kVA is
the unit for apparent power. Apparent power consists of active and reactive
power. Active power is the share of the apparent power which transmits energy
from the source (generator) to the user. Reactive power is the share of the
apparent power which represents a useless oscillation
of energy from the source to the user and back again.
It occurs when on account of some inertia in the system there is a phase shift between voltage and current. This means that the current does not change polarity synchronous with the voltage. But the heat generated in a winding as well as the eddy current losses generated in a transformer core depend on the current only regardless of whether it aligns with the voltage or not.
Therefore the heat is always proportional to the square of the current amplitude irrespective of the phase angle (the shift between voltage and current). So a transformer has to be rated (and selected) by apparent power.
It occurs when on account of some inertia in the system there is a phase shift between voltage and current. This means that the current does not change polarity synchronous with the voltage. But the heat generated in a winding as well as the eddy current losses generated in a transformer core depend on the current only regardless of whether it aligns with the voltage or not.
Therefore the heat is always proportional to the square of the current amplitude irrespective of the phase angle (the shift between voltage and current). So a transformer has to be rated (and selected) by apparent power.
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