L.O pump dose not build pressure

Hello everyone,

we have SKODA 135MW steam turbine and last time it was tripped due to low L.O header pressure. where we have 3 pumps , two of them should be in running and the trip occurred during making change over between pump #A starting and pump #C shutdown
After checking all data we found that motor consumed around 50% of rated current, so we think the motor is not loaded all electrical components checked and found normal
the problem that the current was still consuming 50% for a while then motor stopped due to logic command, after 2 or three trails it consumed 50% of current the increase to rated current and system become normal.
it seems that pump not pumping or insufficient pressure, Mechanical team checked the pump components and they found everything normal. hence it is submersible pump and the oil temp. is ~50c degree
from our side and due to header pressure drop we thing that the pump did not build pressure.
can any one help me regarding this problem, any required data trends, manuals … etc. can be submitted.

best regards.