Ur calculation is wrong. Here is the calculation...
1 unit means 1Kwh that means 1 kw power consumed in 1 hr.
WAP7 = 6000 HP
= (6000 X 746)/1000 Kw
...
more... = 4476 kw
So unit consumed in 1 hr = 4476 kw X 1 hr
= 4476 Kwh
That is, WAP 7 consumed 4476 unit/hr.
Operational cost ll b = 4476 X Rs. 3/-
= 13,428/-