Questions tagged [phasor]
The phasor tag has no usage guidance.
139
questions
2
votes
1answer
86 views
Converting from time domain to phasor domain?
If I have a voltage source of a circuit
\$V_s(t) = 8\cos(24\pi*10^9t-60^{\circ})\$ (V)
and I want to convert it to the phasor domain would it be this?
\$8e^{-j60^{\circ}}\$?
0
votes
3answers
79 views
IQ modulation and phasors: which first?
Do we use IQ modulation because quadrature signals are a good physical implementation of phasors - or is it the other way around?
To elaborate a little:I'm having a hard time getting a clear ...
0
votes
2answers
38 views
Why is the phase angle in the summation of the phasors the negative arctan?
I was reading a textbook and came across the following
$$
\\I_1 = Ae^{j0} = A
\\I_2 = Be^{-j\frac{\pi}{2}}
\\\bf{I} = I_1 + I_2
\\If\ A=10\ and\ B=20
\\|I| = \sqrt{A^2 + B^2}
\\\angle I = -tan^{-1}(B/...
1
vote
1answer
35 views
Can AC harmonic quantities be expressed as a sum of phasors of different frequencies without confusion?
https://www.electronics-tutorials.ws/accircuits/harmonics.html
The problem with AC harmonics is that each term has a different frequency, being a integer factor of the first frequency. I was wondering ...
1
vote
1answer
55 views
What am I doing wrong in finding the phase angle of power?
Consider a voltage supply \$V\angle \phi_1\$ and a circut with impedance \$Z \angle \phi_2\$.
Now the Apparent power(\$S\$) is given by: $$\bar S =\frac{(\bar V)^2} {\bar Z}$$
Thus phase angle of \$S\$...
0
votes
0answers
40 views
is it possible for the phase difference between voltage and current to exceed pi/2 in a RL circuit?
I did an experiment where I made a RL circuit. My IV was resistance and DV was phase difference between voltage and current. To find the phase difference, I took the difference (Δt) between time when ...
0
votes
1answer
52 views
Phase-shift a Broadband Time-Domain Function
Suppose we have an operator \$A_\phi\$ which phase-shifts a sinusoid by \$\phi\$:
$$A_\phi[\cos(\omega t)] = \cos(\omega t + \phi)$$
In phasor domain, \$A_\phi = e^{+j\phi}\$ is a complex constant.
I ...
0
votes
3answers
131 views
Why can't circuit breakers close across a large phase angle difference?
In power systems I understand that breakers have mechanisms preventing their closing if they detect the phase angle (and voltage) across them to be too large. This is usually called a 'sync check'. ...
2
votes
1answer
61 views
RMS values and Phasors
I need to solve these two exercises but I really have no idea where to start.
How should I proceed to solve this kind of problems?
I tried to find something on my teacher's files but haven't ...
1
vote
1answer
27 views
How do I transform this sinusoid in phasor?
If it is a signal like this i(t)=5*sin(100t-pi/3)A, I know how to transform.
But how do I do this e(t)=2-√(2)*sin(10t+pi/4) ?
I meant I don't know what to do with "2-"
Thanks for the help!
3
votes
0answers
86 views
How to calculate rotor flux of the three phase squirrel cage induction motor?
I have a three phase squirrel cage induction motor with given parameters (stator winding connected in delta)
nominal power: \$P_n = 22.4\,\mathrm{kW}\$
nominal stator voltage: \$V_{sn} = 230\,\mathrm{...
0
votes
1answer
66 views
RC circuit - phase current
I have a simple RC circuit as below :
I'm trying to visualize current curve and voltage curve (Vout and I(R1)) vs Vin using LtSpice and I obtain the result below:
It's OK that the Vout is leading ...
0
votes
4answers
65 views
can I also use phasors/concept of impedances for non sinusodial signals?
I know that phasors are great to solve circuits driven by sinusodial input signals but I was wondering if I can incorporate phasor concepts(like impedance) to circuits driven by input signals not ...
1
vote
1answer
65 views
Complex impedances of capacitors/inductors in the phasor domain
I'm trying to verify the complex impedances of passive components in the phasor domain (not s-domain). Take for example the inductor, whose element law is \$ v = L \frac{di}{dt} \$. Assuming a complex ...
0
votes
2answers
51 views
Resonant frequency and maximum signal width
I've seen resonant frequency being defined as the point where the input signal is in phase with the output signal (So reactance/susceptance is 0).
However conceptually, teaching material seems to link ...
0
votes
0answers
24 views
Direction of current in Phasors Analysis
I'm learning AC circuit and phasors form. In the exercise below, when using nodal analysis they choose the direction of current flow in the circuit then calculate the result.
