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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
 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
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.
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.