Under specified operating conditions and operating conditions, the transformer’s key technical data is generally indicated on the nameplate. These primarily include: rated capacity, rated voltage and its tapping, rated frequency, winding connection group, rated performance data (impedance voltage, no-load current, no-load loss, and load loss), and gross weight.
A. Rated capacity (kVA): Rated voltage. This refers to the capacity that the transformer can deliver during continuous operation at rated current.
B. Rated voltage (kV): The operating voltage that the transformer can withstand during extended operation. To accommodate grid voltage fluctuations, transformers have taps on the high-voltage side, which adjust the low-voltage output voltage by adjusting the number of turns on the high-voltage winding.
C. Rated current (A): The current that the transformer can sustain long-term operation at rated capacity.
D. No-load loss (kW): The active power drawn when the rated voltage at rated frequency is applied to the terminals of one winding, while the remaining windings are open-circuited. This value is related to the properties and manufacturing process of the core silicon steel laminations, as well as the applied voltage.
E. No-load current (%): The current flowing through the primary winding when the secondary side of the transformer is unloaded at rated voltage. Generally expressed as a percentage of the rated current.
F. Load loss (kW): The power consumed by the transformer when the secondary winding of the transformer is short-circuited and the rated current is passed through the primary winding at the rated tap position.
G. Impedance voltage (%): The voltage applied to the primary side when the short-circuit current of the secondary winding equals the rated value when the secondary winding of the transformer is short-circuited and the voltage of the primary winding is gradually increased. Generally expressed as a percentage of the rated voltage.
H. Number of phases and frequency: Three-phase is indicated by an S, and single-phase is indicated by a D. The national standard frequency f in China is 50 Hz. Some countries abroad (such as the United States) use 60 Hz.
I. Temperature rise and cooling: The difference between the temperature of the transformer winding or upper oil layer and the temperature of the surrounding environment is called the temperature rise of the winding or upper oil layer. The temperature rise limit for oil-immersed transformers is 65K for the winding and 55K for the oil surface. There are also various cooling methods: oil-immersed, self-cooled, forced air-cooled, water-cooled, tubular, and sheet-type.
J. Insulation Level: There are insulation grade standards. 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 expressed as LI200AC85/LI75AC35, where LI200 indicates the transformer’s high-voltage lightning impulse withstand voltage is 200kV and its power frequency withstand voltage is 85kV, while its low-voltage lightning impulse withstand voltage is 75kV and its power frequency withstand voltage is 35kV. Aux High-Tech’s current oil-immersed transformers have an insulation level of LI75AC35, indicating a high-voltage lightning impulse withstand voltage of 75kV and a power frequency withstand voltage of 35kV. Since the low voltage is 400V, this can be ignored.
K. Connection Group Number: Based on the phase relationship between the primary and secondary windings, the transformer windings are connected into various combinations, called winding connection groups. To distinguish different connection groups, a clock notation is often used. The high-voltage line voltage phase is used as the long hand of the clock, fixed at 12, and the low-voltage line voltage phase is used as the short hand of the clock. The number the short hand points to is used as the number of the connection group. For example, Dyn11 indicates that the primary winding is a (delta) connection and the secondary winding is a (star) connection with a center point. The group number is (11).
Post time: Aug-20-2025