But I wonder why that ...
0
votes
1answer
51 views
Finding the total impedance and voltage across open terminals
The question that I'm trying to solve is the following:
In the circuit shown below, what is the total impedance in ohms across the open terminals? What is \$v_{T}\$ if \$v_{L}\$ is 80 vrms?
This is ...
0
votes
1answer
248 views
Calculating Phase angle from instantaneous voltage
For background info I am an EE/CE that is 10 years out of school and has since worked writing firmware and dealt mostly with digital communications and signals, so now I am having to reach back to my (...
0
votes
3answers
75 views
How can current be in different phases in the same wire at the same time?
We know that either in ideal or practical transformer in no-load condition, the exciting current has two components Ic(core loss component) and Im(magnetizing component). Now since the same current ...
1
vote
0answers
36 views
Rotating magnetic field discrepancy
This may be a noob question
Lets consider a balanced 3 phase supply namely
\begin{align}
R&= V \sin(x)\\
Y&= V \sin(x-120)\\
B&= V \sin(x+120)
\end{align}
At a neutral point we would ...
0
votes
1answer
137 views
How to calculate voltage across capacitor C1?
If the voltage
\$v_I = \frac{jωC1R3}{1 + jωC1R3}*Vs \$
does that mean the voltage across the capacitor would be equal to \$v_S - v_I\$ ?
2
votes
1answer
254 views
Integral of phasor
Say \$v(t) = V_m\cos(\omega t+\phi)=\Re[V_me^{j(\omega t +\phi)}] = \Re[Ve^{j\omega t}]\$,
where \$V_me^{j\phi} = V\$.
Integrating gives
\$\int\limits_0^t v(t)\,dt = \Re\int\limits_0^t Ve^{j\omega ...
2
votes
1answer
558 views
Polar form vs phasor form?
I know that polar form has two parts. Amplitude and angle but
What is difference between polar form and phasor form of complex numbers? Or phasor form just includes amplitude form of a complex number?...
0
votes
0answers
53 views
What is the current in this circuit? (Using Phasors)
simulate this circuit – Schematic created using CircuitLab
I have attempted the question with the following working although the answer does not match the real answer, are there mistakes in my ...
1
vote
1answer
58 views
Current divider usage
I was solving this exercise where I have to find the current through each of the circuit branches. Sorry if the image is a bit confusing but after determining the current I I used the current divider ...
0
votes
2answers
60 views
Finding 70% Voltage Point
Let \$v_1\$ be the input AC voltage and \$v_2\$ be the output AC voltage such that gain \$\dfrac{v_2}{v_1} = \dfrac{A+jB}{D+jE}\$ where \$j = \sqrt{-1}\$. How should I find the 70% point (the point ...
0
votes
1answer
176 views
Help on (another) triphasic exercise
Second this week... But was it easy I wouldn't be here...
A problem asked me to identify the diagrams from this picture:
The following are the correct answers, acording to the test developers.
a. ...
0
votes
0answers
140 views
Relation between phase angle and current direction
In a triphasic system (any), is there a way to tell if the current is entering or leaving a phase/line/load just by the angle of the phasor of the source ?
In the following picture we can see the ...
2
votes
2answers
110 views
Derivation of telegrapher's equations
I'm currently going over the derivation of the telegrapher's equations shown here, but there's a step that I'm not fully grasping.
I think I can follow some of how you get from eq.3 to eq.5:
If the ...
2
votes
5answers
2k views
Does an oscilloscope subtract voltages as phasors?
I want to measure two voltages on an oscilloscope. They are not in phase. I want to know the magnitude of the voltage difference. The oscilloscope has an in-build math function to subtract the ...
0
votes
0answers
154 views
Superposition theorem with phasors [duplicate]
Can someone explain the superposition theorem step by step when applied with phasors (AC circuits)?
I think books and websites mostly include examples of how to solve something with superposition but ...
0
votes
1answer
50 views
Complex Amplitudes and Exp'l Increase/Decrease
The following are quotes from a textbook,
If S(t) is represented as a rotating phasor, the angular frequency
of the phasor can be thought of as velocity at the end of the phasor.
In particular ...
2
votes
4answers
129 views
Is the frequency response of a circuit only valid for steady state (phasors)?
This is my first post. I just finished a course about advanced circuit analysis techniques (the content was taken from textbooks by Sadiku, Hayt and Irwin.) As you know, phasors are used to solve ...
1
vote
1answer
258 views
Transformer's Primary and Secondary Voltages
In general, which is the phase relationship between the primary and secondary voltages of an ideal transformer? Does it depends on the dot convention?
