Electrical Equipment Handbook - Troubleshooting And Maintenance (Mcgraw-Hill, 20040 Ww.pdf
Source: ELECTRICAL EQUIPMENT HANDBOOK CHAPTER 1 FUNDAMENTALS OF ELECTRIC SYSTEMS CAPACITORS Figure illustrates a capacitor. It consists of two insulated conductors a and b. They carry equal and opposite charges ϩq and Ϫq, respectively. All lines of force that originate on a terminate on b. The capacitor is characterized by the following parameters: ● q, the magnitude of the charge on each conductor ● V, the potential difference between the conductors The parameters q and V are proportional to each other in a capacitor, or q ϭ CV, where C is the constant of proportionality. It is called the capacitance of the capacitor. The capac- itance depends on the following parameters: ● Shape of the conductors ● Relative position of the conductors ● Medium that separates the conductors The unit of capacitance is the coulomb/volt (C/V) or farad (F). Thus 1 F ϭ 1 C/V It is important to note that dq dV ᎏϭ C ᎏ dt dt but since dq ᎏϭ i dt Thus, dV i ϭ C ᎏ dt This means that the current in a capacitor is proportional to the rate of change of the voltage with time.