"L di/dt" vs. "i dL/dt" I have heard many times that the positive "inductive" part of a circuit's reactive power is equal to "L i di/dt". I also know that "L di/dt" is just one of two terms that is derived from applying derivative of "L i" with respect to time. The other term is "i dL/dt". My concern is the relationship between "L i" and the integration of "L di/dt" with respect to time t. I have heard that "L i" is equal to magnetic flux. However, I know that in cases when L changes over the course of time that it is possible that "L i" to be greater than integration of "L di/dt" with respect to time t. What if the magnetic circuit is changing such that the inductance of the coil changes with respect to the surrounding and interior (magnetic) permeabilities? Taken to an extreme, if the inductance is increasing and the current is not changing, then it appears that the reactive power "L i di/dt" is still zero. But it seems apparent that the increases of inductance increases the potential energy in the field given the current already there. Perhaps the problem I have originates from the convention where inductive reactive power is equal to "L i di/dt", ignoring cases where "i dL/dt" is non-zero. Perhaps inductive reactive power is really "L i di/dt + (1/2) i^2 dL/dt". That is the complete derivative of (1/2)Li^2. Does anyone know of an independent peer-review source that gives credence to my concern?