X and R Values 2

[nonsinusoidal]

Is there a way to find the X and R values for 600 volts,THHN cables installed in a single and three phase circuit configuration. I need to do a voltage drop calculation but I am not sure if I can find such information in the NEC or any where else. Please advice and thank you in advance

 

[davidbeach]

There are some values in the NEC. The specific X value depends on many different variables that you will probably never find an exact value, but generally the code table values should be sufficient. You could also try the IEEE Red Book.

 

[dpc]

See Table 17 in this old GE reference:

http://www.geindustrial.com/publibrary/checkout/38652.30055.29438.9182/generic/GET-3550F.pdf

"The perfect is the enemy of the good." -- Voltaire

 

[duong12]

Hi! Cable size can be determined by table 310.16 NEC2008 on page 70-148. Check this link

http://www.electrical-designer-guide.com/wire-size.html

This page for Voltage loss:

http://www.electrical-designer-guide.com/voltage-drop.html

Hope this help.

 

[xnuke]

Let me preface this by saying I work in controls, not in power, so I rarely have to size conductors or calculate voltage drops. However, I don't trust those links by duong12 at all. The first seems to be providing incorrect sizing information and doesn't include all the derating requirements. The second is strange: why would voltage drop go down when pf drops? The voltage drop is caused by both the total real and reactive current flowing, not just the real. Anyone else care to comment?

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[jghrist]

The voltage drop can go down when the pf drops. Voltage drop will be highest when the load current angle Ø=acos(pf) equals the impedance angle of the source atan(X/R). If the source X/R is high, then voltage drop will be lower with a low pf.

VD = R·cosØ + X·sinØ

 

[xnuke]

Thanks for the reminder. Anyone care to comment on the wire sizing link?

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[burnt2x]

xnuke,
Those are guides. You can come calculate on your own and may want to compare your values with the table 310.16. As David said, there are other variables to consider and each calculated value differs depending on the things factored in.

 

[nonsinusoidal]

Thank you everyone for the valuable information you all have provided. Here is where I am with my original question:
The NEC 2005, Table 9. provides information for Alternating-Current Resistance and Reactance for 600 volts Cables, 3-Phase, 60 Hz, 75 degrees,- Three single conductors in conduit. This information can be utilize to calculate the voltage drop for 600 volt cables by using VD = R·cosØ + X·sinØ with a given power factor. However, I am in search of finding the X and R values for a single phase system at 90 degrees temperature for the conductor. Similarly, I would like to know which standard in the IEEE or ICC has a variety of information for the X and R values for different voltage configurations and temperatures for the conductor. Primarily, low and medium voltages for single phase and three phase systems for distribution systems. The distributions systems here are said to be from 5 to 35 Kv. Please advice and thank you in advance

 

[jghrist]

http://www.kerite.com/catalog/catalogfiles/impedance_data_power.htm

has pos- and zero-sequence impedances for 5kV - 138kV cables. Pay attention to the assumptions listed at the end of each table. Spacing in particular is important in determining the impedance.