High Voltage Ac Lines Research Articles

The propagation of the Ion-Flow Near the AC Transmission Lines

The series of physical processes contained in the corona layer is the source of space ions formed by the corona discharge of the high-voltage AC line. However, since these physical processes are difficult to calculate accurately and the corona layer thickness is usually small, the corona layer is ignored in the published literature on the corona discharge of the AC line, and the ions are considered to be emitted directly from the conductor surface. In this paper, the distribution area of the charged particles is divided into the corona plasma region and the unipolar drift region. A mathematical physical model of the photoionization and photoemission, which sustain self-sustaining discharge in the positive and negative half-cycle of corona plasma region of the AC conductor in dry air, are established. The influence of the ions generated in the previous cycle is also considered in the numerical simulation process. Finally, a complete microscopic physical model describing the corona discharge of the AC conductor under dry air is established. The validity of the physical model proposed in this paper is demonstrated by comparison with experimental results reported in the literature. Through the numerical simulation of the ion flow field of positive and negative half-cycle and the corona current, the physical process of the corona discharge around the AC line is better understood and analysed. Further positive and negative half-cycle charged particle motion and corona plasma regions were compared and analyzed. This work provides a brand new mathematical physics method for understanding and applying AC corona discharge.

Theoretical analysis of tuned HVAC line for low loss long distance bulk power transmission

One of the main objectives of the smart grid initiative is to enable bulk power transmission over long distance, with reduced transmission losses. Besides the traditional high-voltage alternating current (HVAC) transmission, with the advancement in power electronics, high-voltage direct current (HVDC) transmission is increasingly becoming important. One of the main factors impacting the transmission line parameters and the losses is the length of the transmission line (overhead). In this paper, a concept of tuned high-voltage AC line is presented for long (> 250 km) transmission line. A tuned line is where the receiving-end voltage and current are numerically equal to the corresponding sending-end values. This paper presents the detailed theoretical analysis of the tuned HVAC line, suggesting adaptation of the transmission frequency as per the length of the line. The simulation of a tuned HVAC line is performed using the PSCAD/EMTDC. Simulation results for two different line lengths, substantiate the theoretical analysis of reducing the reactive power absorbed in the line, while increasing the active power transmission.

Comparative Stability Analysis of a Combined DFIG-based and PMSG-based Offshore Wind Farm Connected to a Large Power Grid through a LCC-HVDC Link and an HVAC Line

This paper presents the comparative dynamic-stability analysis of an integration of a doubly-fed induction generator (DFIG)-based offshore wind farm (OWF) and a permanent-magnet synchronous generator (PMSG)-based OWF fed to a large power grid through a high-voltage AC (HVAC) line and a high-voltage direct-current (HVDC) link based on line-commutated converter (LCC). The operating performance of the studied 60-MW PMSG-based OWF is simulated by an equivalent PMSG driven by an equivalent wind turbine (WT) while an equivalent DFIG driven by an equivalent WT through an equivalent gearbox is used to simulate the operating characteristics of the 80MW DFIG-based OWF. A frequency-domain approach based on a linearized system model using eigenvalue technique and a time-domain scheme based on a nonlinear system model subject to various disturbance conditions are both utilized to compare the damping characteristics contributed by the HVAC line and the proposed LCC-HVDC control scheme. It can be concluded from the simulation results that the proposed LCC-HVDC link is capable of rendering better damping characteristics to stabilize the studied integrated two OWFs fed to power grid subject to a severe fault than the HVAC line.

Possibility of Power Tapping From Composite AC–DC Power Transmission Lines

A recently proposed concept of simultaneous ac-dc power transmission enables the long extra high-voltage ac lines to be loaded close to their thermal limits. The conductors are allowed to carry a certain amount of dc current superimposed on usual ac. This paper presents the feasibility of small power tapping from composite ac-dc power transmission lines which would pass over relatively small communities/rural areas having no access to a major power transmission network. The proposed scheme is digitally simulated with the help of a PSCAD/EMTDC software package. Simulation results clearly indicate that the tapping of a small amount of ac power from the composite ac-dc transmission line has a negligible impact on the normal functioning of the composite ac-dc power transmission system.

Effect of a modulated HVDC link on power system transients

This paper presents the details of a digital computer study of the effects of transient interactions, during large system disturbances, between an AC system and an associated high voltage DC transmission line with the rapid change in power transfer capability (modulated HVDC). The combined system consists of a large turboalternator synchronized to an infinite bus through two long-distance high voltage AC lines in parallel with an equally long controlled HVDC link. In the analysis, a rigorous nonlinear mathematical model, based on Park's equations, is formed by transforming the machine variables and the AC and DC transmission line parameters to a rotating reference frame attached to the alternator rotor, thereby providing the detailed transient behavior of the interconnected AC/DC system. Results of the studies demonstrate that a modulated HVDC link can provide significant increases in the loadability of AC lines by reducing or eliminating the constraints imposed by transient stability limitations. It appears, however, that, for certain systems, adverse stability behavior may result if the modulation setting exceeds 50%. Possible effects of HVDC modulation on the incidence of turboalternator torsional interactions are also considered. These interactions, however, are dependent upon parameters such as AC transmission, configuration, and the control mode characteristics of the HVDC terminals.

Intermountain Power Project Carrier Interference Study

The authors summarize the results of an interference study performed for the Intermountain Power Project. Interference by noise generated at the converter stations to open-wire carrier telecommunication lines and to power-line carrier systems is investigated. The frequency range considered is 10-200 kHz. The noise level at the converter stations is estimated using a detailed high-frequency digital computer model and measurement of the noise current from a single thyristor position. The highest interference to open-wire communication lines adjacent to the DC line is for exposures along the electrode section of the DC line where the noise current was found to vary little in amplitude along the section. Interference which may be harmful was found for power-line carrier systems operating on two HVAC (high-voltage AC) lines sharing the right of way with the DC line. In this case, the interference is caused by bipolar noise current, with the effect that one of the lines is affected in spite of the fact that it is located far from the converter stations. For AC lines crossing the DC line, the induced noise is so low that no problems are expected. In the AC systems connected to the converter stations interference is not expected beyond one switching station away from the converter stations. >