Today we Study about different types of three phase connections in Brief :-
1.(Star-Star) Connection - It gives line voltage root3 times of phase voltage. It is economical for small rating and the high voltage as the number of turns per phase and the amount of insulation required is less.
2.(Delta-Delta) Connection -This arrangement is generally used in a system which carry large current on the low voltage and specially when continuity of service is to be maintained even through one of the phase develop fault. The conductor is required of smaller X-section as the phase current is 1/root3 times the line current.
3.(Star-Delta) Connection -Such connections are used principally where the voltage is to be stepped down at the end of transmission lines. The neutral of the primary is earthed.
4.(Delta-Star) Connection -Such connections are used where it is necessary to step up the voltage at the beginning of high tension transmission lines. In this case neutral point is stable and will not float in case of unbalanced loading.
This arrangement is very popular in a distribution system because it can be used the both three phase power equipment and the single phase lighting circuits. The neutral of the secondary is earthed to provide 3-phase,4-wire system.
In such cases the 11,000/400V transformer connections provide a 4-wire secondary with the neutral supplying 4th wire.
The 3-phase equipment is connected to the line wire to operate at 400V when the lightning equipment is connected b/w one of the line wires and neutral to operate at 230V.
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