Deterioration Of Power Quality Research Articles

A high power quality anti-islanding method using effective power variation

Islanding phenomenon is undesirable because it leads to a safety hazard to utility service personnel and may cause damage to power generation and power supply facilities as a result of unsynchronized re-closure. In order to prevent the phenomenon, various anti-islanding methods have been studied. Until now, frequency or start phase shift methods of inverter current have much attention as active anti-islanding methods, which cause reactive power variation to the utility. However, these methods deteriorate usually the power quality like power factor or harmonic performance. This paper proposes a high power quality active anti-islanding method using effective power variation, which is implemented by periodically increasing/decreasing variation of inverter current magnitude. If it causes the large variation of inverter output voltage after islanding, active frequency drift (AFD) method as a simple anti-islanding method will be injected into the inverter current for a designed period and islanding can be detected. In case of large voltage variation when the grid is connected, AFD method will be removed after the designed period. Unlike most active anti-islanding method deteriorating power quality, the proposed method will have high performance of islanding detection and good power quality. For the verification of the proposed method, simulated results and experimental results in addition to analysis are presented using a 3 kW PV inverter.

Prony Analysis for Power System Transient Harmonics

Proliferation of nonlinear loads in power systems has increased harmonic pollution and deteriorated power quality. Not required to have prior knowledge of existing harmonics, Prony analysis detects frequencies, magnitudes, phases, and especially damping factors of exponential decaying or growing transient harmonics. In this paper, Prony analysis is implemented to supervise power system transient harmonics, or time-varying harmonics. Further, to improve power quality when transient harmonics appear, the dominant harmonics identified from Prony analysis are used as the harmonic reference for harmonic selective active filters. Simulation results of two test systems during transformer energizing and induction motor starting confirm the effectiveness of the Prony analysis in supervising and canceling power system transient harmonics.

전기철도 급전시스템의 순시전압강하 보상을 위한 단상 배전 STATCOM의 적용

AC 전기철도 시스템은 동적 단상부하가 빠르게 변화하고, 전철 급전변전소에서 3상 전력을 단상 전력으로 변환한다. 이것은 일반 배전 시스템과 비교해서 AC 전기철도 시스템의 전기적인 현상들이 다르다는 것을 나타낸다. AC전기철도 열차부하의 전기적인 특성은 동적부하의 운영과 운행 스케쥴, 트랙의 구배 등에 따라 연속적인 변화를 받고 있다. 이와 같은 열차부하의 운영에 따른 급전거리가 길어 전압강하, 전압 불평형 및 고조파 왜곡현상 등의 전력품질 저하요인이 발생하게 된다. 이러한 문제점은 상위계통인 송전시스템의 안정도에 악영향을 줄뿐만 아니라, 전기철도 급전시스템의 전력품질 저하, 전기철도차량의 통신장비, 운행 및 수송량 제한에도 영향을 미치게 된다. 따라서 본 논문에서는 전기철도시스템의 과도상태 평가를 위해 PSCAD/EMTDC를 이용한 평가모델을 제시하고, 전압 강하에 주안점을 두어, 전기철도 급전시스템의 말단 분기점(Sectioning Post)에 정지형 무효전력 보상장치인 단상 배전 STATCOM(Single-phase Static Synchronous Compensator)을 설치하여 그 작용에 따른 전압강하 보상을 평가하였다.

需要家の二次電池を用いた系統制御手法とその検証

Advanced energy storage systems have been widely applied to industries and are being installed at large buildings and factories to realize efficient energy usage. This paper presents a control method involving load frequency control and distribution network control (loss reduction control) using a part of customers' owned battery capacity. When 10% of total battery capacity of 100 MW in a network of 30-GW generator capacities is used for load frequency control, a total of 1500-MW generation units for load frequency control, at maximum, can be stopped without deterioration of power quality. In addition, when batteries are used for loss reduction in a distribution network, 2% of the loss on a summer day can be reduced. To realize both effects to their fullest, a novel integrated control algorithm is proposed and its economic effect is evaluated by numerical simulations. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(4): 11–20, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20704

Study on power fluctuation characteristics of wind energy converters with fluctuating turbine torque

