Answer / siva

MVa Rating is Depends upon the Load when Load is
increased current will increase so we design for different
rates of Mva Depends upon the load

S= 1.732* V*I for Ex 50 MVA

50* 10^6 = 1.732* 220* 10 ^3*I To Calculate the I Value
is 131 in Hv side Lv side 218 A

Answer / j.karthik

The MVA rating is only based upon the generating MW capacity
of the plant.
For Example:
50MW is generated in the Powerplant.(i.e. Generator
capacity is:50MW,11kV,0.8P.F,3000RPM)
Now we like to connect this 50MW power to the E.B.grid
then we use one Step UP Transformer i.e. to step up the
voltage from 11kV to 220kV.
Now we can calculate the MVA rating of that step up
transformer as:
i) MVA = MW/costeta
MVA = 50/0.8 = 62.5MVA.

This is the answer.....

By,
Karthik(Engineer)

Answer / srikanth.kondru

very simple

we need to know the Load of the sub station ..
for example it is 1000 H.P
as we know that 1 H.P =1.5 amps
voltage is 220 KV
power ,p = 746KW = 1.732*0.8*220KV*I
I = 746 KW/1.732*0.8*220KV
= 2.4 amps
S=220*2.4*10^6 =532 MVA

Answer / milinda4p

The MVA rating of a power transformer depends on the load
connected to the transformers. this can be calculated (for a
grid transformer) by calculating the total MVA of the
primary substation transformers connected to it.Generally
this is calculated with a extra space for load connection.

Answer / k.prakashchandra

The present load and anticipated load growth in the coming
10 years.

Answer / raju

transformer is working only based on load. frequency was not changing, so it is called mva

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