Control.com - Nerds in Control

Is it possible to have a flow of Reactive power when active power is Constant?

dsp_guy,

> Is it possible to have a flow of Reactive power when active power is Constant?

I'm not going to respond to the flow component nor the reactive power statement (see below).

I will respond by saying that the VAr component of an AC machine is not entirely a function of the active power of the machine. For example, a synchronous machine (motor or generator) operating at any stable active power can have zero VAr's if the excitation of the machine is maintained at the level required to make the terminal voltage equal to the grid or mains source with which the machine is connected. Increasing the excitation (which would tend to increase the terminal voltage over the grid/mains voltage) while holding the active power constant results in a lagging power factor and VAr indication (on a large or infinite grid), while decreasing the excitation results in a leading power factor and VAr reading. So, it is possible to have leading- or lagging reactive component to the load of a synchronous AC machine while it is operating at a stable active power load.

The reactive component (VAr) of an inductive motor, on the other hand, is somewhat related to the active power (load) being provided by the motor, but is mostly related to the physical construction of the machine. The VAr of an induction motor will never be zero when it is providing torque to some device or process. Even if the amount of torque (real, active power) remains constant, the reactive component of the motor will be lagging.

I hope this answers your question.