Star point

The scheme is termed a closed transient switching. A comparison of the two methods in terms of voltage transients and current overshoots is given in Table 4.1. In an AIT starter The same logic can be applied as discussed above. The star point of the AIT is opened and connected through the main contactor C3 to provide a near replica to a Y A switching. Figure 4.7 illustrates the revised scheme. 

In HT motors, however, these tenninal boxes are always separate because two or more voltages (main and auxiliary). For main terminals there are normally two terminal boxes - one on one side of the stator to house the main three-phase stator teiminals and the second on the other side to form the star point. These boxes are generally interchangeable to facilitate cable routing. 

Continuous All types of system grounding (i) Between lines or (it) Between transformer star point and ground... 

Voltage polarization depends upon the location of the relay and the location of the fault. It is possible that the residual voltage, at a particular location in the system, is not sufficient to actuate the voltage coil of the directional G/F relay. In such an event, current polarization is used to supplement voltage polarization. Current polarization is possible, provided that a star point is created on the system, even through a A/t> power transformer, if such a transformer is available in the same circuit. Figure 21.20. Else a grounding transformer may be provided as... 

A generator neutral bus to form the generator star point. 

Tap-offs with a neutral CT, from star point of the generator, to the neutral grounding transformer (NOT). 

Note that, again, three different types of variables were combined chain length, component ratio, and absolute component level. Thus, a "standard" constrained mixture design was not appropriate. In this case a full factorial, central composite design was used, with a total of 20 data points. The star points were... 

The same analysis techniques were used in this third design as were used in the first design. The final models and R values are shown in Table VIII. Note that models for Properties C, D, and E are not given. Measurements for the first two responses were not taken on the star point formulations. 

Fig. 4. Generalized Kratky plot of the experimental form factor of an 18-arm PI star (points) solid line fit to the Benoit function, Eq. (23) dashed line fit to the RG curve described in [66]. Reprintedwith permission from [67]. Copyright (1994) American Chemical Society...

Figure 13.2 Central composite design. Square points 2, star points 4, = 3, DF = 3.

The lower left panel in Figure 13.2 shows the central composite design in the two factors X, and X2. The factor domain extends from -5 to +5 in each factor dimension. The coordinate axes in this panel are rotated 45° to correspond to the orientation of the axes in the panel above. Each black dot represents a distinctly different factor combination, or design point. The pattern of dots shows a central composite design centered at (Xj = 0, Xj = 0). The factorial points are located 2 units from the center. The star points are located 4 units from the center. The three concentric circles indicate that the center point has been replicated a total of four times. The experimental design matrix is... 

The normalized information at the center (and at the edges) of the factor space in Figure 13.3 is less than the normalized information at the center (and at the edges) in Figure 13.2. These effects are a result of the relative compactness of the star points in this rotatable design which allows the FSOP model to flex more at the comers of the factor space and, consequently, at the center as well. 

This design is similar to previous designs, but the star points are located 2 from the center, not 4 or 2 2 or 2. The star points have been brought inside the faces of the square. This design is sometimes called an inscribed central composite design . 

The rotatable central composite design in Figure 13.7 is related to the rotatable central composite design in Figure 13.3 through expansion by a factor of V2 the square points expand from 2 to 2 2 from the center the star points expand from 2 2 to 4 from the center. The experimental design matrix is... 

Figure 13.9 Central composite design. Square points 4, star points 2, DF = 2, DF = 4.

Figure 13.10 shows the effect of placing the four replicates at each of the star points. The experimental design matrix is... 

This allocation of experiments has the effect of emphasizing the star points in the normalized uncertainty and normalized information contours. The contours are bumpier now, with the bumps occurring at the star points. Because no experiments are being carried out at the center point, the amount of uncertainty is greater there (and the amount of information is smaller there) than in the original design of Figure 13.2. 

Figure 13.21 An inscribed central composite design with distantly located extra star point. DF = 4, DF = 3.

The experiments depicted in Figs. 1 and 4 did not determine true optima. In the study of carbon and nitrogen interactions, the optima appeared to lie in the range of 2.4 to 4.0 g/1 for carbon and 0.084 to 0.14 gA nitrogen. One point fell in this range, and it was the maximum for this series of experiments but it is not necessarily an optimum. Likewise, in the partial factorial design depicted in Fig. 4, all of the maxima occurred at star points rather than within the matrix, so it is apparent that the optimum or optima lie somewhere outside the limits of the experimental design. Despite these limitations, several useful inferences can be drawn from these data. 

If the F-test is significant then there is evidence of a quadratic effect due to at least one of the variables. With the present design, however, the investigator will not be able to determine which of the variables has a quadratic effect on the response. Additional experimentation, perhaps by augmenting the current design with some star points to construct a central composite design (see section on central composite designs below), will need to be conducted to fully explore the nature of the quadratic response surface. 

One final point it should be noted that the experimenter is not constrained to use a resolution V design or to add star points for all of the factors. In particular, if it is believed that certain two-factor interactions... 

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