Difference Between Three Phase and Single Phase

Three Phase vs Single Phase

Three phase power and single phase power are two types of electrical power we use in our daily lives. Our homes run on single-phase power while factories run on three-phase power. Three phase and single-phase power are required in fields such as electrical engineering, industrial designing and even basic home wiring. It is vital to have a proper understanding in these concepts in order to excel in fields that have heavy usage of these concepts. In this article, we are going to discuss what phase is, what single phase power and three phase power are, their definitions, applications, similarities, and finally the differences between three phase power and single phase power.

Single Phase Power

To understand what single phase means, we must first understand the term phase. A travelling wave can be defined using the equation Y(x,t) = A sin (ωt – kx), where Y(x,t) is the displacement on the y axis at point x at time t, A is the amplitude of the wave, ω is the angular frequency of the wave, t is the time, k is the wave vector, or sometimes referred as wave number, and x is the value on the x axis. The phase of a wave can be interpreted in several ways. The most common one is that it is the (ωt – kx) part of the wave. It can be seen that at t=0 and x=0, the phase is also 0. A single phase current has only one sinusoidal wave. Single-phase power is what we use in our homes. Since the devices in our homes do not require any special power mode, it is safe and cheap to use single-phase current.

Three Phase Power

A three-phase system consists of three sinusoidal waves, which are 120° or 2π/3 radians out of phase to each other. Three-phase electrical power is the most common method of transmission of electricity. The three phase electrical current generates a constant power throughout the cycle. Therefore, this is highly suitable for electrical circuits in industrial settings. When a rotating device such as a lathe machine rotates at the same frequency as the light source, the machine looks like not rotating. A three-phase power supply can solve this by giving a constant power throughout the cycle. The three waves in the three phase current can be represented by Y1(x,t) = A sin (ωt – kx), Y2(x,t) = A sin (ωt – kx-2π/3) and Y3(x,t) = A sin (ωt – kx-4π/3). The initial phase of the Y1 wave is assumed to be zero.


What is the difference between Single Phase and Three Phase?

• Single phase has only one sinusoidal current and one sinusoidal voltage. Three-phase power has three sinusoidal currents that are 2π/3 radians out of phase to each other.

• The instantaneous power dissipation of the single-phase power depends on time as well as the resistance. The power dissipation of three-phase power supply is constant.


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