Longitudinal and widthwise voltage drop

[electrics]

Hello, can you tell me why do we classify voltage drop as long. and widt. ?
Does it mean or show anything in practice?? Can we say anything of a line parameters looking at these guys?

 

[charlie b]

I have no context for the terms you are using. There will be a voltage drop along the path of current flow. In what sense are you postulating current to flow along the width of a path?

 

[electrics]

no no, lengthwise means the voltage drop is along the source voltage namely in the same phase, widthwise means it is 90 degree forward or backward. imagine phasor diagramme of this analysis...

 

[markstg]

I think what you are describing is the phasor components of the voltage drop

The resistive component and the reactive component.

 

[electrics]

as far as I know Voltage drop can not be divided into 2 component as reactive and resistive but current can be divided as such,

 

[jtester]

as far as I know Voltage drop can not be divided into 2 component as reactive and resistive but current can be divided as such,

Voltage drop is a complex number, we are just used to dealing with magnitude and not phase.
A rigorous calculation of voltage drop should include phase angle as well as magnitude.

Jim T

 

[markstg]

as far as I know Voltage drop can not be divided into 2 component as reactive and resistive but current can be divided as such,

Sure it can, just as a current can be current flow due to resistance, and current flow due to reactance, voltage drop can be broken up into voltage drop due to resistance and voltage drop due to reactance.

 

[electrics]

so I am asking if we can say looking at these magnitudes anything about resistance and reactance? it is certain that these two component (of voltage drop lengthwise and widthwise) are not proportional with reactance and resistence separately, but maybe these two component of voltage drop have a meaning I dont know..

 

[jghrist]

Maybe this diagram will help. The resistive portion of the voltage drop VDR results from resistive current flowing through a resistance (I?R?cos?) and inductive current flowing through a reactance (I?X?sin?).

For small voltage drops, the difference in the magnitude of sending end VS and receiving end VR is approximately equal to the resistive portion VDR.

 

[bphgravity]

For a typcial premises wiring system, I have never seen a need or purpose for analyizing voltage drop beyond the basic I x R calculation. Even for the most stringent LEED / IECC energy uses forumals, just a simple 2% / 3% allowance is given. No other considerations needed.

Perhaps this is some type of need for an extremely rigorous power quality installation or purpose just an academic matter?

 

[markstg]

For a typcial premises wiring system, I have never seen a need or purpose for analyizing voltage drop beyond the basic I x R calculation. Even for the most stringent LEED / IECC energy uses forumals, just a simple 2% / 3% allowance is given. No other considerations needed.

Perhaps this is some type of need for an extremely rigorous power quality installation or purpose just an academic matter?

I agree that for garden variety feeder and branch circuits resistance is the predominant impedance. On the other side the coin, Transmission lines, Reactance is the predominant impedance.

 

[LarryFine]

It seems to me reactive voltage drop is a consideration any time power factor is.

 

[electrics]

Dear jghrist, If you make a simple calculation you will see that Vdr and Vdx are not simply multiplication of active current and resistance & reactive current and reactance respectively, Vdr for example is equal to the sum of Ia x R +Ir x X that is not only Ia x R am I right?

 

[markstg]

Dear jghrist, If you make a simple calculation you will see that Vdr and Vdx are not simply multiplication of active current and resistance & reactive current and reactance respectively, Vdr for example is equal to the sum of Ia x R +Ir x X that is not only Ia x R am I right?

The voltage drop component of the total voltage drop due to reisistance is I x R
The voltage drop component of the total voltage drop due to reactance is I x X
Where I is the magnitude of the total current flowing through the impedance component, not just the resistive or reactive component.

 

[markstg]

It seems to me reactive voltage drop is a consideration any time power factor is.

Not really, Reactive Voltage Drop is a consideration anytime it can substantially contribute to the voltage drop in the line. Are we saying the same thing?


A .9 or .5 pf load draws a certain current. To get the current to get drawn, the voltage to the load must be maintained within acceptable operating values. To get those acceptable voltage values to the load only depends on the voltage drop in the line. The voltage drop in the line is dependant on what the line impedance is, predominantly resistance, reacatance, or both.

 

[LarryFine]

Not really, Reactive Voltage Drop is a consideration anytime it can substantially contribute to the voltage drop in the line. Are we saying the same thing?

I think so. Reactive current must be carried, and sized for, which is why proper, and properly-placed correction can reduce the installed cost of an installation. I think ...

The voltage drop in the line is dependant on what the line impedance is, predominantly resistance, reacatance, or both.

Agreed. Both contribute to voltage drop, conductor heating, etc.

 

[Smart $]

so I am asking if we can say looking at these magnitudes anything about resistance and reactance? it is certain that these two component (of voltage drop lengthwise and widthwise) are not proportional with reactance and resistence separately, but maybe these two component of voltage drop have a meaning I dont know..

The Vd components are not proportional to the resistantance and reactance because the resistive component is factored by the power factor (cosθ) while reactance component is factored by its trigonometric compliment, i.e. sinθ.

As for having meaning...???

 

[electrics]

yesss absolutely right...