Questions tagged [reactive-power]

Reactive power (measured in vars) is present in a system containing reactive (inductive or capacitive) components and can be either produced or consumed by different load/generation elements. Though "imaginary", the reactive power has great physical significance and is essential to the operation of the electrical system as a whole.

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Reactive power compensation

For a solar power plant with a capacity of around 800 kW AC, the night time power factor reading was around -0.13 noted from the meter at interconnection. Night time reactive power consumption of the ...
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How can two-fifths of a milli-watt proceed from next to nothing? [closed]

How can two-fifths of a milli-watt proceed from next to nothing when the only sources of energy are the behavioral voltage sources inside the macro which defines the neon bulb of the Micro-Cap ...
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How does negative (or export) kVAR and kW affect maximum demand charges?

I am trying to calculate enegy costs using data from an energy meter that provides me with halfhourly data points for the following 4 channels: Import kW Export kW Import kVAr Export kVAr and in ...
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66 views

How to calculate reactive power of a capacitor with a current waveform which consists of a sum of sinusoids?

Assume that there is a current which consists of a sum of sinusoids flowing through a capacitor with capacitance C. How to calculate its reactive power? It is quite simple with a pure sine wave but ...
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Why does reactive power injection mitigate sagging grid voltage?

I understand that reactive power injection can be used by generators to support the grid voltage when sagging, but I’ve never understood why this works. I thought it could be charging transmission ...
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Active and reactive power formula

From generic voltage and current: $$v(t)=V_Mcos(\omega t + \varphi_v),\space \space i(t)= I_Mcos(\omega t + \varphi_i)$$ the complex power is $$p(t) = v(t)i(t) = \\...\\ = \frac{1}{2}V_MI_Mcos(\...
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Reactive power and eletro-mechanical analogy

Regarding this question, I will try to use the analogy of the differential equations $$F = m\frac{dv}{dt}$$ and $$V = L\frac{dI}{dt}$$ and $$w = \int Fv dt$$ with $$w = \int VI dt$$ to figure out the ...
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66 views

Is the association of useful work to active power a convention?

I know that there are many questions about reactive power. What I am trying to understand is what is sometimes called useful work associated to active power, compared to no useful work for reactive ...
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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 \$ \...
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Short circuit analysis

Im given the next distribution line with a generator and a load The generator is set at \$23\,kV\$ the line impedance is \$9.5\Omega +j19.055\Omega\$ and the aparent power is \$1.5MW+j2MVars\$ in the ...
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106 views

What does mean if there is P+ and Q-?

If in a circuit there is real power positive and reactive power negative, what does mean in terms of power flow? I undestand that the real power is produced in the generator/source and goes to the ...
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What's the meaning of three-phase reactive power of a three-phase device in balanced sinusoidal conditions?

I'm trying to make physical sense of the three-phase reactive power (a.k.a. total reactive power) for a three-terminal or four-terminal three-phase device (e.g. an AC motor, an AC generator, a load) ...
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Is reactive power periodic in nature? What is the exact difference between active power, average power, and real power?

Consider an RC circuit which is supplied by a sine source $$v(t)=V_m\cdot \sin(\omega t)$$ The current through the circuit will be $$i(t)=I_m\cdot \sin(\omega t+\phi) \\ \phi=\arctan \left(\dfrac{1}{\...
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925 views

Reactive power in AC circuit

What is meant by reactive power in AC circuits? Power is joules per second. Real power is the energy dissipated in the resistor per second. What is meant by the reactive power? Does this mean the ...
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479 views

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 ...
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Reducing reactive power by using a resistor

I have a school exercise that goes like this: Voltage is 230V. Frequency is 50Hz. Inductor is 400mH. How big of a resistor should be added with the inductor (in a series) to reduce reactive power by ...
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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 ...
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283 views

Using capacitors to reduce reactive power

I have been trying to understand the concept of reactive power in power systems. From what I have read so far, I understand that any inductive load like a motor needs some reactive power to function (...
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314 views

Can battery inverters output reactive power?

This inverter manufacturer's Paper Bad Power Factor? – A reason to oversize your inverter mentions that "inverters can generate reactive power without using any active power." Can battery inverters ...
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38 views

In a transmission line, does the real current interact with reactive impedances?

simulate this circuit – Schematic created using CircuitLab According to the diagram above, if real currents do not interact with reactive impedances, then reactive loads should not worry the ...
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368 views

How does oscillation of reactive power take place between source and load?

I have come to read that reactive power is that power which is constantly oscillating between the source and the load. Can anyone please explain this to me? Suppose an AC source is connected with an ...
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What is meant by average power in AC circuits?

I read that "The average power is the power averaged over a cycle or number of cycles." I know that the average value of power for both active and reactive power is a constant number. Buy I am ...
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Instantaneous and active power in an ideal switch powered by real source and squared wave

This is a somewhat theoretical question, but one that has some impact on power theory. The circuit in the figure is composed of a real DC source (with non-negligible internal resistance) and feeds a ...
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187 views

What is the required VA rating of the transformer in this LTSpice power supply?

I have this circuit that I'm going to build, including the transformer. It is a simple power supply, with RC filters and one choke, I know all the voltages and currents. Because I will design, wind ...
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237 views

How does energy dissipates in a purely reactive circuit?

