Lightning activity is frequent in the main grid from west to east of China Southern Power Grid, where the terrain and adverse weather conditions are bad, differentiated distribution of lightning fault is significant, and it’s a big challenge to carry out effective protection. Research progress of lightning performance evaluation technology of EHV and UHV overhead transmission lines of China Southern Power Grid in recent years are introduced in this paper. Firstly, lightning activities within China Southern Power Grid area and operation against lightning of EHV and UHV overhead transmission lines are researched and summaried, and the causes of lightning trip are analyzed. A numerical simulation model aimed at calculating the distribution of corona space charge of UHVDC transmission lines under lightning conditions are proposed, the initial condition of positive upward leader produced by large-sized bundled conductors are obtained through experiments. A numerical model aimed at calculating the lightning surge response of complex conductor system are proposed based on FDTD, and the accuracy of the model is verified through actual measurement on model line transient response. Lightning protection analyzing system for transmission line(LPTL) is developed. By using LPTL, comparisons between lightning performance evaluation results and operating experience of typical transmission lines are carried out, so that the engineering applicability of the software is verified. In the future, further works should be done to develop the basic research on mechanism of lightning shielding failure of DC lines, correct and improve LPTL, in order to provide effective means for lightning protection design and improvement of transmission lines.

With the rapid development of HVDC transmission in China, the earth return current during monopolar operation of HVDC system have caused serious electromagnetic compatibility problems. From a general aspect, the numerical computation method of wide-area current field considering the deep earth resistivity is presented, and a complex image method based on self-adaptive sampling is proposed to compute the Green’s function with complex horizontal multi-layer ground accurately. The new and valuable concepts given in this paper can provide a useful reference for analyzing the electromagnetic compatibility problems caused by the earth return current of HVDC transmission.

Lightning failure rate is an important indicator for substation construction. Current calculation methods of insulation failure rate depend on the operation data of the substation and computer simulation, and are complex and have big errors. Thus, the rationality of substation design and the reliability of lightning protection could not be predicted. Based on the statistical method, a new method is proposed. By using the parameters of the transmission lines and towers, the lightning frequency of tower is calculated, then the lightning failure rate of substation is calculated by using the probability of the amplitude of lightning current. Taking a 500 kV HGIS substation in Guangdong Province as the research object, a simulation model is established based on EMTP-ATP, and the process of lightning striking the top of the tower and invading the substation along transmission line is simulated to determine the critical lightning current amplitude. According to the historical data of the area, the probability of the amplitude of the lightning current is obtained by fitting the measured values, then the lightning failure rate of the substation is calculated.

AC filters (ACFs) for different harmonics are installed in HVDC stations, they switch on and off very often with circuit breakers for reactive power compensation. ACF breakers bear transient recovery voltages (TRV) comprising AC and DC voltages after switching off large capacitive current, because the DC voltage component is decided and divided by resistance which is influenced by the ambient environment of porcelain breaker external insulation, the TRV may exceed the insulation requirement. Using a typical 550 kV AC filter procelain breaker with two breaks used in HVDC stations as an example, a simulation model of TRV is established based on PSCAD to simulate the influencing factors of TRV. The simulation results show that the ambient environment, such as humidity, dirt and dry zone, can seriously affect the TRV of breaks. With specific ambient environment conditions, when the break resistance decreases and the diffence between the two break resistances is large, the maximum break TRV may approach or even exceed the theshhold value, which will result in breaker restrike or flashover.

To understand the future developing trend of UHVAC XPLE cable, the paper investigates and summarizes the application and technical challenges of UHVAC XLPE cable in transmission projects over the world, and considers that UHVAC XLPE cable is becoming a mainstream of land-based urban transmission projects. Some key technologies for on-site acceptance testing of ultra high voltage and long distance cable transmission projects, and on-line cable monitoring and diagnosis techniques are reviewed. It’s of a reference for the similar projects in China in the future.

The development and preparation method of nano-modified transformer oil are summarized. The influence of nanoparticles on the electrical properties including breakdown strength and dielectric property is summarized. The mechanism of the influence of nanoparticles on dielectric property is discussed. Meanwhile, the effect of nanoparticle on the thermal property is discussed along with the corresponding mechanism. At last, the research of the new environmental-friendly vegetable oil modified by nanoparticles is summeried. It is found by correlative study that the electrical and thermal properties of transformer oil could be improved by proper nanoparticles. The nano-modified transformer oil meets the requirements of miniaturization and higher voltage of electric devices in power system.

The corona discharge phenomenon of UHVDC transmission line in high altitude area is very complicated, it is affected by line parameters, meteorological parameters, conductor surface electric field distribution and many other external factors. On one hand, the existing UHVDC transmission line electromagnetic environment parameter prediction formula is the empirical formula obtained in low altitude and standard atmospheric conditions, on the other hand, the influence of meteorological factors are ignored. Based on the massive amounts of electromagnetic environment data tested in the past six years in the National Engineering Laboratory for UHV Technology (Kunming), the big data processing method (i.e. LASSO LME method) is introduced to establish the prediction formula, which can calculate the electromagnetic environment parameter considering the comprehensive physical factors of wind speed, temperature, relative humidity and the circuit parameters of UHVDC transmission line. At last, the accuracy and applicability of the formula is verified by comparison between traditional forecasting formula and experimental data.

