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Article
Publication date: 1 April 2014

Jerzy Golebiowski and Robert Piotr Bycul

The purpose of this paper is to prepare procedures for determination of characteristics and parameters of DC cables on the basis of transient and steady thermal field…

Abstract

Purpose

The purpose of this paper is to prepare procedures for determination of characteristics and parameters of DC cables on the basis of transient and steady thermal field distribution in their cross-sections.

Design/methodology/approach

Steady-state current rating was computed iteratively, with the use of steady thermal field distribution in the cable. The iterative process was regulated with respect to this field by changes of the mean surface temperature of the sheath of the cable. It was also controlled with respect to the unknown current rating by deviations of the temperature of the core from the maximum sustained temperature of the insulation (material zone) adjacent to the core. Heating curves were determined (in arbitrarily selected points of the cross-section of the cable) by a parallel algorithm described thoroughly in the first part of the paper. The algorithm was used for computing of transient thermal field distribution throughout the whole cross-section. Thermal time constant distributions were determined by the trapezium rule, where the upper integration limit of respective thermal field distributions was being changed.

Findings

Using the methods prepared the following characteristics/parameters of the cable were determined: steady-state current rating, spatial-time heating curves, mean thermal time constant distribution. The results were verified and turned to be in conformance with those of the IEC 287 Standard and a commercial software – Nisa v. 16. Speedup and efficiency of the parallel computations were calculated. It was concluded that the parallel computations took less time than the sequential ones.

Research limitations/implications

The specialized algorithms and software are dedicated to cylindrical DC cables.

Practical implications

The knowledge of the determined characteristics and parameters contributes to optimal exploitation of a DC cable during its use.

Originality/value

The algorithms of determination of the steady-state current rating and thermal time constant are original. The software described in the appendix has also been made by the authors.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 24 no. 3
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 28 March 2019

Jerzy Gołębiowski and Marek Zaręba

The purpose of this paper is to analyse the dynamics of a thermal field generated in a tubular bus with rated current by using two models of electrical resistivity of copper.

Abstract

Purpose

The purpose of this paper is to analyse the dynamics of a thermal field generated in a tubular bus with rated current by using two models of electrical resistivity of copper.

Design/methodology/approach

The boundary-initial problem of the modified heat equation was formulated for the tubular bus. Analytical solutions were obtained by means of Green’s functions as the kernels of the integral operator inverse to the corresponding differential operator. The results were presented graphically and verified using the finite element method. The calculations were made by considering the example of the Storm Power Components tubular bus (USA).

Findings

Analytical field models were used to determine time- and space-variable heating curves, time constants and steady-state current ratings.

Research limitations/implications

This paper is related to the structure of a hollow cylinder. Other bus sections can be taken into account by using the coordinate systems of different curvilinear orthogonal symmetry.

Originality/value

Using the analytical method, the influence of the variable (temperature dependent) electrical resistivity on some important parameters and characteristics of the tubular bus was investigated. The system was considered as an element with distributed parameters.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 38 no. 2
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 3 July 2017

Jerzy Golebiowski and Marek Zareba

The purpose of this article is investigating the impact of the spatially variable heat transfer coefficient on the thermal field in the double insulated wire.

Abstract

Purpose

The purpose of this article is investigating the impact of the spatially variable heat transfer coefficient on the thermal field in the double insulated wire.

Design/methodology/approach

The effect of the air boundary layer was modelled by means of changing the total heat transfer coefficient on the external perimeter of the wire. This leads to an elliptical boundary problem with Hankel’s condition dependent on the angular coordinate. The eigenfunctions of the problem were determined analytically. On the other hand, the unknown coefficients of eigenfunctions and the constants were calculated numerically by solving a respective system of algebraic equations. The steady state current rating was determined with an iterative method.

Findings

By means of the presented method, the thermal field distribution deprived of axial symmetry in the double insulated wire was determined. The obtained results have good physical interpretation and were verified with the finite element method (by means of NISA v. 16 software). The determined values of the steady-state current rating were compared with those calculated by means of the equivalent heat transfer coefficient method and the International Electrotechnical Commission (IEC) standard.

Research limitations/implications

The method is applied to analyse scalar fields in layered cylindrical structures. This could be expanded to the case of a wire of any number of insulation layers. What is more, one could also consider heat sources without axial symmetry and located within the external area.

