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# Steady State Power Calculation - PowerPoint PPT Presentation

Steady State Power Calculation. Section 10.1-10.4. Instantaneous Power. Instantaneous Power. Use current as point of reference. Apply Some Trig Identities. Power for Purely Resistive Circuits ( θ v = θ i ). For purely resistive circuits , θ v = θ i. θ v = θ i.

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Presentation Transcript

Section 10.1-10.4

Use current as point of reference

• For purely resistive circuits , θv= θi

θv= θi

(all the electric energy is dissipated in the form of thermal energy)

Power for Purely Inductive Circuits (θv= θi+90 deg)

• For purely inductive circuits , θv= θi+90 deg

θv= θi+90 deg

(Q is 1 VAR)

Volt-Amp Reactive

(Voltage leads current by 90 deg)

(No transformation of energy from electric energy to nonelectric form)

Power for Purely Capacitive Circuits (θi= θv+90 deg)

• For purely inductive circuits , θi= θv+90 deg

θi= θv+90 deg

(Q is -1 VAR)

Volt-Amp Reactive

(Current leads voltage by 90 deg)

(No transformation of energy from electric energy to nonelectric form)

(power factor angel)

Knowing the power factor does not tell you the value of power factor

angle.

We need to use descriptive language:

Lagging power factor: current lags voltage. (most appliances such as

lighting fixtures and washing machine…etcoperate at a lagging power

factor. We usually want to operate a power factor of 1.

A 120 V, 100W lamp has a resistance of 1202/100=144 Ohms

We can use a capacitor in parallel of L1 and L2 to correct

Power. We would ideally like to have a power factor of 1.