Abstract:As the rated voltage of the transmission line increases, the electromagnetic environment of ultra-high voltage transmission lines has become one of the main factors to determine the tower size. The comparison of the electromagnetic environment is analyzed between the 1 000 kV three-phase double-circuited transmission line and the six-phased 578 kV. The numerical results show that the electromagnetic environment of a six-phased transmission line is much improved with the same tower configuration and nominal tower height. Further more, the characteristic of the electromagnetic environment of a six-phased transmission line with respect to the nominal tower height is studied in detail. With the decrease of nominal height, the electric field strength on the surface of the ground wire and the two highest transmission lines decreases, while that of the other conductors increases. The ground-level electric field, radio interference and audible noise increases as the nominal height decreases. In comparison with a three-phased transmission line with the same phase voltage, the electric intensity on the surface of the conductor of the six-phased transmssion line is much lower than that of the three-phased ones. The six-phased technology of the transmission line can essentially improve the electromagnetic environment of the high-voltage AC transmission lines.

Abstract:DC access capability of the receiving power grid is one of the key issues in the planning and operation of the HVDC transmission system. Starting from the influence of the controllable capacitor commutating converter connected to the weak AC receiving power grid on the commutation failure, based on the analysis of the basic principle and topology of the controllable capacitor commutating converter, a steady-state mathematical model of the controllable capacitor commutating converter is established. In order to get closer to engineering practice and improve control precision, the response characteristics of the DC control system are considered, and the response control strategy of the controllable capacitor commutated converter with the commutation voltage time area as the control target is studied. For the commutation failure caused by short circuit fault, a fault recovery strategy using a MOV-parallel gap combination protection device is proposed to shorten the fault recovery time of the capacitive commutated converter during the fault. Finally, based on the PSCAD/EMTDC platform, the simulation verification and comparison with other schemes prove that the above control strategy is effective in reducing the risk of commutation failure and fault recovery of weak receiving end network.

Abstract:The extensive penetration of open-phase running distributed generators such as photovoltaic generators to distribution systems may lead to a serious three-phase unbalanced condition, which is an intrinsic characteristic of distribution systems. The effect of the traditional evaluation of the power supply capability for distribution network is poor without considering the unbalanced problem. In order to accurately analyze the influence of unbalanced three-phase characteristics on the power supply capability for distribution network, the evaluation model of power supply capability for unbalanced three-phase distribution network with distributed generators is proposed, which takes the maximum load parameter of the distribution network as the objective function, considers the state variables such as branch thermal constraints and nodal voltage, and the control variables such as active and reactive power of the distribution power supply. The phase with the most serious voltage sag is selected as the continuous parameter to ensure the continuation power flow algorithm of prediction and correction is accurate. Finally, the simulation result of the modified IEEE 33-bus three-phase test system shows that the proposed model and method are effective.

Abstract:In order to evaluate the effect of fireproof belt on cable load and temperature,a 220 kV cable carrying capacity verification platform is built in the laboratory to analyze the current carrying capacity and monitoring temperature of high voltage cable for different kinds of fireproof belt. The experiment and theoretical analysis shows that: the temperature gap ratio between of out-and-in fireproofing strip and metal wire core and environment for ceramic fiber, PVC and rubber fireproof are 29.44%, 4.74% and 4.52%, meaning that rubber fireproof belt has the best heat dissipation effect, the PVC fireproof belt is slightly less than that of rubber fireproof belt, and the heat dissipation performance is far better than that of ceramic fiber fireproof belt. Wrapping fireproof belt will reduce cable carrying capacity, the carrying capacity wrapped with ceramic fiber,PVC and rubber fireproof are 81.9%,96.2% and 96.4% of unwrapped cable. When the cable reaches maximum allowable load, the surface temperature of ceramic fiber, PVC and rubber fireproof are 38.7 ℃,52.7 ℃and 52.9 ℃ respectively, lower than the maximum allowable temperature of cable sheath unwrapped fireproof belt. Therefore, in order to ensure the core temperature does not exceed 90 ℃ with maximum carrying capacity in the distributed optical fiber temperature measuring system, the alarm threshold should be reduced accordingly.

