Power Dissipation AC Circuits Flashcards
what is the purpose of rms values
they provide the ac equivalent to dc, an ac voltage of equal rms to dc will have the same heating affect
how to convert from peak to rms
divide pk by sqrt of 2
What is the average power dissipated in a circuit
Irms * Vrms * cos(phi)
What is the power factor
cos(phi) where phi is the phase difference between the current and voltage
In a purely inductive or capacitive circuit what is the power dicipation
0 as the value of phi = +-90 therefore cos phi =0
When dealing with power factors what must be noted carefully for the currents
the currents of an equivalent dc voltage to deliver the same power are way lower, however the cables must be capable of taking the higher ac current due the power factor reducing the power generated from Irms currents over the same resistance
what is power factor corrections
using an inductor to to cancel the effect of a capacitor, or vice versa
How are inductors or capacitors implemented in power factor corrections
in parallel so as to not affect the voltage across the load
what is meant by a lagging power factor
we have an inductive circuit ie the current lagging behind the voltage
What is mean by leading power factor
we have a capactive circuit ie the current leading the voltage
What is a VA rating
Irms*Vrms is a form of measurement, where a machine is rated to provide certain current at certain voltage
what is VAR
reactive power VIcos(phi)
What can you not do with VAs
simply add them together as they are not in phase with each other
What is a unity power factor
a unity power factor is a power factor of 1 ie phi=0
Relationship between the voltages across a resistor a capacitor
Vs^2 = Vc^2 +Vr^2
similar for inductor
