In the power system, the application of the signals transmitted from the sensors to the controller can significantly improve the dynamic performance. However, cyber-attacks and time delays exist widely in the communication network, which has a considerable effect on stability, operation, and control. In this paper, an H_ load frequency control (LFC) scheme for multi-area power systems under cyber-attacks and time-varying delays is investigated. First, false date injection attacks (FDIA), as well as denial of service (DoS) attacks, are viewed as two typical cyber-attacks and introduced into the multi-area power system. Then, the state-space equations of the LFC power system under these two attacks and time-varying delays are analyzed and modeled. Furthermore, by using Lyapunov stability theory and linear matrix inequality (LMI) method, an H_ LFC scheme for attacked and delayed power systems is developed. The purpose of the proposed controller is to guarantee the closed-loop system exponentially mean-square stable with prescribed H_ performance. Finally, a three-area LFC system is employed to demonstrate the effectiveness of the proposed mechanism. The simulation results verified that the control performance of an attacked and delayed system can be improved significantly via the designed controller.

With increasing requirements of online monitoring of Overhead Transmission Lines (OTL) in smart grids, contact-free measurement technologies have been updated these decades. However, the contactless sensors in past research are still limited to the application environment like wind deflection. This paper proposes an advanced detection approach with a novel structure to enhance the possibility of implementation and reduce cost. Three pairs of detection probes arranged in a curved pattern can collect differential voltage signals based on the principle of electric field radiation. With three-phase vector decomposition, the 9 unknown variables including voltage to be measured and status of lines (sag and wind deflection) in 9 equations can be constructed. The voltages to be measured can be calculated by solving this nonlinear equation system by iteration. Also, the position of the device installation is optimized by Particle Swarm Optimization (PSO) algorithm regarding accuracy. The whole measurement device can be easily implemented on the towers according to the distance of insulation requirement regardless of the position of lines. The simulation of level 110 kV is investigated and a model system is built to measure a lower-level voltage for verification. The results show that the proposed non-contact OTL voltage approach can reach the desired accuracy with low costs and monitor the status of lines.

The contact-free measurement of current and voltage technologies are key points to achieve online monitoring tasks in the modern power system, which are updated in these decades. However, ensuring accuracy and a convenient level of operation in the meanwhile is also a difficult task that needs to be solved in advance. Besides, there are unidealized situations in the process of application of existence measure methods. According to the principle of electric field radiation, this paper proposes a non-contact voltage measurement approach based on three pairs of dual-probes circle measurement structures to measure the voltage of transmission wire online. Compared with the other methods, firstly, in this proposed approach, the sensor structure is optimized to be simple, low-cost, and easy to install and operate. Secondly, the potential error in the measuring process caused by the other electric field in the environment is eliminated with dual probes, and the influence of unidealized situations like off-center wire can be also avoided by calculating algorithm. Third, in no matter DC (Direct Current)/AC (Alternating Current) monitoring scenarios, with the proposed structure and methodology, the accuracy can be ensured to reach the acceptance level (below 1.63 %) even when the core of the wire to be measured is in any position instead of in the center. In the final, the simulation results and circuit tests verify these advantages to encourage us to implement them in the realistic power system.

The non-intrusive condition monitoring of overhead transmission lines is a key method to ensuring the safe and stable operation of transmission systems. Especially, their sag/wind deflection are important parameters that should be monitored along with its current. In this paper, an innovative approach for non-contact and cost-effective monitoring of High Voltage Overhead Transmission Lines (HVOTLs) is developed, utilizing three uni-axis magnetic sensors strategically positioned on the tower, below (or above) the transmission lines. Initially, a magnetic field decoupling method in the context of spatial state variations across multiple conductors is proposed. Subsequently, an algorithm is presented to perform sag estimation, wind deflection detection, as well as current reconstruction. The efficacy of the proposed approach is corroborated through numerical simulations and finite-element analysis (FEA). Further validation is achieved using a scaled-down model in laboratory, reinforcing the practical feasibility of the method.