Difference Between 3 Phase and Single Phase

Main Difference – 3 Phase vs. Single Phase

3 Phase and single phase are both types of power distribution systems. The main difference between 3 phase and single phase is that, in single phase, an alternating current is transmitted along a single wire whereas, in 3 phase, three wires carrying currents with a phase difference of 120o between them is used to provide current.

What is Single Phase

Single phase power refers to situations where power is supplied by one wire containing an alternating current — i.e. a current which is constantly switching direction. The voltage of a single phase supply varies periodically, as shown below. The y-axis gives the relative voltage, while the x-axis is given here in terms of the “phase angle” of voltage. However, you can take the x-axis to represent time:

Difference Between 3 Phase and Single Phase - Waveform of Single Phase

Difference Between 3 Phase and Single Phase – Waveform of Single Phase

In single phase supplies, as the voltage varies the power supplied also varies continuously. Homes are usually provided with sngle phase power.

What is 3 Phase

3 Phase power refers to cases where power is supplied using 3 wires carrying current. The alternating currents in every cable has the same frequency and the same peak voltage. However, they maintain a phase differrence of 1/3 the period (or 120o) with respect to each other. The diagram below illustrates this concept:

Difference Between 3 Phase and Single Phase - 3 phase waveform

Difference Between 3 Phase and Single Phase – 3 phase waveform

The sum of currents in the three wires is always 0. As a result, 3 phase supplies can provide constant power to a connected load which helps reduce vibrations in the case of a motor. The power supplied never has to drop to 0 as with single phase supplies. In addition, the three wires produce a rotating magnetic field that allow 3 phase motors to be self-started. Consequently, motors work much more efficiently under a 3 phase supply. Most large motors with industrial applications require 3 phase suplies.

3 phase supplies also do not require a neutral wire (although sometimes neutral wires are also used, depending on the usage). The three wires in the 3 phase supply can provide 3 times the power as the two wires (live and neutral) do in single phase. This means that it is much more cost-efficient to use a 3 phase system to deliver power, especially over long distances. Electrical power stations use 3 phase supplies to transmit current. 

Difference Between 3 Phase and Single Phase - High Tension

Difference Between 3 Phase and Single Phase – These high tension lines use 3 phase to transmit electricity.

Difference Between 3 Phase and Single Phase

Current Conduction

Single phase uses only one wire with an alternating current.

3 Phase uses 3 wires, carrying current with same frequency and peak voltage, but out of phase with each other by 120o.

Power Variation

In single phase systems, the power delivered varies constantly.

3 phase systems deliver constant power to the load.

Usage

Single phase is typically used for domestic purposes.

3 phase is used to operate industrial machinery and to transmit power from power stations.

Requirement of a Neutral wire

Single phase requires a neutral wire.

3 phase does not necessarily require a neutral wire.

Image Courtesy
“Sine wave with effective value HI” by Booyabazooka at English Wikipedia (Transferred from en.wikipedia to Commons) [Public Domain], via
“Three Phase alternating current waveform” by Eyrian (User:J JMesserly modification of original svg by User:SiriusA) [], via
“high-tension” by Gisela Giardino (Own work) [], via 

About the Author: Nipun


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