Zero-sequence Parameters Research Articles

Geographic information data processing and physical simulation for power transmission lines

To address the issue of traditional transmission line characteristic parameter testing methods being susceptible to external environmental interference. Proposed a method for processing geographic information data of transmission lines and physical simulation. Firstly, the parameters of the transmission line are tested, a model is established at both ends of the transmission line, and variable frequency signals are collected using 3D GIS technology to develop a lead control box for transmission line parameter testing. Then, the transmission line parameters are calculated online, and real-time voltage and current measurements are conducted at both ends of the transmission line. A zero sequence current simulation diagram of the transmission line is constructed, and circuit parameters are calculated based on the simulation results, Finally, measure the zero sequence parameters of the transmission line using electricity and obtain the zero sequence impedance value of the transmission line using the least squares method. The six zero sequence parameter values were measured in a disturbance environment. The results show that when the power line reaches a certain length, the error of the traditional method has reached 50%, and the testing error of the method studied by the author is less than 3%. The measurement error value of the transmission line characteristic parameter test method based on 3D GIS technology is less than that of the traditional method.

Upgrading low-voltage network models for power quality investigations with a focus on voltage unbalance

An increasing number of high-power devices in low-voltage distribution grids, such as electric vehicles, can cause a significant decrease in power quality. For simulative investigations of the impact of future network usage, valid simulation models of low-voltage networks are necessary. A network model generator has been used to create such network models. Those models have been extended by zero-sequence parameters to allow the simulation of unbalanced load situations. The models have been validated by building the model of a field test network and by using measurement data obtained in field measurements. A final comparison with well-esta

New method of measuring the zero-sequence distributed parameters of non-full-line parallel four-circuit transmission lines

This paper proposes a measurement method of zero-sequence distributed parameters for non-full-line parallel four-circuit transmission lines. Considering the distribution effect and different parameters of each part of the transmission lines, the distributed parameter models are used for modelling. Deriving the line models’ transmission equations by applying the Laplace transform to the Telegrapher’s Equations. Synchronously measuring voltages and currents at two ends of the transmission lines under four measurement modes, and substituting the zero-sequence phasors into the total transmission equations to calculate the elements of the transmission matrix. According to the elements of the transmission matrix and intermediate variables, 24 zero-sequence distributed parameters of the whole transmission lines can be calculated, including 6 zero-sequence parameters of the double-circuit part and 18 zero-sequence parameters of the four-circuit part. The simulation results by using PSCAD/EMTDC show that compared with the traditional method, the proposed method overcomes the influence of distribution effect and considers the parameters are different due to the different electromagnetic coupling relationships, and the measurement accuracy is greatly improved. The sensitivity analysis of the line parameters shows that the proposed method can be applied to non-full-line parallel four-circuit transmission lines under arbitrary mixed voltage conditions. The simulation analysis under noise environment and measurement errors shows that the proposed method has strong anti-noise and anti-measurement-errors ability.

Study of Partial-Phase Steady-State Operation Modes of Phase-Shift Transformer with Hexagonal Circuit and Regulating Autotransformer

The scope of the work was the study of the phase failure operating for the new FACT’s type phase-shifting device, intended for the flexible connection of AC power systems. The mathamatical model has been developed for conducting this study. The device contains the main phase-shifting transformer based on hexagon circuit with additional regulating autotransformer, this creates the possibility of circular regulation of phase shift angle between connected systems. The model includes two 6-winding three-legs transformers, for which two sets of parameters can be independently set based on the data for the short circuit and no-load modes. The data for the direct sequence parameters is usually provided by the transformer manufacturers, and the data for the zero sequence parameters could be obtained upon additional request. As a result of modeling, the vectors of the voltages and currents were obtained in all windings in the investigated modes with supply source phase failure. This makes it possible to analyze the admissibility of such modes and estimate the need for taking special measures of protection against them. It is shown that the voltages on the windings of the main transformer insignificantly depend on the connection mode of the regulating autotransformer, while the pattern of currents distribution in the windings of the main and regulating transformers to a large extent is determined by said connection mode of the autotransformer. The presence of perceptible zero-sequence current flowing through the grounded neutrals of the power supply source and load is noticed. This fact is connected with the release of insignificant magnetic flux from the magnetic circuit in the surrounding space

Air Gap Inductance Calculation for Transformer Transient Model

Zero sequence characteristic and parameters play a vital role in some transformer transients involving unbalance or saturation conditions such as inrush, ferroresonance, and Geomagnetically Induced Current (GIC). An important parameter of the zero-sequence characteristic is the inductance of the air gap between the core and the tank. Based on a Finite-Element Method (FEM), this letter determines the air gap inductance, considering fringing flux effects. The comparison of the simulation results with an analytical method shows a good agreement for small air gaps but reveals a significant difference for relatively large air gaps. Thus, an inductance enhancement factor (IEF) is introduced to correct the analytical results and facilitate the transformer modeling parameter estimation from the design data. Furthermore, the significance of the accurate calculation of the air-gap inductance is demonstrated in the time-domain simulation of different saturation levels of the transformer core, when the transformer is subjected to GIC.