In recent years the installed capacity of wind power generation has significantly increased in countries including Japan. This increase has given rise to growing concerns over the power quality of a power system with large penetration of wind power because fluctuation of its output power is significantly larger than that of conventional power sources. Tower shadow effects, the fluctuation frequency of which is determined by rotating speed of wind turbine, considerably contribute to the fluctuation. While a power fluctuation due to tower shadow effects can cause flicker and thereby deteriorate power quality, its amplitude varies with constants of induction generators and impedance of the distribution/transmission system connected to the generators. This paper examines the relationship between the amplitude of the power fluctuation in the input torque of induction generators while making machine constants or back impedance at the connection point parameters. The study derives a transfer function describing the relationship by linearizing related differential equations and verifies its validity through a simulation study with MATLAB/Simulink. Implication of the results on amplitude of 3p components of wind power output is discussed. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(4): 1–11, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20221

Compensation of Flicker Emitted by Wind Turbines

Changes and pulsations in the active and reactive powers generated by wind turbines due to wind speed variations and tower shadow effect may cause serious problems in operation of isolated or distant areas of power grids. Particularly resulting flicker effect may deteriorate power quality in connected power networks. Use of doubly fed machines with suitable control method may substantially reduce impacts of these phenomena. Vector control of doubly fed machines is analyzed and discussed in the paper with respect to the compensation of varying mechanical torque produced by wind turbines.

Phase balancing using mixed-integer programming [distribution feeders

Unbalanced feeder systems cause deteriorating power quality and increase investment and operating costs. Feeder reconfiguration and phase swapping are two popular methods to balance the systems. For an unbalanced feeder system, feeder reconfiguration is difficult to meet the phase balancing criterion due to the limited number of sectionalizing switches available. Phase swapping is another alternative and direct approach for phase balancing. Phase swapping has not received its deserved attention due to the complexity of feeder systems, the dimension of problems, and totally overlooking the impacts of phase imbalance. Phase swapping can economically and effectively balance the feeder systems to improve power quality and reduce power system total cost. Deregulation arises competition on power quality, service reliability and electricity price. Therefore phase swapping can enhance a utilities' competitive capability. This paper proposes a mixed-integer programming formulation for phase swapping optimization. Single-phase loads are treated differently to three-phase loads. Nodal phase swapping and lateral phase swapping are also introduced. An example is used to illustrate the proposed method.

Attributing harmonics in private power production

The deregulation of the electric power industry raises new concerns for equitable attribution of harmonics between the private power producers and the rest of the power network. This paper presents a concept for sharing the responsibility for harmonics. The sharing is based solely on measurements during the operation and at the point of connection. The concept is also applicable to other types of steady-state power quality deterioration, namely repetitive RMS fluctuations, waveform distortion and three-phase unbalance.

Measurement of the electric power quality and related problems

AbstractManufacturers, customers and the International Standards are paying more and more attention to the concept of “quality” of an industrial product. In particular, the definition and measurement of the electric power quality is destined to become a big problem. Under sinusoidal, symmetric and balanced conditions, the power‐quality problem is basically a loading quality problem; otherwise, it may be also a supplying quality problem. The paper discusses the measurement of some electric power‐quality indices. It also considers the problem of separating the utility's contribution to the power quality deterioration from the customer's one.

A method and related digital instrument for the measurement of the electric power quality

The ever increasing number and power of polluting loads (nonlinear, time-variant loads) connected to the electric power network causes a significant distortion in the line current and, as their overall power is no longer negligible with respect to the network power, also some distortion in the line voltage. This causes a deterioration of the electric power quality that may disturb the other connected loads. The availability of an instrument able to quantify the deterioration of the power quality due to the harmonic distortion, to assess whether or not this deterioration is caused by a polluting load connected after the metering section and to quantify the effects of such a load on the power quality therefore represents an important point for the correct operation of the electric power system. This paper proposes a measurement method, based on the evaluation of the harmonic powers, for the identification of the source producing pollution in a three-phase power system. Some parameters are also defined in order to quantify the electric power quality and the deteriorating effects of a polluting load. A digital instrument is also described, realized by means of virtual instrument techniques to implement the proposed method and to verify it experimentally. The measurement accuracy is discussed. >

Pricing electric harmonics

Rapid growth in power electronic equipment (PEEs) implies that in about 10 years, more than 50% of electric utility output will be consumed by PEEs. While PEEs yield benefits of large energy savings and product reliability, they cause the problem of harmonics. Harmonics deteriorate power quality, produce metering errors, increase reactive power, and exacerbate line losses and heat in transmission cables and power equipment. Thus, harmonics directly affect electric utility revenue and costs. Our objectives are: (i) to characterize harmonics, (ii) to describe the effects of harmonics on utility revenue and costs, and (iii) to propose alternative strategies for pricing harmonics. We show that pricing harmonics efficiently by using the marginal cost principle is implementable with current metering technology and existing utility billing systems.