Polyphase system

Summary

A polyphase system is a means of distributing alternating-current (AC) electrical power where the power transfer is constant during each electrical cycle. AC phase refers to the phase offset value (in degrees) between AC in multiple conducting wires; phases may also refer to the corresponding terminals and conductors, as in color codes. Polyphase systems have three or more energized electrical conductors carrying alternating currents with a defined phase between the voltage waves in each conductor; for three-phase voltage, the phase angle is 120° or 2π/3 radians (although early systems used 4 wire two-phase). Polyphase systems are particularly useful for transmitting power to electric motors which rely on alternating current to rotate. The most common example is the three-phase power system used for industrial applications and for power transmission. Compared to a single-phase, two-wire system, a three-phase three-wire system transmits three times as much power for the same conduct

Official source

https://en.wikipedia.org/wiki/Polyphase_system

About this result

This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.

Related publications (5)

Related publications

Related people

Related units

Related concepts (25)

Related concepts

Related courses (6)

L'objectif de ce cours est d'acquérir les connaissances de base liées aux machines électriques (conversion électromécanique). Le cours porte sur le circuit magnétique, le transformateur, les machines synchrones, asynchrones, à courant continu et les moteurs pas à pas.

Les étudiants seront capables de modéliser, de simuler et de mesurer des actionneurs électromagnétiques et des moteurs électriques.

Related courses

Related lectures (7)

Related lectures

Most techniques for power system analysis model the grid by exact electrical circuits. For instance, in power flow study, state estimation, and voltage stability assessment, the use of admittance parameters (i.e., the nodal admittance matrix) and hybrid parameters is common. Moreover, network reduction techniques (e.g., Kron reduction) are often applied to decrease the size of large grid models (i.e., with hundreds or thousands of state variables), thereby alleviating the computational burden. However, researchers normally disregard the fact that the applicability of these methods is not generally guaranteed. In reality, the nodal admittance must satisfy certain properties in order for hybrid parameters to exist and Kron reduction to be feasible. Recently, this problem was solved for the particular cases of monophase and balanced triphase grids. This paper investigates the general case of unbalanced polyphase grids. Firstly, conditions determining the rank of the so-called compound nodal admittance matrix and its diagonal subblocks are deduced from the characteristics of the electrical components and the network graph. Secondly, the implications of these findings concerning the feasibility of Kron reduction and the existence of hybrid parameters are discussed. In this regard, this paper provides a rigorous theoretical foundation for various applications in power system analysis.

2018

Performance Assessment of Kron Reduction in the Numerical Analysis of Polyphase Power Systems

Andreas Martin Kettner, Mario Paolone

This paper investigates the impact of Kron reduction on the performance of numerical methods applied to the analysis of unbalanced polyphase power systems. Specifically, this paper focuses on power-flow study, state estimation, and voltage stability assessment. For these applications, the standard Newton-Raphson method, linear weighted-least-squares regression, and homotopy continuation method are used, respectively. The performance of the said numerical methods is assessed in a series of simulations, in which the zero-injection nodes of a test system are successively eliminated through Kron reduction.

IEEE2019

Modelling Hydration Kinetics of Cementitous Systems

Aditya Kumar

The modeling platform µic has been extended to study the hydration of cement based systems. It is shown that the hydration kinetics of alite can be described through the implementation of two mechanisms: a solution controlled dissolution (SCD) mechanism for the first two stages of hydration and nucleation and densifying growth (NDG) of products for the last three stages of hydration. The dissolution rate is varied according to the ratio between the ion activity product and the equilibrium solubility product. The solution concentrations are computed directly from the amount of alite dissolved taking into account the amount of water present and the amount of products formed, with activities and complex ions formation according to standard thermodynamic rules. Saturation index calculations are implemented to compute the time of precipitation of C-S-H and portlandite individually. After the precipitation of portlandite, the rate controlling mechanism is switched to nucleation and densifying growth. C-S-H grown in a diffuse manner in which the packing density increases with hydration. The overall heat-evolution profile is obtained by combination of heat evolved as obtained from the SCD and NDG mechanisms. The approach is used to describe the influence of particle sizes, thermal treatment, mixing conditions and additions of alkali hydroxides, alkali sulfates and gypsum on hydration of alite. Through a study of systems with wide variations in the process parameters, it is shown that the hydration kinetics of alite can be generically described using the combination of SCD and NDG mechanisms and a limited number of fit parameters. The results obtained from simulations were found to be in good agreement with a variety of experimental results. The various simulations parameters are shown to be strongly correlated to the initial states of the systems. A model is presented to describe the hydration of aluminate+gypsum systems. It is shown that the reaction rate profile can be numerically reproduced by using two mechanisms: dissolution of the aluminate phase in the first stage and boundary nucleation and growth of monosulfate phase in the second stage of reaction. It is shown that the effects of particle sizes and composition on hydration of aluminate can be described using just one fit variable, isotropic growth rate of monosulfate phase, which correlates well the space available in the microstructural volume. Using the combination of mechanisms that describe hydration of alite and aluminate, a model is presented to describe the hydration of multi-phase systems. Preliminary simulations of the heat-evolution profiles of alite-aluminate-gypsum and commerical cementitous systems are presented. Good agreement was found between the simulated and measured results. The current study demonstrates the versatility of µic and shows that the use of mechanistic, rather than empirical, rules can be an important tool to achieve better understanding of cement hydration.

EPFL2012

Modelling Hydration Kinetics of Cementitous Systems

Aditya Kumar

EPFL2012