Power factor leading

The existing and/or required power factor (leading or lagging) must be stated for a synchronous motor. 

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... 

Sufficient titanate leads to a fully hardened polymer. Using only enough titanate to react with free hydroxyls, the resin may subsequently be cured at lower cost with conventional cross-linking agents. The titanated epoxy resin has a low power factor, which is important in electrical appHcations, eg, potting components and insulation (see Embedding). Titanates improve adhesion of metals to epoxies. 

Field current is an important control element. It controls not only the power factor but also the pullout torque (the load at which the motor pulls out of synchronism). For example, field forcing can prevent pullout on anticipated high transient loads or voltage dips. Loads with known high transient torques are driven freqiiently with 80 percent power-factor synchronous motors. The needed additional field supplies both additional pullout torque and power-factor correc tion for the power system. When high pullout torque is required, the leading power-factor machine is often less expensive than a unity-power-factor motor with the same torque capabihty. 

Automatic correction is always recommended to eliminate manual dependence and to achieve better accuracy. It also elimintites the risk of a leading power factor by a human error that may cause an excessive voltage at the motor and the control gear terminals. 

In addition to power factor considerations, synchronous motor efficiency is higher than similar induction motors. Efficiencies are shown in Table 7-1 for typical induction and unity power factor synchronous motors. Leading power factor synchronous motors have efficiencies approximately 0.5-1.0% lower. 

With polar molecules the value of the dielectric constant is additionally dependent on dipole polarisation and commonly has values between 3.0 and 7.0. The extent of dipole polarisation will depend on frequency, an increase in frequency eventually leading to a reduction in dielectric constant. Power factor-frequency curves will go through a maximum. 

The chemical resistance of polyethylene is, to a large measure, that expected of an alkane. It is not chemically attacked by non-oxidising acids, alkalis and many aqueous solutions. Nitric acid oxidises the polymer, leading to a rise in power factor and to a deterioration in mechanical properties. As with the simple alkanes, halogens combine with the hydrocarbon by means of substitution mechanisms. 

The insulating properties of polyethylene compare favourably with those of any other dielectric material. As it is a non-polar material, properties such as power factor and dielectric constant are almost independent of temperature and frequency. Dielectric constant is linearly dependent on density and a reduction of density on heating leads to a small reduction in dielectric constant. Some typical data are given in Table 10.6. 

Oxidation of polyethylene with the formation of carbonyl groups can lead to a serious increase in power factor. Antioxidants are incorporated into compounds for electrical applications in order to reduce the effect. 

Preheating techniques are commonly employed since these lead to shorter cures, easier flow and generally better products. The high power factor of the material enables high-frequency preheaters to be used successfully. It is also frequently advantageous to pellet the powders as in the case of phenolics. 

The power factor indicates the portion of total power which is consumed by the load. The power factor is leading in capacitive loads, lagging in inductive loads, and unity in resistive loads. Figure 17-2 shows power triangles to illustrate power factor terms. 

Available with unity or a leading power factor. 

Power-factor can be rated at unity, leading, or even lagging. The synchronous motor can supply corrective kvar to counteract lagging power factor caused by induction motors or other inductive loads. 

Figure 14-10 compares the efficiencies of the synchronous and induction motors. For a synchronous motor designed with an 0.8 power factor, the motor delivers a leading magnetizing kva component equal to 60% of the motor kva rating. The power factor of an induction motor is always... 

The pull-out or breakdown torque must be greater than the maximum torque required by the driven equipment to prevent stalling, usually 150% of full load torque for unity-power fector motors and 220-225% for 0.8 leading power factor motors. ... 

Review the types of motors proposed for a process plant with a qualified electrical engineer thereby evaluating whether the mix of synchronous and induction motors will help the net power factor for the plant, because a net lagging factor for plants means that all power to that plant will cost more than if the factor were unity or leading. From Brown and Cadickd ... 

The usual synchronous motor power factors are unity (1.0) or 0.8 leading. Values of 0.7 or 0.6 leading will give more leading correction to an otherwise lagging system. 

The induction motor usually requires irom 0.3 to 0.6 reactive magnetizing kva per hp of operating load, but an 0.8 leading power factor synchronous motor will deliver from 0.4-0.6 corrective magnetizing kva per hp depending on the mechanical load carried. Thus, equal connected hp in induction and 0.8 leading power factor synchronous motors will result in an approximate unity power factor for the system. 

However, the power factor of the current drawn from the supply will only improve if the power factor of the generated current is less than that of the parallel loads, since the active power drawn from the supply will also be reduced by the amount of actual power generated. In each case increasing the excitation so that the power factor of the current drawn from the supply can improve to unity or become leading can increase the reactive current produced by the synchronous machine within the capabilities of the machine. In this case, the installation becomes a net exporter of lagging reactive current to the supply. Figure 16.8 illustrates these two cases. 

For relatively small loads, the power factor correction equipment usually takes the form of static capacitors. In larger installations, it may be more economic to install an A.C. synchronous motor that, if its excitation is adjusted correctly, can be made to draw a leading current from the supply. In most industrial plants, the load is variable, and to gain the maximum benefit from the power factor correction plant this must be varied to suit the load conditions. 

Fs is the stopping power factor. Electron penetration is a function not only of the incident electron energy (which is constant for a given analysis) but also on the stopping power of the sample, which depends somewhat on atomic number. Reed (1993) derives equations for the generated characteristic X-ray intensity, leading to expressions for Fs. 

Two common alternatives are available for electrodepositing tin 30 alkaline and acidic baths. The alkaline bath has good throwing power but consumes more power than the acid bath. Tin is present in the alkaline bath as stannate(TV), [Sn(OH)6]2, the bath being approximately 0.25 M in free hydroxide ion (pH 13.4). The hydroxide ion is the principal charge carrier. Potassium is superior to sodium as the counter ion (greater ionic mobility) but economic factors lead to the continued use of sodium in many plants. The hydroxide ions, acting as a sink for dissolved CO2, also prevent two undesirable reactions (equations 24 and 25). 

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