Where to find voltage drop factor of 22kV cable? 2

[BabaRhum]

Hi,

I need the voltage drop factor of a cable to calculate the voltage drop along the cable. It is an aluminium 4 core cable with cross section 240mm2 (4x240 mm2, AL) to been used on 22kV network. I have been provided with the value 0.30 V/A/m for voltage drop factor. However, i want to know where this value come from? Can we calculate it? Or it from a standard(IEC/BS)?

Thanks in advance.

 

[LittleInch]

What you're referring to is resistance per metre or km.

A quick google on cable vendors shows 240mm Al has a resistance of 0.125 ohms per km at 20c or 0.155 at 80C. Note this is a single cable.

No idea where your other figure comes from unless someone is using a certain current in the cable.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[waross]

"0.30 V/A/m"
m = mile?
You need impedance, not resistance.
For example my code table for voltages up to 600 Volts is based on impedance, not resistance.
The code makes the assumption that the conductors are in contact in a conduit or cable.
The inductive reactance is related to conductor spacing.
Look for a voltage drop cable rather than a resistance table for your cable.
or
Look for the formula to calculate the inductive reactance of a unit length of the cable and use that figure with the resistance to calculate the impedance.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

Try this calculator:

https://www.calculator.net/voltage-...anceunit=meters&amperes=1&x=52&y=13&ctype=nec

Voltage drop per 1000 Meters = 0.24 Volts per Amp at unity power factor.
NOTE 1. Power factor matters.
Note 2. Based on 500 MCM conductors. 253 mm[sup]2[/sup]
0.24 volts per Amp @ 253 mm[sup]2[/sup] x (253/240) = 0.253 Volts per Amp per 1000 meters @ 240 mm[sup]2[/sup]
The extrapolation error is negligible for small ratios.
Extrapolation error for large ratios may be unacceptable.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[7anoter4]

DOHA Catalogue 12/20(24)kV This data is applicable for 12.7/22kV cables.
Three Cores, Aluminium Conductor Cables
Three Cores [Copper or] Aluminium Conductors, XLPE Insulated, Steel Tape Armoured and PVC Sheathed.
No neutral provided
90oC ac resistance 0.1618 Ω/km reactance .0968 Ω/km
The above data is approximate and subjected to manufacturing tolerance

 

[waross]

From the DOHA Catalogue;
ALUMINUM CONDUCTOR | UNARMOURED | 12/20 (24)kV
Size 240 mm[sup]2[/sup]
Voltage drop per phase V/A/km, 0.281 Volts
With a poor power factor the voltage drop per phase may exceed 0.3 V/A/km


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

Voltage drop is quite variable depending on cable construction.
The inductive reactive component of the impedance is effected by the insulation thickness, jacket thickness, the presence of steel armour and power factor.
After looking at numerous tables in the DOHA Catalogue for different constructions of cable, I see a range of values from around 0.22 V/A/km to 0.28 V/A/km.
The DOHA tables do not consider power factor.
Other tables indicate that an extremely low power factor may increase the voltage drop by 25% or more.
The figure that you were given of 0.3 looks safe and reasonable when power factor is considered.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!