Ioan Popa

Numerical modeling of DC busbar contacts

The paper presents two electro-thermal numerical models which can be used for the modeling and optimization of high currents busbar contacts for DC. The models are obtained by coupling of the electric model with the thermal field problem. The coupling is carried out by the source term of the differential equation which describes the thermal field. The models allow the calculation of the space distribution of the electric quantities (electric potential, the gradient of potential and the current density) and of the thermal quantities (the temperature, the temperature gradient, the Joule losses and heat flux). A heating larger than that of the busbar appears in the contact zone, caused by the contact resistance. The additional heating, caused by the contact resistance is simulated by an additional source injected on the surface of contact. The 2D model has been solved by the finite volumes method while the 3D model, by the finite elements method. Both models were experimentally validated. Using the models, one can determine the optimal geometry of dismountable contact for an imposed limit value of the temperature.

Thermal modeling and experimental validation of an encapsulated busbars system

In this paper, we propose an approach for the magnetic and thermal modeling of an encapsulated busbars system for high voltage using QuickField software. This paper proposes a numerical model developed by coupling of the magnetic field problem with the stationary and transient heat field problems for the geometry of a single-phase execution busbars system. The coupling of problems is realized by importing specific losses from the magnetic field problem as heat sources for thermal field problem. The magnetic field problem is also coupled to the electrical circuit. The shields are short-circuited at both ends and they are connected to the ground. For this constructive solution, in the shields occur induced currents, approximately equals to those of conductors. Due to the shielding effect, the magnetic field is practically zero outside of shield and therefore the electrodynamic forces do not occur between phases. In the model it was taken into account the variation of electrical conductivity with the temperature. The thermal model has been validated by experiment. The global coefficient of heat transfer by convection and radiation used in thermal model was estimated using the power losses computed by magnetic model. There is a good agreement between numerical and experimental temperature values. The presented model can be used for analysis, design and optimization of three-phase busbars system in single phase execution.

Numerical modeling of three-phase busbar systems: Calculation of the thermal field and electrodynamic forces

The paper presents numerical models obtained in QuickField software for analysis of the three-phase systems of rectangular busbar, of low or medium voltage, in steady-state and in short-circuit regime. Using a magnetic harmonic model coupled with a steady-state thermal model, the distribution of the thermal field for rated current is determined. By coupling the thermal steady-state model for the rated current and the magnetic model for short circuit current with a thermal model in transient regime, can be determined the time evolution of the temperature distribution in the short circuit regime (undeveloped in this paper). For determining the electrodynamic forces, a transient magnetic model is used. Different types of busbar systems are analyzed, with one or more conductors per phase in aligned arrangement.

Crimped connections heat transfer coefficient law determination using experimental and numerical results

In this paper the global heat transfer coefficient law corresponding to two types of superposed crimped connections has been obtained, using experimental and numerical determination. The samples use copper wire crimped by two methods: the first method uses one crimp indents and the second is a proposed method with two crimp indents. The ferrule is a parallel one. For obtaining the experimental results the samples are heated in A.C. current at different current values until steady state heating regime. Then, the 2D model of crimped connections has been created to obtain the numerical results. Using experimental and numerical results, a law for global heat transfer coefficient corresponding to the two types of crimped connections was proposed. The temperature dependence of global heat transfer coefficient has been taking into account.

Static force characteristic of e-type single phase AC electromagnets

In this paper, we propose an approach for the determination of static force characteristic of E-type single phase AC electromagnet using 2D numerical models developed in QuickField and FEMM software. The magnetic attraction force is estimated using Maxwell stress tensor method. The results obtained with numerical models were validated by an analytical method combined with experimental data. The numerical model is an AC magnetics problem coupled with the coil electric circuit. Necessary experimental data are electromagnet coil current values at different air gaps for a known voltage. Also, the ohmic resistance of the coil, the number of turns and wire diameter are known. The numerical results for attraction force obtained in QuickField agree well with those obtained by analytical method combined with experimental data. The correspondent numerical values obtained in FEMM do not match with them, although the air gap magnetic flux density values are practically identical to those obtained in QuickField. More specifically, the numerical values obtained in FEMM for attractive force are half of QuickField values. Considering the distribution of magnetic flux density on polar surfaces and using Maxwell formula in its integral form for calculating the force, it was proved that the numerical values of force are in very good conformity with those obtained in QuickField. The authors point out that in software FEMM the AC force is wrongly calculated based on Maxwell stress tensor method although in DC this calculation is correct.

Numerical model for a plunger-type AC electromagnet

In this paper we propose an approach for the determination of static force characteristic of a plunger-type AC electromagnet using 2D numerical model developed in QuickField software. The attraction electromagnetic force is calculated using Maxwell stress tensor method. The numerical model is an AC magnetics problem coupled with the coil electric circuit. The numerical model has been experimentally validated.

Numerical modeling of an eddy current sensor used in a metal separation device

This work deals with the numerical analysis of the electromagnetic field problem for one proposed Ferrite - Cored Eddy Current Sensor, using the Quick Field software; this sensor can be used in the waste management for metal separation. Using this software, many specific cases are analysed, namely, when sensor probe coil is placed on different types of metallic samples (ferromagnetic and non ferromagnetic); due to the magnetic flux of the induced eddy currents in the metallic samples, the changing of the coil parameters values and the currents passing through the coil versus supplied voltage frequency are presented and discussed.

Numerical modeling of power cables

The paper presents numerical models developed in QuickField software to determine load capacity for single-or three-phase cables so that not to exceed allowable temperature limits. The models allow determining cables parameters: self and mutual inductances, self and mutual partially capacitances. As a result, the application of an optimized arrangement of cable can be used to make the temperature rise of cable as low as possible. Using transient magnetic model can determine under short-circuit conditions, the variations in time and consequently the peak values of the short circuit currents and of the electrodynamic forces.

Magneto-thermal modeling of an encapsulated busbars system with common shield

In this paper, we propose an approach for the magnetic and thermal modeling of an encapsulated busbars system, in three-phase execution, for high voltage using QuickField software. The paper proposes a numerical model developed by coupling of the magnetic field problem with the stationary and transient heat field problems for the geometry of a three-phase execution busbars system with common shield. The coupling of problems is realized by importing specific losses from the magnetic field problem as heat sources for thermal field problem. The magnetic field problem is also coupled to the electrical circuit. The electrodynamic forces that occur between conductors in the presence of the ferromagnetic shield have different values compared to those that occur in an unshielded system. In the model it was taken into account the variation of electrical conductivity with the temperature. The global heat transfer coefficient by convection and radiation used in thermal model was estimated using the power losses computed by magnetic model. When evaluating the global heat transfer coefficient was taken into account the temperature dependence of the physical properties of the air. There is a good agreement between numerical and analytical temperature values. The presented model can be used for analysis, design and optimization of three-phase busbars system with common shield.

Numerical Modeling And Experimental Results Of High Currents Dismountable Contacts.

The paper presents an electro-thermal numerical model which can be used for the modelling and optimization of high currents dismountable contacts for dc current. The model is obtained by coupling of the electrokinetic field problem with the thermal field problem. The coupling is carried out by the source term of the differential equation which describes the thermal field. The model allows the calculation of the space distribution of the electric quantities (electric potential, the gradient of potential and the current density) and of the thermal quantities (the temperature, the temperature gradient, the Joule losses and heat flow). A heating larger than that of the current lead appears in the contact zone, caused by the contact resistance. The additional heating, caused by the contact resistance, is simulated by an additional source injected on the surface of contact. Using the model, one can determine the optimal geometry of dismountable contact for an imposed limiting value of the temperature