Power factor converter

The power user should also be concerned about power factor, which is the ratio of the real power (watts) consumed to the total apparent power (voltamperes) drawn from the source. In an ideal world, all apparent power drawn will be converted to useful work and supply any losses associated with performing the work. For several reasons, which will be discussed in a later chapter, this is not so in the real world. As the ratio between the real power needs of the system and the apparent power... 

Power factor (PF) may be viewed as the percentage of the total apparent power that is converted to real or useful power. Thus, active power (/ ) can be defined by ... 

In an electrical system, if the power factor is 0.80, 80% of the apparent power is converted into useful work. Apparent power is what the transformer that serves a home or business has to carry in order for that home or business to function. Active power is the portion of the apparent power that performs useful work and supplies losses in the electrical equipment that are associated with doing the work. Higher power factor leads to more optimum use of electrical current in a facility. Can a power factor reach 100% In theory it can, but in practice it cannot without some form of power factor correction device. The reason why it can approach 100% power factor but not quite reach it is because all electrical circuits have inductance and capacitance, which introduce reactive power requirements. The reactive power is that... 

This equation includes the first derivative of the energy with respect to the parameter a, Eq. It is also an equation with a very real correspondence to first-order perturbation theory, and that suggests how best to use it. Indeed, the general procedure being outlined here differs from a perturbation expansion in only one minor way. A perturbation expansion is in terms of powers of one or more parameters. The derivative expansion is a Taylor-series-type expansion that has each nth power series term divided by n. That factor converts perturbative energy corrections into energy derivatives. So, Eqn. (30) is conveniently rearranged, just as is usually done in an elementary introduction to perturbation theory ... 

Electrical energy is furnished to the plant at 5000 volts, 50 cycles, three phase. Two 1300-kva. transformers step the voltage down to 115 volts. The 50-cycle power is converted to 500 cycles by alternators with a capacity of 36 kw. A single motor drives two alternators, and a self-induction coil is used to regulate the power factor and ensure operational stability. The 500-cycle current is stepped up to 10,000 volts for the tubular ozonizers and 18,000 to 20,000 volts for the plate type. 

An item of concern to all, in evaluating an experiment, or in scaling up for pilot plant operation, is the electrical efficiency of a process. Care must be taken not to confuse equipment power factor with what might be called electrical efficiency of conversion, though both may contribute to the same end result. Power factor relates to ability to convert equipment input volt-amperes (not necessarily in phase) to available chemical-result-producing watts. This is a function of electrical equipment and electrical circuit design. 

As the human body is homeothermic, heat production from the body should ideally equal heat loss. The metabolic rate can vary from about 80 W at rest up to over 1000 W during most strenuous activities, and a large part of this power is converted into heat (typically 80-85%). If the heat production is high, the largest part of this heat has to be evacuated to the environment. The heat exchange with the environment depends on four environmental factors the air temperature, the radiant temperature, the relative humidity in the air and the wind speed. Heat transfer can occur by four different means ... 

The loss is converted to heat (dissipation). For low values of 6, the losses are low so that in the limit 6 = 0, there is no loss (this is the ideal capacitor). Low values of tan 6 may be approximated as tan 6 sin 6 cos 6, where cos 6 is defined as the power factor, 6 represents the angle between the direction of the voltage and current in an alternating current. Then Power = Voltage X Current x Power Factor. The loss factor approximately equals the product of the power factor and the dielectric constant, all values taken at a frequency of 60 Hertz. In nonpolar polymers (Teflon, polyolefins, polystyrene)... 

For the purpose of the present document, the area of interest here is the Incoming Power Conversion section of the Variable Frequency Drive (VFD), the Front End of the drive, this is what the AC feeder network sees and from which the effects in concern originate from. All other considerations downstream such as Inverter frequency, motor harmonics, motor power factor etc. are totally independent of the AC front end side, effectively isolated by the DC intermediate circuit. In the above diagram, the term AC to DC converter is used as a generic term to describe Passive and Active Front End types. 

