Systems Overall introductionMicro physical simulation system of electric power system contains all the modules in the actual system, including micro generation, transmission, transformation, load, and synchronous monitoring systems.Micro generation module contains the simulations of prime motor, generator, AGC (Automatic Generation Control) and AVC (Automatic Voltage Control) in traditional thermal power generation and hydroelectric power generation.It also contains the simulations of renewable energy generation and nuclear power generation.Micro transformation module contains the simulations of transformers with
High impedance arc faults (HIAFs) happening in the medium-voltage distribution system may result in damages to devices and human security. However, great difficulties exist in identifying these faults due to the much weaker features and the varieties when grounded with different surfaces. This paper presents an integrated algorithm to detect the HIAFs with high-resolution waveform data provided by distribution-level PMUs deployed in the system. An improved arc model is proposed, which can continuously imitate the randomness and intermittence during the "unstable arcing period" of arc faults. The integrated algorithm consists of two branches. First, the variations of HIAFs during unstable arcing period are identified with the unified harmonic energy and global randomness index, which can unify the scales of harmonic content in different fault situations and enlarge the disparities from non-fault conditions. Then, the waveform distortions of HIAFs during the stable arcing period are identified with discrete wavelet transform to extract the detailed distribution characteristics. The reliability and security of the proposed algorithm are verified with numerical simulations and field tests in a 10-kV distribution system.
It is determined by the nature of AC power grid that the disturbance in high voltage power grid can be reflected in low voltage power grid to some extent. The idea of the light synchronized phasor measurement unit (PMU Light) and that of the light wide-area measurement system (WAMS Light) was proposed and implemented in low voltage grid. Comparing the data recorded by WAMS and that recorded by WAMS Light, it is clear that the dynamic responses in high voltage power grid and low voltage power grid are strongly correlated. WAMS Light has already recorded several typical large disturbances. So WAMS Light has a broad application prospect in many fields. It also enlightens scholars to dig the value of the dynamic behavior of low voltage grid, the grid measurement theory, and even the way of the decentralized control of the power system.
Accurate modeling of arc is significant for the researches on the high impedance arcing fault (HIAF), which performs variations of nonlinear distortions under different fault conditions. The diversity of the waveform distortions during HIAFs is rarely investigated previously. This paper proposes a black-box HIAF model to simulate the nonlinear distortions of currents with improved controllability and higher accuracy. Firstly, with field HIAFs experimented in a 10 kV distribution network, three major characteristics varying in the distortions of currents are summarized and illustrated, including the offset, extent, and duration. Secondly, a distortion-controllable (DIST-C) HIAF model is proposed based on the heat balance equation after mathematical assumptions and transformations. The three characteristics of distortions can be independently controlled by the proposed model, specifically, by the three parameters with practical meanings. After illustrating the implementation of the model in PSCAD, an automatic parameter determination method is presented by taking advantage of the particle swarm optimization in a Python-PSCAD-MATLAB co-simulation platform. Finally, the controllability and accuracy of the proposed model are verified by comparing it with the existing typical black-box models.
Phasor measurement is widely used in fault detection and localization of power systems. To improve the phasor measurement accuracy when the fault signal contains the decaying dc component (DDC), this article proposes a half-cycle DFT (HCDFT)-based phasor estimation algorithm. The error caused by DDC is estimated and removed from the phasor estimate by combining multiple HCDFT results that are computed using both the conventional basis vector and its corresponding complex conjugate. Both the numerical tests and the IEEE 39-bus system simulation tests are implemented to evaluate the performance of the proposed algorithm in comparison with four related phasor estimation algorithms. Test results show that the proposed algorithm can achieve accurate phasor estimation in the presence of DDC of a wide range of time constants under the interference of harmonics and noise. Moreover, the proposed algorithm is computationally efficient and its performance is independent of sampling rate. These merits make the proposed algorithm suitable to be applied in measurement and protection devices in real power systems.
In the active distribution networks (ADN), the interharmonic distortion level is aggravated due to the growing penetration of distributed generations and wide application of power-electronic loads. The interharmonics, even at a low amplitude level, can cause power-quality problems, deteriorate the measurement accuracies of the advanced metering infrastructures, and increase the possibilities of power system oscillations. In this paper, an interharmonic detection scheme is proposed to effectively extract the interharmonic components of the power system even with the extremely noisy signals, and then to estimate their frequencies and magnitudes. In the scheme, a totally data-dependent threshold is proposed to detect interharmonics adaptively. This adaptive threshold is determined iteratively based on the statistical character of the background noise bins. And then the time-varying frequencies and magnitudes of the detected interharmonics are estimated using the time-domain method. Case studies show that the adaptive threshold is robust under the conditions with high noisy signal, and the proposed scheme can estimate precisely the frequencies and magnitudes of the interharmonics detected for both the steady-state and dynamic interharmonic conditions. Furthermore, the proposed scheme is also verified using the field 10-kV current signal of one fuel company and 0.4-kV voltage signal of one electric vehicle's charging station.
In the active distribution network (ADN), the interharmonic distortion level is aggravated due to the growing penetration of distributed generations and wide application of power electronic loads. The interharmonics, even at a low amplitude level, can cause power quality problems, deteriorate the measurement accuracies of the advanced metering infrastructures, and increase the possibilities of power system oscillations. In this paper, an interharmonic detection method is proposed to effectively detect the interharmonic components of the power system even with the extremely noisy signals using a totally data dependent threshold. This adaptive threshold is determined iteratively based on the statistical character of the background noise bins. Case studies show that the adaptive threshold is robust with severely noisy signal for both the steady-state and dynamic interharmonic conditions.
Fundamental phasor plays a prominent role in fault identification, location, and clearance. However, because of the transient process of fault transmission line and current transformer (CT), the fault current trends to contain decaying dc component (DDC). This makes it difficult for the precision of phasor estimation algorithm to meet the requirements of advanced applications based on fundamental phasor. In order to eliminate the adverse effects of DDC, a Full-cycle DFT(FCDFT)-based phasor estimation algorithm is proposed in this paper. The sum of four quarter-cycle samples at interval combinations are utilized to extract and remove frequency domain error terms introduced by DDC into the fundamental phasor. The algorithm is compared with existing techniques in MATLAB environment. The comparison results reveal the proposed technique can eliminate DDC interference with any decay time constant under noise with a small amount of additional computation based on traditional DFT. Moreover, the proposed algorithm has strong robustness to interferences.
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