Originality/value

The analytical method of determining a thermal field deprived of axial symmetry in heterogeneous cylindrical system (the wire composed of three different materials) was developed.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 36 no. 4
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 2 January 2018

Mahmoud M. Elkholy

The paper aims to present an application of teaching learning-based optimization (TLBO) algorithm and static Var compensator (SVC) to improve the steady state and dynamic…

Abstract

Purpose

The paper aims to present an application of teaching learning-based optimization (TLBO) algorithm and static Var compensator (SVC) to improve the steady state and dynamic performance of self-excited induction generators (SEIG).

Design/methodology/approach

The TLBO algorithm is applied to generate the optimal capacitance to maintain rated voltage with different types of prime mover. For a constant speed prime mover, the TLBO algorithm attains the optimal capacitance to have rated load voltage at different loading conditions. In the case of variable speed prime mover, the TLBO methodology is used to obtain the optimal capacitance and prime mover speed to have rated load voltage and frequency. The SVC of fixed capacitor and controlled reactor is used to have a fine tune in capacitance value and control the reactive power. The parameters of SVC are obtained using the TLBO algorithm.

Findings

The whole system of three-phase induction generator and SVC are established under MatLab/Simulink environment. The performance of the SEIG is demonstrated on two different ratings (i.e. 7.5 kW and 1.5 kW) using the TLBO algorithm and SVC. An experimental setup is built-up using a 1.5 kW three-phase induction machine to confirm the theoretical analysis. The TLBO results are matched with other meta heuristic optimization techniques.

Originality/value

The paper presents an application of the meta-heuristic algorithms and SVC to analysis the steady state and dynamic performance of SEIG with optimal performance.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 37 no. 1
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 4 January 2011

Faïçal Jallali, Afef Bouchhima and Ahmed Masmoudi

The purpose of this paper is to investigate the steadystate stability and features of the brushless cascaded doubly fed machine (BCDFM), which is made up of two…

Abstract

Purpose

The purpose of this paper is to investigate the steadystate stability and features of the brushless cascaded doubly fed machine (BCDFM), which is made up of two wound‐rotor induction machines: the power machine (PM) and the control one, with their rotors mechanically and electrically coupled.

Design/methodology/approach

The machine modelling is first treated considering a Park reference frame linked to the rotating field of the PM. Then, a state representation related to small perturbations is established following the linearisation of the BCDFM model around a steadystate operating point. This allows the investigation of BCDFM steadystate stability, power flow and the torque‐speed characteristics.

Findings

It has been found that the electrical variables of the control machine greatly affect the BCDFM steadystate stability and characteristics.

Research limitations/implications

The work should be extended considering a validation of the established results through experimental tests.

Originality/value

The steadystate small perturbation of the BCDFM model has been introduced for the first time, which is the key of the machine steady‐stability analysis and features investigation.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 30 no. 1
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 1 June 2000

K. Wiak

Discusses the 27 papers in ISEF 1999 Proceedings on the subject of electromagnetisms. States the groups of papers cover such subjects within the discipline as: induction…

Abstract

Discusses the 27 papers in ISEF 1999 Proceedings on the subject of electromagnetisms. States the groups of papers cover such subjects within the discipline as: induction machines; reluctance motors; PM motors; transformers and reactors; and special problems and applications. Debates all of these in great detail and itemizes each with greater in‐depth discussion of the various technical applications and areas. Concludes that the recommendations made should be adhered to.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 19 no. 2
Type: Research Article
ISSN: 0332-1649

Keywords

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Abstract

Details

Quantitative and Empirical Analysis of Nonlinear Dynamic Macromodels
Type: Book
ISBN: 978-0-44452-122-4

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Article
Publication date: 1 January 2012

Faïçal Jallali and Ahmed Masmoudi

The paper seeks to investigate the effect of the rotor‐phase sequence connection on the steadystate stability of the brushless cascaded doubly‐fed machine (BCDFM). The

Abstract

Purpose

The paper seeks to investigate the effect of the rotor‐phase sequence connection on the steadystate stability of the brushless cascaded doubly‐fed machine (BCDFM). The stability analysis is carried out considering the eigenvalue method.

