More nonsense.
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More nonsense.
Hameedulla-Ekhlas
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Dear all,
Let me try to explain in some detail and if there is any mistake please advise.
Let me explain the instantaneous in another method.
e = Em sin(0) ---1
e is the instantaneous voltage, Em is the maximum voltage, 0 is the angle of the generator armature, and "sine" is one of the trigomoetric function.
The instantaneous voltage, e depends on the sine of the angle. It rises to a maximum positive value as the angle reaches 90 degree. this occurs because the conductor cuts directly across the flux at 90 degree. It falls to zero at 180 degree because the conductor cuts no lines of flux at 180 degree and etc.
Another form of the trigonometric equation for a sine wave of voltage involves the angular velocity refers to the number of degrees(angle) through which a voltage vector rotates per second. generally omega(w) given in radians per second rather than degrees per second.
There are pi radians in half a circle and 2pi radian in the circumference of a complete cricle.
the equation is
e = Emxsin(wt)
it is used to determine the voltae of a rotating vector at some given instant of time. The starting reference or "time zero" is usually when the voltage vector is at zero. The equation time factor t is the elapsed time from time zero and is the exact instant at which the voltage is to be determind.
For example consider a 60 Hz voltage whose peak value is 100 volts. To determine the voltage 0.00139 second from the zero point the equation would be:
sinwt = sin*2*f*t sin 360(60)(0.00139) = sin30 degree
=0.5
The instantaneous voltage e is
e = Em x sin 30 degree
e = 100 x 0.5
e = 50 volt.
Similarly the equation for the instantaneous value of a sine wave of current would be.
i = Im x sin(0) ;
i = 10 * 0.5
i = 5 ampere
K = v / i = 50 / 5 = 10 So it is only a constant and it is also called R with ohm unit.
Let me try to explain in some detail and if there is any mistake please advise.
Let me explain the instantaneous in another method.
e = Em sin(0) ---1
e is the instantaneous voltage, Em is the maximum voltage, 0 is the angle of the generator armature, and "sine" is one of the trigomoetric function.
The instantaneous voltage, e depends on the sine of the angle. It rises to a maximum positive value as the angle reaches 90 degree. this occurs because the conductor cuts directly across the flux at 90 degree. It falls to zero at 180 degree because the conductor cuts no lines of flux at 180 degree and etc.
Another form of the trigonometric equation for a sine wave of voltage involves the angular velocity refers to the number of degrees(angle) through which a voltage vector rotates per second. generally omega(w) given in radians per second rather than degrees per second.
There are pi radians in half a circle and 2pi radian in the circumference of a complete cricle.
the equation is
e = Emxsin(wt)
it is used to determine the voltae of a rotating vector at some given instant of time. The starting reference or "time zero" is usually when the voltage vector is at zero. The equation time factor t is the elapsed time from time zero and is the exact instant at which the voltage is to be determind.
For example consider a 60 Hz voltage whose peak value is 100 volts. To determine the voltage 0.00139 second from the zero point the equation would be:
sinwt = sin*2*f*t sin 360(60)(0.00139) = sin30 degree
=0.5
The instantaneous voltage e is
e = Em x sin 30 degree
e = 100 x 0.5
e = 50 volt.
Similarly the equation for the instantaneous value of a sine wave of current would be.
i = Im x sin(0) ;
i = 10 * 0.5
i = 5 ampere
K = v / i = 50 / 5 = 10 So it is only a constant and it is also called R with ohm unit.
mivey
Senior Member
So I guess you eventually added enough qualifiers to your OP until you got it to match the answer you had in mind all along.
yes
Zo is only for a uniform transmission line and can be the same as the instantaneous impedance. However, even if it is uniform but terminates in something that does not match the characteristic impedance, the impedance will change. Think about a uniform open-ended line where the instantaneous impedance starts out the same as the characteristic impedance but eventually goes to infinity.
But what I had in mind was fault analysis where the impedance changes with time. From the IEEE Violet book:
mivey
Senior Member
Now you are just toying with us. :grin:
Who is toying with whom?
Who is toying with whom?
Not really, just adding clarification.
Now you are talking about TDR and delay lines which I did not think to disqualify from the discussion.
But even there, they make the assumption of constant reactances.
"However, for the sake of simplicity the reactance is considered fixed over the time interval for which the fault current is calculated."
Who is toying with whom?
Not really, just adding clarification.
Now you are talking about TDR and delay lines which I did not think to disqualify from the discussion.
But even there, they make the assumption of constant reactances.
"However, for the sake of simplicity the reactance is considered fixed over the time interval for which the fault current is calculated."
Your clarification is analogous to putting blinders on a horse, or forcing someone to have tunnel vision.
Ultimately, your goal appears to be...
mivey
Senior Member
But not "constant" like in the steady-state case. In the transient case, the value is picked so the current can be approximated using a constant voltage input. One is a derivation, the other is a replacement.
"Fixed" or "constant" in this case mean the same thing, no? Doesn't really matter tho. It is just that in this case, the approximations are more drastic than it is in our steady state cases. And, I would think the inductance would be a function of current rather than time.
Now does "transient impedance" mean it is not constant, or does it mean a value to be used in a transient analysis?
mivey
Senior Member
I'm thinking there is a difference in a value that can be derived vs one that you pick as a substitute.
There are certainly time-dependent impedances, although not within the walls of the city you have built.
It is not constant but does eventually reach a steady-state value.
There are impedances that may never reach a steady-state value in a short time period, like something that is in a state of decay or even a biological impedance (again, not quite the circuit you are trying to discuss). Even so, they are impedances. They may not exactly be functions of time (maybe we just can't find the correct time function) but they don't have to be constant.
Mivey,
Granted, impedances do sometimes change for various reasons, but they are not defined by the ratio,
v(t)/i(t)
which is at the heart of the original question.
I would think that one would perform a separate linear calculation for each of several situations such as max and min temps, best and worst case, etc. That is the way we did it in the old days!
Whatever, to perform a linear calculation, impedances must be assumed constant.
Granted, impedances do sometimes change for various reasons, but they are not defined by the ratio,
v(t)/i(t)
which is at the heart of the original question.
I would think that one would perform a separate linear calculation for each of several situations such as max and min temps, best and worst case, etc. That is the way we did it in the old days!
Whatever, to perform a linear calculation, impedances must be assumed constant.
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