3Phase Power Modern Electrical Engineering

Power engineering also called Power systems engineering is a sub field of that deals electrical engineering with the generation transmission distribution and utilization of electric power as well as the electrical devices connected to such systems including generators, motors and transformers. Although much of the field is concerned with the problems of three phase. AC power the standard for large scale power transmission and distribution across the modern world a significant fraction of the field is concerned with the conversion between AC and DC power as well as the development of specialized power systems such as those used in aircraft or for electric railway networks. It was a sub field of electrical engineering. In a three phase system three circuit conductors carry three alternating currents (of the same frequency) which reach their instantaneous peak values at one third of a cycle from each other.

 

Taking one current as the reference, the other two currents are delayed in time by one third and two thirds of one cycle of the electric current. This delay between phases has the effect of giving constant power transfer over each cycle of the current and also makes it possible to produce a rotating magnetic field in an electric motor.
   

Generation and distribution:

At the power station an electrical generator converts mechanical power into a set of three AC electric currents one from each coil (or winding) of the generator. The windings are arranged such that the currents vary sinusoidal at the same frequency but with the peaks and through of their wave forms offset to provide three complementary currents with a phase separation of one third cycle (120° or ^2π⁄₃ radians). The generator frequency is typically 50 or 60 Hz varying by country. Main power systems at the power station transformers change the voltage from generators to a level suitable for transmission minimizing losses. After further voltage conversions in the transmission network the voltage is finally transformed to the standard utilization before power is supplied to customers. Most automotive alternators generate three phase AC and rectify it to DC with a diode bridge.

Three-phase loads:

An important class of three phase load is the electric motor. A three phase induction motor has a simple design inherently high starting torque and high efficiency. Such motors are applied in industry for many applications.

A three phase motor is more compact and less costly than a single phase motor of the same voltage class and rating and single phase AC motors above 10 HP (7.5 kW) are uncommon. Three phase motors also vibrate less and hence last longer than single phase motors of the same power used under the same conditions. Resistance heating loads such as electric boilers or space heating may be connected to three phase systems. Electric lighting may also be similarly connected.

 Rectifiers : 

May use a three phase source to produce a six pulse DC output. The output of such rectifiers is much smoother than rectified single phase and, unlike single phase does not drop to zero between pulses. Such rectifiers may be used for battery charging electrolysis processes such as aluminum production or for operation of DC motors. Zigzag transformers may make the equivalent of six-phase full-wave rectification twelve pulses per cycle, and this method is occasionally employed to reduce the cost of the filtering components, while improving the quality of the resulting DC.

   
Phase converters:   

Phase converters are used when three phase equipment needs to be operated on a single phase power source. They are used when three phase power is not available or cost is not justifiable. Such converters may also allow the frequency to be varied (re-synthesis) allowing speed control. Some railway locomotives use a single phase source to drive three phase motors fed through an electronic drive.