Abstract:Power cable conductor temperature is an important parameter to evaluate the ampacity and operation status of transmission line. However, the current cable temperature calculation model can not accurately describe thermal dynamic process of cable operation for ignoring the axial conductor temperature distribution. To solve this problem, a state space model of conductor temperature estimation considering axial heat conduction for middle and low voltage single core power cable was proposed in this paper which based on thermal equilibrium principle. To overcome the shortcoming that the thermal parameters are difficult to accurately calculate, a power cable conductor thermal parameter identification algorithm based on particle swarm optimization (PSO) was proposed. To verify model accuracy, a cable temperature experiment platform was established and the axial temperature of air laying power cable under various current was measured. Comparison of calculation results and experimental results shows that the precision of proposed model is higher than that of IEC 60287 model, the proposed model can meet the precision requirement of middle and low voltage power cable conductor temperature calculation under various current which can be applied to describe the single core power cable thermal dynamic process more accurately.

Abstract:The temperature of the high voltage power cable can reflect the operation status of the cable, and the prediction of the joint temperature can improve the safe operation level of the cable. Using the least squares support vector machine to establish the temperature prediction model for cable joint. Cable joint history temperature, environment temperature, environment humidity and wire core/sheath current ratio can be adapted as the input samples, the surface temperature of the cable joint for the output. Particle swarm optimization algorithm is adopted to dynamically optimize the normalized parameter and regularization parameter to improve the accuracy of prediction, and the concrete steps of the prediction method are given. A 110 kV cable joint in Shanghai is used as an example. The results prove that method can predict the temperature of cable joint with high prediction accuracy. It can also provide a reliable basis for cable temperature detection and early warning system.

Abstract:In order to analyze the influence of grid connected PV power plant on the reliability of power generation system, a multi-state reliability model of PV power plant is established based on the clearness index and fluctuation characteristic, a state division principle of equal interval and equal frequency is proposed,and two state division methods according to different coordinate orders are gave. Then sequential Monte Carlo simulation technology is utilized to assess the reliability of generation system with PV power plant. Simulation results on Roy Billinton test system(RBTS)are in line with measured data demonstrate the rationality of proposed model. Finally, simulation results show that the model with equal frequency division principle and k_DCI/k_VI state division method can get more accurate results in reliability analysis of the generation system with PV power plant.

Abstract:In order to quantify the impact caused by the fluctuation and randomness of wind power, the method of conditional value at risk (CVaR) is proposed to build the spinning reserve model of the electric power system incorporated wind power which includs the conventional unit operation cost, the pollution cost, expected energy not supplied cost and spinning reserve capacity cost in the environment of electricity market, and the model is solved by quantum-inspired and differential evolution algorithm in Matlab environment, and then the advantages of quantum differential evolution algorithm, the impact of different profit risk levels on spinning reserve capacity and the influence of different degrees of confidence on the system total operation cost and the value of CVaR are analyzed by simulation examples. It is concluded that the higher the risk level (the more conservative attitude towards wind power), the smaller the up-down spinning reserve of the system, and the higher the confidence of the up-down spinning reserve capacity of the system, the lower the total operating cost and CVaR value of the system.

Abstract:The energy Internet can utilize a variety of energy sources comprehensively, optimize the scheduling with the redundancy of paths of energy transportation and improve the efficiency and economy. Based on the analysis of the operation mechanism and architecture design, four types of optimal scheduling model are expounded, including the basic model in the steady state, the transient model considering the energy difference, the unified model considering the energy similarity and the model considering the randomness of the system. And the application scenarios, modeling characteristics and solving methods of all kinds of optimization scheduling model are introduced.

Abstract:DC offset in current of circuit breaker is non-ignorable during transmission lines energizing with shunt reactors, especially when transmission lines have a high level of compensation or overcompensated. In most cases, there is a long time without any zero-crossing point of current when energizing, and it will cause arc extinction problem for the circuit breaker if there is a trip operation. Based on the principle of DC offset generation and the failure risks of circuit breakers caused by DC offset, conventional measures to suppress DC offset are discussed,which include addtion of closing resistors for the circuit breaker, reducing compensation degree and controlled closing. A method which combine the controlled closing technology and dynamic delay closing for each phase are proposed, then the risk can be successfully eliminated during transmission lines energizing. The effectiveness of above method is validated by RTDS simulation and field test on several transmission lines.

