Tuesday, 6 June 2017

Dialy lessons-Introduction to Substation chapter-1

       Dialy lesson-Introduction to Substation chapter-1 


Substations   serve as a sources   of energy supply for the local areas of distribution  in which these are located.  They   have   several   functions.  Of  them  the  main  functions  are  to receive energy  transmitted  at high  voltage  from the generating stations and to reduce  the  voltage  to a value appropriate  for  local   distribution. There are some substations  which  act  as  switching  stations   where  different  connections  between  various  transmission  lines  are  made, others  are   converting  substations  which  either  convert  ac  into  dc  or   vice versa or  convert  frequency  from  higher  level  to  lower  level or  vice versa . Substations   are   of  various  types  on  the  basis  of  nature  of  duties , service rendered ,operating  voltage , importance and  the  design.  Here  we  are  going  to  discuss  of  220/132/33kv  substation  which  we  find  normally  for  distribution  purpose.

1.2.CLASSFICATION  OF  SUBSTATIONS                                                               

                       Substations are classified into numerous ways such on the basis of The following.

They are

  • Nature of duties

  • Service rendered

  • Operating voltage

  • Importance

  • Design


Classification of  substation  on  the  basis  of  nature  of  duties :

There are three   types of substations based on this classification.    They are

  1. Step-up or  primary  substation  which  are  usually  associated  with  generating  stations  where  the  low  voltage  is  stepped  up  to  primary  transmission  voltage .

  2. Primary grid  substations   which  are  usually  located  at  suitable  load    centers  along  the  primary  transmission  line  where  transmission  voltage is stepped down to different suitable secondary voltages.

  3. Step-down substations  are  located  at  the  load  centers , where  the  primary  distribution  voltage  is  stepped  down  to  secondary  distribution  voltage . These  are  the  substations  which  feed  the  consumers  through  distribution  networks  and  service  lines .

Classification of substation on the basis of  service  rendered:

The substations according to the service rendered are

  1. Transformer substations to transform  the   power  from  one  voltage  level  to  another  voltage  level  as  per  needs .

  2. Switching substations used  for  switching  operation  of  power  lines  without  transforming  the  voltage .

  3. Converting substations  used  for  either  converting  ac  to  dc  or  vice- versa  or  converting   frequency  from  higher  to  lower  or  vice-versa .


Classification  of  substation  on  the  basis  of  operating  voltage :

The substations according to the operating voltage is     categorized as

  1. High voltage substation involving voltages between 11kv and 66kv

  2. Extra high voltage substation involving voltages between 132kv

and 400V.

  1. 3. Ultra high voltage substation involving voltages above 400kv.


Classification of substation on the basis of importance:

The substation  on  the  basis  of  importance  is  classified  as  follows

  1. Grid substations are  the  substations  where  bulk  power  is  transmitted  from  one  point  to  another  point  in  the  grid .

  2. Substations which step-down  the  voltages  at  33/11kv  for  further  distribution  in  towns  and  any  failure  in  such  substations  results  in  the  failure  of  supply  for  the  whole  town .

Classification of substation on the basis of design:

The  substation  on  the  basis  of  design  is  classified  as  follows :


These are again further classified as pole  mounted  substation  which  are  used  for  distribution  of  power  in  localities . It   uses  the  transformers  of  capacity  up to  25 KVA ,125 KVA  and  above 125  KVA . The  maintenance  cost  of  such  substations  is  low  and  by  using  a  large  number of  such  substation  in  a  town , it  is  possible  to  lay  the  distributors , at  a  lower  cost .Foundation  mounted  substations  which  are  used  for  transformers of  capacity  above  250 KVA  and  are  usually  used  for  voltages  of  33,000  volts  and  above.


For the purpose of equipment design, the following data should be taken into consideration

Site elevation above mean sea level:  < 1000m

Ambient air temperature

Highest max (in shade) for about: 55°C 6 hours a   day

Lowest minimum: (-) 10°C

Max yearly average: (+) 30°C

Max daily average: (+) 40°C

Maximum relative humidity: 92% at 40 deg




The following factors are considered while making selection for substation.

  • Availability of suitable and sufficient land

The  land  proposed  for  a  substation  should  be  normally  level  and  open  from  all sides. It should not be water logged particularly in rainy season.

  • Communication facility

Suitable  communication  facility  is  desirable  at  a  proposed  substation  both  during  and  after its  construction .

  • Atmospheric pollution

Atmosphere around factories, which may produce metal corroding gases, air fumes, conductive dust etc. Therefore substations should not be located near factories or seacoast.

  • Availability of essential amenities to the staff

The  site  should  be  such  where  staff  can  be  provided  essential  amenities  like  school , hospital , drinking  water, housing  etc .

  • Drainage facility

The  site  selected  for  the  proposed  substations  should  have  proper  drainage  arrangement.

Type of substation                         Area required

400 KV substation                                       50 acres

220 KV substation                                       25 acres

132 KV substation                                       10 acres

Generally, substation gets the supply through feeders. There are six incoming   sources   for   220/132/33kv sub-station, in order to supply an uninterrupted power to the consumers

lesson will be continued.....


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