Metrological properties of a two-current-source bridge circuit were tested with the use of the method of measuring resistance increments of strain gauges. An unconventional system was investigated in comparison with the commonly used Wheatstone’s half-bridge, quarter-bridge and Anderson’s loop. Input-output characteristics of the systems tested with a current supply were examined experimentally. Error values of offset and gain of the characteristics in relation to the characteristics of reference were taken as the criterion of comparison. Moreover, standard uncertainties of y-intercept and slope coefficients (of the straight lines) were analysed. The coefficients with their uncertainties are presented in tables. Errors for three tested systems with two metal strain gauges or with one semiconductor are presented on graphs. Additionally, the errors change, resulted from the spread of initial resistances as the quantity influencing the uncertainties of offset and gain coefficients, was defined for the bridge circuits.DOI: http://dx.doi.org/10.5755/j01.eie.22.6.17220

The simplified method of analysis of the thermal field in the futuristic model of a DC cable is presented. The thermal conductivity of a non-conducting layer is very small comparing with the same parameter of conducting regions. The above causes very fast heat propagation in the core and coating, which in the consequences are approximated by inert elements of the first order. Spatial changes in the field in insulation cannot be neglected, because of the significantly slow heat transfer. For that reason, insulation is treated as an element of distributed parameters. The boundary-initial parabolic problem of a non-conducting region is solved by means of Duhamel’s theorem. The fundamental solutions of superposition integrals are determined by the separation of variables method. The maximal deviation of results obtained by the finite element method does not exceed 7.2%. The heating curves and results of verification are presented in a graphic form.

The passage of current generates heat and increases the temperature of electrical components, which affects the environment, support insulators and contacts. Knowledge of the temperature allows for the determination of important operational parameters. Time-varying currents result in a nonuniform current density distribution due to the skin and proximity effects. As a result, temperature and energy losses are increased compared to the uniform DC current density case. In this paper, these effects are considered for three-phase systems with round conductors in flat and trefoil arrangements. In the first step, the analytical expressions for current distributions are determined and used to construct the heat source density. Then, a suitable Green’s function, which allows for obtaining temperature distribution in analytical form, is used to evaluate temperature at any point throughout the conductors. The temperature differences throughout individual wires are usually negligible, whereas noticeable differences can be observed between the wires. The impact of various parameters is examined, and an approximate closed formula is derived to assess the influence of the skin and proximity effects. When the skin depth is not smaller than the wire radius, the skin effect enlarges the temperature increase by around 2% compared to the DC case. As for the proximity effect, the additional increase can be neglected if the distance is above around 10 wire radii, but for closely spaced wires, it can reach up to around 17%, depending on the arrangement and the distance between the wires. Such an additional increase may result in exceeding the permissible temperatures, which damages particular components of the system; therefore, it is important to take it into account at the design stage.

The principle of operation, its practical realization and measurement research of a reconfigured system of a signal conditioner are presented. A two-sourced conditioner supplied by direct current with four resistance sensors and four switching keys was experimentally tested. In the example application the resistance of sensors in the function of the same point load, caused by perpendicular force, was measured. In order to compare the results achieved with the use of a conditioning circuit, similar tests were carried out for a four-channel Wheatstone’s bridge-based commercial acquisition card. The research aimed at confirming the possibility of implementing the constructed signal conditioner in cheap measurement equipment.DOI: http://dx.doi.org/10.5755/j01.eie.22.2.14587

The paper investigates the dynamics of the thermal field of the ACCC (aluminum conductor composite core) line. The system was heated by solar radiation and current flow. Conductor cooling was modeled using the total heat transfer coefficient as the sum of convective and radiative components. The temperature increase generated by the current is described by a system of parabolic differential equations with an appropriate set of boundary, initial and continuity condition. The mentioned boundary-initial problem was solved by a modified Green’s method, adapted to the layered structure of the system. For this purpose, Green’s functions, as the kernels of integral operators inverse to differential ones, were determined. Aluminum resistivity and heat transfer coefficient change significantly with temperature. For this reason, the solution to the problem is presented in the form of a lower and upper estimation of the heating curve and local time constant. A steady-state current rating was also determined. The results are presented graphically and verified by other methods (power balance and finite element). The physical interpretation of the presented solution is also given.