DISTRIBUTION SYSTEM

DISTRIBUTION SYSTEM

By Engr. Aneel Kumar   October 26, 2014

That part of power system which distributes electric power for local use is known as distribution system. In general, the distribution system is the electrical system between the sub-station fed by the transmission system and the consumer’s meters. It generally consists of feeders, distributors and the service mains. Fig. 12.1 shows the single line diagram of a typical low tension distribution system.

(I) FEEDERS:

A feeder is a conductor which connects the sub-station (or localized generating station) to the area where power is to be distributed. Generally, no tapings are taken from the feeder so that current in it remains the same throughout. The main consideration in the design of a feeder is the current carrying capacity.

(II) DISTRIBUTOR:

A distributor is a conductor from which tapings are taken for supply to the consumers. In Fig. 12.1, AB, BC, CD and DA are the distributors. The current through a distributor is not constant because tapings are taken at various places along its length. While designing a distributor, voltage drop along its length is the main consideration since the statutory limit of voltage variations is ± 6% of rated value at the consumers’ terminals.

(III) SERVICE MAINS:

A service mains is generally a small cable which connects the distributor to the consumers’ terminals.

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TYPES OF CABLE FAULTS

TYPES OF CABLE FAULTS

By Engr. Aneel Kumar   October 26, 2014

Cables are generally laid directly in the ground or in ducts in the underground distribution system. For this reason, there are little chances of faults in underground cables. However, if a fault does occur, it is difficult to locate and repair the fault because conductors are not visible. Nevertheless, the following are the faults most likely to occur in underground cables:

(i) Open-circuit fault
(ii) Short-circuit fault
(iii) Earth fault.

(I) OPEN-CIRCUIT FAULT:

When there is a break in the conductor of a cable, it is called open circuit fault. The open-circuit fault can be checked by a megger. For this purpose, the three conductors of the 3-core cable at the far end are shorted and earthed. Then resistance between each conductor and earth is measured by a megger. The megger will indicate zero resistance in the circuit of the conductor that is not broken. However, if the conductor is broken, the megger will indicate infinite resistance in its circuit.

(II) SHORT-CIRCUIT FAULT:

When two conductors of a multi-core cable come in electrical contact with each other due to insulation failure, it is called a short-circuit fault. Again, we can seek the help of a megger to check this fault. For this purpose, the two terminals of the megger are connected to any two conductors. If the megger gives zero reading, it indicates short circuit fault between these conductors. The same step is repeated for other conductors taking two at a time.

(III) EARTH FAULT:

When the conductor of a cable comes in contact with earth, it is called earth fault or ground fault. To identify this fault, one terminal of the megger is connected to the conductor and the other terminal connected to earth. If the megger indicates zero reading, it means the conductor is earthed. The same procedure is repeated for other conductors of the cable.

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CONVENTIONAL SOURCES OF ELECTRICAL ENERGY

CONVENTIONAL SOURCES OF ELECTRICAL ENERGY

By Engr. Aneel Kumar   October 03, 2014

Thermal (coal, gas, nuclear) and hydro-generations are the main conventional methods of generation of Electrical Energy. These enjoy the advantages of reaching perfections in technologies for these processes. Further, single units rated at large power-outputs can be manufactured along with main components, auxiliaries and switch- gear due to vast experiences during the past century. These are efficient and economical.

These suffer from the disadvantages listed below:

1. The fuels are likely to be depleted in near future, forcing us to conserve them and find alternative resources.

2. Toxic, hazardous fumes and residues pollute the environment.

3. Overall conversion efficiency is poor.

4. Generally, these are located at remote places with respect to main load centers, increasing the transmission costs and reducing the system efficiency.

5. Maintenance costs are high.

Out of these, only two such types will be dealt here, which have a steam turbine working as the prime mover. While remaining two use Internal Combustion Engines (I.C. engines) or Gas turbine as the prime mover, and these will not be dealt with, in this introductory treatment.

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