Difference between Power Transformer and Distribution Transformer

Main Differences

Power transformers are applied in high - voltage transmission networks for step - up and step - down operations (with voltage levels such as 400 kV, 200 kV, 110 kV, 66 kV, 33 kV). Their rated capacity is generally above 200 MVA. In contrast, distribution transformers are utilized in low - voltage distribution networks as a means to connect end - users (with voltage levels such as 11 kV, 6.6 kV, 3.3 kV, 440 V, 230 V). Their rated capacity is usually less than 200 MVA.

Transformer Size / Insulation Level

Power transformers are used for power transmission in heavy - load scenarios with voltages higher than 33 kV, boasting an efficiency of 100%. Compared with distribution transformers, they are larger in size and are applied in power - generating stations and transmission substations, featuring a high insulation level.
Distribution transformers are used to distribute electrical energy at low voltages, with voltages below 33 kV for industrial applications and 440 V - 220 V for domestic use. They operate at a relatively low efficiency, ranging from 50 - 70%. They are small - sized, easy to install, have low magnetic losses, and do not always operate at full load.

Iron Losses and Copper Losses

Power transformers are used in the transmission network and are not directly connected to consumers, so load fluctuations are minimal. They operate at full load for 24 hours a day, so copper losses and iron losses occur throughout the day, and their specific weight (i.e., iron weight/copper weight) is very low. The average load is close to or at full load, and they are designed to achieve maximum efficiency under full - load conditions. Since they are independent of time, calculating efficiency based solely on power is sufficient.

Distribution transformers are used in the distribution network and are directly connected to consumers, so load fluctuations are significant. They are not always at full load. Iron losses occur 24 hours a day, and copper losses occur based on the load cycle. Their specific weight (i.e., iron weight/copper weight) is relatively high. The average load is approximately 75% of full load, and they are designed to achieve maximum efficiency at 75% of full load. Since they are time - dependent, all - day efficiency is defined to calculate the efficiency.

Power transformers serve as step - up devices in power transmission. This helps minimize I²r losses for a specific power flow. These transformers are engineered to maximize the utilization of the core. They operate close to the knee point of the B - H curve (slightly above the knee - point value), which significantly reduces the mass of the core.Naturally, for power transformers, iron losses and copper losses match at peak load, that is, at the point where maximum efficiency is achieved with equal losses.

Distribution transformers, however, cannot be designed in the same way. Thus, all - day efficiency becomes a key consideration during their design. This depends on the typical load cycle they are meant to supply. The core design must take into account both peak load and all - day efficiency, striking a balance between these two aspects.Power transformers generally operate at full load, so they are designed to minimize copper losses. In contrast, distribution transformers are always online and mostly operate at less - than - full - load conditions. Therefore, they are designed to minimize core losses.

Power transformers function as step - up devices in power transmission, enabling the minimization of I²r losses for a specific power flow. They are designed to optimize core utilization and operate closely to the knee point of the B - H curve (slightly above the knee - point value), thereby greatly reducing the core's mass.
At peak load, these transformers inherently exhibit a balance between iron losses and copper losses, which corresponds to the point of maximum efficiency where the two types of losses are equal.

Distribution transformers, in contrast, cannot be designed in the same manner. Therefore, all - day efficiency is a crucial factor in their design process. This is contingent upon the typical load cycle they are intended to serve. The core design must effectively address both peak load requirements and all - day efficiency, striking a delicate balance between these two aspects.
Power transformers typically operate at full load, so their design focuses on minimizing copper losses. On the other hand, distribution transformers are continuously in operation and mostly function under less - than - full - load conditions. As a result, their design emphasizes minimizing core losses.