Andrei Marinescu

Using VNA for IPT coupling factor measurement

Contactless power transmission is a major concern due to its many applications in the modern technique. Different topologies for near field transmission are presented in literature, with emphasis on the efficiency of the process, especially when such systems are used for medium or high power, like those needed for charging of storage batteries in electric/hybrid cars. This paper analyzes one of the systems key elements which provides the magnetic inductive transfer between the power supply and load, hereinafter referred to as inductive coupler. For a fast identification of its parameters, the automatic determination of the transfer function by a vector network analyzer (VNA) is used in this paper.

Fibre optic based clamping force monitoring system for power transformers

The preservation of the initial clamping forces or mechanical stability of the power transformers during their whole active life in very different conditions appearing in operation (mechanical stresses during short-circuits, inrush currents and transportation, frequent heating/cooling processes, paper-oil moisture and ageing) has not been completely kept under control though in the technical literature there are presented and applied many on-line and off-line, intrusive or non-intrusive methods which by means of the offered results try to get into the “black box” represented by the transformer from this viewpoint. The paper present a new direct measuring system for the axial clamping forces of power transformer windings enabling an objective assessment of their mechanical stability. The system is based on an optical intrinsic technology with high electromagnetic compatibility and independent transducers which does not influence in any way the original mechanical / dielectric design of the transformer. There are presented the principle and application of these solution, the performed experiments and the application software enabling measured values correction depending on insulation condition at the measurement moment.

Validation of the software for digital processing of a Rogowski coil output signal

An inductive sensor (Rogowski coil) - based digital measuring system able to operate in any frequency range both in steady state and in transient duty, which uses a self-developed numerical integration system, is presented in this paper. Besides, the measuring system has an extended input signal range achieved by using a nonlinear input attenuator. Software validation is done by using the analytical expression of some typical signals appearing in heavy current technique, power electronics and electromagnetic compatibility applications.

On electric vehicle wireless chargers with tight coupling

Recently the information from industry shows that inductive power transfer electric vehicle chargers that use tight coupling between the inductive coupler coils were achieved. This paper includes a theoretical and experimental study on the possibilities that tight coupling offers versus loose coupling - widely used so far - in what concerns the ratio between the output transmitted power and the efficiency of the input-output transfer. The obtained results allowed defining a preferred domain for the coupling factor that provides a transfer efficiency of about 90% at load powers adequate for the electric vehicle chargers.

Coupling factor of planar power coils used in contactless power transfer

Contactless power transfer is a major concern due to its many applications in the modern technique. Different topologies for transmission in near field (magnetic or electric) are presented in literature, with emphasis on the process efficiency, especially when such systems are used for medium or high powers, like those needed for charging the storage batteries from electric/hybrid cars. One of the key elements of the system that provides the contactless magnetic inductive coupling between the power source and user, herein after referred to as inductive coupler, is analyzed in this paper. For reasons of space, this is usually an air-core transformer, with planar, movable windings, for easy adaptation to the conditions of using it. In order to indentify rapidly its parameters, the automatic determination of the transfer function by a vector network analyzer (VNA), apparatus currently used in laboratories, is utilized in this paper. No previous measurement is required.

Open-core internal resonant transformer with inverter supply

Use of air core or open magnetic core resonant transformers is a modern technique for generating some high reactive powers necessary to test the insulation of power capacitors, cables and high power electric machines. In this paper it is shown the design of a non - conventional open core transformer with internal parallel resonance able to operate within the narrow frequency range agreed by test standards (45 – 65 Hz) by using a simple design power inverter. The transformer - inverter assembly is compact and easily transportable on site as compared to the conventional transformers with closed magnetic circuit.

Development of a wireless battery charger for Dacia Electron EV

Wireless charging of electric or hybrid vehicles is a modern technology based on power electronics with high prospects of extension both due to the advantages it offers against the plug-in charging and as an integral part of the technology for achieving autonomous vehicles, a highly topical issue. Although the theory of these wireless systems is well known, at practical achievement one should take into account the conditions of use, where at least two elements with variable character intervene: the battery charging state and the vehicle ground clearance. Because transferred powers between 3 and 20 kW are involved, the efficiency of this conversion is essential. In this paper there is described the wireless charger used for Dacia Electron EV achieved on the structure of a Dacia Sandero series vehicle.

Direct monitoring of axial clamping forces in power transformers revisited

Transformers are the most complex and costly components of the electric power grid and that is why there are monitoring systems for most operating parameters except for the winding axial clamping forces. It has been demonstrated that they vary in time as a result of stresses to which the transformer is subjected. An objective assessment of the lifetime mechanical stability can be made only by the direct measurement of the static winding clamping forces which, irrespective of the operating regime, must be greater than the associated electro-dynamic forces. The measuring systems described in the paper have evolved over time, thus fiber optic sensors for local or global sensing are used exclusively nowadays. It has been proved that the mechanical stresses resulting from the transformers transport to the putting into operation place can be objectively identified and precisely located using the method described. An application program is being proposed, which is developed in order to relate the measured clamping force to its initial value based on models included in a global correction factor. The system is already used for highly demanded transformers such as those used for internal services in power plants or for short-circuit tests in high power laboratories but can be used both in new large power transformers or in on-site refurbished/repaired ones.

SAR values comparison between GSM and 3G

The paper analyses the level of electromagnetic radiation produced by the mobile terminals and its correlation with SAR value, until now the only method to quantify the harmful effect of using this mode of communication. It is shown that the modern 3G (UMTS) network, although uses an emission power much lower than the 2G (GSM) network and produces a lower mean exposure level, still leads to the highest SAR level. This fact is indicated by manufacturers and confirmed by comparative interlaboratory measurements, one of the latest being presented in the paper. The causes of this situation and the validity limits of the present SAR concept are explained. Finally, the reduction of the SAR test duration for 3G mobile phones is proposed, by giving up in a first stage, the measurements on GSM channels.