Figure 4 shows both the motor current (inverter output) and the converter power (drive input kVA or kW). The converter provides current to the DC bus at unity power factor. Current is supplied at rated drive input voltage and power utility frequency. Because of the separation of the drive input and output sections provided by the DC bus, the average input current at rated input voltage will be less than the average motor current, which is supplied at a lower average output voltage. 

The input RMS kVA appears to be less than the motor power rating. This apparent anomaly is because a large amount of motor current is apphed by the inverter (output) at low motor voltage diuing the hoist creep and acceleration phases. This kVA demand is supplied by the converter at the drive input voltage (3,550V), and so the input current is lower than the motor current dming these phases. While the inverter is subject to the motor ciurent, the converter supplies the only the real power (plus losses) to the drive inverter and motor at unity power factor. 

In the case of constantly fluxed synchronous motors, the stator cmrent will follow the motor torque more closely. After adding excitation losses, the synchronous motor efficiency is still shghtly better than the induction motor. The drive inverter for a synchronous motor supplies the armature or torque producing current, compared to the induction motor apph-cation where the inverter must supply torque producing current and magnetising current In the synchronous motor application, the motor operates at unity power factor, which reduces current demand in the inverter section. As a result, there are fewer losses in the inverter and motor, and to a lesser extent fewer losses in the converter. 

The AC drive reduces the RMS kVA demand by converting incoming power at unity power factor. However, the power system is still subject to a high peak demand at the end of the acceleration phase of the hoisting cycle. By reducing the acceleration at the end of the acceleration phase of the duty cycle, the peak power (and kVA) demand is reduced. Various algorithms can be applied. In the example above, the acceleration rate is reduced at 90% of full speed, for... 

The drive converter normally operates at unity power factor. If the drive converter and inverter are the same frame size (current rating), the converter will have additional capacity after supplying the hoist drive current. This additional capacity can be used in the form of leading VAR s. The converter can be programmed to provide either fixed or variable leading VAR s, and if connected to the site power management system, could be used to dynamically correct power factor at the mine site. 

It seems to be a mis-conception, however, amongst some mine operators that MG sets are old fashioned, maintenance intensive and inefficient and if you are going to upgrade or refurbish a DC winder, you have to replace the MG set with a thyristor converter They fail to understand that, particularly when the power supply to a mine is less robust, subject to voltage fluctuations and sensitive to harmonic and other disturbances, a thyristor converter is possibly the worst form of drive that should be used. Operation of the winder at slow speed produces a very low power factor draw on the AC supply (typically as low as 0.2). Furthermore, if the winder s drive motor is of an old design with a sohd rather than a laminated field frame, its power output would need to be de-rated by is much is 15% in some cases because of additional heating created by the AC components of the DC supply developed by a thyristor converter. 

Before the analysis can begin, feeder loading must be known. Several different methods can be used for this task. If the utility maintains a database on each customer connected to a distribution transformer, it can use the billing data to determine the kilowatt hour supplied by each transformer for a given month. Methods can then be used to convert the kilowatt hour to a noncoincident peak kilovoltampere demand for all distribution transformers connected on the feeder. Ifthis in formation is not available, the kilovoltampere rating of the transformer and a representative power factor can be used as the load. With the metered demand at the substation, the transformer loads can be allocated, for each phase, such that the allocated loads plus losses wiU equal the metered substation demand. 

J.A. Pomilio and G. Spiazzi, Soft-commutated Cuk and SEPIC converters as power factor preregulators , 20th International Conference on Industrial Electronics, Control and Instrumentation, pp. 256-261, 1994. 

Diss Factor Dissipation Factor and power factor are the same for most dielectrics (insulators) and are a measure of how much power is converted to heat. Values may be quoted in two ways, e.g. 0.002 or 20 X 10. Heat conversion is undesirable in an insulator and so the power factor should be as low as possible. 

TMS triflate [27607-77-8] is an extremely powerful sdylating agent for most active hydrogens. It surpasses the sdylating potential of TMCS by a factor of nearly 10. It readily converts 1,2- and 1,3-diketones into disilylated dienes (7). 

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