Abstract:A model of optimal power flow with UPFC and minimum voltage stability constraint is proposed. In the model, equivalent sources of series and shunt side UPFC are built so that amplitude and angle of such sources are treated as variables. Based on Benders decomposition, two sub-models are established. The previous one is OPF model, while the other is used to deal with minimum voltage stability constraint. The coordinated optimization between master and sub-models is established by Benders cut, and the solution of the whole model is finally realized. In the end, southern Suzhou power grid is applied to test the correctness of the above model.

Abstract:With increasing interconnection and interaction among the adjacent microgrids, multi-microgrid is formed. Multi-microgrid has many new characteristics, such as bi-directional power flows, flexible operation modes and different control strategy of inverter interfaced distributed generations (IIDGs), which challenge multi-microgrid protection. Based on the voltage and current distribution characteristics of the line parameters, this paper proposes a new protection scheme for internal tie lines fault of multi-microgrid, which takes the change of measured bus admittance as the criterion. First, measured admittance amplitude of both ends of tie lines, before and after the fault are calculated. Then, comparing the admittance amplitude to select the likely faulty lines. Finally, fault line is located on comparison the phase of measured admittance among the likely faulty lines. This scheme with high sensitivity and reliability, has a simple principle and is easy to be adjusted. PSCAD/EMTDC is used in simulation analysis, and simulation results have verified the correctness and effectiveness of the protection scheme.

Abstract:Based on the least square method and grey relational degree theory, a model for predicting the ownership of electric vehicles is established. The state transition matrix is introduced into the traditional parking demand model to predict the actual parking distribution characteristics of electric vehicles. Based on the Monte Carlo method, this paper aims at electric private cars, electric buses and electric taxis. The charging requirements of electric business vehicles are simulated respectively, and their charging behaviors are simulated respectively. The daily curve of charging load is obtained by simulation. The results show that the peak-valley difference of daily curve of electric vehicle charging load is large, and the demand of electric bus charging load will take up a large proportion.

Abstract:The key to harmonic pollution control in power grid lies is the identification of harmonic pollution responsibility. Aiming at the disadvantage that the traditional harmonic voltage responsibility index is difficult to be implemented into economic accounting, this paper puts forward a definition of the true value of the harmonic active power as a measure index of harmonic responsibility, and discusses its calculation method. In the process of discussion, the equivalent circuit principle and superposition theorem are combined, and the method of double dominant fluctuation difference quotient impedance based on relative phase angle is used to complete the definition and calculation method of harmonic active power responsibility. The calculation of practical cases show that the harmonic active power responsibility index can not only reasonably and quantitatively pay attention to the harmonic pollution responsibility of the side harmonic source, but also is simple in calculation, which is conducive to economic accounting.

Abstract:For distribution networks below 110 kV with power supply task as main, it′s generally protected in remote backup mode, that is, the protection device is a single configuration. However, When the main protection is refused, the remote backup protection can′t selectively eliminate the fault, which reduces the reliability of power supply to some extent. Therefore, it is necessary to study how to improve the protection selectivity in remote backup mode. In addition, when the integrated protection and control equipment is abnormal, protection and remote control function should be blocked, resulting in the primary equipment runs without protection for a long time. Based on technology accumulation of smart substation, this paper introduces an isomeric double configuration scheme of medium and low voltage protection by adding the intelligent interface to realize redundant configuration with lower cost. This scheme can solve the above problems and ensure the selectivity of remote backup protection.

