The rated value of the transformer is the regulation made by the manufacturer for the normal use of the transformer. The transformer operates under the specified rated value to ensure long-term reliable work and good performance. Its ratings include the following:

1. Rated capacity: It is the guaranteed value of the output capacity of the transformer in the rated state. The unit is expressed in volt-ampere (VA), kilovolt-ampere (kVA) or megavolt-ampere (MVA). The design value of the rated capacity of the primary and secondary windings is equal.

2. Rated voltage: refers to the guaranteed value of the terminal voltage when the transformer is no-load, and the unit is expressed in volts (V) and kilovolts (kV). Unless otherwise specified, the rated voltage refers to the line voltage.

3. Rated current: refers to the line current calculated from the rated capacity and rated voltage, expressed in A (A).

4. No-load current: the percentage of the excitation current to the rated current when the transformer is running at no-load.

5. Short-circuit loss: the active power loss when the winding on one side is short-circuited and the winding on the other side is applied with voltage to make both windings reach the rated current. The unit is expressed in watts (W) or kilowatts (kW).

6. No-load loss: refers to the active power loss of the transformer during no-load operation, expressed in watts (W) or kilowatts (kW).

7. Short-circuit voltage: also known as impedance voltage, it refers to the percentage of the applied voltage and the rated voltage when the winding on one side is short-circuited and the winding on the other side reaches the rated current.

8. Connection group: Indicates the connection mode of the primary and secondary windings and the phase difference between the line voltages, expressed in clocks.