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.
a) The substation rating is defined as per the power handling capacity, location and purpose of substation.
b) Thumb rule for the economical voltage rating has been categorized for different power range to be received as below:
- 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.
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