single line diagram

 What is a single-line diagram:-      

      A simplified diagram of an electric power system is called a single-line is indicated by a single line and standard symbols how the transmission lines and associated apparatus of an electric system are together.

 The purpose of the single-line diagram is to supply in concise form the significant information about the system.

Symbolic representation of power system component

The electrical energy is produced at generating stations and transmitted by the transmission network,  to the consumers. Between the generating stations and the distribution stations, three different levels of voltage (1.transmission,2. sub-transmission, and3. distribution station level of voltage) are used.

The high power voltage is required for long-distance transmission and, the low voltage is required for utility purposes. The voltage level is going on decreasing from the high voltage transmission system to the low voltage distribution system. The electrical energy is generated by the three-phase synchronous generator as shown in the figure above. The generating voltage generally produces the 11kV and 33 KV.   

This voltage is very low for transmission over long distances. It is most required to increase the voltages 132KV, 220KV, 400 KV, with the help of step-up transformers. At this voltage, this electrical energy is transmitted to the heavy power substation where energy is supplied from several power substations.

The voltage at the substations is stepped down to 66KV and send to the sub-transmission system for onward transmission to the distribution sub-stations. These substations are located in the local region of the load centers.

The voltage(66KV) is further stepped down to 33KV and 11KV. The large-size industrial consumers are supplied to the primary distribution level of 33KV while the smaller-size industrial consumer is supplied at 11KV.

The voltage is again stepped down further by a distribution step-down transformer located in the local residential and commercial area, where this power is supplied to the consumers at the secondary distribution level of 400V three-phase and 230V single phase.

Advantage of Interconnection of Generating Stations

The power system consists of two or more generating stations that are connected by tie lines. Interconnection of generating stations has many important advantages.

  1. It possibles the mutual transfer of energy from the surplus zone to the deficit zone economically.
  2. by the less overall installed capacity to meet the peak demand.
  3. Lesser standby reserve generating capacity is required.
  4. interconnections provide the generation of energy at the most efficient and cheapest cost at every time.
  5. interconnection reduces the total capital cost, operating cost, and cost of energy generation.
  6. If there is a major breakdown of a generating system unit in an interconnected system, then there is no interruption of the power supply.

The interconnection provides the best uses of power resources and greater security of supply. It allows overall economic generation by optimum use of the high capacity economical generating plant. The interconnection between networks is done by HVAC (high voltage alternating current) links or through HVDC (High Voltage Direct Current) links.



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