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yousef harb
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Join Date: Mar 2010
Posts: 7

voltage drop

03/06/2010 1:35 AM

Ineed an example of how to calculate voltage drop on (MV) a 380 Volt system
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redfred
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#1

Re: voltage drop

03/06/2010 11:58 AM

Simple just follow Kirchhoff's laws, combined with Ohm's laws. Once you have a good grasp of these two laws you can tackle the rest of network theory including the Laplace transform, rules of superposition to even understand even transmission lines. You could try it the hard way by starting with Maxwell's equations for electromagnetics and derive the rest.

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msamad
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#2
In reply to #1

Re: voltage drop

03/06/2010 1:06 PM

Use this simple formula:

Ignoring the reactance:

Single phase system: Voltage Drop = 2 x I x R x L

Three phase system: Voltage Drop = 1.732 x I x R x L

Considering reactance:

Single phase system: Voltage Drop = 2 x I x (Rcosφ + Xsinφ) x L

Three phase system: Voltage Drop = 1.732 x I x (Rcosφ + Xsinφ) x L

Where,

I - Current through the conductor

R - Resistance (in ohm) of the conductor per KM

L - Length of conductor in KM

X - Reactance (in ohm) of the conductor per KM

φ – Load power factor angle

The value R and X are obtained from cable manufacturer (or standard data can be used).

Voltage drop is generally calculated as % of the system voltage. After you calculate the voltage drop, use this formula for % drop:

% voltage drop: (Voltage Drop x 100) / System voltage

- MS

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lazzarus
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Join Date: Apr 2010
Posts: 9
#3
In reply to #2

Re: voltage drop

04/16/2010 6:17 AM

"X" is impedance, not resistance, better to use specific volt drop from cable supplier parameters mV/A/m for volt drops calculations.

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wareagle
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Location: Alabama
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#4

Re: voltage drop

04/16/2010 6:12 PM

Quote lazzrus "X" is impedance, not resistance, better to use specific volt drop from cable supplier parameters mV/A/m for volt drops calculations."

X is reactance. Impedance is generally defined as Z² = R² + X². Better check those books again.
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lazzarus
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Join Date: Apr 2010
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#5
In reply to #4

Re: voltage drop

04/16/2010 7:00 PM

My mistake thanks,

Z=R+jX, exactly

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