IEEE Transactions on Power Delivery

This paper investigates the factors that influence the outcome of financial-loss analysis in voltage sag studies. Focusing on industrial processes, this paper considers the effects of voltage sag profile estimation, plant-load profile modelling, and process cycle modelling on the financial risk associated with process failure. Based on voltage sag monitoring records, sag profile is probabilistical... View full abstract»

This paper presents some difficulties encountered when evaluating information obtained from infrared thermal inspections conducted in uncovered power substations. Technical, physical, and environmental factors are the main influences that have been identified. Based on field data and laboratory tests, mathematical models were derived to understand the load current variation influence on the therma... View full abstract»

In this paper, by creating a 3-D model of power-line equipment and lightning leader progression models, an alternate procedure for calculating the shielding failure rate (SFR) of transmission lines is presented. The stepping nature of lightning downward leader is modeled according to field observations with the use of discrete line charges approaching the earth. A simplified self-consistent model ... View full abstract»

This paper analytically determines the nondetection zone (NDZ) of an active islanding detection method, and proposes a solution to obviate the NDZ. The method actively injects a negative-sequence current through the interface voltage-sourced converter (VSC) of a distributed generation (DG) unit, as a disturbance signal for islanding detection. The estimated magnitude of the corresponding negative-... View full abstract»

Availability of wind energy which differs across locations primarily determines the appropriate location for installing windfarms. However, the grid location of windfarms must always be considered in an attempt to accurately quantify the benefits which can be achieved from windfarms during their lifetime operation to the supply network. The value of wind power is significantly affected by their pe... View full abstract»

One of the major problems in the liquid insulation is the particle contamination, which can seriously degrade the withstand voltage of the insulation. The movement of conducting particles under operation voltage can generate incipient discharges that can lead to the complete failure of the insulation system during operation. The partial-discharge characteristics of the free spherical conducting pa... View full abstract»

This paper presents a new two-terminal impedance-based fault-location algorithm, which takes into account the distributed parameter line model. The algorithm utilizes unsynchronized measurements of voltages and currents from two ends of a line and is formulated in terms of the fundamental frequency phasors of symmetrical components of the measured signals. First, an analytical synchronization of t... View full abstract»

The high-frequency domain characterization of overhead three-phase cables is a critical issue as far as power line carrier communications is concerned. In many instances a detailed knowledge of the electric and magnetic parameters of the cable is not available. Even if manufacturer cable-data are available, strong proximity effects among cable conductors do inhibit the utilization of closed-form e... View full abstract»

Underfrequency load shedding is one of the most important protection systems, as in many cases it represents the last chance to prevent a system blackout after a serious disturbance occurs in a power system. In order to improve traditional schemes, many efforts have been concentrated on attempts to use the frequency gradient as an indicator for determining the lack of active power in a system. Thi... View full abstract»

This paper describes a methodology to estimate post process failure cost of downtime (COD). COD can be estimated using either historical or direct online costs (direct and restart costs) as input to the model. Application of the proposed COD estimation model is illustrated on an actual industrial process that experienced several downtime events due to voltage sags in its electric supply. Raw finan... View full abstract»

A novel algorithm for discrimination between inrush currents and internal fault currents by utilizing the normalized grille curve is proposed. First, the calculation method of the normalized grille curve is presented. Then, two schemes to discriminate the inrush currents from the internal faults in the time and frequency domains are, respectively, developed. A total of 268 experimental measurement... View full abstract»

It is well known that environmental loads, e.g., wind and ice, acting on power transmission lines are highly uncertain, as are the structural strengths of the towers supporting the lines. The design of such systems must take uncertainty into account in order to achieve acceptable reliability at a reasonable cost. The paper presents a simulation-based methodology for the optimal design of a transmi... View full abstract»

This paper deals with the modeling and analysis of a five-legged rectifier transformer that is used for parallel operation of two three-pulse rectifiers, specifically, for low-voltage high-current applications. The five-legged system is compared with the conventional rectifier system consisting of a three-legged transformer and interphase transformer (IPT). Ensuring equal current sharing between t... View full abstract»

Droplets formation on high-voltage transmission lines affected by rainfall amplifies the corona discharges from the conductors. The induced corona vibrations intensify the fatigue of high-voltage conductors and supporting elements. The alternating presence of space charge and the ionic wind associated with the corona discharge are the main causes of this phenomenon. The objective of this paper is ... View full abstract»

Condition-based maintenance (CBM) is a new maintenance strategy for the reliable operation of aged power equipment. Although CBM has been applied for various equipment, the accuracy of condition information from sensors has not yet been sufficiently discussed. Specifications of reliable information are still not clear and CBM sensors have not widely been applied on actual power substations. The in... View full abstract»

It has been suggested that the recommended flicker planning levels provided in IEC 61000 3-7 and IEEE 1453 are too restrictive for high-voltage and extra-high-voltage networks. The premise of this argument is based on a perceived increase in low-voltage (LV) flicker compatibility level. Some believe that flicker measurements made in Europe over a period of several years support the notion of an in... View full abstract»

This paper presents the modeling of high-voltage direct current (dc) transmission systems with voltage-source converters (VSCs) in security-constrained unit commitment (SCUC). The impact of VSC-DC transmission system on the economics and the security of integrated ac/dc transmission systems is discussed. The nonlinear ac/dc equations are linearized and the Newton-Raphson method is utilized to solv... View full abstract»

This paper proposes a voltage- and frequency-control strategy for the islanded operation of dispatchable electronically coupled distributed-resource units, based on a discrete-time mathematical model which is also valid for variable-frequency operation. The proposed control strategy utilizes a combination of deadbeat and repetitive control to enhance the performance of the control system under unb... View full abstract»

This paper analyzes the possibility of using compensated passive loops to obtain a high mitigation effectiveness of the magnetic field generated by underground single-core cables. With that aim, several loops arrangements are simulated in a case study, including new ones called enchained loops, whose geometry reminds short-circuited conductors at both ends, but with the advantage of requiring smal... View full abstract»

Disconnector switching operations in large gas-insulated switchgear (GIS) systems may produce very fast transient overvoltages (VFTOs), causing high electric stress to other apparatuses in the substation, such as power transformers. This paper presents a VFTO measuring technique based on a transformer bushing sensor, which consists of the transformer bushing (C1) and a capacitor sensor (C2) instal... View full abstract»

In this study, the corona onset voltage (COV) of bipolar bare overhead bundle conductors for transmission lines has been investigated using numerical calculations and gas discharge theory. First, an accurate numerical method, the charge simulation method, was used to calculate the electric field distribution in the vicinity of bare sub-conductors in bundles. Then, the electric field values and a c... View full abstract»

New opportunities for optimally integrating the increasing number of distributed-generation (DG) units in the power system rise with the introduction of the microgrid. Most DG units are connected to the microgrid via a power-electronic inverter with dc link. Therefore, new control methods for these inverters need to be developed in order to exploit the DG units as effectively as possible in case o... View full abstract»