Dummy load

Some power tubes can be operated without the need for a protective ferrite isolator. One example is the cooker magnetron (700 W) used in modern microwave ovens (57). At higher power levels, such as 25 kW, it is more common to employ a protective ferrite device, particularly in the form of a circulator (58), as shown in Figure 3. This results in a power loss equivalent to a few percentage points in system efficiency. The ferrite circulator prevents reflected power from returning to the power tube and instead directs it into an auxiHary dummy load. The pulling of tube frequency is thus minimised. 

L If a nuclear power plant loses its connection to the offsite load, it must shutdown because it cannot be cutback sufficiently that its electrical output matches its "hotel" load. Outline a PSA study to determine the risk reduction that might be achieved by switching in a dummy load to avoid shutdown and keep the plant online. 

Answer This problem is related to the risk from the Loss of Off-Site Power (LOOP) initiator. It is necessary to determine the risk from LOOP, and the frequency of the LOOP initiator. Correct the LOOP initiator for the frequency that the plant could not have continued operation if it could have been connected to a load. Then a systems analysis of the dummy load systems must be performed to determine its reliability which is used to correct the LOOP initiator. Any risk associated with the dummy load must be added to the LOOP risk. These corrections give the risk change due to not having to shut the plant down when it loses its connection to the power line. Another way to avoid shutting down when the load is lost is with a steam bypass around the turbine so the turbine-generator only supplies enough power for the hotel load. 

The necessary skills should be on-site to attend to any minor faults but must not be allowed to alter settings from one test to another, except as required by the test procedure. Dummy loads should be ready for use. If sensitive equipment is to be present (as might be the case in upgrading computer room plant) then the interested parties must agree limits previously. This may also apply to parts of the plant itself such as humidity-detecting elements. The latter can be protected physically. The job specification should state which parts of the procedure apply (if not all). 

Fig. 14.5 A modified MW oven for microwave photochemistry experiments. A. magnetron, B. reaction mixture with the EDL and a magnetic stir bar, C. aluminum plate, D. magnetic stirrer, E. infrared pyrometer, F. circulating water in a glass tube, G. dummy load inside the oven cavity [88]. With permission from Elsevier Science.

E.3.3.2 The risk of overspeed is reduced when the driven equipment, such as a pump or fan, caimot reahstically be expected to lose function. The risk is increased when the driven equipment is a generator, since a sudden disconnection from electric power circuits will unload the HPRT. In the latter case, automatic sensing and dummy-load switching should be provided. 

Each of the above was manufd in variant forms. These variants incorporate a number of changes from the basic, including case taper differences, size of primer, wall thickness, type of flechette and tracer. In addition the basic forms (and probably some of the variants too) were produced in proof and dummy loadings The potential of multi-flechette loadings was realized early, and AAI tried, in 1957, a multi-flechette cartridge based on a 12 gauge shotgun... 

Circulator A three port ferrite device allowing transmission of energy in one direction but directing reflected energy into water load (dummy load) connected at the third port. 

Most commercial ovens, whether single-mode or multi-mode models, are protected from potential damage caused by reflected energy by an automatic cut-off mechanism also, some ovens provide additional protection in the form of a circulator that directs reflected energy into a dummy load. A circulator is essentially a device that uses ferrites and static magnetic fields to allow microwaves to pass in the forward direction but diverts reflected waves into a dummy load where the energy is harmlessly dissipated as heat. 

Empty chamber studies are sterilizer specific. Further process validation work is product specific (load specific) and may be done with dummy product if required. If this option is exercised, care must be taken to ensure that dummy loads are truly representative of genuine product. Scrap product is ideal for this purpose but may not be readily available for high cost products (e.g.. cardiac pacemakers). If good product is used in validation, it should nut be released as sterile until the validation program has been completed and signed off as satisfactory. 

The magic-tee is inherently noisy because the receiver sees noise not only from the tank circuit but also from the dummy load and because half of the signal from the tank circuit is sent back towards the transmitter. The easy way out of this limitation is to use a directional coupler instead of a magic-tee. A directional coupler, also described further in V. C. 10., is a three port device which amounts to an asymmetric power splitter and it works well as a duplexer. The isolation between the receiver and the transmitter is achieved when the tank circuit impedance is adjusted to be a real and specified value, just as with the magic-tee. The attenuated path is placed between the transmitter and the tank circuit which means that more input power is required than with a magic-tee... 

An alternative approach is the use of a current drive, in which a programming current is latched in the cell. One approach is to build a current mirror in which one arm is driven through a dummy load and then latched to the other arm (containing the OLED) each cycle. This linearizes the drive in current and also compensates for some spatial variation across the panel. Yet another approach is to drive the latching element itself and sustain the driven current. While complicated from a circuit perspective, this approach has the greatest potential for degradation compensation. Several architectures and their modeling are explored in [135]. 

Table 6.6 A possible schedule for a trial with double dummy loading.

Results internal currents are caused mostly by capacitive effects carbon oxidation occurs simultaneously and has negligible contribution to internal currents Close/open state of outlets and application of dummy load effect on degradation of MEA Results using a thin electrolyte membrane, outlets should be closed to limit degradation during on/off operation using a thick electrolyte membrane, the dummy load should be applied to limit degradation... 

Undesired side reactions occur at high electrode potentials as it is described in Sections 23.3 and 23.4. Long idle phases with cell voltages near OCV should therefore be avoided. This is particularly valid for the upper potential hmit of potential cycles [67], since dynamic operation leads to accelerated cell degradation as explained in Section 20.3. A minimum cell current is required in order to keep the cell voltage significantly lower than OCV. If constant electric consumers are not present in the fuel-cell system, a dummy load can be integrated. 

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