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Out of the following systems of distribution, which system offers the best economy ?
Direct current system
AC single phase system
AC 3 phase 3 wire system
AC 3 phase 4 wire system
Direct current system
The Direct Current (DC) system offers the best economy in terms of conductor material requirements for a given amount of power transmitted and voltage level. In DC systems, the effect of power factor, skin effect, and dielectric loss is absent, leading to lower conductor volume requirements compared to AC systems for the same peak insulation voltage.
The Direct Current (DC) system offers the best economy in terms of conductor material requirements for a given amount of power transmitted and voltage level. In DC systems, the effect of power factor, skin effect, and dielectric loss is absent, leading to lower conductor volume requirements compared to AC systems for the same peak insulation voltage.
VDCтАЛ=VpeakтАЛ тАФ Insulation stress in DC
VACтАЛ=2тАЛVpeakтАЛтАЛ тАФ RMS voltage for AC insulation
The economy of a distribution system is primarily determined by the volume of conductor material required to maintain a specific voltage drop and power loss. In DC, the insulation is subjected to the peak voltage without the RMS-to-peak conversion factor required in AC, and there is no reactive power flow requiring additional compensation, allowing for smaller cross-sectional areas for equivalent power delivery.
DC systems eliminate losses associated with reactance (Inductance and Capacitance).
There is no Skin Effect in DC, allowing uniform current distribution across the conductor cross-section.
For the same voltage to ground, DC requires less insulation than AC.
The absence of reactive power flow improves the utilization of the distribution network.
Lower conductor material cost
No reactive power compensation required
Reduced dielectric stress
No skin effect or proximity effect losses
Difficulty in voltage transformation (requires converters)
High cost of conversion equipment at substations
Increased circuit breaking complexity due to lack of natural current zeros
HVDC transmission
Urban rapid transit systems (trams/metros)
Industrial electrochemical processes
| Feature | DC System | AC System |
|---|---|---|
Conductor Material | Minimum | Higher |
Reactive Loss | Zero | Present |
While AC is dominant due to easy voltage transformation via transformers, DC is technically superior regarding material economy for bulk transmission or specific distribution loads.
Option B (AC single phase) is the least efficient due to high conductor material requirement compared to 3-phase systems.
A is correct тАФ The DC system is the most economical because it requires less conductor material for a given power delivery and voltage stress as compared to AC systems.
In competitive exams, remember that DC is best for economy of material, but AC is best for flexibility and transformation.