Suppose in a home, power factor drops to zero. It means that the circuit becomes purely inductive. If the energy meter is connected at incoming power supply point,will the energy meter still keep on ...
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1answer
221 views

Understanding equation for the quality factor of an RLC circuit?

In my textbook for a course on Circuit Analysis I came across an equation for the quality-factor of an RLC circuit. However, I don't quite understand their reasoning. The explanation that follows is a ...
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Is there a mathematical proof that reactive power regulates voltage?

So after studying the power triangle and trying to conceptualize real power and reactive power, I seem to have come across a contradiction, at least in my own head. Most explanations disregard ...
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Calculating reactive power on kVAr?

I think I understand how to answer this question but am missing how to do a certain part which stops me from getting their. For this question this is all I know how to do. cos-1(0.31) = 71.94° ...
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What is the source of reactive power generated by the alternator?

We know an alternator or in general any source of energy does not generate energy but converts one type of energy into some other usable form. An electric generator produces both real and reactive ...
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Why transformer is heating without load [closed]

I'm working as technician in computer store and I have a lot of scrap transformers . Most of them small and have 6-8 pins .I wonder, can I use them for my projects ? If I remember correctly these ...
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200 views

Adding an additional motor to a load

You have a 500kVA load with a power factor of 0.6 lag. You add an additional synchronous motor with an input of 80kW and max power factor of 0.8 leading. Determine the reactive power and the overall ...
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129 views

Example of Electrical Apparatus that draw leading VARS and Electrical Apparatus that draw lagging VARS [closed]

I understand that an AC inductive circuit will draw lagging vars while a capacitive AC circuit will draw leading vars (ELI the ICE man), but what are some examples of real-life electrical apparatus ...
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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 ...
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278 views

Reactive vs Real Power in DC-DC Converters

I don't understand which form of power, reactive or real, should be dominant in a maximally efficient DC-DC boost converter. As the circuit charges the inductor, the current and voltage will be out ...
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442 views

simulate a motor with resistor and inductor

I want to simulate a motor with a resistor and inductor. It means I want to connect a resistor and inductor to 1-phase or 3-phase instead of a motor. For achieving this goal I have to measure both ...
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Why is power factor such a meaningful quantity?

In my current electrical engineering course the concept of power factor has been a large topic, defined as the ratio of real power to apparent power. It is a measure of resistive power consumption in ...
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4answers
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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 ...
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63 views

Static VAr Compensation

I have to design a 3 phase Reactive Power Compensation System with using only reactors, no capacitor is needed. Total capacity is 505kVAr, but 475kVAr will be done with contactors, rest (30kVAr) will ...
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295 views

Determine the power dissipated in W in the 5 Ω resistor [closed]

simulate this circuit – Schematic created using CircuitLab Excuse me for my really bad use of the schematic feature I just didn't know how to switch to the phasor domain. Anyway, I'm asked to ...
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528 views

Parallel resonant induction heater

I implemented a parallel LC induction heater using theory. I made a simple square wave Inverter providing a frequency of 20kHz to the tuned LC circuit. The problem I'm facing is that my tank is not ...
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272 views

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 ...
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Calculating the reactive and active power

This is probably an easy one for you. In the following circuit simulate this circuit – Schematic created using CircuitLab I want to calculate the active and reactive power in load R2-C3. I've ...
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414 views

Reactive-Voltage (QV) Droop Curve and droop constant of Statcoms

I have a question about voltage droop curve of statcoms. I read many articles about it but I did not figure out how to calculate it and how to add droop curve in control systems. My system parameters ...
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1answer
98 views

Does Reactive Power flow between Energy storage elements in a three phase system?

I noticed that unlike the single phase ac power sources, the power in three phase is constant which means the instantaneous power is the same as the real power which is $$3V_{rms}I_{rms}\cos{\theta}$$ ...
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90 views

Reactive Power in grid side converter for Doubly fed induction generator

Does the grid side converter in a DFIG absorb/provide reactive power or is it reactive neutral? Also, what can we say about reactive power exchange in the rotor side converter?
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334 views

Nonzero current at voltage zero-crossing when consuming reactive power

In a circuit that consumes some reactive power, the current waveform indicates current flow even when the supply voltage is at the zero crossing. This seems paradoxical since there cannot be current ...
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262 views

No battery rechargeable led light

I want to make a tiny led glow for 10 minutes once charged by induction. I want the entire PCB not greater than 20x20x5mm. Is it possible? I have come up with the following circuit, I don't know if it ...
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759 views

Why does a fault lead to increased reactive power demand?

When we have a fault, say on one line out of three, the reactive power demands increase, which leads to voltage instability if the source can't provide it. My question is, what causes reactive power ...
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How to pick a capacitor to adjust loop compensation caused by reactive load?

I do wish to add a voltage regulator between a Li-Ion battery pack and a 36V 220W rated mid drive pedalling assist motor with integrated controller. The caps of that controller have a 63V rating. That ...
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703 views

How does a conventional generator produce only reactive power?

For a class that's rather far outside of my background, I am reading a paper about supply-demand balance in an islanded microgrid. The active power demand of the whole system can be met with ...