dielectric. A highvoltage capacitor that has a thick

dielectric must have a relatively large area in order to have

the same capacitance as a similar lowvoltage capacitor having a

thin dielectric. The working voltage also depends on the

applied frequency because the losses, and the resultant heating

effect, increase as the frequency increases.

A capacitor that may be safely charged to 500 volts dc cannot be

safely subjected to an alternating voltage or pulsating direct

voltage having an effective value of 500 volts. Since an

alternating voltage of 500 volts (root mean square, rms) has a

peak value of 707 volts, a capacitor to which it is applied

should have a working voltage of at least 750 volts. In

practice, a capacitor should be selected so that its working

voltage is at least 50 .percent greater than the highest

effective voltage to be applied to it.

f. *Capacitor Losses*. Power loss in a capacitor may be

attributed to dielectric hysteresis and dielectric leakage.

Dielectric hysteresis may be defined as an effect in a

dielectric material similar to the hysteresis found in a

magnetic material. It is the result of changes in orientation

of electron orbits in the dielectric because of the rapid

reversals of the polarity of the line voltage. The amount of

power loss due to dielectric hysteresis depends upon the type of

dielectric used. A vacuum dielectric has the smallest power

loss.

Dielectric leakage occurs in a capacitor as the result of

leakage of current through the dielectric. Normally, it is

assumed that the dielectric will effectively prevent the flow of

current through the capacitor.Although the resistance of the

dielectric is extremely high, a minute amount of current does

flow. Ordinarily this current is so small that, for all

practical purposes, it is ignored. However, if the leakage

through the dielectric is abnormally high, there will be a rapid

loss of charge and an overheating of the capacitor.

The power loss of a capacitor is determined by loss in the

dielectric. If the loss is negligible and the capacitor returns

the total charge to the circuit, it is considered to be a

perfect capacitor with a power loss of zero.