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Effective Resistance and Q-Factor

Reff expresses the a-c resistance, which is generally greater than the d-c resistance. This is particularly true when the cross section of the wire in the winding of the self-inductance is large, or when, as in the case of some devices, such as motors and generators, the wire is embedded in slots. The leakage fluxes in transformers and stray fluxes in reactors and choke coils produce losses in the metal tanks or cases that enclose the core and windings. Such losses are reflected into the effective resistance values.

The quality factor, QF, or simply Q1, of a coil is the ratio of reactive power to real power. Hence


Other definitions are



Equations 4-109, 4-110, and 4-111 are equivalent. The term, energy lost per cycle, represents the irreversible energy, i.e., the energy that is converted into heat and the energy stored in the circuit represents the reversible energy.

1 Unfortunately the symbol for quality factor is the same as that for reactive power and care should be exercised not to confuse the one with the other.

Last Update: 2011-01-08