In order to improve the dynamic response performance of LCC-HVDC transmission system, a controller parameter optimization method based on small-signal dynamic model and transfer function model is proposed. Firstly, a small-signal dynamic model of double-terminal LCC-HVDC transmission system considering the difference between the output phase of the PLL and the actual phase of the AC bus voltage is established, and the simulation results verify the accuracy of the small-signal dynamic model. Based on the root trajectory method, the critical value of the control parameter that causes the instability of the system with small disturbance is obtained. Finally, the small-signal dynamic model is transformed into the transfer function model, and the particle swarm optimization (PSO) algorithm is applied to optimize all the controller parameters by taking the integral of time multipled by the absolute value of error (ITAE) index as the objective function. The simulation results show that the dynamic response performance of the system is improved after optimization.

In order to realize the rapid and accurate closed-loop calculation of high-voltage direct-current (HVDC) system under multiple fault types, dynamic phasor method is used to model the complete HVDC system including converter transformers. Firstly, in the case of AC asymmetry, the deviation of the actual firing angle and the unbalance of each commutation process are analyzed. Then, an advanced dynamic phasor model for converter, which is suitable for asymmetric faults, is proposed. Subsequently, the ideal converter transformer model is replaced with a new one that considers voltage loss, which improves the calculation accuracy of the AC voltage on the valve side. By combing it with the dynamic phasor model of DC line, the simulation process of HVDC system is reconstructed and closed loop calculation is realized. Based on the CIGRE Benchmark standard system, the proposed model is compared with the simulation results from PSCAD, and the result further proves the effectiveness.

DC power grid has the characteristics of low inertia and weak damping, and power surplus caused by disturbance may develop quickly and lead to the breakdown of the power system. Firstly, the mechanism of solving power surplus in voltage source converter (VSC)-based DC grid by AC bus independent operation changing from parallel operation is analyzed. When sending-end station monopolar blocks, AC bus independent operation can prevent the normal polar from loading power initially loaded by faulty polar, thus protecting the normal polar. When receiving-end station monopolar blocks, corresponding polar in normal station can be blocked to eliminate power surplus. DC energy consumption device and this scheme are contrasted and their advantages and disadvantages are analyzed. Strategies to reduce voltage vibrating are proposed. PSCAD simulation of a four-terminal VSC-based DC grid model is performed, which verifies the correctness of the theoretic analysis.

In order to meet the demand of low carbon and cleanliness in the transformation of energy structure, the situation that microgrid participates in the energy market, real-time energy market and carbon trading market at the same time is considered. In view of the high forecasting accuracy and error distribution law of market electricity price, the stochastic programming method is used to deal with its uncertainty. In view of the randomness and intermittence of photovoltaic output, the dynamic robust optimization method is used to deal with it. A two-stage robust optimal scheduling model of microgrid considering the uncertainty of electricity price and photovoltaic output is constructed, and the bad scene identification algorithm is used to decompose the original problem into the main problem and sub-problem iteratively. The sub-problem is used to identify the worst photovoltaic scenario, and the single-layer optimization model under this scenario is solved by the main problem, which greatly reduces the number of scenarios needed and improves the computational efficiency of the model. A numerical example is given to verify the effectiveness of the algorithm, and the results show that the microgrid participating in multiple power markets at the same time can significantly increase profits, and the use of bad scene identification algorithm can reduce the computational burden and effectively improve the computational efficiency, and it is more adaptable in large-scale scenarios.

Automatic generation control (AGC) is an important function in the power system dispatching automation system. The importance of AGC control function is becoming more and more prominent in the unified frequency control and electricity spot market environment. A grid level and provincial level AGC joint closed-loop testing scheme based on real-time simulation is proposed in this paper. Then the communication interface between real-time simulation platform and heterogeneous system of grid-province AGC as well as the real-time closed testing technologies are researched and developed. The data interface methods such as parallel synchronization of multi-GTNET cards and "single terminal interface-data forwarding" are proposed to solve the problem of massive real-time interface data in the grid-province AGC joint closed-loop testing. Finally, the parallel synchronous high-speed communication ability and interface delay characteristics of multi-GTNET cards are verified through the interface test case.

At present, the power grid is carrying out the construction of unified frequency modulation market, and the difficulty of automatic generation control (AGC) function test in the actual power grid will be further increased. Dispatching automation urgently needs a simulation environment that can simulate the actual power grid to support the AGC function test. Real time simulation has the ability to carry out AGC closed-loop test in terms of technical feasibility. In order to verify its effectiveness, this paper builds a AGC closed-loop test system based on real-time simulation, and inverses the actual AGC action events in the field. The test results show that the RTDS real-time simulation model has the ability to simulate the frequency change of large power grid system, and the RTDS system has the ability to apply the closed-loop test with AGC, which can help the AGC function test of power grid.