Design/methodology/approach

The BCDFM includes a two wound‐rotor induction machines: a power machine cascaded to a control one. The BCDFM modeling is firstly treated considering a Park reference frame linked to the rotating field of the power machine, and for both rotor‐phase sequence connections. Then, a state representation related to small perturbations is established following the linearisation of the BCDFM model around a steadystate operating point. This allows the investigation of the BCDFM steadystate stability and efficiency.

Findings

It has been found that the electrical variables of the control machine power supply greatly affect the BCDFM steadystate stability and efficiency.

Research limitations/implications

The work should be extended considering a validation of the established results through experimental tests.

Originality/value

The small perturbation model of the BCDFM has been introduced for the first time which is the key of the machine steadystate stability analysis and efficiency investigation.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 31 no. 1
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 2 August 2019

Moumita Basu and Ranjanendra Narayan Nag

This is a theoretical paper in the field of international macroeconomics. The purpose of this paper is to focus on a dynamic interaction between current account imbalance…

Abstract

Purpose

This is a theoretical paper in the field of international macroeconomics. The purpose of this paper is to focus on a dynamic interaction between current account imbalance and unemployment in response to some policy-induced shocks for a small open economy under a flexible exchange rate.

Design/methodology/approach

The paper uses a two-sector framework: one sector is traded and another is the non-traded sector that is subject to an effective demand constraint. The current account imbalance arises due to the discrepancy between production of traded goods, household consumption of traded goods and government purchases of importables. The authors keep the asset structure simple by considering only domestic currency and foreign bonds that are imperfect substitutes. The paper considers a standard methodology of dynamic adjustment process involving change in foreign exchange reserves and exchange rate under perfect foresight. The saddle path properties of the equilibrium are also examined.

Findings

The results of comparative static exercises depend on a set of structural features of a developing country, which include asset substitutability, wage price rigidity and sectoral asymmetries. The paper shows that expansionary monetary policy, balanced budget fiscal expansion and financial liberalization have an ambiguous effect on the current account balance, foreign exchange reserves, non-traded sector and the level of employment.

Originality/value

The existence of Keynesian unemployment with fixed prices is the key ingredient of this paper. The paper introduces the problem of effective demand to analyze the dynamics of current account balance and exchange rate, which, in turn, determine the sectoral composition of output and level of employment.

Details

Journal of Economic Studies, vol. 46 no. 3
Type: Research Article
ISSN: 0144-3585

Keywords

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Article
Publication date: 1 January 2006

Eric Kam and Mohammed Mohsin

The purpose of this paper is to derive the real implications of inflation targeting using optimizing models characterized by endogenous time preference.

Abstract

Purpose

The purpose of this paper is to derive the real implications of inflation targeting using optimizing models characterized by endogenous time preference.

Design/methodology/approach

To ensure consistent consumption and savings behavior, the rate of time preference is modeled as an increasing function of real wealth.

Findings

The results are not uniform and depend on the methods for modeling money in the general equilibrium framework; money in the utility function (MIU) and cash‐in‐advance constraints (CIA). With MIU, time preference wealth effects link the monetary and real sectors by endogenizing real interest rate. Monetary growth raises steady state capital and consumption by the Tobin effect. However, if money is introduced through CIA constraints, inflation policies are sensitive to the structure of the constraint itself. If the constraint applies to consumption and capital purchases, monetary growth lowers the steady state demand for both commodities and reverses the Tobin effect. If the constraint applies only to consumption goods, the same monetary policy is superneutral. This time preference specification has important advantages. It is consistent with the literature that integrates reinforcing wealth effects into aggregative models using ad‐hoc consumption or savings functions. Allowing the rate of time preference to depend positively on real wealth implies that optimizing behavior, not ad‐hoc specification yields wealth effects that endogenize the real interest rate and generate a Tobin effect. This time preference specification provides optimizing foundations for modeling savings as a decreasing function of real wealth, which is empirically verifiable and consistent with empirical predictions of consumption as an increasing function of real wealth.

Originality/value

This paper demonstrates the different effects that monetary policy maintains on steady state capital, consumption and real balance holdings in economies characterized by an endogenous rate of time preference.

Details

Journal of Economic Studies, vol. 33 no. 1
Type: Research Article
ISSN: 0144-3585

Keywords

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