Voltage Drop for 2400V system

[JCHENHI]

Dear All,

I am new to this forum and I have one question here. During our design for an airport ILS project, I find I need to calculate the voltage drop for a cable between the step-up and step-down transformer. It's about 3,170ft long and is the load is about 12amp at 2400V. My problem is that NEC Table 9 only provides cable information at 600V. How can I obtain cable info for 2400V?

Your help is highly appreciated and if there is anything wrong with my first post, just let me know.

James

 

[davidbeach]

An ohm is an ohm and an amp is an amp. Voltage drop in a function of amp-feet (or amp-meters) through a given impedance.

 

[itsmoked]

As davidbeach sez, just do the per foot thing.

 

[JCHENHI]

Thanks, davidbeach and itsmoked. But can I use the table value for 600V cable to calculate impedance of 2.4kv cable?

 

[rbulsara]

Cable manufacturer publishes impedance values or charts for MV cables. Contact Okonite, Kerite or Pirelli etc.

 

[RalphChristie]

JCHENNI:

Contact the cable manufacturer and obtain the data from them.

Either:
the approx. impedance / given distance (ohm/km, ohm/mile, etc.)
or
the voltage drop per amp metre (or feet)

[red]Failure seldom stops us, it is the fear for failure that stops us - Jack Lemmon[/red]

Make the best use of Eng-Tips.com
Read the Site Policies at FAQ731-376

 

[alehman]

Impedance depends on the type of cable (shielded vs. non-shielded) and physical arrangment. I agree with Ralph. The manufacturer should have impedance tables for typical installations.

Is this a series lighting circuit? Airfield systems are commonly series connected circuits, fed by a constant current transformer. In that case voltage drop may not be a significant to the design.

 

[wareagle]

The resistance of #2 cu = .194 per 1000 ft and #2 AL = .319
per 1000 ft. An estimate of the voltage drop is

#2Cu .194 x 3.170 x 12 = 7.4 volts and for
#2al .319 x 3.174 x 12 = 12.1 volts.

 

[BJC]

A rough rule of thumb- One mile per 1 KV.
2.4 KV 2-1/2 miles.
YMMV depending on load.