1. Parallel operation: Important power stations have two or more synchronous generator sets as the main power source. Two or more generators simultaneously supplying power to the grid is the process of parallel operation of generator sets, and the units are put into parallel operation. Also known as parallel operation, or parallel or full step operation.

2. Cold standby operation: refers to the situation where there are no safety measures on each side of the connected equipment, and there are obvious or identifiable disconnection points on each side of the connected equipment. The equipment itself has no abnormalities, and all circuit breakers and isolation switches are in the open position waiting for the closing command. Once closed, the equipment can operate normally.

3. No load operation: refers to the working state in which the primary winding of a transformer is connected to the power supply and the secondary winding is open circuit. At this point, the current in the primary winding is called the no-load current of the transformer. The no-load current generates a no-load magnetic field. Under the action of the main magnetic field, electromotive force is induced in the primary and secondary windings.

In summary, there are currently three operating modes for transformers: parallel operation, cold standby operation, and no-load operation.