Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_68270 ( "Unit" text, "Type" text, "Gross MW" text, "Construction start" text, "Operation start" text )

### Question ###
Gross MW of 220, and a Unit of kakrapar 1 involves what operation start?

### Accurate SQL ###

SELECT "Operation start" FROM table_68270 WHERE "Gross MW" = '220' AND "Unit" = 'kakrapar 1'