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Tuesday, August 6, 2013

PPT On Power Distribution System


Power Distribution System Presentation Transcript:
1.Basic Considerations


Distribution System Layout

Utility Load Classifications
Power Factor Correction
Utility Factor
Distribution System Layout
Line Losses
Voltage Levels

3.Power Distribution System
The portion of distribution system that connects the individual     
   customer to the source of bulk power.
 Electricity distribution is the final stage in the delivery of electricity to
  end users.

4.Utility Load Classifications
Loads are the reason for electrical power system.
The types of loads are:
Resistive     (e.g. Lighting and heating)
Inductive     (e.g. Motor Loads)
Capacitive     (e.g. Rectifier Bridges with capacitor filters)

5.Residential loads are predominantly lighting , heating and motors for appliances such as air conditioners , washing machines and refrigerators.
In numbers, residential loads are the largest group of electric utility customers , comprising up to 85%.
Commercial loads typically make up about 15% of an electric utility customers. (consist of office buildings, schools , shopping malls etc. )
Industrial Loads seldom make up to 5% of an electric utility customers but they make up to 25 to 30% of the kilowatt hours supplied. (These loads consist of large motors , three phase motors , control panels & production equipment).

6.Power Factor Correction
What is Power Factor?
Power Factor is the ratio of true power or watts to apparent power or volt-amps.

7.Importance of P.F
A power factor of one or "unity power factor" is the goal of any electric utility company since if the power factor is less than one, they have to supply more current to the user for a given amount of power use.
In  doing so, they incur more line losses. They must also have larger capacity equipment in place than would be necessary  otherwise. As a result, an industrial facility will be charged a penalty if its power factor is much different from 1.

8.Power Factor Correction
Most commercial and industrial loads are inductive in nature the kVAs drawn from the utility are larger than the kWs and the current lags the voltage as shown in Fig 3.1
Only the component of the current that is in phase with the voltage provides useful work. The out of phase component increases the total current that utility must supply.

8.The overall power factor of a customer`s internal electrical system is brought closer to one by adding capacitance across line at various points.
If the system is capacitive , inductance would be added across the line for power factor correction.
The cost of correcting power factor to one as opposed to the modest correction between 0.95 and 0.99 may be much higher and the return on investment for the optimal correction may be too small to justify.

9.Correction to a power factor of unity under one set of operating conditions may result in a leading power factor under differing load conditions. The leading power factor may result in excessive line voltage which is illustrated in fig . 3.7 on the next slide

10.Utility factor is a measure of how much of the total capacity of a utility is in use. If all of the power a utility can generate is being used the utility factor is 100%.
 The requirement for reserve power and the load diversity is illustrated in fig 1.2

The reserve requirements are for both spinning reserve and stand-by reserve.
Spinning reserve refers to reserve power available from generators that are spinning but are not producing full rated output power.
The spinning reserve requirement is typically 10% of the anticipated or actual load.

12.A stand by reserve equal to the largest single unit in the system is required. The stand by reserve does not include the spinning curve.
    Fig 3.8 to be embedded.

13.Service Factor
Service factor refers to the amount of time a load can be fed by the system. A service factor of 100% means the system feeding a particular load , was never out of service.
Lightning storms , other weather events and scheduled maintenance cause service factor to decrease to less than 100%.

14.Distribution System Layout
The different types of distribution systems are:
Radial Sub Transmission & Distribution Layout.
Loop Arrangement.
Combination of Loop & Radial.

15. In this layout , distribution lines extend from the substation to the last load with service drops to customers along the way.
Major advantage is that radial layout are simpler and more economical to install than other types of layouts.
Disadvantage is that any problem usually leaves a number is customers out of service until the problem is resolved.
Figure 3.9 the radial layout distribution.

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