Basically 33 kV / 11 kV is used for distribution of power at the substation and 66 kV / 11 kV is also used for the distribution. But whether to use 66/11 kV or 33/11 kV depends on many factors. Following are some of the factors which are taken care for the selection of voltage of substation.
- Load up to 150 MVA – voltage rating of 132 kV.
- Load up to 80 MVA – voltage rating of 66 kV.
- Load up to 5 MVA – Voltage rating of 33 kV.
Thus, when a substation is of rating 66/11 kV, means substation has been designed to receive 80 MVA on 66 kV and it will distribute the received power on 11 kV.
Again, substation of rating 33/11kV means, the substation has been designed to receive 5 MVA of power at 33 kV and it will distribute the same on 11 kV.