Usually only the power transformers rating will be in MVA's and distribution transformers rating's will KVA's and power transformers are only used in sub-stations. and standrand ratings of power transformer are 13.5MVA, 33MVA..etc
why there is 1 phase and 3 phase but not 2 phase and 4 phase?
Answer
There is 2phase supply, but it is dedicated only to the railways not for commercial and domestic use. and about 4phase, it's not Indian standards, and more conductors are required and structure of transmission tower will be huge in case for 4phase.