The quality of the insulation of a winding is a vital part of generators and electrical machines that require special attention. To know the quality of winding insulation it is necessary to test the isolation resistance that is by Tan Delta method. In this research the test is done on winding stator generator unit 2 PT. PJB UBJ O & M PLTU 1 Pacitan East Java. Testing with Tan Delta method aims to find out the insulation resistance value of the stator generator winding. The results of this test which will be a reference whether the quality of stator winding insulation is still in good condition. Also the current value leak (Charge current) is small. A winding insulation is said to be good if the insulation resistance value (Tan Delta) is ≤4%. In accordance with the standard used by IEEE std 286-2000 and VDE 0530 Part 1.