Power Distribution

Certain applications, such as incandescent lighting and induction motors, require alternating current (AC) directly, while modern devices (such as televisions, computers, and battery chargers) require converting it into direct current (DC). This difference in requirements sparked a famous historical debate known as the “Battle of the Currents” between Thomas Edison (supporter of DC) and George Westinghouse (supporter of AC).

Why do we use alternating current (AC) for power transmission?

The goal is to transmit power from the generation stations to the consumer with the least possible loss. Power is the product of voltage and current ( 𝑃 = 𝑉 × 𝐼 ) .

If we want to transmit a power of 1 megawatt (1 MW) at a voltage of 100 volts, we would need an enormous current of 10,000 amperes. According to Joule’s law of thermal losses ( 𝑃 𝑙 𝑜 𝑠 𝑠 = 𝐼 2 𝑅 ) , transmitting 10,000 amperes through wires with even a small resistance would result in a huge amount of energy being dissipated as heat into the air.

• The impossible scenario (low-voltage DC): To transmit 1 megawatt over a long distance at 100 volts, we would lose more than 10 megawatts as heat in the wires before the electricity reaches the consumer!
• The efficient scenario (high-voltage AC): By using transformers, we can raise the voltage to 500,000 volts (500 kV). At this voltage, to transmit 1 megawatt, we would need only 2 amperes of current. This low current reduces thermal losses to less than 1 watt over long distances.

The brilliance of AC lies in the ability to use transformers to raise the voltage during transmission to reduce the current, and then lower it upon reaching the consumer (120V or 220V) so that it is safe for household use.​

Three-Phase Power

Industrial generators produce electricity of the “three-phase” type through three stator coils arranged at an angle of 120 degrees from each other around a rotating magnet.

• Industrial advantage: In single-phase motors, the voltage passes through zero twice in each cycle, which makes the motor operate in pulses. In the three-phase system, while the voltage of one coil is dropping, another is at its peak, giving the motor a constant and continuous torque throughout its rotation.

Types of connections (Delta & Wye):

• Wye connection (Y): The three coils are connected at a common central point, which provides a “neutral point.” This connection is characterized by offering two different voltages (the voltage between phase and neutral, and the voltage between two phases).
• Delta connection (Δ): The coils are connected in the shape of a triangle. There is no neutral, but it provides a purer sine wave due to its suppression of the third harmonic frequencies.

Residential Distribution

Residential buildings are supplied with power through a single-phase system at 120/240 volts (in North America).

• 120-volt circuit: It is obtained by connecting a “hot” wire with the “neutral” wire.
• 240-volt circuit: It is obtained by connecting two “hot” wires together (this produces 208 volts or 240 volts depending on the system).​

 (Breaker Box):

• The loads are distributed between the two phases (Phase A and Phase B) to balance the loads.
• 120-volt breakers are connected to one phase and the neutral.
• 240-volt breakers are connected to two phases (without the need for a neutral for large appliances).

Self-generated solar power (Consumer Solar)

Solar panels produce direct current (DC), and therefore advanced inverters must be used to:

1. Converting DC into AC compatible with the frequency of the public power grid.
2. Synchronization: Perfectly matching the grid waveform (voltage and frequency) to allow exporting surplus power to the grid or importing shortages from it (Net Metering).
3. Self-protection in case of a public power outage (Anti-Islanding).