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Abstract A fault properties identification scheme for a hybrid multi‐terminal DC (MTDC) system is proposed to improve the power supply reliability in the system recovery stage. Firstly, a current signal injection strategy based on line commutated converter (LCC) is proposed using the fault control capability. Secondly, the difference between the calculated value (CV) and the measured value (MV) of the current signal under permanent and temporary faults is analyzed for the distributed parameter line model. By introducing the dynamic time warping (DWT) algorithm to represent the difference between CV and MV, a fault properties identification scheme for permanent fault identification is constructed. Finally, the proposed scheme for permanent fault location with the distributed parameter model is obtained by introducing the trust region reflection (TRR) algorithm. The simulation results show that the proposed fault properties identification scheme has the function of permanent fault identification and location. The proposed scheme fully considers the effects of fault impedance, sampling rate, noise, and data loss. It can be applied to high voltage DC long‐distance transmission lines with LCC.

To further improve the performance of distance protection in renewable energy systems, a distance protection method is proposed, which considers the effects of control system and the distributed capacitance effect of the line. When an asymmetric fault occurs in the system, combined with the control characteristics of the converter, the sequence impedance characteristics of the grid and the pure resistive feature of the fault resistance, three unknowns in the fault loop equation can be eliminated, and the solution of the fault distance can be solved in the R-L model. Then, the setting point is set based on the calculation results in the R-L model, and the real electrical quantity at the setting point can be deduced by the calculation formula in Bergeron model. Finally, the equation from the setting point to the fault point is simultaneously solved to reduce the distributed capacitance effect on the distance protection. The simulation results testify that the method is less influenced by the fault features of the converter and fault resistance. It still has good performance in long line.

The coal mine power supply and distribution system usually adopts the neutral point non-effectively grounded method. Most of the power supply lines in this method use cable lines. The underground power supply system is complex and uses many voltage levels. When a single-phase to ground fault occurs, it is easy to form intermittent arcs at the grounding point. Moreover, the existing single-phase to ground fault arc suppression technology of the neutral point non-effectively grounded distribution network has the problem of poor arc suppression effect and difficulty in accurately measuring the parameters of the distribution network to the ground. The most common connection method of transformer winding in 10 kV substation of coal mine in China is delta connection. This mode needs to lead out neutral point and connect arc suppression coil artificially through special grounding transformer (mostly Z-type grounding transformer). In order to solve the above problems, a flexible arc suppression system for single-phase to ground fault of distribution network based on Z-type grounding transformer is designed. When the initial time of grounding fault occurs in the distribution network, the three-phase power supply electromotive force and the neutral point voltage of the power distribution network are firstly measured in real time. When the amplitude of the neutral point voltage is greater than 15% of the three-phase power supply electromotive force, it can be judged as a grounding fault. Compared with the three-phase power supply electromotive force, the phase with the smallest power supply electromotive force is the fault phase. After a single-phase to ground fault occurs, the fast switching switch corresponding to the fault phase is quickly closed. And the active inverter and the Z-type grounding transformer power conversion module are simultaneously put into operation. The Z-type grounding transformer power conversion module clamps the voltage of a neutral point in an opposite phase to be close to the electromotive force of the fault phase power supply. And the amplitude and the phase of the difference between the neutral voltage and the fault phase supply voltage are precisely compensated by the active inverter. Therefore, the control target of suppressing the voltage and the current at the fault point to zero is achieved. After a certain time delay, the fast switching switch is cut off. If the voltage of the neutral point is effectively reduced, it can be judged that the fault is a transient ground fault. And the normal operation of the power distribution network system can be restored. Otherwise, it is judged as a permanent fault. The measures to isolate the fault feeder are taken to restore the normal operation of the distribution network. The simulation results show that when the single-phase to ground fault transition resistance is 500 Ω and 3 000 Ω, the power conversion is only through the Z-type grounding transformer. The voltage and current suppression rate at the fault point reaches 79%-83%, which cannot fully achieve the effect of arc suppression. The flexible arc suppression system can effectively suppress the voltage and current at the fault point, with a suppression rate of more than 98%, realizing reliable arc suppression of single-phase to ground faults in the distribution network.

Most of the existing methods for harmonic analysis are from frequency‐domain perspective. In fact, the essential factor for generating harmonics is non‐linear characteristic or time‐varying property. Therefore, the harmonic generation mechanism and the harmonic source location method are investigated from the time domain perspective in this paper. Firstly, a general model of non‐harmonic sources is established. The non‐harmonic sources will match well with the proposed general model while the harmonic source will not. Then correlation coefficient that reflects compliance degree between each device and the general model is defined for distinguishing harmonic sources from non‐harmonic sources. On this basis, a novel time‐domain harmonic source location method is proposed. Numerous simulations and experiments have demonstrated that the proposed method has good performance under fluctuations, saturations, pre‐distortions, transient process, and resonances. The defined correlation coefficient can reflect non‐linearity/time‐varying degree of the harmonic source, which can be used for evaluating harmonic emission level of each harmonic source. On this basis, a simple harmonic responsibility division method is proposed, which is immune to possible fluctuations, pre‐distortions, saturations, resonances, and impedance variation. [ABSTRACT FROM AUTHOR]

Abstract This paper aims to investigate the feasibility of smart metering system based on narrowband power line communications (NB‐PLC) by using low‐voltage (LV) and medium‐voltage (MV) power line channels. The LV and MV networks of two different sites are selected to carry out comprehensive field measurements to investigate the characteristics of NB‐PLC channels for narrowband frequencies. The NB‐PLC channels of both sites are classified into two categories, that is, bad and good channels of LV and MV networks by considering their characteristics and performance. On the basis of measured results, the simulation models for the modeling of LV and MV NB‐PLC channels are developed and thus proposed. The measured and simulated results are compared to validate the efficiency of proposed methods. A state of the art mechanism for the modelling of capacitative coupling device and impedances of LV and MV networks is developed. It is proposed that simulation‐based NB‐PLC channel models and analyses can play a vital role in examining the residential and industrial types of channels. This research work will pave the way to standardize the future smart metering equipment and sensing devices of power system protection.

This paper investigates the response and characteristics of the narrowband power line communication (NB-PLC) technique for the effective control of electric appliances such as smart air conditioners (SACs) for demand side management (DSM) services. The expression for temperature sensitivity by examining the influence of atmospheric temperature variations on power consumption profile of all possible types of loads, i.e., residential, commercial, and industrial loads is derived and analyzed. Comprehensive field measurements on these power consumers are carried out in Lahore, Pakistan. The responses of low voltage channels, medium voltage channels, and transformer bridge for a 3–500 kHz NB-PLC frequency range are presented for DSM services. The master control room transmits control commands for the thermostat settings of SACs over power lines, crossing the transformer bridge to reach the SACs of power consumers by using communication protocol smart energy profile 1.0. The comparison of hourly and daily power consumption profiles under evaluation loads, by analyzing typical and variable frequency air conditioners on setting thermostat temperature at 25 °C and 27 °C conventionally and then by using DSM control technique, is analyzed. A prominent reduction in power consumption is found with the implementation of the DSM control technique.