DGA monitor needs to pump oil in
both directions during initialization and maintenance. To make sure this is
possible, check that:
Intake and return valves are
both below oil level in the transformer. There should be no risk of
drawing gas into the oil lines even when the flow is reversed. It is
recommended to connect oil intake and return lines with two separate
valves.
There are no flow direction
control valves on the oil lines.
Intake and return valves below oil level
In cold environments, trace heating
elements and thermal insulation may need to be placed over the exposed sections of the oil pipes:
Mineral oil: Required heating power and insulation thickness depends on the pour
point of the transformer oil that is used. Temperature of the oil in the lines must exceed
the pour point with a reasonable margin in order to keep the oil flowing normally during
operation.
Ester liquid: Recommended heating
power for trace heating is at least 10 W/m and recommended thermal insulation thickness in
extremely cold conditions is 20 mm (0.787 in) (elastomeric foam). Depending on the
environmental conditions, trace heating with lower heating power and thinner thermal
insulation may also be sufficient. Temperature of the liquid in the lines should stay
above 0 °C (32 °F).