Sir,
Electrical transformer is a capital goods. Transformer oil used in the said transformer also qualifies as capital goods as definition of 'Capital goods' contained in rule 2 (a) (A) (iii) of Cenvat Credit Rules, 2004 since transformer oil is an accessory of the transformer on the ground that without transformer oil the transformer cannot function.
As per rule 5A (b) “input service” means any service, -
(i) used by a provider of 26[output service] for providing an output service; or
(ii) used by a manufacturer, whether directly or indirectly, in or in relation to the manufacture of final products and clearance of final products upto the place of removal,
As per sub-rule 5 (A) (b) of rule 3 of Cenvat Credit rules, 2004, if the capital goods are cleared as waste and scrap, the manufacturer shall pay an amount equal to the duty leviable on transaction value.
In view of the above you have ti discharge duty on the transaction value @ 12.5%.