Effects of imbalance on single-phase to ground fault characteristics in low-resistance grounded systems

Single-phase to ground faults (SPGFs) are common in low-resistance grounded systems (LRGSs), a type of medium-voltage power distribution network (MVDN). Imbalance is one of the main characteristics of MVDNs. However, there has been little research on the effects of imbalance on SPGF characteristics in LRGSs, especially from the perspective of theoretical analysis. Hence, in this study, a controlled source-based simplified linear model suitable for calculating SPGFs in unbalanced LRGSs is proposed. Based on the model, the effects of unbalanced loads and asymmetrical lines on SPGF are discussed. The analysis results show that “zero-sequence (ZS) parameter intrusion” of loads is absent in LRGSs, and asymmetrical line parameters have a substantial effect on the phase angle between the ZS line current and the ZS bus voltage, which is related to the fault resistance, fault phase and line parameters. Finally, two phase-related detection methods are analyzed, and both methods produce erroneous detection results. Therefore, it is recommended that the effects of imbalance be considered when using detection methods based on the relationship between the voltage and current in LRGSs.

Improved Finite-State Model Predictive Current Control With Zero-Sequence Current Suppression for OEW-SPMSM Drives

In order to suppress zero-sequence current (ZSC) for open-end winding surfaced permanent magnet synchronous machine (OEW-SPMSM) drives with single dc voltage source, many methods have been employed. Actual solutions imply either proportional-integral-based control or direct torque control cannot present the characteristic of fast dynamic responses and low torque ripples at the same time. Hence, finite-state model predictive current control (FS-MPCC) based on a cost function with ZSC suppression was proposed. To suppress model parameter mismatch, many previous works have proposed related strategies but few work considered zero-sequence parameter disturbances such as zero-sequence inductance, resistance, and rotor flux linkage disturbances. This article improves the ZSC prediction model based on the previous ZSC errors and zero-sequence voltage deviations, and at the same time ZSC is reduced. A comparison between the conventional FS-MPCC and the improved one is carried out in simulation and experiment to verify the effectiveness of the proposed FS-MPCC scheme.

Fault Location in Resonant Grounded Network by Adaptive Control of Neutral-to-Earth Complex Impedance

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 point grounds are 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. 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 location. 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 the faulty feeder change with the system's neutral-to-ground complex impedance. The detection criterion is certain and unique, without comparing all of the feeders. This paper also proposes an adaptive jitter adjustment and decoupling control of neutral-ground complex impedance by EHPC, which is adaptive to the grounding transient resistance and is repeatable, and can ensure that the magnitude of the zero-sequence parameter is large enough to be measured while without arc re-ignition, including in high impedance fault states. Simulations and experiments verified the feasibility of this fault location method and its control strategy.

Estimation of zero sequence parameters of mutually coupled transmission lines from synchrophasor measurements

The authors consider the problem of estimating zero sequence parameters of a transmission line using synchrophasor data. When a set of three-phase transmission lines share, partial or complete, right of way, then their zero sequence models exhibit mutual coupling. As such the zero sequence parameters cannot be estimated by linear least squares or total least squares (TLS) technique which are the preferred methods when dealing with the positive sequence line parameter estimation problem. Further, method design has to factor the constraint of a sparse data set when dealing with zero sequence phasors. Therefore, the authors propose orthogonal distance regression approach for solving the zero sequence parameter estimation problem. This generalises the method of TLS to the non-linear parameter estimation problem considering noise in both the voltage and current synchrophasor measurements. Extensive case studies and comparative evaluations are presented to demonstrate the efficacy of the proposed approach.

New Approach for Precisely Measuring the Zero-Sequence Parameters of Long-Distance Double-Circuit Transmission Lines

Based on transmission-line equations and the distributed parameter model, a new approach is proposed to accurately measure the zero-sequence parameters of long-distance double-circuit transmission lines using voltages and currents measured at the ends of lines. The mathematical model of the proposed method is explained in detail, and the differential equations of two coupled lines with different self parameters were solved for the first time with Laplace transform to obtain all of the zero-sequence parameters. And this approach is easy to implement since the measurement process is simple. PSCAD simulation experimental results of double-circuit 500 kV transmission lines with line lengths changing from 200 to 1000 km and a comparison of the measurement results between the proposed method and the traditional method are shown. Simulation experiments validate that whether the two lines are short or long, the new approach has high accuracy even if there is system white noise and interference from other coupled lines.

