The term used for the loss of electrical energy in the flow through a conductor or electrical device is referred to as voltage drop. The conductor or device has a resistance and will therefore retard the flow of such electric charges, which results in falling voltage. Implication is that at the time the current leaves a point in the circuit for another point, the energy at those points is not fully utilized because there will always be a difference in voltage when the current exits and where it entered.

For example, consider an electrical device with a voltage of 20 volts at point A where the current enters and the voltage at point B where the current exits is 16 volts. The difference between the two voltages, 20 volts – 16 volts, is called the voltage drop, which in this case is 4 volts.

Voltage drop occurs since any conductor, whether a wire or some other device, has resistance. Current flowing through such elements means the charges will lose energy as heat. The greater the resistance of the conductor, the more the voltage will drop.

The amount of voltage drop depends upon many factors such as the length of the wire, cross-sectional area of the wire, and the material the wire is made from, affecting its resistivity. The longer the wire, the greater is the resistance, and therefore larger is the voltage drop. A smaller cross-sectional area of wire, that is, a thinner wire, would result in greater resistance and larger voltage drop. More, conversely, a thicker wire or cross-sectional area translates to smaller resistances and lesser voltage drops.

To sum up:

• Longer wires result in higher resistances and a larger voltage drop.
• Thicker wires (which is a lesser gauge number) means lower resistances and minor voltage drops.
• Thin wires correspond to a larger gauge number which will result in larger resistances and more massive voltage drops.

As an example

Factors Affecting Voltage Drop in Wires:

• Longer the L = higher Resistance.
• Cross-sectional Area (A): The thicker the wire, the smaller the cross-sectional area, and the lower the resistance.
• Resistivity (ρ): The wire material also impacts resistance. Every material has a specified value of resistivity. This is based on how easily electric current can pass through it.

The formula for the resistance of a wire is:

    R = ρ × (L / A)
  

• R is resistance
• ρ is the resistivity of the material
• L is the wire’s length
• A is the cross-sectional area of the wire

What happens in case of excessive voltage drop?

Voltage Rise

Voltage Rise Example – The Ferranti Effect:

Voltage drop vs Voltage rise

• Voltage Drop is the decrease in voltage that happens as electric current passes through conductors and other resistive elements within a circuit. It is usually undesirable because it causes energy loss and inefficiency.
• Voltage Rise is that situation where the voltage at the receiving end of a system, say a transmission line, increases because of the capacitive property of the system. This is undesirable as it forces the voltage up to unsafe operating levels, particularly as experienced in the Ferranti Effect.

Summary

Voltage Drop is the voltage drop that occurs when current flows through the resistive elements of a circuit. This occurs because of resistance in conductors or devices, which results in energy loss. It is usually undesirable because it reduces efficiency and can even damage equipment.

Voltage Rise refers to an increase in voltage, mainly happening in high-voltage transmission lines under light load conditions. This is normally caused by the Ferranti Effect whereby the receiving end of a transmission line will be higher in voltage than at the sending end because of capacitive effects.

Both concepts are critical in knowing how electrical systems work, and the management of voltage drop and rise is of great importance in ensuring efficient and safe operations of electrical circuits and power systems.