Due to the lack of physical protection for smart meters (SM) in advanced measurement system (AMI), and a large number of sensitive data will be generated. However, the existing security protection methods can not meet the security requirements of AMI. Therefore, a security protection method for smart terminals and smart meters based on blockchain is proposed to protect SM from network attacks. Firstly, the "cloud edge end" AMI system architecture, which is composed of massive SM, smart terminals (edge computing nodes) and cloud master station, is constructed to realize the local marginalization of most of the data. Then, the link fingerprint is formed by quantifying SM data, and then encoded and transmitted to the smart terminal of the station area, which integrates the credit consensus mechanism to preliminarily analyze the data and strengthen the security protection of AMI. Finally, all smart terminals are regarded as blockchain nodes, and the key information of each SM is taken as the transaction information of blockchain, so as to realize the reliable management of key and data based on blockchain. The received signal strength indicator (RSSI) values obtained by MICAz motes micro wireless measurement system are analyzed based on MATLAB. The results show that when there is network attack in AMI, its Pearson coefficient is negative or approximately zero, and the change of RSSI is no longer linear. Compared with other methods, the proposed method has the least energy consumption and the best security performance.

In recent years, extreme disasters have been the main threat to the power distribution network. Allocation of disaster prevention resources before the disasters is of great significance to promote the power distribution network’s resilience and guarantee continuous power supply of load. However, current allocation strategies have not fully considered the outage risk of each node. This paper utilizes the Bayesian network to calculate the outage probability of each node, and according to it, this paper proposes a pre-disaster resource allocation strategy considering load capacity, importance level, and outage risk. Furthermore, an optimization model for allocating resources has been formulated. By case analysis, the strategy proposed by this paper fully consideres the indices, including outage risks, and reduces the outage risk of the whole network, and thus the resilience of the power distribution system has been promoted. The effectiveness and robustness of the strategy have been validated.

The ultra-low frequency oscillation is caused by the instability of the primary frequency regulation control process due to the negative damping of hydropower unit mechanical torque. In actual operation, the existing monitoring system cannot monitor the mechanical power of the unit, which causes the operator to be unable to identify the dominant unit and quickly calm down the oscillation. This paper analyzes the relationship between the damping characteristics of mechanical torque and electromagnetic torque, and proposes an online evaluation method of mechanical torque damping, which realizes the online identification of the ultra-low frequency oscillation dominant unit, and exits its primary frequency regulation to suppress frequency oscillation. The simulation results and the actual PMU recording curve verify the effectiveness of the proposed method which provides effective technical means for online control of ultra-low frequency oscillations.

In order to perform electromagnetic transient analysis on a part of a large-scale power system by PSCAD, the whole system has to be divided into two parts, namely the internal system and the external system, and then the equivalent simplification of the external system is carried out. Because the equivalent parameters of the external system obtained by Ward equivalent method contain the ground admittance parameters of the transmission line simulated by π equivalent circuit of the internal system, the original system power flow cannot be reproduced after the external equivalent system is spliced with the internal system. For this reason an equivalent method for regional power network based on boundary branch is proposed, by means of the boundary branch with minimum impedance between internal system and external system, the equivalent parameters of the external system obtained by Ward equivalent method will not contain any parameters of the internal system.The proposed method also overcomes the limitations of PSD-SCCP which can only calculate the equivalence of the whole system. And then the specific steps of realizing the equivalence method of external network based on boundary branch by PSD-SCCP are given. Theoretical analysis and results of an actual system simulation show that this method has a high veracity and practicability.

The coordination of directional overcurrent relays considering different topologies is an essential fundamental work for overcurrent relays applied to the power grid projects. In order to solve the problem of difficulty in solving the model of optimal coordination of relays and the poor performance of the obtained relay settings after taking into account different network topologies, a novel method for optimal coordination of directional overcurrent relays under different topologies based on topology grouping and equivalence is proposed. Based on the established network topology description model suitable for relay coordination, the different network topologies are clustered by using the aggregation hierarchical clustering algorithm. The equivalent representative topology of each topology cluster is obtained by calculating the topological trajectory similarity. The model of optimal coordination of directional overcurrent relays based on equivalent representative topology is finally established to determine the relay settings. The results of the case study of the IEEE 30-node power system show that the proposed method effectively can reduce the constraint dimension and guarantee the performance of the obtained relay settings towards different network topologies.

There are few lightning protection measures available for 10 kV overhead lines. In view of their characteristics of being mostly subjected to induced lightning and short circuit trips between phases, single-phase installation of parallel gaps can be used to improve the lightning resistance level. But the exising single-phase different-line installation mode cannot improve the lightning resistance level when short-circuit happens between two phases on different pole bases. Therefore, this paper proposes a new single-phase same-line installation mode, that is to install the parallel gap on only one phase of the same line. According to the characteristics of the 10 kV overhead line, the principle of the installation mode to improve the lightning resistance level is analyzed, and the 10 kV overhead line model is established by ATP-EMTP. Simulation results show that when the single-phase same-line installation of the parallel gap is applied to the 10 kV overhead line, the lightning resistance levels under induced lightning overvoltage and overvoltage by lightning striking at cross-arm, are increased by 84.87% and 103.53% respectively cwompared with those without parallel gap; Comparing with the single-phase different-line installation mode, the increase is 62.26% and 78.35% respectively. However, the lightning resistance level under the overvoltage of the lightning striking on line does not incease significantly. Through experiments and calculations, the optimal distance range of the single-phase same-line installation of parallel gap is 80.01~106.31 mm. Single-phase same-line installation of parallel gap can significantly improve the lightning resistance level of the distribution line when lightning is induced and the cross arm of the tower is struck by lightning, effectively protect the line insulators, and improve the operational reliability of the distribution network.

