Parallel ac Networks Summary

The following is a review of important conclusions that can be derived from the discussion and examples of the previous sections. The list is not all-inclusive, but it does emphasize some of the conclusions that should be carried forward in the future analysis of ac systems.
For parallel ac networks with reactive elements:
  • The total admittance (impedance) will be frequency dependent.
  • The impedance of any one element can be less than the total impedance (recall that for dc circuits the total resistance must always be less than the smallest parallel resistor).
  • The inductive and capacitive susceptances are in direct opposition on an admittance diagram.
  • Depending on the frequency applied, the same network can be either predominantly inductive or predominantly capacitive.
  • At lower frequencies the inductive elements will usually have the most impact on the total impedance, while at high frequencies the capacitive elements will usually have the most impact.
  • The magnitude of the current through any one branch can be greater than the source current.
  • The magnitude of the current through an element, compared to the other elements of the network, is directly related to the magnitude of its impedance; that is, the smaller the impedance of an element, the larger the magnitude of the current through the element.
  • The current through a coil is always in direct opposition with the current through a capacitor on a phasor diagram.
  • The applied voltage is always in phase with the current through the resistive elements, leads the voltage across all the inductive elements by $90^\circ$, and lags the current through all capacitive elements by $90^\circ$.
  • The smaller the resistive element of a network compared to the net reactive susceptance, the closer the power factor is to unity.