Of the power you use throughout your day, 90 percent of that is AC power. AC power is an alternating current, meaning that the direction and magnitude of the current change direction periodically. This is also considered sinusoidal voltage since when it’s plotted on a graph, it takes the form of a sine wave.
AC power can be delivered in two forms; single-phase and 3-phase systems.
How Single and 3-Phase Power Supplies Work
“Phase” refers to the distribution of the electrical load. The distribution of the load is different in single-phase and 3-phase systems, this is most evident in the design of the individual systems.
A single-phase power system is the simpler network of the two AC power supply types. The network consists of just two wires; one wire is responsible for carrying the current to the load, while the other wire provides the return path. With only one power supply wire, this creates a single sinusoidal wave.
As you can see from the graph, single-phase systems have peaks and dips in voltage. These rises and falls mean that constant power cannot be delivered to the load.
A 3-phase system, on the other hand, is a three wire AC power circuit. All three wires are phase wires in this system, meaning that there are three sinusoidal voltages which are 120 electrical degrees out of phase from each other.
Some 3-phase systems do use a fourth wire, a neutral wire. This configuration is called the Wye or Star configuration, while the three-wire system is called the Delta configuration.
Power Consumption or Electrical Loads Required
The big difference between single-phase and 3-phase power supplies is the consistency of the delivered power. As mentioned above, single-phase power is delivered in an inconsistent manner with peaks and dips in voltage. Three-phase power, with its three sinusoidal waves out of phase from each other, delivers a steady and consistent flow of power to the load. Power is also distributed among the phases allowing for a lower current.
With only one additional wire, 3-phase power transmits three times as much power compared to single-phase systems. The consistent flow of power makes 3-phase systems much more efficient than its counterpart and gives the system the ability to handle higher loads.
Residential vs Commercial and Industrial Applications
Due to their design, single-phase systems don’t generate a rotating magnetic field. Without this, they can’t create enough torque in the circuit to start electric motors without the addition of another circuit (often in the form of capacitors).
Single-phase systems are low voltage (120/240V) and cannot accommodate heavy loads. Instead, single-phase systems are more commonly sources for lighting and heating rather than for large equipment. This is why you find single-phase power in most residential homes.
3-phase systems are higher voltage (460/575/4160V). They provide enough power to run large equipment and enough torque to start electric motors and are much more efficient than single-phase systems. As such, commercial and industrial buildings and worksites are usually supplied with 3-phase power to provide the needed power at a lower cost.
Though most residential homes are supplied with single-phase power, some equipment or systems may require 3-phase power. When installing workshop equipment, large air-conditioning systems, and the like, ensure that you double-check the voltage and power needs of the new equipment. 3-phase power cannot be delivered to your home.
The power in our grid system is 3-phase power. The single-phase power delivered to our homes is created from this 3-phase power using a transformer.
Though single-phase and 3-phase power supplies have their pros and cons, they have different applications. The low-cost and simple network of single-phase systems make them ideal for residential applications while the steady and powerful 3-phase system is ideal for commercial and industrial applications. The power consumption and capability of each system must be considered before making a selection for your application.