Voltage Drop Equation

[shsweet28]

Lets say I am calculating Voltage Drop (Vd) and have a load with a lagging PF, then arcos(PF) gives the angle, I make the angle negative since the load is lagging.

So Vd=Vo-(I<-Angle)*(R+j*X).

But Vd=abs(I)*(R*cos(angle)+sin(angle).

Why do I use the positive angle in the second equation and the negative in the first?

Maybe I am missing something simple.

 

[shsweet28]

the second equation should be Vo-abs(I)*[R*cos(angle)+X*sin(angle)]

 

[shsweet28]

I see yet another error so I will start over.

Lets say I am calculating Voltage Drop (Vd) and have a load with a lagging PF, then arcos(PF) gives the angle, I make the angle negative since the load is lagging.

So,Vd=(I<-Angle)*(R+j*X)

Vd=abs(I)*(R*cos(angle)+X*sin(angle)

Why do I use the positive angle in the second equation and the negative in the first?

 

[shsweet28]

I found the answer to my question. Please see the image below in case you were curious.

 

[MyBeardAndMe]

Is this accurate? I am having a hard time finding anything online to back up the + for lagging, - for leading.

In the NEC Handbook it only shows Rcos(theta)+Xsin(theta) and doesn't state whether the power factor is leading or lagging.

 

[poosri]

I have the same confusion...but i am planning to use only + because nec doesnt say anything about the sign. Can someone help?

 

[dayrongarcia]

Is this accurate? I am having a hard time finding anything online to back up the + for lagging, - for leading.

In the NEC Handbook it only shows Rcos(theta)+Xsin(theta) and doesn't state whether the power factor is leading or lagging.

Yes it is correct and it will also affect the voltage regulation equation.

http://www.nct-tech.edu.lk/Download/Technology%20Zone/Performance%20of%20Transmission%20Lines..pdf

 

[poosri]

If the source is a 1 phase center tap line (V LN= 110V and V L-L = 220V), which voltage would you use to calculate voltage at receiving end?

 

[dayrongarcia]

You always use phase voltage and then multiply by Square root of 3.