Wattmeter Method Research Articles

Some aspects of the theory of iron-testing by wattmeter and bridge methods

The paper, which is an attempt to survey the present position, opens with a discussion of the limitations of the dynamometer wattmeter. Compensation for voltage circuit phase angle and for eddy current and voltage circuit losses is discussed. The effect of the iron circuit is noted, the influence of leakage flux being pointed out. The effects of distortion are noted, and attention is drawn to some hitherto unformulated rules relating the distortion in the current and voltage waves. Null methods of using the wattmeter are briefly described, and a new circuit is proposed. The concept of complex permeability is introduced as an approach to bridge measurements, and an equivalent circuit for a test transformer is deduced. It is shown how this may be used in a novel circuit in such a way as to eliminate copper losses. The limitations of the bridge method are briefly discussed, and the relation between bridge and wattmeter methods is shown to lead to the concept of “distortion coefficient,” a new characteristic property of the iron, which can be determined experimentally and which may provide a succinct approach to distortion problems.

Some aspects of the theory of iron-testing by wattmeter and bridge methods

The paper, which is an attempt to survey the present position, opens with a discussion of the limitations of the dynamometer wattmeter. Compensation for voltage circuit phase angle and for eddy current and voltage circuit losses is discussed. The effect of the iron circuit is noted, the influence of leakage flux being pointed out. The effects of are noted, and attention is drawn to some hitherto unformulated rules relating the in the current and voltage waves. Null methods of using the wattmeter are briefly described, and a new circuit is proposed. The concept of complex permeability is introduced as an approach to bridge measurements, and an equivalent circuit for a test transformer is deduced. It is shown how this may be used in a novel circuit in such a way as to eliminate copper losses. The limitations of the bridge method are briefly discussed, and the relation between bridge and wattmeter methods is shown to lead to the concept of distortion coefficient, a new characteristic property of the iron, which can be determined experimentally and which may provide a succinct approach to problems.

Alternating-current permeability and the bridge method of magnetic testing

A method for the direct measurement of the quantities involved in the a.c. permeability of a specimen, namely Bmax. and Hmax., is described. It is applied in an investigation of the dependence of the a.c. permeability of commercial sheet materials on frequency and wave-shape at power and telephonic frequencies. In agreement with other observers, the effect of frequency is found to be neglible up to 500 cycles per sec. apart from a reduction, attributable to eddy currents, at magnetizing forces for which the permeability is high. Tests on a range of specimens with magnetizations giving wave-shape conditions varying between sinusoidal voltage and sinusoidal current, failed to show the increased permeability with approximation to a sinusoidal current wave which was observed by Lombardi and McLachlan. Within the accuracy of the measurements, the permeability appeared independent of wave-shape between these two practical limiting conditions. In the second part of the paper a comparison between the results of loss measurements on magnetic meterials by bridge and wattmeter methods is described. The discrepancies observed are shown to be entirely attributable to the errors in the bridge results due to the presence of harmonics, and the conditions under which the bridge method may be used satisfactorily for iron-testing, at both power and telephonic frequencies, are deduced.

Measurement of Power and Efficiency of Radio Transmitting Apparatus

This paper reports the various methods and results of the measurement of power and efficiency in radio transmitting apparatus. High-frequency power measurements are classified as wattmeter, ammeter, calorimeter and indirect methods. The high-frequency wattmeter method and the methods based on the current and resistance measurements are briefly discussed. The direct and indirect calorimeter methods are upheld by the authors on account of their advantages, which are enumerated. The experimental results employing calorimeter methods for direct and indirect power measurement are quantitatively reported and the degree of precision obtainable in practical applications is shown.

Low power-factor measurements at high voltages

The paper describes a study of methods of measuring dielectric losses which has been carried out with the object of determining the nature and magnitude of the various errors to which different methods are liable. The most important errors are those due to stray capacitance currents, which affect especially the phase angle of the currents in resistors commonly used in wattmeter methods. A method is developed of shielding a simple resistor of flowing water, so that the current is in phase with the voltage within about 0.0001 radian. A resistor has been developed on these lines for 150 kV. The standard of reference has been a specially designed air condenser of the parallel-plate type. The separation of the plates is variable; and at 10 cm separation, suitable for 100 kV, the capacitance is about 500 cm. The curvature of the edges and of the guard plates was decided as a result of studying the electric stress distribution by models in an electrolyte. The use of a condenser with the Schering bridge form of circuit has been found to be almost free from errors of importance which are difficult to allow for. The work has been carried out for the British Electrical and Allied Industries Research Association, more particularly with reference to the measurement of the power loss in cable dielectrics.

