Stator current appears before the generator is connected to the grid

There are three main situations in which a large stator current appears before the generator is connected to the grid:

The first is the over-excitation of the main transformer, high-voltage transformer, and excitation transformer caused by the overvoltage of the generator. The working magnetic flux density of the transformer continues to increase until saturation, the iron loss increases sharply, and the leakage magnetic enhancement will also cause eddy current loss on the surface of the core and other magnetic materials, and the stator current of the generator increases. The premise of this situation is that there is a fault in the voltage measurement circuit, which cannot reflect the actual voltage at the machine end. It keeps rising, and when it is serious to a certain extent, there will be a protection alarm or the demagnetization switch will trip. Because the second voltage boost was normal without any treatment, you are not in this situation.

The second is that the transformer is not demagnetized after the DC resistance test, so that the transformer core has a relatively serious residual magnetism. This residual magnetism will not disappear automatically. The residual magnetism and the generator excitation are superimposed, resulting in the core excitation saturation in the half-wave consistent with the magnetic field direction, and the other half-wave is not saturated, dynamically changing the inductance parameters of the equivalent circuit, causing the winding voltage to jump, the transformer overvoltage, overexcitation, and the principle is the same as the first case. This situation occurs after the transformer is overhauled, tested, modified, or the excitation system is modified. The on-site operator will demagnetize in time, no treatment is required, and the voltage will be boosted again to return to normal. Judging from the situation, you are more like this.

The third type is that there is indeed a fault in the primary circuit, such as a short circuit in the stator, high-voltage transformer, excitation transformer, or main transformer. This fault will not disappear automatically, but this is not the case with you.