How it is correct to calculate wires, considering loss of tension?
When calculating wires are usually known: tension of Ur of the source of the electric power (generator), distance of L from this source to the place of power consumption, the current intensity of I or power Rn of loading and tension of Un (rated voltage) which is necessary for normal operation of receivers of the electric power (for example glow lamps, electric motors, etc.).
Problem of calculation is the choice of such section of wires at which the rated operating voltage (rated voltage) on clips of receivers of the electric power is provided.
A little considerable deviation of this tension of Un from rated value, in particular in lighting installations is very desirable. At undervoltage of Un the network flow of the glow lamp decreases by 5% up to 20%. And at increase in tension for 5% duration of burning of the lamp decreases by 50%. According to the Ohm's law in the chain
Ur=irpr + Irn,
where rn – the loading resistance, and Irn = Un.
Resistance of wires of the line
rpr =p (2l: s),
where 2l - the total length of the line, p - the unit resistance of material of wires, s - the required section of wires.
Let's designate the difference of Ur-Un =? U – it is loss of tension in the line.
Having made the corresponding transformations in the formula, we will receive required section: S = I (2lp:? U).Top