The main technical data of a transformer are generally indicated on its nameplate under specified usage environments and operating conditions. These primarily include: rated capacity, rated voltage and its taps, rated frequency, winding connection group, rated performance data (impedance voltage, no-load current, no-load loss, and load loss), and total weight.  

Rated Capacity (kVA)

The capacity that can be delivered under continuous operation at rated voltage and rated current.  

Rated Voltage (kV)

The operating voltage that the transformer can withstand during prolonged operation. To accommodate grid voltage fluctuations, the high-voltage side of the transformer is equipped with tap connections, allowing adjustment of the low-voltage output by varying the number of turns in the high-voltage winding.  

Rated Current (A)

The current permitted to flow continuously under rated capacity.  

No-Load Loss (kW)

The active power absorbed when the rated voltage at the rated frequency is applied to one winding's terminals while the other windings remain open-circuited. This is related to the performance and manufacturing process of the core silicon steel sheets, as well as the applied voltage.  

No-Load Current (%)

The current flowing through the primary winding when the transformer operates at rated voltage with the secondary side unloaded. It is usually expressed as a percentage of the rated current.  

Load Loss (kW)

The power consumed by the transformer when the secondary winding is short-circuited and the rated current is applied to the primary winding at the rated tap position.  

Impedance Voltage (%)

The voltage applied to the primary winding when the secondary winding is short-circuited and the short-circuit current reaches the rated value. This is generally expressed as a percentage of the rated voltage.  

Phase Number and Frequency

Three-phase is denoted by "S," and single-phase by "D." The standard frequency in China is 50Hz, while some countries (e.g., the U.S.) use 60Hz.  

Temperature Rise and Cooling

The difference between the temperature of the transformer winding (or upper oil layer) and the ambient temperature is referred to as the winding or oil surface temperature rise. For oil-immersed transformers, the winding temperature rise limit is 65K, and the oil surface temperature rise limit is 55K. Cooling methods include oil-immersed self-cooling, forced air cooling, water cooling, tube-type, sheet-type, etc.  

Insulation Level 

T here are standard insulation classes. For example, the insulation level of a transformer with a high-voltage rated voltage of 35kV and a low-voltage rated voltage of 10kV is denoted as LI200AC85/LI75AC35. Here, LI200 indicates a lightning impulse withstand voltage of 200kV and a power frequency withstand voltage of 85kV for the high-voltage side, while LI75 indicates a lightning impulse withstand voltage of 75kV and a power frequency withstand voltage of 35kV for the low-voltage side. Currently, the insulation level of oil-immersed transformers produced by Aokesi High-Tech Co., Ltd. is LI75AC35, meaning the high-voltage side has a lightning impulse withstand voltage of 75kV and a power frequency withstand voltage of 35kV. Since the low-voltage side is 400V, it can be disregarded.  

Connection Group Symbol

Based on the phase relationship between the primary and secondary windings, transformer windings can be connected in various combinations, known as winding connection groups. To distinguish between different connection groups, the clock notation method is often used. In this method, the high-voltage side line voltage phasor serves as the clock's minute hand (fixed at 12), while the low-voltage side line voltage phasor acts as the hour hand. The number pointed to by the hour hand determines the connection group symbol. For example, Dyn11 indicates a delta-connected primary winding, a star-connected secondary winding with a neutral point, and a group number of 11.