This paper proposes a fault location method based on the adaptive control of neutral-to-earth complex impedance in a resonant grounded system, whose neutral grounds via an Electromagnetic Hybrid Petersen Coil (EHPC). The EHPC can be equivalent to a parallel circuit of a negative resistance and an inductance, both of which can be adjusted respectively. When a permanent single line-to-earth fault occurs, the ground-fault current will be compensated to almost zero, and the capacitance to earth and leakage resistance of system can be measured accurately for subsequent fault detection. Then, the complex impedance of EHPC is adjusted, and the faulty feeder and its faulted section can be identified online based on the characteristics that the measurements of zero-sequence admittances of points along faulty feeder change with system's neutral-to-ground complex impedance. The detection criterion is certain and unique, without comparing all the feeders. This paper also proposes an jitter adjustment and decoupling control of EHPC, which is adaptive to the grounding resistance and is repeatable, can ensure that the magnitude of zero-sequence parameter is large enough to be measured while without arc reignition, including in HIF states. Simulations and experiments verified the feasibility of this detection method and its control strategy.

An improved hybrid unified power flow controller (IHUPFC) is developed in this paper to control power flow and increase utilization rate of the existing transmission lines. The IHUPFC is composed of an improved "Sen" transformer (IST) and a small capacity UPFC. After a detail introduction of the structure and voltage regulation performance of the IST, this paper derives the capacity relationship between the IST and the UPFC. Then this paper introduces the technology of IHUPFC in power flow regulation and transmission capability improvement. Besides, the advantages of the IHUPFC in performance and structure are analyzed. The IST has simpler structure and larger power flow control area than "Sen" transformer and the IHUPFC provides a continuous active and reactive power flow control. Simulation and experiment studies are used to verify the practicability and superiority of the IHUPFC.

The saturated core fault current limiter (SFCL) is one of the most effective methods for limiting fault current. A permanent magnet (PM)-biased SFCL (PFCL) can reduce DC bias current and additional energy consumption. However, the thermal stability of NdFeB PMs in PFCL poses a major challenge. This paper proposes a novel hybrid-type SFCL (HSFCL) topology that can reduce this risk. In the HSFCL, a hybrid PM/DC coil is designed to saturate the core, and a fault-limiting reactor is used to guarantee fault-clipping performance. The new structure provides air-gap branches for the time-varying magnetic field produced by alternating current, which reduces the eddy current in the PMs and enhances their stability. Electromagnetic coupling is used to analyze the operating principles and characteristics of HSFCL. Finite-element analysis simulations were performed using Maxwell and compared with verification experiments, proving that HSFCL is efficient in fault clipping and PM reliability enhancement.

If current transformer (CT) is saturated in operation, it will lead to incorrect current measurements and may cause relay maloperation, which can greatly threaten the safety of power grid. This paper analyzed the basic measuring characteristics of the proposed novel current transformer based on virtual air gap. This method can successfully compensate the distorted secondary current and expand the measuring range. Based on the simplified magnetization curve model, its working state is divided into linear working state, partially saturated working state and saturated state. Furthermore, its basic measuring characteristics are deducted theoretically. The theory is verified by FEM simulation results and prototype experiments. The difference between this method and other methods is also discussed. Compared with CT, this method adopts partial-gapped magnetic core and magnetic field sensor (MFS) for current reconstruction. When it works in rated state, this method is like a normal CT. Once the primary current saturated the small section core, it will be like a virtual gap, making the whole core more difficult to saturate and allowing the measurement of leakage flux. It has the advantages of simple and compact structure and can be embedded into the electronic current transformer (ECT) system. In this sense, it can have a good application prospect. The main limitation is the requirement of high permeability material for accuracy performance.

To achieve economical compensation for the huge-capacity negative sequence currents generated by high-speed railway load, an electromagnetic hybrid compensation system (EHCS) and control strategy is proposed. The EHCS is made up of a small-capacity railway static power conditioner (RPC) and a large-capacity magnetic static var compensator (MSVC). Compared with traditional compensation methods, the EHCS makes full use of the SVC’s advantages of economy and reliability and of RPC’s advantages of technical capability and flexibility. Based on the idea of injecting a negative sequence, the compensation principle of the EHCS is analyzed in detail. Then the minimum installation capacity of an EHCS is theoretically deduced. Furthermore, a constraint optimization compensation strategy that meets national standards, which reduces compensation capacity further, is proposed. An experimental platform based on a digital signal processor (DSP) and a programmable logic controller (PLC) is built to verify the analysis. Simulated and experimental results are given to demonstrate the effectiveness and feasibility of the proposed method.

Soft magnetic composites (SMC) are composed of ferromagnetic particles surrounded by electrical insulation. To establish a homogenization technique for the magnetic field analysis of an electrical machine with a SMC core, we have already proposed a method to evaluate the effective permeability and iron loss of the SMC core using a cell model of one particle taking account of the nonlinear magnetic characteristics and eddy currents. However, the measured eddy current loss cannot be represented by using the proposed method. In this paper, a 3-dimensional eddy current analysis method modeling the anomalous eddy current loss due to the movement of domain walls in the cell model is developed based on the Pry and Bean magnetic domain model. The effect of the nonuniformity of the domain structure on the anomalous eddy current loss is investigated. It is shown that the measured eddy current loss can be almost represented by adding the anomalous eddy current loss to the classical one.