Insulator icing directly threatens the safe and stable operation of overhead lines, and through space electric field monitoring, non-contact insulator icing status recognition and ice flash warning are expected to be realized. For this reason, the spatial electric field distribution characteristics of 110 kV composite insulators are simulated, the effects of different icing patterns and their discharge levels on the spatial electric field of the insulators are analyzed, and a non-contact icing monitoring method for composite insulators based on the spatial electric field is discussed. Research results show that in three cases of rime, glaze, discharge, the spatial electric field of the composite insulator along with the string distribution are of obvious differences. When the degree of icing increases and electric discharge develops, the insulator spatial electric field amplitude increases. Spatial electric fiels signals are monitored at the cross-arm with d=0.3 m, and directly opposite to the last three pieces of the 110 kV composite insulator, which verifies that it is feasible to identify icing degree and arc development. The results of the study can be used as a reference for overhead line insulator icing monitoring and ice flash early warning.

Low-wind-pressure overhead conductor is a new type conductor that can reduce wind drag coefficient. There is little research on static characteristics and dynamic response of such conductor caused by wind load. This paper carries out wind tunnel tests of low-wind-pressure overhead conductor and conventional steel reinforced aluminum conductor. Variation rules of drag coefficient are obtained. The difference of wind yaw angels and sag between low-wind-pressure overhead conductor and conventional steel reinforced aluminum conductor are obtained by “catenary equation”. Davenport power spectrum is used to generate the time history of fluctuating wind speed. Wind-induced dynamic response model of overhead conductor midpoint is established. Comparative analysis are carried out between the low-wind-pressure overhead conductor and conventional steel reinforced aluminum conductor on the time history of overhead conductor midpoint displacement, trajectory of displacement and the frequency characteristics. Results show that drag coefficient and wind yaw angels of low-wind-pressure overhead conductor are less than the conventional steel reinforced aluminum conductor with the same radius. The difference of maximum sag between low-wind-pressure overhead conductor and conventional steel reinforced aluminum conductor is associated with the wind attack angle. Trajectory of displacement and the frequency characteristics of low-wind-pressure overhead conductor and conventional steel reinforced aluminum conductor are similar when inspired by the same fluctuating wind in high wind-speed area, but the vibration amplitude of low-wind-pressure overhead conductor is smaller.

The inflatable composite cross-arm served under long-term outdoor conditions may deteriorate its sealing characteristic and cause leakage. When the internal gas escapes and the external humid air invades the cross-arm, it will cause flashover inside the cross arm, threatening the security and stability operation of power systems.Therefore, this article explores the influence of leakage on the inner insulation characteristic of the inflatable composite cross-arm. The influences of different internal temperature and humidity conditions caused by the cross-arm pressure leakage on the flashover voltage and leakage current are studied through experiments, and the flashover voltage, leakage current, and pulse number are analyzed. The results show that the influence of temperature on the internal insulation of the crossarm is related to the humidity, and the difference of temperature causes the difference of internal condensation state and then affects its internal insulation performance. Under the same temperature conditions, humidity significantly affects its internal insulation.The absolute humidity values at 20 ℃, 50 ℃ and -30 ℃ increase from 3.5 g/m³ to 17.3 g/m³, and the flashover voltage amplitudes decrease by 24%, 24.7% and 38.7% respectively. Through the leakage current amplitude and pulse statistics combining with microscope observation, It is shown that the inner surface of the cross-arm had different condensation states at different temperatures. The increase in temperature makes the condensation disappear and the flashover voltage increase. The increase in absolute humidity causes aggravation of condensation, which reduces the flashover voltage and increases the leakage current amplitude.

Traditional cable coaxiality detection is based on X-ray machine image feature detection method, which can’t guarantee the detection accuracy quantitatively, has a small scope of application and poor anti-interference ability. In this paper, with the support of automatic image acquisition system, convolutional neural network (CNN) and line detection technology, a set of intelligent cable coaxiality detection method is proposed. Firstly, the collected cable images are intelligently classified by the trained neural network model; the Canny operator edge detection and Hough transform line detection parameters are adjusted according to different image categories to meet the detection requirements; the coaxiality of the cable is calculated according to the inner and outer diameter of the detection result. This method and process make full use of the advantages of automation and intelligence of machine learning algorithm. It is applied to the coaxiality detection of mineral insulated cable with complex production process. The success rate of CNN model classification reaches 96.87%, and the success rate of coaxiality detection reaches 94%, which can meet the technical requirements of real-time detection of enterprises.