With the global trend to develop digital substation automation systems, measurement devices are required to be reliable, of small size and light weight and of acceptable accuracy in a wide frequency band. This article presents a combined high voltage direct current measurement method which comprises the above-mentioned features that makes it suitable for smart grids protection and control applications. The proposed measurement method utilizes Hall sensor array for dc current measurement. DC voltage is measured using a voltage divider circuit while the harmonic currents are measured using a square Rogowski coil made of four straight bars along with a high precision digital integration algorithm. A four-spectral line interpolation fast Fourier transform algorithm based on trapezoidal convolution window is proposed to improve the extraction accuracy of the dc and harmonic components from the measured signal. Experimental results show that the error variation of the proposed method is less than 0.098% for voltage measurement while it is less than 0.104% for current measurement. The harmonic measurement ratio error is less than 0.2% and the angle error is less than 8'.

While frequency response analysis (FRA) is a well matured technique widely used by current industry practice to detect the mechanical integrity of power transformers, interpretation of FRA signatures is still challenging, regardless of the research efforts in this area. This paper presents a method for reliable quantitative and qualitative analysis to the transformer FRA signatures based on a decision tree classification model and a fully connected neural network. Several levels of different six fault types are obtained using a lumped parameter-based transformer model. Results show that the proposed model performs well in the training and the validation stages, and is of good generalization ability.

As maritime technology advances, multi-energy ship microgrids (MESMs) are widely used in large cruise tourism. In this context, studying cost-effective and highly reliable energy system planning methods for MESMs in their whole lifespan becomes paramount. Therefore, this paper proposes a joint planning method for a MESM during its lifespan. Firstly, a long timescale coordinated planning and operation scheme is formulated with the aim of maximizing the Net Present Value (NPV) value, thereby reducing both project investment and energy supply cost. In addition, this paper introduces novel operation models that incorporate customer thermal comfort levels, considering thermal inertia, and ship navigation, accounting for the effects of waves and wind. These models enhance the flexibility and practicality of the planning process. Finally, to ensure the safe operation of vessel and alleviate the negative effects of uncertain wind and waves during ship navigation, a robust optimization (RO) approach is employed. A case study demonstrates the effectiveness of the proposed method, with several comparison analyses further highlighting its advantages.

With the growing global interest in developing future smart grids, nonconventional instrument transformers have been given much attention. In contrary with the classic magnetic core current transformer, electronic current transformer (ECT) does not exhibit saturation, is of small volume, and can generate a digital signal complying with the recent digital communication protocols such as the IEC61850. However, the measurement accuracy of the ECT is influenced by the mechanical vibration caused by the adjacent circuit breaker (CB) operation and the bus bar electromagnetic forces generated due to short-circuit currents. According to the GB/T 20840.8 and the IEC 60044-8 standards, the root mean square of the ECT output current should not exceed 3% of the rated secondary current after 5-ms duration following a CB operation or a large current of a short duration. Current ECT vibration compliance test does not correlate the ECT output current with the CB or the large current signal to correctly identify their ending moment. As such, the current testing technique may reveal inaccurate outcomes. This paper proposes a new vibration testing platform for ECT in which the status of the vibration source is synchronously correlated with the ECT output signal. A status monitoring circuit is proposed and implemented to achieve synchronous acquisition and comparison of the CB status and the ECT output current. In addition, a primary current sensor is designed to accurately realize the end time of any short-time large current. A software platform is developed to correctly identify the CB breaking moment and the end of the large current. The robustness and superiority of the proposed testing platform are validated through extensive simulation and practical analyses.

Due to the rapid development of phasor measurement units (PMUs) and the wide area of interconnection of modern power systems, the security of power systems is confronted with severe challenges. A novel framework based on data for static voltage stability margin (VSM) assessment of power systems is presented. The proposed framework can select the key operation variables as input features for the assessment based on partial mutual information (PMI). Before the feature selection procedure is completed by PMI, a feature preprocessing approach is applied to remove redundant and irrelevant features to improve computational efficiency. Using the selected key variables, a voltage stability assessment (VSA) model based on iterated random forest (IRF) can rapidly provide the relative VSM results. The proposed framework is examined on the IEEE 30-bus system and a practical 1648-bus system, and a desirable assessment performance is demonstrated. In addition, the robustness and computational speed of the proposed framework are also verified. Some impact factors for power system operation are studied in a robustness examination, such as topology change, variation of peak/minimum load, and variation of generator/load power distribution.

Identification of the optimum location and capacity of Static Synchronous Compensator (STATCOM) in power grids has been given much attention to maximize its technical performance while minimizing operational cost. In this regard, a new multi-objective optimization model that minimizes power loss, enhances system stability and reduces operational cost of STATCOMs is presented in this paper. To overcome the issue of the harmony search (HS) optimization algorithm in solving high-dimensional multi-objective optimization problem, an improved differential evolution harmony search (DEHS) algorithm is proposed. In this algorithm, mutation and crossover operations are adopted instead of the original pitch adjustment operation adopted in the HS optimization algorithm, which enhances the algorithm global search ability. Moreover, opposition-based learning technique is incorporated to the process to broaden the diversity of variables and hence improving the search efficiency of the algorithm. The proposed algorithm is employed to identify the optimal allocation and sizing of multiple STATCOMs within the IEEE 30-bus system. Results reveal the superiority of the proposed optimization algorithm over the conventional multi-objectives adaptive harmony search algorithm.