C Rating and battery capacity.

The capacity of a battery is indicated in Ampere-hours (Ah).  For instance, 200Ah, 80 Ah, etc.  The rate at which the battery can be discharged is indicated by the C rating.  

Batteries are usually rated as C/10, c/8, etc.  a battery with a 200 Ah capacity and a C/10 rating indicates that the battery can supply 20 A for 10 hours. 

The capacity of a battery varies inversely with the discharge rate. Batteries usually have different discharge rates for a fixed capacity. 

Combined Instrument Transformers

Combined Instrument Transformers are special measuring transformers which combine the functions of a current and a voltage transformers.  They are generally used where space is a constraint.  Typical scenarios are when measuring transformers need to be added in a functioning substation.  

Combined instrument Transformers usually have multiple secondaries for both current and voltage measurement.   These specialized transformers have been used upto 300 kV.

What are Primary and Secondary Cells ?

Primary cells are cells in which the chemical reaction which produces the power is not reversible. That is, the cell cannot be charged.  A common example is the dry cell.  Primary cells are cheaper and find application in radios, flash lights, torches, etc.    

Secondary cells are those cells in which the chemical reaction can be reversed by passing an electric current in the reverse direction.  The active material of the battery is reformed and the battery is recharged.