Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [apparent-power]

Total power in an AC circuit, both dissipated and absorbed/returned

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Do circuit breakers trip on Apparent or True Power?

The thermal and magnetic protection for AC circuit breakers take into account both the timing and the magnitude of the AC current passing through. Does a standard circuit breaker trip on the current related to the Apparent (kVA) Power, or the…
Brethlosze
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What is the significance of UPS output power factor?

A UPS's output rating is shown as 2000VA/1800W. I understand that the power factor here is 0.9, but the device or load I will connect to the UPS might have pf<0.9 or pf=1 (for light bulb.) From my understanding, the real and reactive power will vary…
Md. Toufik Zaman
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Importance of the apparent power

It is said that, though only active power can actually do work, we have to consider apparent power to dimension the source. But what would seem important to me for that would be to know the maximum absolute value of the instantaneous power, which…
Jonas Daverio
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What is the correct relationship between active, reactive and apparent power in non-linear AC systems?

I am somewhat troubled by the 'basic' formula that describes the relationship between apparent power (S), active power (P) and reactive power (Q) in AC systems. This formula is S^2 = P^2 + Q^2 and makes sense to me in linear systems with or without…
JeromeBu1982
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What is the direction of negative reactive power

In a R+1/(jwC) load (AC)voltage lags current with θ degrees. Reactive power Q is negative because sin(θ) is negative. My question is how can a capacitive load deliver power to the source wich is supposed to supply the power? Im sure I do not…
N. Berg
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Does reactive power of induction motor vary with load?

I know that the power factor of an induction motor varies with load and is very low at no load and high at full load, but does the reactive power vary as well? If so, how much can it vary?
Kestis
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Why is apparent power more important\relevant than maximum instantaneous power?

Given an AC circuit, the instantaneous power in the circuit can be determined by the formula $$P(t)=\frac {VmIm}2cos(\theta)+\frac {VmIm}2cos(\theta)cos(wt)-\frac {VmIm}2sin(\theta)sin(wt)$$ where \$ \theta \$ is the power factor angle, or the phase…
Gary Allen
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What are the exact meanings of reactive and apparent powers? Do we say they are supplied or consumed?

(The following doubt is from the topic of Sinusoidal Steady-State Analysis of electrical circuits) I understand the meaning of real power - it is the average power consumed (or delivered) by an element in a circuit. But I do not get what reactive…
Aditya
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Active Energy, Reactive Energy or just Energy?

I understand the concepts of active power, reactive power and apparent power. I am not sure I am getting the complete concept about the respective energies. I am using an energy monitor to record only the active power consumption of a CNC machine,…
DimP
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Active (P), Reactive (Q, D) and Apparent (S) Power from Instantaneous Power (p)

I am having a difficultly with producing \$S, P, Q \$ and \$D\$ from Instantaneous Power \$p(t)\$. Let's say that both voltage and current are clear sine waves. Then: \$p(t) = Vsin(ωt+φ_V) \cdot Isin(ωt+φ_I)\$ and by using the identity \$sinA sinB…
thece
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Why does line current equals the total apparent power divided by 3 times the phase voltage?

In this circuit with frequency of 50hz and line to line voltage of 400 V why is the current \$ I_A = S_t/3V_P\$ I don't understand the logic behind since there is one Delta connection, I understand why that formula works for a Star connection but…
Pedro
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Apparent power calculation of different loads for transformer sizing

Let's say we have two electrical loads and we would want to calculate the total apparent power in order to size the transformer to supply the demand. I'm currently confused between which two calculation method to use. Load A: P: 3kW, Q: 4kVAr Load…
SeowZH
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Measure 3-phase Power with Lecroy Waverunner

Please note that experience with a Lecroy Waverunner Oscilliscope is most likely required to answer this question. I'm attempting to measure the power draw of a brushless 3-phase motor with a Lecroy WaveRunner 204MXi. I've connected two current…
Brian Dohler
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calculating the average power using the oscilloscope

I am trying to measure the real power of an inductor, and in the manual it is said that I have to connect a resistor with low resistance to the inductor and then see the voltage difference between the current and voltage. Question: Why do I need a…
Jack
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Power In does not Equal Power Out

I have the following setup: 480V, 200A service fed into PWM Drive, Drive output going to 1000kVA step up transformer (8.4 ratio) feeding a 2380V/53A 3phase induction motor. The motor is UNLOADED. When running at NP, I measure (with multiple devices)…
ejjman1
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