cable selection

[quality2007]

Is any one know how volts per ampere per meter and current ratings calculated in different manufacturer brochure for any 4 phase unarmoured cable pvc insulated/pvc sheathed 30 degree ambient and 70 degree operating temperatures for cable 600/1000 volts for particular installation method e.g if 4*95 mm sq unarmoured burried in direct underground duct with trefoil etc how is calculated?

 

[7anoter4]

The maximum permissible current or current-carrying capacity [ or ampacity] usually is not calculated but taken from a standard as:
DIN VDE 0298/ part 2/Application of cables and flexible wires in power installations. Recommended values for current-carrying capacity of cables for fixed installations with rated voltages VO/V up to 18/30 kV.
or :
NEC [NFPA-70] art 310 for U.S.A.
You may calculate it according to IEC 60287 but there are some parameters as drying the soil around the cable, for instance, are not taken into consideration. Or for U.S.:
Neher, J.H., and McGrath, M.H. (1957), "Calculation of the Temperature Rise and Load Capability
of Cable Systems," AIEE Trans., Vol. 76, Part 3, pp. 755-772.

 

[quality2007]

what will be the ampere rating,voltage drop,resistance and reactance for 95mm sq 4/c cu/pvc/pvc 600/1000v volts cable if burried it directly inside duct from manufacturer brochure if ambient temperature 30oc and if 40oc?

 

[7anoter4]

In order to state the current-carrying capacity of this cable you have to specify other data:
1)Is it a single 3 core [3 phase] cable in a single conduit [or pipe]?
2)What is the load factor [0.7-1 usually]?
3)How deep the conduit is buried?[usually 0.7-1.2 m]
4)What is the specific thermal resistance of the soil [usually 1 K.m/W]?
In order to state the reactance you need to know:
5)Is the pipe [or conduit] of steel or other ferromagnetic metal made?
6)The cable length
7)The frequency[50 or 60 Hz].
For voltage drop you need to know the rated voltage of the supply system and if the cable is for an induction motor supply, for instance, and then what will be the starting current [and better also the starting power factor].

 

[quality2007]

thank you. it is 4 core 3phase 95mm2 pvc/pvc 600/1000v, load factor 0.80 assumed, 1m deep, duct is empty 3m * 3m size, no soil, concrete ambient temperature 40oc, 50 meter length of cable, 50hz , distribution purpose, current capacity, voltage drop, reactance to be detemine through brochure and after determining current capacity etc load can apply to is it to be determined.

 

[7anoter4]

It is still not clear. A sketch may clarify better your quest. Could you provide one?

 

[quality2007]

I need to know current capacity max Ib,r,x per phase cable can carry from brochure for this installation method directly burried in concrete duct for any distribution let p.f=0.8 load allowed???

 

[7anoter4]

I think -if the duct- it seems to me more as a channel or a tunnel-is ventilated and maximum temperature is stated as 40oC, you can take it as cable in free-open-air. According to VDE0298 the current-carrying capacity for NYY cable 4*95 sqr.mm copper conductor is 244 A at 30oC free air. For 40oC you have to multiply by 0.87 .Then the current carrying capacity will be 244*.87=212 A.
The inductive reactance could be the same as for circular conductor cable. For 4*95 is 0.0727 ohm/km. The a.c. resistance for 70oC is 0.232 ohm/km.