Capacitor characteristics

Of course, for a given working voltage Uw, the dielectric thickness cannot be reduced indefinitely because the electric field E = Uw/h would eventually attain the breakdown value Eb. In fact, to achieve acceptable reliability the working voltage must be less than the normal breakdown voltage Ehh by a factor ij so that 

From Eqs (5.5) and (5.6) the maximum permissible energy density is given by 

Equation (5.7) indicates that etE is a figure of merit for dielectrics that are to be used at high fields. The various types of capacitor are compared on the bases of volumetric efficiencies and typical working energy densities in Table 5.1. 

Ideally, the d.c. resistance of a capacitor is infinite, but in practice it will have a finite value RL. In the case of the parallel-plate capacitor, and confining attention to the dielectric, 

Although the above analysis is applicable to the great majority of standard capacitors, there are exceptions. For example, where very high working voltages ( lkV) are involved, the d.c. resistance may be determined by that of 

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Barrier anodic oxides covering the surface of aluminum etched foil are usually formed in borate or phosphate solutions. To improve capacitor characteristics, high-purity aluminum is desirable with as low a concentration of impurities as is acceptable in terms of cost. 

The angle 8e describes the deviation of the phase shift between current and applied potential from the ideal value of 90°. Its projection on the real part of the total impedance Z therefore describes the ohmic part of the capacitor characteristic corresponding to a series resistance in the equivalent circuit. In practice, this number is used to specify the polarization losses of a capacitor. Analogously, the total loss factor tan 8C of a capacitor is defined by the ratio of the real and imaginary part of the total impedance Z. In addition to the polarization loss, this number considers unavoidable resistances due to lead wires and losses due to an imperfect insulation, plus the capacitive inductance I ... 

IEEE Transactions on Components, Hybrids, and Manufacturing Technology (capacitors characteristics and parameters, measurements of parameters, technologies). 

Long, J. W. et al. 2009. Multifunctional Mn02 carbon nanoarchitectures exhibit battery and capacitor characteristics in alkaline electrolytes. Journal of Physical Chemistry C, 113,17595-17598. 

Long, J.W., Sassin, M.B., Fischer, A.E., Rolison, D.R., Mansour, A.N., Johnson, V.S., Greenbaum, S.G., 2009. Multifunctional Mn02— carbon nanoarchitectures exhibit battery and capacitor characteristics in alkaline electrol3des. The Journal of Physical Chemistry C 113 (41), 17595-17598. 

Maxcap Double Layer Capacitor, Characteristics, Operation and Use, Sohio Engineered Materials Company, Niagara Falls, NY (1985)... 

Sulfur hexafluoride [2551-62-4] 6 molecular weight 146.07, is a colorless, odorless, tasteless gas. It is not flammable and not particularly reactive. Its high chemical stabiUty and excellent electrical characteristics have led to widespread use in various kinds of electrical and electronic equipment such as circuit breakers, capacitors, transformers, microwave components, etc (see Electronic materials). Other properties of the gas have led to limited usage in a variety of unique appHcations ranging from medical appHcations to space research. 

Several manufacturers of ceramic powders are involved in commercializa tion of hydrothermaHy derived powders. In the United States, Cabot (Boyertown, Peimsylvania) has built a small manufacturing plant and is supplying materials to capacitor manufacturers. Other manufacturers include Sakai Chemical and Euji Titanium in Japan. Sakai Chemical is reportedly producing 1 t/d in its demonstration plant. A comparison of the characteristics of commercially available powders is given in Table 2. 

Electronic and Electrical Applications. Sulfolane has been tested quite extensively as the solvent in batteries (qv), particularly for lithium batteries. This is because of its high dielectric constant, low volatUity, exceUent solubilizing characteristics, and aprotic nature. These batteries usuaUy consist of anode, cathode polymeric material, aprotic solvent (sulfolane), and ionizable salt (145—156). Sulfolane has also been patented for use in a wide variety of other electronic and electrical appHcations, eg, as a coil-insulating component, solvent in electronic display devices, as capacitor impregnants, and as a solvent in electroplating baths (157—161). 