In highly urbanized areas, erecting ± 800 kV polar wires and ground electrode wires on the same tower is the best choice to solve the shortage of transmission line corridors and scarcity of land resources. However, there are few researches on the electromagnetic environment of this type of tower at home and abroad. In this paper, the conventional calculation method is expanded to consider the shielding effect of ground electrode wires to the electromagnetic environment of polar wires. Taking the ±800 kV Dianxibei to Guangdong UHVDC Project as example, the audible noise, radio interference, total field strength above ground and ion current density under horizontally and vertically arranged modes of same tower hybrid transmission lines are discussed. The results show that the total electric field strength above ground of same tower hybrid transmissin lines is less than the DC line, and the transmission line corridors can be compressed about 44% by using the vertical arrangement of same tower hybrid transmissin lines.

Corona inception field strength is one of the important parameters for the design of fittings in ±800 kV DC transmission line. So far Peek formula is still the basis for the prediction of corona inception field strength of DC line fittings with large size at high altitude area. Peek formula was obtained by experimental results of electrode with curvature radius less than 50 mm at standard atmospheric pressure. Because the discharge mechanism of the electrode with large curvature radius(larger than 100 mm, hereafter the same)and 3D structure is different, Peek formula is inaccurate for predicting the corona inception field strength for this kind of electrode, especially at high altitude area. In order to predict the corona inception field strength of the fittings with larger curvature radius and non-cylinder structure accuratly, a test platform for HVDC fittings is set up in Kunming high voltage laboratory at 2 100 m altitude. Corona inception voltages are measured for test tubes and rings in the lab. Correction method to Peek formula is proposed firstly for the electrode with larger curvature and 3D structure at high altitude area. This method will become one of the theory evidences for the design of HVDC fittings at 2 km altitude area.

Adding creepage extender is currently recognized as an effective measure for reducing the occurrence of rain flashover of external insulation. Combining with the 800 kV UHVDC voltage divider model of an existing UHVDC converter station, the electric potentials and electric field distributions of installing creepage extender in different position respectively in clean, wet dirt condition are simulated and analyzed, simulation results show that the electric field strengths are increased near the high-voltage end of the DC voltage divider after installing creepage extender, and different installation positions have a little effect on the internal electric field distribution, which is 5% higher when creepage extender are added on its internal RC node rather than on upper or lower ends of the node.

Based on the needle-plate model, the decomposition products and production mechanism under different humidity and partial discharge voltage are analyzed by experiment and theoretical calculation. The Materials Studio is used to study the possible components, and the components production pathway is studied. Through analyzing the reaction heat and the reaction barrier the components involved in, the reason why the CO and NO₂ components is chosen as the characteristic products to characterize the insulation status of switchgear is fundamentally explained. The theory foundation is established for monitoring the insulation status of the switchgear by detecting the air decomposition components. The air decomposition components: detected in the experiment process are CO and NO₂. When the humility keeps unchanged and partial voltage increases from 6 kV to 7.5 kV with 0.5 kV increment, the concentration of CO and NO₂ increased with the increase of discharge voltage. On the other hand, keeping the discharge voltage still and adjusting the relative humidity to 50%, 70% and 90% respectively, the concentration of CO increased with the increase of humility, and the concentration of NO₂ obviously decreased with the increase of humidity. Under a certain voltage and humidity, the concentration of CO shows a linear increasing trend over time, while the increasing rate of NO₂ gradually reduces over time and tends to saturate ultimately.

Due to the access of overhead ground wires of different voltage level transmission lines, the topology structure of the main grounding grid of substation operating with overhead ground wire will change significantly, and its grounding impedance cannot be measured by simply using the grounding impedance measurement method of power system grounding device. Moreover, it’s usually hard to unlock the overhead ground wire and measure the substation grounding impedance in operation, and the measurement will inevitably be affected by the diversion of overhead grounding wire. In order to eliminate the influence of overhead ground wire, it is required to measure the shunting current of each outlet frame connected with the overhead ground wire. In this paper, a grounding impedance measurement test for the main grounding grid of a substation operating with overhead ground wire is carried out, and a method of measuring the overhead ground wire shunt based on flexible Rogowski coil and frequency selective multimeter is proposed. The results show that the overhead ground wire diversion ratio can reach 43.4%, and the angle between the shunt current and the class power frequency current injected into the main grounding grid as a reference is -19.5°. The grounding impedance of the main grounding grid of the substation is calculated, and the error between the calculated result and the experimental result is very small. The results demonstrate that the measurement method of grounding impedance of substation with overhead ground wire and the measurement method of overhead ground wire shunting are correct.