Single Phase System vs Three phase System

Single Phase System vs Three phase System:

There is two kind of power supply is normally implemented one is single phase and another one is three phase.

What is single phase:

Single phase consists of two conductors one is phase conductor and another one is a neutral conductor. Here neutral conductor is used as the return path of the current. India provides single phase 230 voltage, 50 Hz power system for all home appliances like fans, TVs, mixers etc.  But in US, they provide 110 Volts, 60 Hz power supply to their domestic appliances.

Also, Single-phase power distribution is used to delivered power such as lighting, all domestic application, sometimes industrial purpose with few large electric motors. A single-phase supply connected to an alternating current electric motor does not produce a revolving magnetic field; single-phase motors need additional circuits for starting (capacitor start motor), and such motors are uncommon above 10 kW in rating.

Single Phase Conductor


 

Electrical Notation: P and N. Here P mentions phase and N mentions neutral

Single phase is called as Split phase.

Easy understanding: If you’re not electrically minded, think of 1 (Single) phase power like a one pedal bicycle where one (pushing leg) provides power.

Advantage of single phase over three-phase power supply:

  • Only one conductor is needed ground can be taken as return path. Do not needs addition conductor. This principle is used in electric locomotive. In this the one phase will be placed on the top. The train touches the phase conductor using the carbon brushes and the return path consider as railway tracks. Hence the conductor cost is reduced. In this place we cannot use three phase or some other power supply i.e direct current. (we needs additional cost to implement such system)
  • Easy maintenance
  • Easy installation
  • Used in all control circuit wiring. Example panel wiring
  • Low cost for winding insulation as the reduced voltages
  • Any one of the phase can be taken from the three phase circuit. i.e you can take R or Y or B. All the phase delivers same power supply. Many domestic application uses this technique to balance a three phase distribution transformer’s load.
  • Coming to the Tariff, in single phase power system have less tariff as the increase in loads

The disadvantage of single phase:

  • Power loss in the single phase system is high as the voltage decreases the current increase (increase I2R loss)
  • Low efficiency
  • Frequent power failure. Due to that, we have to purchase the additional inverter to maintain the power failure.
  • Bulk power transfer is not possible. Single phase is just like single highway road lane.
  • Voltage drop is high as the voltage decrease and current increases.
  • Poor power factor. Additionally, we have to install capacitor bank
  • Net Power Transfer P is V*I*cosθ, hence it can transfer only 30 % of power as compared with three phase system.

Application of single phase power supply:

  • All domestic applications
  • The main advantage of single-phase power supply is used in the electric railway system. Already we have explained well in advantage section.

Three phase power supply:

The three-phase supply system consists of four wires, three phase conductors and one neutral. Each phase is out of phase and the phase difference is 120º apart from each other. The three-phase system is also used as a single phase system. For the low load, one phase and neutral can be taken from the three-phase supply.

Three phase balanced system can be established by star connection or delta connection. But star connection is preferred for high voltage power transmission because of the star has an advantage of the neutral point.



Electrical Notations: R, Y, and B are used to notate each phase.

Advantage of three-phase power system:

  • We can transfer high power from the generating station
  • Efficiency is high
  • Less loss
  • Power factor is good
  • Less power failure. Where any one of the phase failures means, we can make a changeover to another phase. It is applicable only the household is having three phase power supply.
  • We can use large size of the motor i.e Even greater than 10 MW motor (such a big motor is used in the oil field)
  • Net Power transfer P is 3*V*I*cosθ, it can transfer power 3 times higher than single phase power system.

The disadvantage of three phase system:

  • Heavy short-circuit current especially phase to phase fault. It may damage the equipment.
  • All the system has to be manufactured with three parallel poles. Example: three Current transformers, three Potential transformers, bus bar, three pole contactor, MCBs, MCCBs, three parallel NO and NC s etc.

 

 

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