Power distribution is the final stage of power supply. It carries electricity from the distribution center to individual consumers. The distribution center is connected to the supply center and step down the transmission voltage between 2 kV and 35 kV using transformers. Primary power distribution lines carry this medium volt power to distribution transformers located near the customer's residence. The distribution transformer further steps down the voltage to produce a voltage suitable for use in lighting, industrial equipment or household appliances. Often many consumers are supplied with electricity from a transformer through a secondary distribution line. Commercial and residential customers are connected to secondary distribution lines through service drops. Consumers who require a lot of power may be directly connected to the primary power supply level or sub transmission level.
Definition of distribution system?
A distribution system originates at a distribution substation and includes the lines, poles, transformers and other equipment needed to deliver electric power to the customer at the required voltages.
Distribution system is a two type
2. Dc Distribution
The AC distribution system is the electrical system between the step-down substation fed by the transmission system and the consumers' meters. AC Distribution is two types , Here discuses two type of AC distribution system.
i) Primary distribution and
ii) Secondary distribution
i) Primary distribution: 11 / 6.6 / 3.3 kV, 3-phase 3-wire system
ii) Secondary distribution: 400 / 240 V, 3-phase 4-wire system
Dc Distribution
DC power system consists of an electrical circuit which is a combination of resistors and constant current sources.
2-wire DC and 3-wire DC systems
Fig:- 2-wire DC system Fig:- 3-wire DC system
Methods of Obtaining 3-wire DC
* Two-generator method: 2 shunt-wound generators connected in series
* 3-wire DC generator: coils of high reactance and low resistance connected permanently to diametrically opposite points of armature winding
* Balancer set: 2 identical dc shunt machines coupled mechanically with their armatures and field windings joined in series across the outers
Fig:- 2-generator method and 3-wire DC generator
Main Components
Feeder: Conductor, no tapping, current carrying capacity
Distributor: Tapping to consumers, voltage drop
Service Main: Distributor to consumers’ end
Connection Schemes :- Radial, ring, interconnected schemes
Radial DC and AC schemes
Ring main scheme
Interconnected scheme
Requirements of a Distribution System
1. Proper voltage
2. Demand power
3. Reliability
Design Considerations
Feeders: main consideration is current carrying capacity
Distributors: main consideration is voltage drop
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