Sunday, July 19, 2015

Voltage drop reduction methods; Voltage drop an evil in electrical systems

Voltage drop is always a problem for electrical engineers. Every possibility is explored by electrical engineers to minimize voltage drop to minimum level so to do effective utilization of generated voltage and losses due to voltage drop.
We Know that Voltage= Current X Resistance
Now Resistance= Resistivity X length of conductor/ Area of conductor
Now we get Voltage= Current X Resistivity X Length of conductor
                                                       Area of conductor

Now we see that voltage has relation with length  of conductor , current carried by conductor, Area of conductor.
So by following means Voltage drop across a conductor can be minimized :-
1.       Increasing the area of conductor
2.       Decreasing length of conductor
3.       Decreasing current across conductor
In additional to above there is fourth factor by which voltage drop can be reduced i.e. by decreasing conductor temperature. Now that factor comes from resistivity as resistivity decreases with decrease in temperature. So there are four factors by which voltage drop across a conductor can be minimized.

1.      Increase the Area of conductor or by increasing Number of Conductors:-
By using parallel conductors or by increasing area of conductor resistance per unit length will be decreased, which ultimately leads to decrease in voltage drop across conductor. With reduced voltage drop across conductor will leads to increased efficiency across conductor. By using parallel conductors will leads to lower the overall power losses which are otherwise more in conductors of standard size

2.     Decrease Current across conductors:-
By limiting current across conductor voltage drop across conductor get reduced proportionally. This can be achieved by reducing the load connected to conductor. Usually capacitor bank is connected across the system so to compensate reactive load current. This way current across conductor get reduced which will leads to lower voltage drop across conductor.
But one should keep in mind that capacitor should not be connected in oversize, otherwise it will leads to higher current across conductor due to over compensation. Which will leads to higher voltage drop.

3.     Decreasing Conductor Length
By reducing length of conductor during design stage voltage drop can be minimized. It should be always practice to keep load near to panels so that voltage drop can be minimized.

4.     Decreasing Temperature of conductor

When conductor is heavily loaded then that will leads to heating up the conductor, thus we can say that conductor temperature is dependent on the factors listed above. As we know that conductor temperature is a major factor in conductor resistance, and therefore in voltage drop. The temperature coefficient of copper i.e., α, is 0.00323/°C, which means resistance change of about 0.3% for each °C of temperature change.
Temperature coefficient of resistance equation is as below:-
R2 = R1 [1 + α · (T2 – T1)]
Where R1 is the resistance (Ω) at temperature T1 and R2 is the resistance at temperature T2.

Temperature T1 is often referenced at 75°C. As noted, voltage drop is a particular concern at high conductor loadings, where conductor temperatures will also be high.

Voltage drop for length of conductor

Table above shows the Maximum Recommended Lengths of Single-Phase Branch Circuits, as a Function of Load Current, Supply Voltage, and Conductor Size, for Both 3% and 1.5% Voltage Drops.

We can say that Voltage drop is necessary evil in electrical systems and great burden for electrical engineers.