In high altitude and high earthquake intensity areas, excellent seismic performance should be the key point for UHVDC (ultra-high voltage direct current) wall bushing design, manufacture and operation. In order to solve seismic performance problems of wall bushing, according to the 9 degree intensity anti-seismic requirement of the Xinsong sending converter station of Dianxibei UHVDC transmission project, in order to evaluate wall bushing seismic performance, the finite element models combined with the wall bushing and valve hall of ±800 kV Dianxibei UHVDC transmission project have been established to get the seismic responses. As the analysis results show that the seismic responses are large, the anti-seismic design of the metal friction type dampers has been carried out to increase the safety and anti-seismic reliability of the wall bushing. Then the bushing support used in the shaking table test has been designed and manufactured based on the numerical simulation. The shaking table test on the DC wall bushing of project supply equipment has been made to compare the seismic response before and after the dampers installed on DC wall bushing. The results show that the existence of metal friction dampers could decrease the seismic response obviously. The maximum stress response decreases 39.2% while the maximum relative displacement decreases 71.3%, and the stress safety factor could increase to 2.52 from 1.53. The anti-seismic performance of DC wall bushing has been substantially increased to fulfill the project seismic requirement.

Combined with the principle of bypass switch protection stage 1 (82BPS-1), the action reason and existing risk of 82BPS-1 protection in Puer-Qiaoxiang UHVDC on September 10 of 2015 is analyzed. Then the defect of bypass switch protection is found that the unreasonable integral counting module can make 82BPS-1 protection maloperation. Aiming at the problem, an improved measure is proposed which using the bypass switch closing order to clear the count of 82BPS-1 protection integral counting module. The effectiveness of the measure has been verified by RTDS simulation tests. At present, the improved measure has been applied to Puer-Qiaoxiang and Chuxiong-Suidong UHVDC transmission systems.

Based on single harmonic current extracting, the paper proposed a control method of grid current and load-side current double-fed composite detection for shunt active power filter. In synchronous rotating coordinate system, the results of the grid current I adjustment feedback and the load-side current P adjustment feedback are integrated. Meanwhile, the harmonic components of the current are extracted as APF compensation command. By constructing the equivalent circuit and the transfer function, dynamic performance and steady-state performance of the control method are analyzed, which can be proved that the influence of control delay, hardware delay and sampling accuracy on compensation effect caused by will be decreased greatly, as well as the system response speed is ensured. Thus the result of zero static error compensation can be achieved. A 380 V/200 A APF prototype is developed to verify the control method of double-fed composite detection.

When power electronic transformer (PET) supplies power to the unbalanced or non-linear loads, the voltage amplitude and frequency of the output-side in PET may be unstable, and even affect the power supply reliability of the PET. Aiming at demands of large output capacity, adjustable capacity modules, and high-quality power supply of PET, and for avoiding the limitations of single inverter output module in handling asymmetric or non-linear loads, a dual-module control strategy with high power quality for parallel output sides (inverters) of PET is proposed. In which, one of the inverter modules in output side is regarded as a voltage source and adopts double closed-loop control strategy of voltage and current, it provides stable output voltage of PET and stabilizes the voltage reference values of the output sides for other inverter modules, which can not only compensate for negative sequence current, harmonics and reactive current to reduce the negative impacts on the output voltage of PET, but also provide active power and reactive power in accordance with established power distribution strategy for output side modules. Other output-side inverter modules treated as current sources adopt the current compensation control strategy. They are used to enlarge the output current and enhance the capacity of PET. Taking two parallel output-side inverter modules as an example, the proposed high power quality control strategy is analyzed theoretically. It is concluded that the proposed strategy can improve the output capacity of the PET, greatly reduce the adverse effects of asymmetric loads on the output voltage stability of PET and effectively enhance the adaptability, capacity expansion and power supply reliability of PET. The simulation results verify the effectiveness of the proposed control strategy.

Hardware-in-the-loop (HIL) simulation plays an important role in the research and development of HV/UHV DC systems, of which the key technology is the real time simulation model of MMC-HVDC. In this paper, the real time modeling technology of MMC-HVDC is studied. Especially, a gate signal equivalent method is proposed for modeling of a half and full bridge hybrid MMC applicable for UHV HVDC system. Simulation results show that the proposed method provides high accuracy, while requiring no extra simulators. A three-terminal UHV HVDC system is modeled, and a series of HIL tests are carried out, which show the effectiveness of both the simulation method and control strategies.

The distributed partial discharge test during AC withstand voltage test of power cable is an effective means to detect the minor defects in the cable body and its accessories. In order to solve some key technical problems of this technology in the practical application, effects of grounding modes on the partial discharge signal accessed are studied through numerical simulation and calculation in this paper. The effect of grounding mode on induced overvoltage of metal protection layer in insulation fault is simulated. The simulation results show that cross connection joint should be changed into a straight type in the cable voltage synchronous distributed partial discharge test, and be grounded through the voltage limiter or grounded directly. The cable voltage synchronous distributed partial discharge test has been applied widely in Guangzhou Power Grid in recent years, and the cable defects have been found sucessfully and located accurately. The research results provide important references for the completion of power grid cable projects.

