Single phase vs three phase power

Single phase vs three phase power
single phase vs three phase power

In this article, we are discussing the Single Phase Vs Three Phase system. There are two types of power supply systems. The first one is Single-phase and the second is a Three-phase system. We use a single-phase system in a place where loads are small and less power is required for running the load. While the three-phase system is used where a large amount of AC power is required such as in large industries, factories, and other manufacturing units.

Definition of Single Phase system

Single phase AC system is that type of system where there is only two wires used for the transmission of electrical power, one is the phase wire while the other is the neutral wire.
The phase wire carries the current while the neutral provides the return path for the  current for the completion of the circuit.

Definition of Three Phase System

Three phase AC power system is that type of electrical system where three wires are used for the transmission of power. The wire combination consists of three conductors on for each phase, and one Neutral for the completion of the circuit. The conductors are placed at a 120-degree angle from each others.

Comparison of Single Phase Vs Three Phase System

Phase system is only used for AC systems not DC, As DC only consists of on system. Our comparison of the Single Phase Vs Three Phase system will be based on different parameters.

  • Number of Wires

As discussed above a single Phase system consist of two wires while a three-phase system consists of four wires. In some three phase loads like large three phase induction motors only 3 wires of phases are necessary for operating the motor.

Single phase and 3 phase wires
Single phase and 3 phase wires
  • Voltage value

Single-phase system caries 230 or 110 Volts (each country has its standard of generation) while three Phase system caries 415 or 380 Volts. Single phase voltage is always equals to three phase one divided by √3 in the same system.
Example
If we have a three phase 400 volt AC system, then the voltage of one phase to the neutral will be 400/√3 = 230 VAC.

  • Capability of power Transfer

Another difference between Single Phase Vs Three Phase is power transfer capability. The power transfer capability of a single-phase system is minimum while that of a three-phase system is maximum. Three phase power supply is more efficient than single phase supply, It can deliver 3 times more power than 1 phase system.
Heavy industrial loads need three phase power source while residential loads, lighting and lower power loads even in industrial workplaces are commonly use single phase power source.

  • Transmission network

Single phase power is transmitted inside cities in low voltages and the transmission network is simple. While Three-phase power network is complicated because the transmission is for medium, high and extra high voltages (up to 500 KV). Because of the high values of the voltages in the three phase power system it is transmitted using very high overhead power lines (OHTL) for safety purposes outside cities.

POwer transmission Three phase
POwer transmission Three phase

Can single phase and three phase loads run on the same power supply?

Three phase power source can deliver single phase power if we just used one phase and the neutral. By this way we can easily run a single phase motors (as an example) on three phase power supply. Some times we can use a three phase dry type transformer to convert 3 phase to 1 phase source this is commonly used in control circuits which need 1 phase while we have only 3 wires 3 phase source with no neutral.
But if we have a three phase induction motor we can’t run it on a single phase power supply. This is clear because the single phase power supply only has 1 phase and neutral. A small modification is done using capacitor connection for three phase motors to run on 1 phase source.

Loads for single and three phase supply

Some loads like heaters have the flexibility of running on both types of power sources. This is a common way for industrial heaters where the heater is consists of three separate single phase heaters, and by connecting them as STAR or DELTA formation we can feed them as one three phase heater (even star or delta). While by connecting the 3 heaters in series or in parallel as one single phase heater we can connect this heater on single phase source.

3 single phase heaters connection
3 single phase heaters connection

If we have 2 power sources, Which one is better Three phase vs single phase?

Assume we have a load which could be run on both single and three phase source (like the heater in the above example). Which is better to connect the load on?

  • Regarding the power consumption, Three phase vs single phase, The power is the same in both connections. As the load power (the heater) is constant.
  • Regarding the cost of installation, Three phase power needs 3 core wire, 3 poles circuit breakers, and the design of short circuit protection requires higher short circuit current of the CB. This means higher cost.

Single phase motor vs three phase motor

Three phase motors are more effective, self starting, need no starting capacitor, need less maintenance compared to 1 phase motors, and always have higher power factor and higher efficiency than single phase motors.

Feature Single phase Three phase
Number of wires 2 wires (one phase and neutral) 3 (3 phases, no neutral)/ 4 wires (3 phases + neutral)
Short circuit current Smaller Higher
Loads Domestic loads and small industrial loads Industrial loads
Power transmission Minimum ability of power Maximum power transmission
Efficiency Less High
Over head lines Small, and can be inside cities Very high for safety and out side cities.
Voltage levels Only low voltage Low, medium, high and extra high voltages.