By: Mohammed alhussaini & Ali Rageh 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 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 . 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. 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. 15 kW Total Load Single-phase Three-phase Conductor Current 125 mps 42 amps Conductor Gauge 3 x 1 AWG 5 x 8 AWG Conductor Weight (100 ft) 96 pounds 25 pounds Conductor Cost (100 ft) $327 USD $85 USD Rectifiers: Using rectifiers as a load produce a six-pulse DC output such ; rectifiers is much smoother than rectified single phase. Three phase motor:- Cost less than one phase motor. Motors aren’t common for power more than 7.5kW. Vibrate less ; last longer. Single phase system can be converted to three phase by using: Mechanical converters : Non-mechanical : Rotary phase converter. 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.