With the maturity of power cable technology and updating of new technology of cable accessories, the failure characteristics of high voltage cable systems and fault causes have changed significantly. In this paper, detailed statistics are carried out for the characteristics and fault cause proportions of 132 failures for 110 kV and above power cable in China Southern Power Grid(CSG)during 2006 and 2016, and 99 failures in the literatures, and the fault characteristics and main reasons of the high voltage cable system in recent years are analyzed. The statistical results show that the present operation reliability of high-voltage cable system in CSG has been improved significantly, while the failure rate has decreased by an order of magnitude compared to 2001. Cable accessories have now already become the weakest part of high-voltage cable systems, the failures of which account for as high as 85.5% without taking external damage into account. For cable, more than 70% of the cable failures are due to external damage, while more than 84% cable accessories failures are due to product quality and improper installation. The statistical result of power cable system can provide a basis for the development of differentiated operation and maintenance strategy.

The composite insulating material composed of polytetrafluoroethylene (PTFE) film and silicone oil is widely used in dry-type high voltage apparatus. Though PTFE film is a key component of composite insulation, the spatial charge distribution of it is not clear yet. However, the existing researches prove that the space charge has a great influence on insulation discharge. Therefore, the space charge distributions of PTFE film at different temperatures are measured by electroacoustic pulse method. The results show that the negative space charge is easy to accumulate in the PTFE medium under the applied DC electric field. Secondly, the increase of temperature helps to accelerate the rate of space charge dissipation in the PTFE medium and dissipate the charge. However, the increase of temperature will also lead to the increase of space charge injection and accumulation of PTFE, and might promote the ionization of impurities in the medium, and lead to the accumulation of lots of space charge in the PTFE medium. Therefore, aiming at eliminating as much space charge a possible,it is recommended that the PTFE insulation medium should avoid to be operated at high temperature.

Lighting return-stroke models are needed to specify the electromagnetic radiation source in studying the production of transient optical emission in the lower ionosphere, the energetic radiation from lighting, and characterization of Earth’s electromagnetic environment, as well as studying lightning interaction with various objects and systems. Electromagnetic models of the lightning return stroke that based on Maxwell’s equations allow a self-consistent full-wave solution. In this paper, the electromagnetic lightning return stroke model with distributed series inductance is disscussed. The finite difference time domain method (FDTD) is employed to calculate the spatial distribution of current along the lightning channel. The dipole technique is used to calculate the radiated electromagnetic field when the source is known. The results show that, by choosing the parameter of distributed series inductance in 2~10 μH/m, the propagation speed of lightning current are in c/3~2c/3. With the rising of distributed series inductance, the current-wave propagation speed decreases, the electric strength in the near field area increases and the attenuation become more significant over distance. The change of distributed series inductance has little effect on the magnetic field.

After a 220 kV transmission line is equipped with a line type terminal arrester, breaker fracture breakdown fault of 220 kV line circuit breaker is still frequent. This paper gives a detailed analysis of 220 kV circuit breaker fracture breakdown fault, and uses the theory of the steepness of the lightning wave to deduce the allowable electrical distance calculation formula between the line type or substation typr arrester and the circuit breaker fracture. When a 220 kV line is strucked by lightning, the following two conclusions can be drawn through calculation: 1) the overvoltage value of circuit breaker fracture when line type arrester is adopted on the 220 kV transmission line is 70% higher than that substation type arrester is adopted; 2) the withstand voltage of circuit breaker fracture line type arrester is adopted is 0.92 times of its overvoltage, while the fracture withstand voltage of circuit breaker when substation type arrester is adopted is 1.56 times of its overvoltage. This shows that there is no effective protection of 220 kV line type arrester on circuit breaker fracture, while substation arrester can effectively protect the fracture of circuit breaker. This paper provides basis for the modification of anti-accident measures and the modification of technical standard.

Frequency detection is one of the most important technologies for the grid-connected inverters of the distributed generation system(DGS). However, DC offset and harmonics in the grid voltage often affect the accuracy of frequency detection. Aiming at this problem, an accurate detection method for frequency synchronization of single-phase grid voltage considering DC offset and harmonic impact is proposed. In the proposed method, the influence of DC offset and harmonic is independently eliminated by using an improved quadrature signal generator (QSG) and an adaptive complex filter. In order to ensure that the proposed method have good dynamic response performance and accurate estimated results even in the frequency-varying situations, a robust frequency adaptive controller realized in αβ axis is suggested. Both the feasibility and validity of the proposed method are verified by simulations and experiments.

Zero-sequence mutual inductance is an important factor affecting the fault characteristics of transmission lines on the same tower. In order to get its accurate value in a convenient way, the zero-sequence parameters of the transmission lines on the same tower when soil resistance, tower structure, height, and sag changes are studied. The results show that the effect of tower structure on mutual zero-sequence inductance is significant, besides the accepted soil resistivity. For the multi-circuit transmission lines, those circuits which near the earth, whose zero-sequence self-inductances are significantly larger than those which near the overhead ground wire. Based on that, the law of zero-sequence mutual-inductance/self-inductance ratio influenced by soil resistivity is also studied, and a method of zero-sequence mutual-inductance estimation based on voltage level and tower structure is proposed. PSCAD simulation verifies the good robustness of using subdivision ratio to estimate the zero-sequence mutual-inductance of transmission lines on the same tower, and the method’s accuracy satisfies the engineering requirement.