Capacitors selection

We would like to find a 0.1 pF ceramic capacitor. Select the CeffllllC subtable in the EXplOfB view ... 

Note that the general output capacitor selection procedure is as follows ... 

Short-chain alkylated biphenyls are the principal biphenyl derivatives in commercial use. They are generally produced by Hquid-phase Friedel-Crafts alkylation of biphenyl with ethylene, propylene, or mixed butenes. A series of mixed ethylated biphenyl heat-transfer fluids (trademarked Therm S-600, 700, 800) is marketed by Nippon Steel. A mixed diethylbenzene—ethylbiphenyl heat-transfer fluid is also available from Dow (63). Monoisopropylbiphenyl [25640-78-2] largely as a mixture of meta- and para-isomers is produced by Koch Chemical Co. Monoisopropylbiphenyl (MIPB) was selected by Westinghouse (64,65) as a PCB replacement in capacitors and this is its primary appHcation today. For a time MIPB was also employed as a PCB replacement in pressure sensitive copy paper, but this outlet has since given way to other dye solvents. A similar product consisting of a mixture of j -butylbiphenyl isomers [38784-93-9] (66) is currently the favored dye solvent for pressure sensitive copy paper (67) manufactured in the United States. 

Referring to the data available from experiments, as shi)wn in Table 23.1, it hits been estimated that a Vp, of I. Hj should be sufficient to account for the harmonic effects. For this dielectric strength is designed a capacitor unit and selected a switching or protective device. 

Based on the system studies carried out and Table 23.1, it has been assessed that in actual operation, effective current through a capacitor circuit may increase up to 1.3 limes its rated cunent, /,., i.e. = 1.3 /, to account for all the harmonic effects (V, - Jf. equation (23.4)). A capacitor unit is thus designed for at least M)9r continuous overload capacity (Section 25.6). Its switching and protective devices are selected along similar lines. 

When selecting the voltage of the capacitor units care must be taken that during operation the voltage across the capacitor units does not fluctuate beyond 10%. If this happens the voltage rating of the capacitor units must be chosen so that the variation across the units under unfavourable operating conditions does not exceed 10%. 

Power capacitors behaviour, switching and improvement of power factor 23/761 Tabfe 23.6 Chari for selection of capacitor rating, to improve the existing p.f. to a higher level... 

If these facts are not borne in mind when selecting the capacitor rating, particularly when the p.f of the motor is assumed to be lower than the rated p.f at full load, then at certain loads and voltages it is possible that the... 

The following example illustrates the method of selecting the capacitors value, their grouping and their control for a system having a number of load points. 

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. 

We have summarized in Table 25.2 the basic parameters to select the correct type of components for capacitor duty. 

Design output indicators select rectifiers and capacitors. 

The minimum operating frequency of the control IC is set by the combination of the R and C on the oscillator pin. First one select the oscillator capacitor from a graph. The discharge period to produce a 200 kHz period (5 qS) can be produced with a 200 to 300 pF capacitor. Make Cose = 220 pF. The oscillator resistor is calculated from... 

I would like a time constant for the R-C filter to be about 1 mS. Selecting the value of the capacitor to be 0.1 uF, the charging resistor should be... 

When connected as switchable banks the rating of each step of the capacitor bank must be selected with care. It is important that the control relay settings are matched to the ratings of each capacitance step in order to prevent hunting (i.e. continuously switching in and out at a particular load point). When capacitors are connected to one particular load (usually a motor) the capacitor bank can be located at the motor, adjacent to but separate from the control switchgear or within the control switchgear itself. 

When located at the motor the capacitor bank will be normally cabled from the motor terminal box, so that the size of the motor cable can then be selected on the basis of the reduced-power factor corrected current drawn by... 

Capacitors, circuit breakers and HRC fuses must be selected with care for use with capacitor circuits, with contractors chosen on the basis that the capacitor current can rise by 25 per cent above nominal line current. Equally, HRC fuses for capacitor applications should be de-rated by a factor of 1.5. 

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