2
votes
1answer
1k views
Phasors and Fourier Transform
I have always been told that for a sinusoidal variable (for instance a voltage signal), the fourier transform coincides with the phasor definition, and this is the reason why the analysis of ...
0
votes
1answer
43 views
AC signal analysis: Voltage dip (amplitude dip) at time = 0
I'm working on a series RLC problem where the input voltage is a sinusoidal function for all time. The catch is, for t < 0, the sinusoidal function is of greater magnitude than t >= 0. There is no ...
0
votes
0answers
32 views
What is the DC component of the sum of phasors?
I am preparing for the written test conducted by IISc Bangalore for admission into their graduate program. I happened to come across a sample paper from 2016, I think.
I am struggling to understand ...
0
votes
3answers
469 views
How does one relate an RC circuit's time domain solution to phasors?
It seems to be a given for phasor analysis that the voltage across a capacitor can be defined as follows:
$$ V_{C}(t) = V_{A}\cos(\omega t + \phi)\tag{1} $$
Where Vc(t) is the capacitor's voltage at ...
0
votes
5answers
361 views
Why can phasors be used simplify getting instantaneous power from instantaneous curent and voltage?
If instantanoeus power is p(t) and instantaneous voltage and current saying for a resistor are v(t) and i(t), then p(t)=i(t)*v(t). But if you convert v(t) and i(t) to their respective phasors and ...
0
votes
1answer
76 views
Is my calculated capacitor sign correct?
I have the following circuit where I would like to obtain an analytic expressions for the value of \$Cs\$ and \$Rs\$ only kowning the phasors \$\bar Vina\$ and \$\bar Vinb\$ there displayed, I don't ...
1
vote
2answers
165 views
Phasors: why is my book using sines?
When I learned phasors I learned we passed from sinusoidal to phasor this way:
$$\sqrt{2} V\cos(\omega t+\phi) \rightarrow \sqrt{2} Ve^{j\phi}$$
However I'm now studying for a book that does this:
$...
0
votes
2answers
96 views
Output of AC op amp circuit has unknown superimposed signal on top of expected output signal
I am trying to find the voltage gain of a certain ideal op amp circuit with a sinusoidal input. However, when I simulate the circuit, the output shown seems to be my calculated output but with a ...
0
votes
1answer
222 views
Determine the power dissipated in W in the 5 Ω resistor [closed]
simulate this circuit – Schematic created using CircuitLab
Excuse me for my really bad use of the schematic feature I just didn't know how to switch to the phasor domain. Anyway, I'm asked to ...
3
votes
4answers
1k views
Phasor vs Vector vs Space Vector
I wonder what is the difference between a Phasor, a Vector and a Space Vector? A phasor is also a rotating vector in space then it means that a space vector is same as a phasor? Also by definition a ...
1
vote
2answers
74 views
Time to Frequency Transform - Where are the Initial Conditions?
In a circuit with sinusoidal source and charged capacitors and inductors we have initial conditions:
$$u_{C}=u(0)+\frac{1}{C}
\int_{t_{0}}^{t}i(\tau)d\tau$$
$$i_{L}=i(0)+\frac{1}{L}
\int_{t_{0}}^{t}...
0
votes
4answers
198 views
Sinusoids represented using Euler's formula notation, confusion
EM plane waves are represented using the equation (ignoring amplitude) $$E(x,t) = e^{j (wt - kx)}$$
They are also represented in this form: $$E(x,t) = \cos(wt - kx)$$
I want to get the electric ...
1
vote
2answers
95 views
Synchronous Generator EMI
In the attached image below, I don't understand the text and phasor diagram that I have highlighted in yellow.
Why does the induced emf on the armature winding lag the magnetic flux of the ...
1
vote
1answer
2k views
How to calculate current from a phasor?
I'm just working through some textbook exercises and have been stuck on this one for a while.
The question is:
The current in an AC circuit is represented by the phasor \$I = I_0 e^{j(120\pi t + \pi/...
1
vote
1answer
141 views
Odd step in derivation of phasor Telegrapher's equations
In the derivation of the phasor form of the Telegrapher's equations (in "Fundamentals of Applied Electromagentics" by Ulaby), there is a step I'm not following:
When going between eq. 2.16 and eq. 2....
2
votes
1answer
452 views
Working of a Doubly-Fed Induction generator (DFIG) in wind turbines
I am unable to understand how a Doubly-Fed Induction generator works (in Wind Energy conversion system)? I do not understand how the reactive power fed into the stator interacts with the rotor so as ...
