Average Power Factor Research Articles

Average Power Factor and Power Efficiency for Traction Duty Cycles

The line-side characteristics of ac traction drives are usually specified in terms of the power factor. By standards, this factor is defined for steady state conditions only. An average power factor throughout a load cycle according to the normal operation of a railway drive is presented. Different approaches to an average power factor have been reported in the literature. The approach presented here is based on a physical background. In contrast to previous definitions of an average power factor the new factor has the value of one if and only if constant active power is taken from the supply throughout the load cycle. As the power consumption as a function of time is rather a characteristic of the load cycle than of the power converter it is further suggested that the new average power factor be split into two factors, one specifying the load cycle, the other describing the converter.

Micromonitor: a microprocessor module for power system monitoring

This paper describes a microprocessor module that scans three-phase voltages and currents, computes RMS voltages and currents, and calculates average power, voltamperes, reactive power and power factor. This module is versatile inasmuch as it can find application in power system data acquisition and logging, power system relaying, etc. The module is based on the Texas Instruments 16-bit microprocessor board TMS 990 189 . The principle underlying the computation of RMS and average value is introduced first, followed by choice of sampling frequency and details of hardware and software design.

An Electronic Energy and Average Power-Factor Meter with Controllable Nonuniform Rate

The first part of the paper describes the design of an electronic watthour meter competitive in price and performance with the electromechanical (Ferraris) type. The circuit uses only integrated circuits (IC's) and passive components in a multiplier low-pass filter voltage to frequency converter (VFC) configuration and satisfies the design criterion. The basic design is then modified to obtain an average power-factor meter.

Some technical considerations concerning power factor in relation to tariffs

The paper draws attention to the desirability of clear definition of such terms as power factor, kVA, etc., with regard to tariffs. Ambiguities are possible, and Sections (1) to (6) deal with those relating to polyphase power factor. The “ vector sum ” and “ arithmetic sum ” definitions of 3-phase power factor are stated, and a hypothetical 3-phase case is considered in order to support the contention that the latter definition is more advantageous as a tariff basis than the former. A suggestion is made with regard to the basis of a tariff when there is diversity of incidence of demand on individual phases. Sections (7) et seq. deal with the use of sine and cosine meters and the possible ambiguities resulting from variable power factors. Two single-phase meters on 3-phase balanced loads give rise to the same ambiguities from the same cause. A table of figures and a set of curves are given exhibiting the range of errors which may result in estimating kVA-hours and average power factor from these combinations of meters. The conclusion is drawn that it is not advisable to use them in certain circumstances. Section (17) summarizes the author's opinions on current practice in kVA measurement. Appendix 1 contains observations relating to the ideal neutral point of a 3-phase system when no real neutral is accessible.

Power factor and tariff

The great amount of attention now being given to the question of poor power factor suggests that tariffs such as are commonly used to-day are unsuitable in present circumstances. The paper contends that a wattless component of current, despite its having no energy content, involves the supply undertaking in extra running costs, and that therefore a charge should be levied for supplying it. A three-part tariff is proposed, embracing a periodic charge per kVA of maximum demand, a charge per kWh of energy, and a charge per kVA-hour of lagging wattless component. The additional running costs caused by wattless component are briefly touched on, and it is suggested that in a station with an average power factor of 0.7 the charge per kVA-hour of wattless component should be about one-ninth of the charge per kWh of energy. The question of metering the three-part tariff is discussed, and a method is shown whereby, with balanced load, a three-phase wattmeter may be ?biased? to record the total energy consumption, plus or minus any desired fraction of the kVA-hours of lagging or leading wattless component.

Power factor: its technical and commercial aspects

The author submits that the highest possible efficiency of an electrical undertaking can only be attained by studying all the factors which at present militate against a low selling price per unit. The low average power factor existing on many undertakings could be raised, and consumers should be encouraged to improve their power factor by the establishment of a principle of granting a rebate for a high power factor.It is considered that a kVA charge plus a kWh charge is more equitable to power suppliers and consumers than a pure kWh basis of charge, and, now that the 1922 Act provides for a kVA basis at the option of any supplier, it is felt that a change should be made as soon as possible.Consumers should be educated and advice given gratuitously by a supply department so that the most suitable plant may be installed in order to obtain the highest all-round efficiency. By increasing the average power factor on any a.c. system the capital expenditure on generating, transforming and distribution plant, and also energy losses, can be considerably reduced to the advantage of both supplier and consumer.Power-factor-correcting apparatus is now on the market and is suitable for all requirements. Each type should be considered on its merits for every installation. The selling price of electrical energy per unit should be reduced on an improvement of power factor, and increased where it falls below a pre-determined standard.

The mean error of an electricity meter

Questions concerning the accuracy of electricity meters in actual service have reference to the error of registration over a period, rather than the speed error at any particular value of the power in the circuit. There will be a certain load at which the speed error is the same as the error of registration over the period in question, and the purpose of the author is to investigate a method of ascertaining this load. From a consideration of the sources of error in electricity meters it appears that, in meters in which a constant frictional torque is the only disturbing factor, the error of registration over a period is the speed error at the average load over that period. In meters having in addition a disturbing torque proportional to the square of the speed, the error over a period will be slightly slower than the error at the average speed. A discussion of the effect of varying power factor leads to the result that the error of registration due to this cause is equal to that determined by a speed test at an average power factor deduced from the readings of an energy meter and a meter integrating the wattless component of the power in the circuit.