Download Three Phase Systems

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
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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 .
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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.
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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
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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.
