Saturday, November 7, 2015

Star vs Delta - advantages & disadvantages


STAR (WYE) ADVANTAGES

- Y used for high voltage
- common neutral point
- neutral point can be earthed
- availability of single phase at a lower voltage
- ability to spread load between the phases
- good for unbalanced loading
- each phase is a separate circuit
- dual voltage applications (3-phase and 4-wire system)
- star connected alternator requires lesser number of turns than delta for the same voltage
- star connected alternator requires lesser insulation
- star connection can distribute the load evenly



STAR (Y) DISADVANTAGES

- less torque
- construction involves combining 3 single phases into 1
- secondary distribution, light duty applications
- construction cost is more expensive (4 conductors)



DELTA ADVANTAGES

- efficient
- more torque
- simple motor design
- protection is simple and less costly
- construction cost is cheaper (3 conductors instead of 4)
- heavy duty applications
- used in rotatory conveyors
- less current per winding for the same power output
- major applications in power generation, transmission and distribution
- the transformer secondary provides all the 3 phases (if one is lost, you still have 2)



DELTA DISADVANTAGES

- no common neutral point
- detecting earth ground faults is difficult
- low voltage connection




Note 1:
If Power is kept constant,
Delta (parallel) has lower voltage but higher current (amperage) capacity
Star (series) has higher voltage but lower amperes

Note 2:
Some motors are soft started with star and then switched to delta.

Note 3:
Most modern motors have windings connected in delta.
Most 3-phase induction motors are connected in delta.

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