) for different interferences are implemented. Typical output characteristics of acquisition cards for different tests are analyzed. Innovatively, this paper proposes a quantitative evaluation method of output waveform disturbance to evaluate the acquisition card’s performance. This disturbance distortion is of great significance to the EM environment estimation of the acquisition card.

An Improved Control Strategy for the Bus Interlinking Converter Based on Three-level Topology in AC-DC Hybrid Microgrid

Considering the increasing requirements of the AC-DC hybrid microgrid (HMG) for the transmission power capacity and voltage level, the several bus interface converters (BICs) with the two-level PWM converter topology, need to be connected between AC bus and DC bus in parallel, which could generate circulating current and cycle power. The cost of the modular multilevel converter topology based BIC is too high. Hence, this paper proposes to apply the BIC with three-level topology to the HMG, and a droop control strategy with the midpoint potential hysteresis regulation link is designed, which can effectively suppress the fluctuation of midpoint potential without affecting the normal operation of the BIC in the grid connected or off mode. In addition, the principle of neutral point fluctuation and the process of hysteresis control are introduced, and the detailed design of dual-mode control strategy based on droop curve are also given. Finally, the effectiveness of the improved control strategy is verified by simulation.

Polycyclic Compounds Affecting Electrical Tree Growth in Polypropylene Under Ambient Temperature

Polypropylene (PP) has great potential to be used as recyclable high-voltage direct current (HVDC) cable insulation material. Electrical tree is the key factor that leads to cable insulation failure and limits the increase of HVDC transmission voltage level. In this study, three different polycyclic compounds, namely 4,4'-bis(dimethylamino)phenylazo, 2-hydroxy-2-phenylacetophenone and 4-phenylbenzophenone, are added into PP matrix with the addition content of 0.1 wt%. The electrical treeing experiments are conducted under impulse superimposed DC voltage at 30, 70 and 90 °C. Then the polycyclic compound with the best effect on inhibiting electrical tree is selected, and its filling ratio is further changed from 0.1 wt% to 0.3 wt% to get the optimal inhibition effect. It is found that the addition of 2-hydroxy-2-phenylacetophenone can inhibit the electrical tree degradation. However, the addition of 4-phenylbenzophenone and 4,4'-bis(dimethylamino)benzene will increase the electrical tree length and accumulated damage. As the content of 2-hydroxy-2-phenylacetophenone increases, the electrical tree length and accumulated damage decrease firstly, and then increase. The effect of polycyclic compounds on the electrical tree degradation is affected by the relative polarity of impulse superimposed DC voltage and temperature. The experimental results reveal that adding 0.1 wt% 2-hydroxy-2-phenylacetophenone polycyclic compound to PP can effectively inhibit the electrical tree degradation, which has great potential for application in recycle HVDC cables.

Commissioning of UHV Indoor Double Shielded Laboratory for Radio Interference Voltage and Partial Discharge Measurement

In recent years, due to advancement of technology, the transmission voltage levels are goes on increasing. Worldwide 800 kV systems is very common and in India experimental 1200 kV AC is successfully commissioned. Testing of vital equipment of such UHV transmission network is paramount importance to provide uninterrupted, reliable and quality power to the customers. Worldwide few testing laboratories having facility to test upto UHV class equipment, the Ultra High Voltage Research Laboratory (UHVRL) of Central Power Research Institute (CPRI), India is one among them. Recently, 2X600 kV, 2 A, 2400 kVA HVAC test system is commissioned in double shielded indoor laboratory at UHVRL, Hyderabad, India. This manuscript elaborates the experiences of commission of AC test system along with radio interference voltage and Partial Discharge (PD) measurement.