A Bayesian Approach for Fault Location in Medium Voltage Grids With Underground Cables

This paper proposes a statistical approach for section-based fault location in medium voltage (MV) grids with underground cables, using Bayesian inference. The proposed approach considers several important uncertainties in the MV grid, including measurement errors, fault breakdown resistance, and the inaccuracies of zero-sequence parameters. The approach first obtains the prior distribution of the fault position from the component failure database, the readings of the transmitted fault indicators, and the relevant digging activity record. With the estimated prefault grid status and the measured transient voltages/currents, the posterior distribution is then calculated based on Bayes’ theorem. To solve the problem numerically, the Monte Carlo integration is applied and a two-step calculation procedure is proposed. Simulations are performed on a typical European MV feeder to demonstrate the feasibility of the approach. The distribution grid operators can use the calculated posterior distribution to rank the possible faulted sections and to facilitate the restoration process, which can reduce the interruption duration of power supply.

Study on Mixed-Measurement of Zero-Sequence Parameters of Two Parallel Coupled Transmission Lines

Based on WAMS technology and the demand of real projects, a method of mixed measurement of zero-sequence parameters for two parallel coupled transmission lines is proposed. The principles and specific methods of mixed measurement mainly based on the incremental method are explained in details.The mathematical model is given and a digital simulation of coupled transmission lines with different zero-sequence parameters is conducted to verify the method.

Live Line Measuring the Parameters of 220 kV Transmission Lines with Mutual Inductance in Hainan Power Grid

A live line measurement method for the zero sequence parameters of transmission lines with mutual inductance is introduced. The mathematical models of the measurement method are given. Global Positioning System (GPS) is used as the synchronous signal for the measurement carried out at different substations simultaneously. The measurement system and digital simulation results are given. Finally, the live line measurement results of two 220 kV transmission lines with mutual inductance in Hainangrid are given. Results from both simulation and on-site measurement show that the live line measurement method is feasible, and its measurement accuracy can satisfactorily meet the requirements of engineering measurement.

Transmission line parameter identification using PMU measurements

AbstractAccurate knowledge of transmission line (TL) impedance parameters helps to improve accuracy in relay settings and power flow modeling. To improve TL parameter estimates, various algorithms have been proposed in the past to identify TL parameters based on measurements from Phasor Measurement Units (PMUs). These methods are based on the positive sequence TL models and can generate accurate positive sequence impedance parameters for a fully transposed TL when measurement noise is absent; however, these methods may generate erroneous parameters when the TLs are not fully transposed or when measurement noise is present. PMU field‐measure data are often corrupted with noise and this noise is problematic for all parameter identification algorithms, particularly so when applied to short TLs. This paper analyzes the limitations of the positive sequence TL model when used for parameter estimation of TLs that are untransposed and proposes a novel method using linear estimation theory to identify TL parameters more reliably. This method can be used for the most general case: short/long lines that are fully transposed or untransposed and have balanced/unbalance loads. Besides the positive/negative sequence impedance parameters, the proposed method can also be used to estimate the zero sequence parameters and the mutual impedances between different sequences. This paper also examines the influence of noise in the PMU data on the calculation of TL parameters. Several case studies are conducted based on simulated data from ATP to validate the effectiveness of the new method. Through comparison of the results generated by this novel method and several other methods, the effectiveness of the proposed approach is demonstrated. Copyright © 2010 John Wiley & Sons, Ltd.

Object-oriented sequence-domain representation of transformers for network analysis

An object-oriented admittance matrix representation of transformers with any number of circuits is developed for direct use in modern network analysis programs. An analysis of manually adjusted and load-tap-changing taps shows that the effective impedance can vary by 2:1 over the full range of taps and should therefore be considered-for accurate network studies. The principal innovation lies in the preservation of the neutral nodes of Y-connected circuits by including their axes in the admittance matrix. This makes it possible to attach neutral impedances and connections to the neutral points, retaining their identities also instead of modifying the transformer zero-sequence parameters to account for them. Conversion of the transformer admittance matrix to engineering units makes it possible to use neutral impedances in ohms without conversion to any per-unit base.

Zero-sequence dynamic braking and parameter determination

The performance of AC and DC zero-sequence dynamic braking is compared with conventional DC dynamic braking. In addition, a method of determining the zero-sequence parameters and parameter variations of a 3-phase squirrel-cage induction motor, having a current-displacement rotor, is described. It is indicated how these parameters may be used to help determine the type of dynamic braking system to be employed in a practical situation.

The zero-sequence parameters and performance of three-phase induction motors

The authors have already demonstrated1 that zero-sequence currents can produce a finite torque in a 3-phase induction motor, and that it is the predominant component torque in certain cases of asymmetrical connection. The present paper shows, for the first time, how the relevant parameters for zero-sequence operation may be determined from certain test results, and how they may be utilized to predict the performance of the machine when zero-sequence voltages only are applied to the primary winding.It is suggested that the considerable torque available may find useful application in providing a speed reduction of 67% for brief periods of operation.

The zero-sequence parameters and performance of three-phase induction motors

The zero-sequence parameters and performance of three-phase induction motors