I'm going through our specs on pad mounted oil filled transformers and came across the term filter press connection.

Does anyone here know if the filter press is actually on the transformer oil compartment itself or is just a connection to connect an external pump and filter?

A filter press is an exernal rig used to porcess your oil if necessry. 

Typically a connection in the gas space for an oil processing unit, in addition to the connection at the bottom occupied by the drain plug.

Some people (me included) tend to rtreat pad-mount transformers below 1000kVA as commodity items and do not do a whole lot of testing on them, including oil processing.

Pad mounted transformers are covered under ANSI/IEEE C57.12 series standard numbers 25( single phase up to 167 kVA),26(3 phase up to 2.5 MVA) & 34 (3 phase up to 5 MVA compartmental type) For 3 phase  units 1 inch NPT upper plug for filling and 1 inch NPT drain plug are standard.When size is above 750 KVA, built in sampling device is provided with drain plug.

In other countries,say India, valves are preferred to plug .Above 10 MVA 2 inch flanged valves are standard and below 10 MVA 32 mm valves are standard. The upper and lower plug/valves are used for connecting to filter machine when oil is reconditioned to get adequate oil BDV and water content.

Kidney pumps (on-line filteration devices) are OK for OLTC diverter switch oils,but not very  effective ( as volume of water removed is so low compared to total water in paper)in drying out paper insulation  in main transformer esp in case of very large units.

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