1. By: Mohammed alhussaini & Ali Rageh
Three Phase Systems
By: Mohammed alhussaini & Ali Rageh

2. Why three phase systems?
Carry three alternating currents (of the same frequency) which reach their instantaneous peak values at one third of a cycle from each other.
The delay between the three current phase gives a constant power transfer and produce magnetic field in the electric generator .
Using a neutral wire allows higher voltage to be used in a single phase

3. Properties and advantages
Smaller size of the neutral conductor sience all the currents tend to cancel out each other.
Constant power which helps in reducing generator and motor vibration .

4. Three Phase Vs. Single Phase
A three phase transmission system requires less copper or aluminum to transmit the same quantity of power of a specific distance than a single phase system.
Three phase motors are self-starting due to the rotating magnetic field induced by the three phases. On the other hand, a single phase motor is not self starting, it requires a capacitor and an auxiliary winding.

5. Three Phase Vs. Single Phase
In Single phase systems, the instantaneous power is not constant and is sinusoidal. This results in vibrations in single phase motors. In a three phase power system, however, the instantaneous power is always the same.
Three phase motors have better power factor compared to single phase motors.

6. Three-phase
Single-phase
15 kW Total Load
42 amps
125 mps
Conductor Current
5 x 8 AWG
3 x 1 AWG
Conductor Gauge
25 pounds
96 pounds
Conductor Weight (100 ft)
$85 USD
$327 USD
Conductor Cost (100 ft)

7. Three-phase loads Rectifiers:-
 Using rectifiers as a load produce a six-pulse DC output such ; rectifiers is much smoother than rectified single phase.

8. Three-phase loads Three phase motor:- Cost less than one phase motor.
Motors aren’t common for power more than 7.5kW.
Vibrate less ; last longer.

9. Extra info:-
Single phase system can be converted to three phase by using:-
Mechanical  converters : Rotary phase converter.
Non-mechanical : Transformers.
connecting the phases in the right order is required to ensure correct rotation
Each phase of the three phase system has different color which is vary from one country to another.