Power transfer

Maximum power transfer to electrons for a given internal field occurs when = u). The plasma frequency, CO, is the frequency at which e = 0 ... 

Various data sources (44) on plasma parameters can be used to calculate conditions for plasma excitation and resulting properties for microwave coupling. Interactions ia a d-c magnetic field are more compHcated and offer a rich array of means for microwave power transfer (45). The Hterature offers many data sources for dielectric or magnetic permittivities or permeabiHty of materials (30,31,46). Because these properties vary considerably with frequency and temperature, available experimental data are iasufficient to satisfy all proposed appHcations. In these cases, available theories can be appHed or the dielectric parameters can be determined experimentally (47). 

The power transferred by the stator to the rotor, P, also known as air gap power at synchronous speed, can be expressed in kW by ... 

Optimizing power transfer through reactive control 24/792... 

In FIT systems too the concept is very similar. Now. besides the p.f., the stability of the system also defines the prerequisites for efficient power transfer over long distances. The tise of both shunt and series compensations may now be necessary to achieve the desired goal. 

Enhancing the steady-state power transfer capability of the lines over long distances, or making sliort lines capable of transferring larger powers. 

It has been established that the active power transfer through a power system can be expressed by... 

Maximum power transfer is possible when 8= 90°. If the line is compensated, say, at the midpoint, as shown in Figure 24.16(a), then the maximum power transfer will improve to... 

To optimize this power transfer through reactive control let us study equation (24.10) for the parameters that can be varied to achieve this objective. The active power transfer will depend upon the following factors ... 

Equation (24.3) defines the active power as independent of p.f. However, depending upon the p.f. of the load, this will adjust the load angle S. The larger the angle of transmission, the higher will be the power transfer. Figure 24.19 illustrates the power transfer characteristics of a 250 km line selected from Table 24.5. 

The element Pg/sin B can be considered as the steady-state stability limit of the line, say P ax- I tie length compensation can improve the voltage profile and hence the power transfer capability of the line as follows. 

Figure 24.20 illustrates three power transfer or load curves ... 

When the line is compensated, and a near-flat voltage profile can be ensured so that during all such disturbances the receiving-end voltage will stay within permissible limits, the load angle can be raised to 45-60° to achieve a high power transfer. 

For each p.f. and line length the curve V,. versus P describes a certain trajectory. Maximum power can be transferred only within these trajectories. Each line length has a theoretical optimum level of power transfer, P,nax. which is defined by PoFtn 6. In Table 24.5 we have worked out these levels for different line lengths, for the system considered in Example 24.1. 

Z plays a very significant role in the power transfer capability of a line. By reducing the value of Z , the power transfer capability of a systein can be increased. Since... 

Limit the switching surges as discussed in Section 23.5.1. But they may affect the steady-state power transfer capability of the system (V,-/Z). Refer to reactive power control (equation (24.10)). 

Application of series capacitors and analysis of an uncompensated transmission line and the capability of power transfer and system regulation with and without series compensation are also presented. 

The on period of the power switeh must be set to the resonant period of the tank eireuit. The power transferred to the load is done by varying the amount of on-times per seeond of the power switeh. So the ZCS quasi-resonant eon-verter needs a fixed on-time, variable off-time method of eontrol. The eontrol ICs presently available on the market perform just this funetion. The eontrol equation is given by... 

Underground transmission lines are preferred in places where rights-of-way are severely limited because they can be placed much closer together than overhead lines. They are also favored for aesthetic reasons. They may be directly buried in the soil, buried in protective steel or plastic pipes, or placed in subterranean tunnels. The conductors are usually contained within plastic insulation encased in a thin metallic sheath. The conductors enclosed in steel pipes may be immersed in oil, which may be circulated for cooling purposes. For all types of underground lines, the capacitance is higher than for overhead lines, and the power transfer capability is usually limited by the resistive losses instead of the inductance. Wliile not exposed to environmental... 

A second German effort, designated HSST, has been undeiway since 1974. This is a lower speed EMS design and uses a LIM with power transfer via sliding contacts. This system has been demonstrated on several occasions and there are pending plans for implementation, but past plans have never been carried out and the future is uncertain. 

One alternative to planning in this environment of unknowns is called scenario planning. Utility planners in 2000 continue to estimate resource requirements for five to ten years into the future. These resources could be constructed indigenous to their systems or external to their systems, or purchased from off-system. By considering multiple alternatives for generation sources, the planner can simulate power transfers from within and outside each system. The results of these scenario analyses can be used to estimate where critical transmission might be constructed to be most effective for wide-area power transfer. Similarly, analyzing multiple transfers across a system can provide further justification for a new transmission path. 

Figure 5.2. Two of the more common types of low pressure CVD reactor, (a) Hot Filament Reactor - these utilise a continually pumped vacuum chamber, while process gases are metered in at carefully controlled rates (typically a total flow rate of a few hundred cubic centimetres per minute). Throttle valves maintain the pressure in the chamber at typically 20-30 torr, while a heater is used to bring the substrate up to a temperature of 700-900°C. The substrate to be coated - e.g. a piece of silicon or molybdenum - sits on the heater, a few millimetres beneath a tungsten filament, which is electrically heated to temperatures in excess of 2200 °C. (b) Microwave Plasma Reactor - in these systems, microwave power is coupled into the process gases via an antenna pointing into the chamber. The size of the chamber is altered by a sliding barrier to achieve maximum microwave power transfer, which results in a ball of hot, ionised gas (a plasma ball) sitting on top of the heated substrate, onto which the diamond film is deposited.

The subtractive method was adapted from Horwitz [182], and is easiest in use. The principle is to measure the power delivered to the system, including the tuned matching network, in the case that the discharge is on (Ptot) and in the case that it is off, i.e. when the system is evacuated (Pvac)- with the constraint that in both cases Plot and Pvac are measured for the same electrode voltage Vpp. The matcher efficiency [181] or power transfer efficiency r]p [183] then is defined as... 

For two plane parallel surfaces, both of area A and of emissivities s2 at respective temperatures 7j and T2, the radiative power transfer is ... 

It is worth noting that the p in formula (5.6) is the pressure inside the dewar (e.g. the vacuum jacket) which is different from the pressure measured by a gauge at room temperature connected to the vacuum space at low temperature. The power transferred by the gas in the sub-kelvin range is usually negligible. 

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