Abstract:Recently, several transformer failures happened due to the corrosive sulfur in insulation oil. Corrosive sulfur in oil can attack insulation winding, leading to the decrease of oil-paper insulation characteristic, the decrease of which brings potential safety hazard to the operation of transformer. Adding the metal passivator into the insulating oil is widely used to suppress the formation of copper sulfide in oil-immersed transformer, which can delay the combination between corrosive sulfur and copper ions. This paper deeply studies the suppression effect of metal passivator benzene (BTA) on the formation of copper sulfide, and the effect of BTA on the properties of insulating oil. The results show that high concentrations of benzotriazole (BTA) showed a good anti-corrosion effect when the oil contained different amounts of the metal deactivator. However, the content of copper ions dissolved in the oil would increase on the contrary. Therefore, the content of BTA added into the insulation oil should be controlled.

Abstract:According to the current technical specifications for infrared diagnostic technology for live equipment, positive temperature rise of 1 K is a criterion for low-value porcelain insulators. However, the 1 K temperature difference threshold is loose in many real cases, which may cause a high miss rate as to the infrared detection. This paper summarizes and statistically analyzes the infrared detection data of porcelain insulators in a provincial electric power research institute. Firstly, the distribution function of low-value temperature difference samples is fitted, and then the log-likelihood, Kolmogorov-Smirnov and AIC criteria are used to test the goodness of fit of the model, and then a low-value insulator temperature difference mathematics based on inverse Gaussian distribution is proposed. The model is used to obtain the model parameters by using the maximum likelihood estimation method, and the error analysis is carried out. Finally, the accurate temperature difference threshold model of the infrared detection low value porcelain insulator is obtained. The research shows that the inverse Gaussian distribution can well fit the low-value temperature difference data, and the resulting temperature difference threshold model can improve the infrared detection accuracy of low-value porcelain insulators, and can be used to reasonably optimize the temperature difference threshold for low-value porcelain insulators.

Abstract:The reliability of ultra-high-voltage (UHV) alternating current (AC) switch-gear and bushing during its whole life cycle has always been a major concern of Power Grid Corporation and manufacturers. The study of long term live test is the key to ensure safe and stable operation of bulk power grid. In this paper, the layout of test field, the technical parameters of main test equipment, impedance calculation of the 1 100 kV/10 kA test loop and the design of auxiliary grounding grid are described in detail. As the gas-insulated switch-gear (GIS) enclosure of 1 100 kV/10 kA power current transformer (power CT) has no external circulating channel, a special copper bar grounding grid is designed to form a complete loop. Its active power consumption, terminal voltage are calculated and verified. Meanwhile, considering that the project is located in the middle thunderstorm region, this paper designs a lightning protection system, which improved the lightning protection level of the test equipment and test object.

Abstract:Leakage currentamplitude of lightning arrester is affected by ambient weather conditions. The model of leakage current is significance for health diagnosis of lightning arrester. In this paper, a model of leakage current of lightning arrester is established with multiple linear regression and ambient weather analysis. Firstly, the factors effect on the leakage current is collected. These factors include ambient temperature, humanity, atmospheric pressure and light intensity. Then, the factors are analyzed by using scatter diagram and trend line and the multiple linear regression model of leakage current is given with the least square. This proposed model is diagnosed with the varianceinflationfactor. Finally, the proposed model is used to predict the leakage current of lightning arrester for next ten days. The predicted results show that the proposed model have high accuracy and can be used in actual engineering.

Abstract:In order to optimize the self-powered supplies on transmission lines, including reducing the volume of the energy power coil and improving its economy, the optimal number of coil turns for self-powered supply is studied. Based on the Jiles-Atherton hysteresis theory, the hysteresis characteristics of the energy power coil are simulated to select the suitable coil material. Furthermore, the calculation method for the optimal number of coil turns, which can make the coils stably work in the unsaturated region, is proposed. Considering installation convenience, open-close coil is used and the influence of its air gap width on the optimal number of coil turns is discussed. The calculation results show that air gap causes the decrease of optimal turn optimal number of coil turns. However, power loss caused by air gap increases significantly with the increase of air gap width, so the air gap width should be reduced as much as possible. Finally, the effectiveness of the design scheme is verified by simulations and experiments.

