The distributors of AC and DC distribution system are generally classified as per the way they are being fed by the feeders. The main distributor types in power system are as under:
- Distributor fed at one end.
- Distributor fed at both ends.
- Distributor fed at the center.
- Ring mains or Ring distributor.
Distributor Fed at One End
In this type, the distributor is connected to supply at one end and loads are tapped at different points along the length of the distributor. The single line diagram of a distributor AB fed at point A is shown in the figure. The various loads I1, I2 and I3 are tapped at point C, D and E respectively. The following points are worth noting in this case:
- The current in the various sections of the distributor from the far end B goes on increasing as we approach the feeding point A. Thus, current in section CD is more than DE and current in section AC is more than CD.
- The voltage across the loads away from the feeding point goes on decreasing. The minimum voltage occurs at the farthest load point E.
- Whenever the load on the distributor is switched on, or off, there are heavy voltage fluctuations at the farthest load point E.
- If a fault occurs on any section of the distributor, the whole distributor will have to be disconnected from the supply mains for its repair. Therefore, continuity of supply is interrupted.
Distributor Fed at Center
In this type of feeding, the distributor is connected to supply at the center and the loads are tapped on both the sides of the distributor along its length. The figure shows the single line diagram of distributor AB fed at the middle point M. The various loads I1, I2, I3 and I4 are tapped at points C, D, E and F respectively.
It is equivalent to two singly fed distributors (MA and MB), each one having a common feeding point and length equal to half of the total length. It is preferred over a distributor fed at one end because of the following advantages.
- The various sections of the distributor carry lesser current which reduces the voltage drop in the distributor.
- The voltage reaching the farther points (i.e. C and F) is more.
- There are fewer voltage fluctuations at the farther ends.
- The conductor size required for the distributor is less.
Distributor Fed at Both Ends
In this type, the distributor is connected to supply at both ends and loads are tapped at different points along the length of the distributor. The supply voltage at the two feeding points may or may not be equal. The single line diagram of a distributor fed at point A and B is shown in the figure. The various loads I1, I2and I3 are tapped at point C, D and E respectively.
In this case, the voltage goes on decreasing as we move away from one feeding point (say A), reaches the minimum value and then again starts rising and attains the maximum value when reaches at the other feeding point (B). That load point obtains the minimum voltage which is fed from both sides i.e. point D in this case.
However, the point of minimum potential is never fixed, it is shifted with the variation of load on the different sections of the distributor.
Advantages of Distributor Fed at Both Ends
- If the supply of any feeding end fails, the continuity of power supply to the consumers is maintained from the other feeding end.
- In case, the fault occurs on any section of the distributor, the faulty section can be isolated and the supply is maintained to the remaining sections. This improves the reliability of supply.
- The area of cross-section required for a doubly fed distributor is much less than a single fed distributor. Hence, it is economical.
Ring Distributor or Ring Mains Distributor
In this type, the distributor is in the form of a ring (closed circuit) and is supplied at one or more than one points. When the distributor is fed at one point only, it is just a doubly fed distributor fed at equal voltages at both ends being brought together to form a closed ring.
The figure shows the single line diagram of a DC 2-wire ring distributor fed at point A The various loads I1, I2 and I3, are tapped at point B, C and D respectively.
It has all the advantages which have been mentioned for the doubly fed distributor.
A ring main distributor may also be fed at more than one point. For the purpose of calculations, in that case, the distributor can be considered as a distributor consisting of a series of open distributors fed at both ends.
Thanks for reading about distributor in power distribution system.
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