Owing to increased capabilities of power quality monitors, synchronized harmonic phasor data are becoming more widely available. Taking advantage of the new data, this paper presents a new and effective method to solve the problem of how to estimate the harmonic impact of several individual loads on the harmonic voltages at a specific location of a power network. The method uses the independent fluctuation of the harmonic sources and is solved as a blind source separation problem. The proposed method has been verified through simulation verification where harmonic currents measured at actual substations are used as input so realistic load fluctuations are considered. Furthermore, lab experiments are conducted to validate the proposed method.
Flicker is an important power quality disturbance and has received an increasing concern from power system researchers. Interharmonics are the non-integral frequencies other than harmonic frequencies. Nowadays, research has shown that interharmonics and flicker seem to be closely related. To clarify this relationship, flicker is characterized in the frequency domain. The traditional Fourier-based methods have shown some drawbacks in representing non-stationary, non-periodic power signals and therefore other methods should be investigated for accomplishing this task. This paper introduces the most common signal processing approaches to assess the problem, power spectrum estimation methods and linear transforms. The wavelet transform has shown superior performance comparing to other methods and circumventing the problem time-frequency resolution.
This paper studies the harmonic impact of modern residential loads on the secondary power distribution systems. Several issues of concern to utilities, such as the neutral-to-earth voltage rise, the overloading of service transformers, the impact of compact fluorescent lights (CFL), and the benefits of adopting IEC 61000-3-2 limits, have been investigated. A bottom-up probabilistic harmonic assessment method proposed in the companion paper was applied to conduct the study. Several interesting results have been obtained. For example, the adoption of CFLs based on market trend could result in an increase of voltage total harmonic distortion by about 10% per year over the next couple of years. Adopting the IEC limits on CFLs will drop the growth rate to 2% per year. In addition to the results of interest to utility companies, this paper demonstrates the usefulness and necessity of a bottom-up-based approach to conduct harmonic assessment for residential loads.
In this brief, an online discrete-time event-triggered cubature Kalman filter (DECKF) is designed to estimate the state of a synchronous generator. First, we define a fourth-order nonlinear model for a single synchronous generator, then we design an event-triggered mechanism to transfer data through the communication channel when the triggered error is above a certain preestablished threshold. We then design a nonlinear discrete-time CKF for the nonlinear system. We show that the data communication between the sensors and the state estimator is reduced, and the state estimation error is bounded if one selects a proper event-triggered threshold. An example is given to verify the performance of the proposed filter.
The effective cable insulation condition monitoring can significantly reduce the outages caused by cable failure. This paper proposes an on-line method for cable insulation monitoring, utilizing the natural power disturbances originated from the outside of cable. In this method, the relative permittivity of cable insulation is used as the indicator to be monitored, which is closely associated with cable tanδ. The relative permittivity is extracted from the power disturbances and their responses, which are of sufficient strength and wide range of frequencies. This method doesn't need the remote synchronized phase angle information of measurements, which is beneficial to the on-line monitoring. The case studies and sensitivity studies are also conducted and the results are presented in the paper.
The data collected by smart meters contain a lot of useful information. One potential use of the data is to track the energy consumptions and operating statuses of major home appliances. The results will enable homeowners to make sound decisions on how to save energy and how to participate in demand response programs. This paper presents a new method to breakdown the total power demand measured by a smart meter to those used by individual appliances. A unique feature of the proposed method is that it utilizes diverse signatures associated with the entire operating window of an appliance for identification. As a result, appliances with complicated middle process can be tracked. A novel appliance registration device and scheme is also proposed to automate the creation of appliance signature database and to eliminate the need of massive training before identification. The software and system have been developed and deployed to real houses in order to verify the proposed method [summary form only given].
Concentric neutral cables are commonly used in medium-voltage power distribution systems. Presently, the cable ampacity calculation methods can take into account only the fundamental frequency current and the harmonic currents in the phase conductors. In reality, the cable neutral can carry fundamental frequency and harmonic currents (induced and unbalanced), leading to a further increase of cable temperature. In view of the increased harmonics and load imbalance in power distribution systems and the need to determine their impact on concentric neutral cables, this paper presents a method to estimate the ampacity of concentric neutral cables, especially for multigrounded neutral systems. The proposed cable derating factor can be used to determine the increase in cable loading caused by unbalanced load and harmonics. A chart is also presented as a simplified method for cable ampacity and cable loading estimation, for which only the total harmonic distortion and zero-sequence current ratio of the phase current are needed.
Flickers and interharmonics have an inherent relationship. The magnitude of a voltage can fluctuate if it contains interharmonics. This paper investigates the amount of voltage fluctuation caused by two interharmonic components since interharmonics are often produced in pairs. The impact of the interharmonics on the flicker frequency and flicker magnitudes (expressed in the form of RMS and peak value fluctuations) is quantified. Analytical solutions to assess the impact are developed. One of the interesting findings of this work is that the two interharmonic components can be equivalenced into one interharmonic component that yields the same level of voltage fluctuation
Summary form only given: A grounding grid of a substation is essential for reducing the ground potential rises inside and outside the substation during a short-circuit event. The performance of a grounding grid is affected by a number of factors, such as the soil conductivity and grounding rod corrosion. Industry always has a strong desire for a reliable and cost-effective method to monitor the condition of a grounding grid to ensure personnel safety and prevent equipments damage. In view of the increased adoption of telecom and sensor technologies in power industry through the smart grid initiative, this paper proposes an online condition monitoring scheme for grounding grids. The scheme monitors touch and step voltages in a substation through a sensor network. The voltages are created by a continuously-injected, controllable test current, which is generated by a pair of thyristors. The results are transmitted to a database through wireless telecommunication.
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