Single Phase vs Three Phase: What’s the Difference?
When it comes to powering industrial and commercial buildings, there are two main options: single-phase and three-phase power. While both types of power can provide the necessary energy to run equipment and machinery, there are some key differences between the two that can affect the overall efficiency and cost of the operation. Understanding the differences between single-phase and three-phase power is crucial for making informed decisions about the electrical needs of a facility.
Single-phase is an electrical system that uses the phase and neutral wires in the distribution of electrical energy. The phase wire carries the current load, while the neutral wire provides a path where the current returns.
With a single phase, the voltage rises to a peak in one direction of flow, subsidies to zero, reverses, rises to a peak in the opposite direction, subsidies to zero, and so on. The cycle repeats itself 60 times every second, which is where we get the term 60-cycle or 60-hertz alternating current. (In America) (For Europe it’s 50 Hz.)
Single-phase service is the most common type of electrical service or power available to consumers. Single-phase power is known as “residential voltage,” since it is what most homes use. It is mostly used for running small home appliances like fans, coolers, grinders, heaters, televisions, etc. In a single-phase system, one transformer is used between the distribution line and the meter. Usually, three wires, two “hot” and one neutral are installed to provide 120V and 240V single-phase service. Single-phase service may also be supplied with three-phase service.
Three-phase is the electrical system that uses four wires in the distribution of power. It has one neutral wire and three conductor wires. These three conductor wires have a 120-degree distance from each other.
In the waveform of a three-phase current, there are three separate and distinct single-phase currents, which are combined so they can be transmitted over three or four wires. The three currents rise to a peak in one direction, subside, reverse, and so on; however, they do not peak at the same time. Each phase reaches its peak 120 degrees apart from the others. Three-phase current requires two or three transformers.
Three-phase service is designed especially for large electrical loads. Three-phase service is more expensive due to the installation of four wires and three transformers. Three wires are “hot” and one is neutral. With three-phase power, the total electrical load can be divided among the three phases, requiring smaller wires and transformers.
Differences Between Single-Phase and Three Phase
The major differences between single phase and three phase are:
- A single-phase power supply requires two wires: Phase and neutral. On the other hand, a three-phase power supply only works through four wires, including three-conductor wires and a neutral wire.
- Residential homes usually utilize a lower power supply. That is why they have generally 1 phase systems. Commercial and industrial companies require heavier electronic loads. That is why they have generally 3 phase systems.
- All electric power systems in the world use 3-phase to generate, transmit and distribute. One-phase and two-phase can be taken from a three-phase system rather than generated independently.
- Three-phase current offers a steadier source of power. A magnetic force that causes motor rotation is strongest when the current flow is at its peak in the cycle.
- Single-phase current peaks twice during one cycle, whereas, three-phase current peaks six times during one cycle.
- Three-phase motors are simpler, cheaper to buy and maintain, and safer to use around combustible materials since there is no sparking when they start. This is because a three-phase current allows a motor to be self-starting since it produces a rotating field of magnetism in the motor. This eliminates the need for a separate starting winding, centrifugal switch, starting capacitor, or a system of brushes.
- Three-phase motors are available in larger horsepower sizes than single-phase motors. Current is supplied to the motor with three conductors rather than two. This allowed the power supplied to larger three-phase motors to be on the same size conductor as that required for smaller single-phase motors.
- A balanced three-phase is a three-wire circuit with equal voltages that uses 75% of the copper required for conductors.
- The power delivered by a single-phase system pulsates. The power falls to zero three times during each cycle. The power delivered by a three-phase circuit pulsates also, but it never falls to zero. In a three-phase system, the power delivered to the load is the same at any instant. This produces superior operating characteristics for three-phase motors.