The use of the dynamometer wattmeter for measuring the dielectric power loss and power factor of the insulation of high-tension lead-covered cables

The use of the dynamometer wattmeter for measuring the dielectric power loss and power factor of cable and capacitor insulation is not new, but dates from about 1890. Dynamometer wattmeters as available today are suitable for making these measurements. Care and attention must be given to their application. The usual methods of application are: 1. Compensated dynamometer wattmeter method, with air capacitor, 2. Inductance variation method (phase-defect compensation method), with air capacitor, 3. Series resistor and wattmeter method, 4. Resonance wattmeter method. Comparative measurements of dielectric power loss and power factor of cable samples indicate that results are being obtained with the dynamometer wattmeter wherein the probable departure from the true value is within from 10 to 20 per cent. There is need for an effective means of standardizing any measuring equipment. Study of the calorimeter method for this purpose seems desirable.

IV---The Use of the Dynamometer Wattmeter for Measuring the Dielectric Power Loss and Power Factor of the Insulation of High-Tension Lead-Covered Cables

The use of the dynamometer wattmeter for measuring the dielectric power loss and power factor of cable and capacitor insulation is not new, but dates from about 1890. Dynamometer wattmeters as available today are suitable for making these measurements. Care and attention must be given to their application. The usual methods of application are: 1. Compensated dynamometer wattmeter method, with air capacitor, 2. Inductance variation method (phase-defect compensation method), with air capacitor, 3. Series resistor and wattmeter method, 4. Resonance wattmeter method. Comparative measurements of dielectric power loss and power factor of cable samples indicate that results are being obttained with the dynamometer wattmeter wherein the probable departure from the true value is within from 10 to 20 per cent. There is need for an effective means of standardizing any measuring equipment. Study of the calorimeter method for this purpose seems desirable.

The effect of temperature upon the hysteresis loss in sheet steel

In the paper which the writer presented before the Institute last year upon this subject <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∗</sup> it was shown that there was no apparent change in the law governing the variation of the hysteresis loss with the induction for all temperatures from atmospheric up to near the point where the steel became non-magnetic. The writer suggested at that time that the rate of heating the sample might affect the change in hysteresis loss with changing temperature and the measurements described below were carried out to investigate this point. It was thought also that some additional light might be thrown on this subject if hysteresis loops were obtained from the sample near the non-magnetic temperature. This had not been done in the previous tests as the samples had been prepared for the two-frequency method of measurement in order to obtain results quickly at any temperature over as wide a range of induction as possible. An attempt was made at that time to obtain a few characteristic loops at high temperatures, but the use of iron wire for the secondary winding on the sample introduced errors on account of variable thermal currents in the galvanometer circuit which could not be readily eliminated. It was also found that the insulation resistance between primary and secondary at high temperatures was hot sufficiently good to permit measurements by the galvanometer method, although no error could be detected from this source with the two-frequency wattmeter method.

The testing of transformers and transformer iron

1. Introduction. 2. Regulation diagram. 3. Diagram of voltage characteristic. 4. The short-circuit test. 5. Proposed standard transformer test. 6. The 3-point wattmeter method. 7. Standard tests for-(a) core losses: separation by constant-frequency test ; (b) copper losses; (c) efficiency; (d) heating ; (e) regulation. 8. The auxiliary transformer. 9. Special tests-(a) by means of extra turns ; (b) at half power factor; (c) out-of-phase test; (d) 3-phase transformers. 10. Hysteresis by slow cyclic change-(a) method of constant induced voltage ; (b) theory; (c) application to testing of small samples. 11. Conclusion.

Wattmeter methods of measuring power expended upon condensers and circuits of low power factor

Wattmeter methods of measuring power expended upon condensers and circuits of low power factor