Rating capacitors

The capacitors rating must be enhanced by the rating of fhe reactor to obtain the same levei of effective kVAr. 

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... 

Recommended capacitor ratings for direct switching with induction motors, to improve power factor to 0.95 or better at... 

Motor Capacitor rating in kVAr at a motor r.p.rn. Motor Capacitor rating in KVAr a a motor r.p.rn. ... 

Ttible 2.5.7, based on the recommendations of motor manufacturers, suggests the likely capacitor ratings for different motor ratings and speeds. For higher ratings, interpolate orcaladtite the rating as illustrated in Section 2.5.12.2. 

In instances where a capacitor is connected directly across the terminal of the motor, the capacitor can act as a source of excitation current after the control device is opened. In order to prevent this the capacitor rating should not exceed 90 per cent of the motor no-load magnetizing current. 

The dual slope converter is superior to the successive approximation type in many respects, e.g. in having an automatic zero capability, good noise suppression, and accuracy which is not affected by capacitor rating or clock frequency. However, the use of the latter type of converter is limited because of its slow conversion time (about 30 ms). 

Color Significant figure Multiplier % Tolerance Capacitor Rating (V)... 

Capacitor Rated TC Tolerance, Resistance, Dissipation Absorption, Temperature Comments, ... 

Equipment designers have decided that it is sometimes preferable to use components with higher specifications than those strictly necessary for a particular application because they offer better reliability and lower rework costs, a significant factor if their additional cost is far less than reworking. For example, a capacitor rated at 105 C may be a better buy than a standard unit rated at 85 C. 

BiaxiaHy orieated PPS film is transpareat and nearly colorless. It has low permeability to water vapor, carbon dioxide, and oxygen. PPS film has a low coefficient of hygroscopic expansion and a low dissipation factor, making it a candidate material for information storage devices and for thin-film capacitors. Chemical and thermal stability of PPS film derives from inherent resia properties. PPS films exposed to tolueae or chloroform for 8 weeks retaia 75% of theh original streagth. The UL temperature iadex rating of PPS film is 160°C for mechanical appHcatioas and 180°C for electrical appHcations. Table 9 summarizes the properties of PPS film. 

Zinc Costing of Ca.pa.citors, In the zinc coating of paper strip for capacitors, the paper strip is fed from air through locks into a vacuum environment. There, it is coated by thermally evaporated zinc. The rate of evaporation is so high that contamination of the zinc vapor is excluded. The paper is fed at the maximum rate permitted by its own strength. 

Q = charge stored by the capacitor unit C = capacitance of the capacitor dvidt = rate of voltage change or a.c. ripples in the d.c. link... 

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. 

Figure 15.6(a) Capacitor voltage transformer (CVT) rated voltage 36-420 kV and above (Courtesy ABB)... 

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. 

Harmonic output of a capacitor unit The rating of a shunt capacitor unit... 

The rating of a capacitor unit will thus vary in a square proportion of the effective harmonic voltage and in a direct proportion to the harmonic frequency. This rise in kVAr, however, will not contribute to improvement of the system p.f. but only of the overloading of the capacitors themselves. 

When a capacitor circuit is compensated through a series reaetor. either to suppress the system harmonics or to limit the switching inrush currents (Section 23.11) or both, it will require suitable adjustment in its voltage and capacitive ratings, fhe series reactor will dampen the switching currents but consume an inductively reactive power and offset an equivalent amount of capacitive kVAr. and require compensation. The following example w ill elucidate this. 

Then the voitage rating of the capacitor units should be chosen for... 

The rating of the capacitor banks should be chosen for = 3000 + 180 = 3180 kVAr. 

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