摘要:

The question of total and local measurement of loss in transformer core iron, on load and open circuit, is discussed. Local loss measurement methods are reviewed and one used to find loss levels due to flux normal to the laminations. A mechanism for the generation of such flux is hypothesised and experimental evidence of its existence is presented. Experimental results are given for a test butt-lap joint in which gap and overlap were varied. The possibility of direct measurement of core loss under loaded conditions is discussed and a test method is described.

DOI:10.1049/ip-a-1.1985.0026

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The problem of estimating the error due to time discretisation in sampling digital wattmeters is dealt with in the paper; in particular, those instruments based on the simultaneous sampling of the voltage and current waveforms at equally spaced time instants in one or more periods are considered. As the discretisation error is a periodic function with zero mean value of the initial sampling instant, its RMS value can be adopted as a useful parameter for evaluating its magnitude. An algorithm for the average power computation is proposed, which also allows for the estimation of the RMS value of the error component. Some examples of application in the area of power electronics systems are discussed. The proposed method can also be used in all those problems (e.g. FFT techniques) where the integral of a periodic function is approximated by an average of equally spaced samples.

DOI:10.1049/ip-a-1.1985.0028

出版商:IEE    

年代:1985

数据来源: IET

摘要:

Electrical steels, which are used to form the magnetic flux paths of electrical machines, are categorised according to the specific total loss of the material determined by the Epstein frame method, under defined conditions of magnetic excitation. A brief review is given of the types of steels now produced, with a description of the primary magnetic parameters; e.g. permeability, power loss and apparent power which are of importance to the constructor of electrical machines. Because specific total loss and specific apparent power are derived units of measurement, the standards system which has been developed to provide an industry-based reference for these parameters is built on the traceability of base units to national standards. The problems associated with the measurement of the magnetic parameters of electrical steels are related primarily to the magnetic nonlinearity of these materials, so that uncertainty budgets must take into full account the characteristic behaviour of the test piece as well as instrumentation contributions.

DOI:10.1049/ip-a-1.1985.0030

出版商:IEE    

年代:1985

数据来源: IET

摘要:

A new technique is described for the comparison of two contours which are nominally identical. It is applicable to two-dimensional shapes and is intended to be used in the inspection of nominally identical mechanical components by comparison with a master component. The method uses the medium of a trace generated on a cathode-ray tube, as an exact copy of the master, by an optoelectronic feedback technique. This trace is then compared with the inspected contour. High overall accuracy is obtainable at relatively low cost because most of the elements of the system have no absolute accuracy requirements. The output signal measures the difference in size between the two components normal to the contour as they are scanned. A laboratory model has proved the feasibility of the method and shown an accuracy of ±15 μm in this difference measurement in a range of ±150 μm. Although, locally, this is a large proportional error, it does allow precise comparison and forms the basis of a useful instrument.

DOI:10.1049/ip-a-1.1985.0031

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The corona extinction voltage for two cylindrical conductors and a vibration damper as a function of atmospheric humidity using radio influence voltage measurements has been determined. For the 5.0 cm conductor and the vibration damper, the corona extinction voltage increases with increasing humidity. It is postulated that this is due to the capture of free electrons by water-vapour molecules. For the smaller 2.8 cm conductor, the corona extinction voltage decreases with increasing relative humidity. This different behaviour is ascribed to surface conditions, but more data is required to verify this.

DOI:10.1049/ip-a-1.1985.0032

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The optical method using a Pockels device has been used to investigate an electric field distorted by space charges due to discharge development in air. A Pockels device placed in the discharge area has the advantage of directly measuring such a field. This method is successfully applied to the measurement of the electric field in and around the leader column propagating in a rod-plane gap of 1 m subjected to positive switching impulse voltage of 0.4 MV, and 1.03 MV in a rod-plane gap of 3 m. Moreover, in the 1 m gap system, the leader propagation is effectively controlled by using a conductive thread so that the leader column passes through the Pockels device and the exact electric field in the leader column is measured. The electric field at the device increases with the approach of the leader column and reaches its peak value on the arrival of the tip of the leader column. Finally, it falls to a low constant value during the leader propagation. From the results, it is found that the peak field at the tip of the leader column is 0.8 ∼ 1.4 MV/m and that, subsequently, the low field in the leader column is 0.1 ∼ 0.5 MV/m, notwithstanding the gap spacing of 1 ∼ 3 m. Furthermore, the electric field calculated theoretically by using a space-charge model whose shape is a cylinder of 0.5 m in radius together with a hemisphere at the head of it agrees with the measured field.

DOI:10.1049/ip-a-1.1985.0033

出版商:IEE    

年代:1985

数据来源: IET