The characteristic shown also suggests that the MPCBs can withstand current transients up to 100 times the rated current (or the current setting) and hence are capable of switching a capacitor and protecting them against overloads. 

With this particular arrester, the motor has to be specially designed for the higher level of FOW impulse voltage withstand. But the manufacturer can always modify the protective characteristics of the arrester, depending upon the system s requirements. The matter may therefore be referred to the manufacturer for recommendations. The arrester may be fitted with a 0.25, uF surge capacitor in parallel, to reduce the steepness of the FOW (for the arrester of example 17.5, it is 14/0.2 kV/jUS) to a safer value. 

The metallized film capacitors have the characteristic of self-healing. On a small dielectric failure the capacitor element is not rendered completely unserviceable. After clearing the fault, the affected capacitor element returns to the circuit and the capacitor unit functions normally. Only the punctured area is eliminated from the element and causes a negligibly small reduction in its capacitance value. Such a characteristic is termed self-healing and such capacitors are known as the self-healing type. 

Such types of loads may require special design of capacitor elements and their dielectric impregnation, cooling arrangement, size of shell or surface treatment. For all these applications therefore it is important to know the actual operating conditions, behaviour and characteristic of the load and its duty cycle before selecting the capacitors. 

Protection with internal fuses is easier, as fuses are provided for each element which can contain the severity of the fault well within the safe zone in all probability. Some users even recommend capacitor units 250/300 kVAr and above with internal fuses only. Figure 26.1 shows a typical operating band of (he internal fuses for an internally protected unit. It demonstrates a sufficient margin between the operation of (he fuses and (he shell s safe zone. The fuse characteristics are almost the same for all manufacturers. 

These types of reactors can now be used as current limiting reactors and also as harmonic suppressors. They are also recommended for capacitor application due to their linear characteristic which will not disturb the tuning of the filter circuit. 

These are meant to be used with a capacitor to tune a filter circuit, with resonances in the audio frequency range for reducing and filtering the harmonics or communication frequencies. They provide a near short-circuit for the required harmonics to filter them out of circuit. They may be single-phase or three-phase and connected in series or parallel of the capacitor circuit and may have a fixed or variable reactance, rated continuously with saturated magnetic characteristics. They may incur heavy losses. 

The capacitors used for this function are high-voltage Aim or ceramic capacitors that exliibit very good high frequency characteristics. These capacitors... 

As one can see, there is the familiar choke input filter (T-C) on the output, which is characteristic of the buck and all forward-mode converters. The configuration shown in Figure 4—10 is called a parallel resonant topology because the load impedance (the T-C filter acting as a damping impedance) is placed in parallel to the resonant capacitor. The input to the T-C filter stage... 

Let us examine how one determines the values of the inductor and capacitor. Several assumptions have to be made at the beginning of the design process since several of the tank circuit s characteristics are variable within the application. The first is to assume a value for the Q of the tank circuit. In the application, the Q varies greatly with the amount of load placed on the output of the supply. So, a good value to start with is... 

The form of compensation is the 2-pole-2-zero method of compensation. This is to compensate for the effect of the double pole caused by the output filter inductor and capacitor. One starts by determining the control-to-output characteristic of the open-loop system. 

This causes the control-to-output characteristic to add gain and phase above the location of this zero. This can be a problem with respect to the stability of the supply. Unfortunately, many capacitor manufacturers do not present the value of the ESR for their capacitors. Typically, the zero caused by the output filter capacitor falls in the following range ... 

As one can see, the choice of the type of output filter capacitor can influence the control-to-output characteristic, sometimes detrimentally. 

The zero attributed to the output filter capacitor is still present in the control-to-output characteristics. Its location is found in Section B.2.1 and Equation B.9. 

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