What parameters can an oil tester for transformers measure on-site?

On site testers commonly measure dielectric breakdown voltage, moisture content, and sometimes temperature compensated conductivity or resistivity. Portable instruments may also assess dissipation factor or power factor, and can provide quick screening for contamination. Some field kits support basic dissolved gas screening, but full DGA usually requires lab analysis. On site results are useful for go no go decisions, post maintenance verification, and rapid assessment after events like overload, suspected moisture ingress, or oil handling operations.