Factor Overall power

The overall power conversion PCE efficiency (if) of the photovoltaic cell (range 0 to 1, or percentage from 0% to 100%) can be calculated from the photocurrent density (/ph A m-2), the open-cell circuit photovoltage (Voc), the geometrical fill factor of the cell (FF), and the intensity of the incident light (typically Js = 1000Wm 2 = 0.1 Won-2) as... 

Where a plant load is predominantly induction motors it is reasonable to assume the overall power factor of a switchboard to be 0.87 lagging for low voltage and 0.89 lagging for high voltage situations. If the overall power factor is important with regard to payment for imported power, and where a penalty may be imposed on a low power factor, then a detailed calculation of active and reactive powers should be made separately, and the total kVA determined from these two totals. Any necessary power factor improvement can then be calculated from this information. 

Under full sunlight (air mass 1.5 global, intensity Is = l,000W/cm ), short circuit photo-currents ranging from 16 to 22mA/cm are reached with state-of-the art ruthenium sensitizers, while Voc is 0.7-0.86 V and the fill factor valnes 0.65-0.8. A certified overall power conversion efhciency of 10.4% was attained [62] in... 

To keep the power factor as close as possible to 100%, utility companies place capacitor banks at various locations in the distribution system, offsetting the inductive loading (lagging power factor) of most user equipment. The goal is to create an equal amount of leading PF in the system to match the lagging PF of the load. When balanced, the power factor is 100%. In practice, this is seldom attainable because loads are switched on and off at random times, but utilities routinely maintain an overall power factor of approximately 99%. To accompHsh this, capacitor banks are switched automatically to compensate for changing load conditions. 

It is desirable for all of the above parameters to have as low values as possible and this is particularly importemt in the case of high-speed, high-frequency devices and circuitry working at frequencies up to 10 MHz. Low values are indicative of minimum conversion of electrical energy to heat and little overall power loss in the system. These factors are again generally functions of frequency, temperature, humidity and the purity of the polymer. 

Noting that power = volumetric flow rate x pressure drop, the overall power per unit mass of liquid is straightforward to calculate for single-phase systems given the friction factors and voidage fraction in the mixer as supplied by mixer manufacturers or measured in the laboratory. For gas-liquid systems the volume of fluid in the mixer must be multiplied by (1 — c )) to obtain the liquid volume, so the gas fraction 4) must be known (see Section 11-5). It has been found that the Lockhart-Martinelli (1944) correction for the effect of the gas phase on pressure drop in pipe flow can be applied to static mixers with reasonable accuracy ( 20%). 

The total kVA and the overall power factor for these loads is most nearly ... 

From these calculations, the interfuel assembly gap size is determined to be 4.0 mm. In this case, the local power peaking factor takes the lowest value of 1.06 without fuel rod enrichment controls. The relative fuel rod power distribution for the case with inter-fuel assembly gap size of 4.0 mm is shown in Fig. 2.38 [9]. The pin number (from 1 to 46) on the x axis of this figure corresponds to the pin number position shown in Fig. 2.37 [9]. Although the pin powers tend to be relatively high near the middle of the water rods, and relatively low at the corners of the water rods, the overall power distribution is flat. 

Just as the efficiency of an induction motor may be reduced as its load decreases, the same is true for the power factor, only at a faster rate of decline. A typical 10-horsepower, 1800 rpm, three-phase, design B motor with a full-load power factor of about 80 percent decreases to about 65 percent at half load. Therefore, it is important not to overmotor. Select the right size motor for the right job. Figure E-8 shows that the correction of power factor by the addition of capacitors not only improves the overall power factor but also minimizes the fall-off in power factor with reduced load. 

The power factor of a motor decreases sharply at loads lower than rated as discussed in Section 1.8. All the above factors, contribute to reducing the overall system power factor, which is sometimes seen to reach a low of 0.6 or even less on an LT distribution network. 

The pressure in the regenerator depends on several factors. As the actual inlet pressure is adjusted to 0.22-0.24 MPa, the expander matches the system, but power loss is considerable. The power consumption on the air blower may be reduced at the same time as the pressure in the regenerator is lowered. However, the overall efficiency of the power recovery system is not significantly affected. 

Ranking equipment and teehnology options for an intended applieation then beeomes a matter of seleeting those projeet options with the shortest paybaek period. So, for example, if we compare a baghouse versus an electrostatic filter for a dust control application, an overall payback period for each option can be determined based on the capital investment for each piece of equipment, operating, maintenance, power costs, and other factors. 

But for power station applications, the thermal efficiency is not the only measure of the performance of a plant. While a new type of plant may involve some reduction in running costs due to improved thermal efficiency, it may also involve additional capital costs. The cost of electricity produced is the crucial criterion within the overall economics, and this depends not only on the thermal efficiency and capital costs, but also on the price of fuel, operational and maintenance costs, and the taxes imposed. Yet another factor, which has recently become important, is the production by gas turbine plants of greenhouse gases (mainly carbon dioxide) which contribute to global warming. Many countries are now considering the imposition of a special tax on the amount of CO2 produced by a power plant, and this may adversely affect the economics. So consideration of a new plant in future will involve not only the factors listed above but also the amount of CO2 produced per unit of electricity together with the extra taxes that may have to be paid. 

In the unit price of electricity (Kk) derived in Section B.2, the dominant factors are the capital cost per kilowatt (CJW), which generally decreases inversely as the square root of the power (i.e. as the fuel price the overall efficiency tjq, the utilisation H hours per year) and to a lesser extent the operational and maintenance costs (OM). 

When an A.C. synchronous machine operating as a motor in parallel with other loads and an external supply system is over-excited the machine will contribute reactive kvar to the supply. The net effect of this will be to reduce the amount of reactive current drawn from the supply, and this will improve the overall system power factor. 

Type of drive Power range (kW) Speeds Drive efficiency (%) Overall efficiency (%) including motor Power factor Main characteristics related to pump drives... 

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