Abstract:Pole and tower planning of trasmission line is a non-liner and multi-dimensional optimization problem which maybe has an discontinous or underivable objective function,so it is difficult to be resolved by traditional methods such as exhaustive method, trial-and-error method or analytical method. To solve these problems,Nelder-Mead simplex method and exterior point penalty function are used in combination to resolve pole and tower planning problem. The results show that the algorithm, supplemented by the external point method which takes the constraint condition as exponential penalty function to construct the augmented objective function, can easily deal with the constraints of various constraints.This algorithm is efficient 、and robust. It is easy to be programed,while,the possible local optimum should be excluded by engineering experience, so this algorithm has strong applicability.

Abstract:As the latest generation of FACTS device, unified power flow controller (UPFC) can control the system voltage and power flow rapidly, precisely and continuously, which provides an effective means to break the restrictions on urban power grid development. The protection configuration of UPFC project is studied in this paper. Firstly, the 2 out of 3 principle of UPFC self-protection is introduced, and then based on protection system configuration and action strategy, the restart strategy and coordination strategy of UPFC self-protection with AC line protection, transformer protection and other protections is proposed. At last, combining with southern Suzhou 500 kV power grid UPFC project RTDS simulation and system commissioning, the function and effects of the actual protection coordination strategy are given, the results show that UPFC can be effectively protected with the coordination strategy.

Abstract:A vector mode of one-cycle control for single-phase three-level APF is proposed, which can effectively reduce the switching losses by making one leg of single-phase APF work in a high-frequency switching state and the other work in frequency switching state. The working principle of single-phase APF is analyzed. Based on the fully considering of equalization control for the DC side capacitor voltage, five vector modes of one-cycle control for single-phase three-level APF are proposed and their control objectives equations are derived. Simulative results show that the five vector modes of one-cycle control are able to compensate the reactive and harmonic current effectively, which verifies its validity and feasibility.

Abstract:To prevent the series transformer and inverter valve from over-voltage in the Unified Power Flow Controller (UPFC) during system fault, the two wingdings of series transformer should be paralleled with fast bypass devices such as mechanical bypass switch, thyristor bypass switch (TBS), MOV and etc. TBS that utilizes the fast conduction of thyristor is studied. The overvoltage protection principle of UPFC is introduced first, then taking the Nanjing UPFC project as an example, the structure and parameters of TBS are designed, the components selection of TBS is introduced and the overvoltage matching between the BOD protection of TBS and MOV is checked. The performance of TBS is verified by maximum short-time current withstand test in the synthetic test circuit and temperature rise test. In the end, the structure and detection process of the state detection system of the TBS are introduced.

Abstract:Aiming at the operation mode of 110 kV ring network, this paper analyzes the problems existing in the traditional protection configuration scheme, and advances a comprehensive backup protection device for busbar. The comprehensive backup protection of 110 kV line is proposed by using the bus connection breaker′s trip signal of the transformer′s far backup protection, and integrated with the failure protection of the circuit breaker to form a complete solution. When 110 kV line occurs faults, the device can effectively prevent the transformer backup protection′s no selective overstep tripping by current breaker because of the rejection of the single line protection device or the failure of the circuit breaker, reducing the power outage range and improving the reliability of the power supply. Results of simulation and prototype experiment verify the effectiveness of the proposed theory and control strategy.

Abstract:The inter-turn short-circuit fault of the generator rotor winding is seriously threatening the safe and stable operation of the electrical main equipment of the power plant due to the frequent occurrence, the difficulty of fault diagnosis and the serious consequences of the fault. Therefore, how to diagnose the fault of large turbo generator rotor winding inter-turn short circuit becomes one of the most difficult problems to be solved in power industry. In this paper, the causes of short-circuit faults in the rotor turn, the classification of faults and the analysis and diagnosis methods of faults are first introduced. Then, based on the case of short-circuit faults occurring in the rotor windings of the 1 000 MW turbine generators that have just been put into production. The diagnosis method and process of the inter-turn short circuit fault of the rotor are explained. According to the results of the electrical test and the on-site inspection, it is determined that the insufficient copper wire grinding at the corner of the rotor coil is the main cause of short-circuit faults between the rotor turns.