X-capacitor

Line to line capacitors are called X-capacitors ( X-caps ). X-caps when used in off-line applications before the input bridge must be safety approved. But after the bridge (on the rectified side), it s basically a don t care situation from the safety point of view. Note that since it is essentially a front-end component, approved X-caps are typically impulse-tested up to 2.5 kV peak. 

Note that if this is a standard two-stage off-line filter, we need to look at the DM equivalent circuit presented in Figure 10-1 in Chapter 10 to realize what exact values of the various X-capacitors in the figure this C really corresponds to in that schematic. 

In general, interference-suppression capacitors have low inductances. These capacitors can be separated into two classes depending on their use Class X and Class Y. Class X types are used in applications with lower safety requirements, for example, where a collapse would not pose a danger. Class Y types are used in environments or applications that have strict safety requirements. These two classes have different test conditions. For example, an 1100 V test voltage is used for testing Class X capacitors such as a 4 pF/250 V capacitor a... 

Equation (8.18) is vahd for linear dielectric materials (i.e., polarization is directly proportional to electric field). Ferroelectric materials used in high-X capacitor dielectric materials are nonlinear. Figure 8.34 illustrates the relationships between polarization, electric field, and dielectric constant for a ferroelectric material as given by the following equation ... 

Japanese suppHers generally dominate the electronic ceramic business. Japanese production of ferroelectric devices in the first nine months of 1990 was valued at 711 x 10 for ceramic capacitors and 353 x 10 for piezoelectric devices, representing growths of 7 and 10.8%, respectively, over the previous year. 

The first commercial use of tantalum was as filaments ia iacandescent lamps but it was soon displaced by tungsten. Tantalum is used ia chemical iadustry equipment for reaction vessels and heat exchangers ia corrosive environments. It is usually the metal of choice for heating elements and shields ia high temperature vacuum sintering furnaces. In 1994, over 72% of the tantalum produced ia the world went iato the manufacturiag of over 10 x 10 soHd tantalum capacitors for use ia the most demanding electronic appHcations. 

V( = voltage across the capacitor banks = Ic Ul = voltage across the series reactor = /[ X ... 

By providing 12 turns of 150 mm mean diameter of the 50 mm flexible copper cable connecting each 60 kVAr capacitor bank a self-inductance of roughly 42.93 x 10 H can be introduced into each switching circuit, which will limit the switching inrush current to almost the permissible value of the making current (/, ) of the switching device. 

Vp, = system voltage V(- = voltage across the capacitor banks Xc = capacitive reactance X] = inductive reactance... 

Compensation required = 0.61 X o per unit length. Series capacitors making up 0.61 Xlq introduced... 

This value can be reduced by decreasing the value of X , which is possible by providing series capacitors in the line. If X(2c is the series compensation, then the modified impedance... 

The factors discussed in Section 23.5.2 give rise directly to the current drawn by the capacitor unit and indirectly add to its rating. The relevant Standards on this device recommend a continuous overload capacity of 30% to account for all such factors. A capacitor can have a tolerance of up to -t-15% in its capacitance value (Section 26.3.1(1)). All current-carrying components such as breakers, contactors, switches, fuses, cables and busbar systems associated with a capacitor unit or its banks, must therefore be rated for at least 1.3 x 1.15/,., i.e. 1.54. For circuits where higher amplitudes of harmonics are envisaged, for reasons of frequent load variations or more... 

Determine the discharge device for the discharge of a three-phase 6.6 kV, 50 Hz, 1000 kVAr, yconnected capacitor bank, connected in units of 10 x 100 kVAr each, through an automatic p.f. correction relay, having a closing cycle of 10 seconds. Data available from the capacitor manufacturer,... 

Because the Geiger counter produces pulses independent in size of x-ray wavelength, it is the best detector for the method of counting that employs a capacitor to accumulate the individual counts (2.3, 2.10). 

Fig. 2-6. Schematic diagram illustrating the essential components of the phototimer circuit. When the total x-rays reaching the multiplier phototube, P, generate sufficient current to charge capacitor, C, to a predetermined potential the thyratron, T, fires and turns off the x-rays by means of the relay. (After Morgan, Am. J. Roentgenol. Radium Therapy, 48, 220.)...

Since the capacitor without electrolyte shows a linear behavior of the electrostatic potential between the electrodes, (x), at the hypothetical moment when the electrolyte is added to the system (t = 0 s), the electrochemical potentials of the ions. 

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