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Anonymous Poster

Calculate the Voltage Drop of Busway

07/02/2008 4:34 AM

Hi guys,

I find that in the catalogue of most busway supplier, they provide the table and formular to calculate the voltage drop. the formular (line-to-line) is:

Vd(table) = I (load) x (Rcosφ + XSinφ)x L ( where L is the length)

Vd = Vd(table)x (I/In) x L/100ft.

But in table, the Vd(table) is increased when powerfactor is increased. Is it possible?

For example, With 100m of 1000A Busway, Vd (table) = 10.53V where P.f = 0.8. R =5.41ohms*10Exp(-3)/100m. X = 2.92ohms*10Exp(-3). and Vd(table) =9.67V where P.f = 0.6.

and I don't know to tell line-to-line Voltage drop and Line-to-neutral voltage drop apart.

Someone pls help me!

Thank you all!
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Lendog
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Join Date: Jun 2007
Posts: 141
Good Answers: 2
#1

Re: Calculate the Voltage Drop of Busway

07/02/2008 12:05 PM

To answer your first question, if you look at the equation for Vd(table), the "cos(theta)" term is your power factor. As cos(theta) approaches 1, sin(theta) approaches 0. Since the resistance is greater that the reactance, the voltage drop increases as you approach unity power factor.

For the second question, I think the line to line voltage drop refers to the drop to the load and back when connected line to line, and same for the neutrally. I sure someone will correct me if I'm wrong.
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Tuan_vn
Participant

Join Date: Jul 2008
Posts: 4
#2
In reply to #1

Re: Calculate the Voltage Drop of Busway

07/03/2008 5:39 AM

Because i don't know how to attach file in this rum. so Pls give me your email addr. I'll send you file and you can see this problem more clearly.

Thank you!
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Lendog
Power-User

Join Date: Jun 2007
Posts: 141
Good Answers: 2
#4
In reply to #2

Re: Calculate the Voltage Drop of Busway

07/03/2008 10:55 AM

Just exactly what kind of file did you want to send? If it is an image of some type, you may be able to insert it using that little camera icon when you post a message.
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Blitz
Associate

Join Date: Aug 2007
Location: Boston area
Posts: 38
#3

Re: Calculate the Voltage Drop of Busway

07/03/2008 10:09 AM

Voltage drop increases as the gap between the load power factor and busway power factor grows.
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BabyGuinness
Power-User
Ireland - Member - New Member Engineering Fields - Energy Engineering - New Member

Join Date: Aug 2007
Location: Northern Ireland
Posts: 197
Good Answers: 17
#5

Re: Calculate the Voltage Drop of Busway

07/03/2008 7:22 PM

See phasor diagram below.

Although the magnitude of resistive and reactive volt drop of the cable (phi in the diagram below) remains the same, it must be added (lagging) or subtracted (leading) depending on the power factor of the load (theta in the diagram below). You need to read a cable volt drop text book or standard for more detailed explanations. Busduct tends to have a higher reactive component than cable so the effects are greater.

Line-to-line is the 3-phase volt drop. Line to neutral is the single phase volt drop. You should use line-to-line if you intend the busduct to feed a balanced load.

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ramvinod
Guru

Join Date: Jun 2007
Location: chennai,India
Posts: 592
Good Answers: 19
#6
In reply to #5

Re: Calculate the Voltage Drop of Busway

07/03/2008 11:29 PM

Great.

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 Ramesh,Freelance Electrical/automation Consultant
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nesubra
Guru

Join Date: Nov 2006
Posts: 729
Good Answers: 2
#7
In reply to #5

Re: Calculate the Voltage Drop of Busway

07/12/2008 9:30 AM

How did u do it? great .I would love to know the tehnique.

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Anonymous Poster
#8
In reply to #5

Re: Calculate the Voltage Drop of Busway

03/16/2010 7:13 PM

Phasor diagram is not correct!

Angle Φ is between IRc and IZc

Radomir
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pradomir
Participant

Join Date: Mar 2010
Location: Belgrade, Serbia
Posts: 4
#9
In reply to #8

Re: Calculate the Voltage Drop of Busway

03/17/2010 1:09 AM
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Users who posted comments:

Anonymous Poster (1); BabyGuinness (1); Blitz (1); Lendog (2); nesubra (1); pradomir (1); ramvinod (1); Tuan_vn (1)

Previous in Forum: Discharging P.F.C Capacitor Banks.   Next in Forum: GE -MM2 Motor Protection Relay - Starting Current in mm2 Mis Match with Measured

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