System Three-phase star connected

High voltage supphes within a plant are invariably arranged as three-phase star-connected systems. The star point of the transformer secondary winding or the generator stator winding is... 

A three-phase three-wire, star connected isolated neutral system,... 

Isolated neutral In i symmetrical ihree-phtise three-wire star-connected system the summation of all phase quantities, voltage or cunent will be zero, as illustrated in Figure 21.7. When a few harmonics exist in such a system, this balance is disturbed and the sum of these quantities is not zero. The third harmonic quantities can find their outlet only through t neulral of the system. Since there is no neutral available in this system, no third harmonic quantities will tlow into or out of the supply system and affect the equipment associated with it or a communication network if existing in the vicinity (Figure 23.12(a)). 

In any star-connected system currents flow along the lines (/O, through the load and return by the neutral conductor connected to the star point. In a balanced three-phase system all currents have the same value and when they are added up by phasor addition, we find the resultant current is zero. Therefore, no current flows in the neutral and the star point is at zero volts. The star point of the distribution transformer is earthed because earth is also at zero potential. 

A star-connected system is also called a three-phase four-wire system and allows us to connect single-phase loads to a three-phase system. 

A load connected to the three phases of a star-connected three-phase four-wire supply system from the local substation would have a voltage of ... 

This is the most commonly used method for measuring power in a three-phase, three-wire system since it can be used for both balanced and unbalanced loads connected in either star or delta. The current coils are connected to any two of the lines, and the voltage coils are connected to the other line, the one without a current coil connection, as shown in Fig. 4.19. Then,... 

This equation is true for any three-phase load, balanced or unbalanced, star or delta connection, provided there is no fourth wire in the system. 

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