Users and design institutes tend to determine the transformer capacity based on the development of the load plus some margins and add all the peak loads together to determine the load base. In fact, any load is in the midst of a change, and it is impossible to determine the load by adding peak loads together in 12 hours. Therefore, it is very important to determine the capacity value when changing the load. Too large or too small capacity may cause waste or affect the operating life.
IEC standards and national standards have "load guide", the transformer overload operation has a very detailed rules and calculation methods, which also means that the variable load husbander short-time overload operation is a normal mode of operation. Due to short-term overload may increase the hot spot temperature insulation insulation caused by the loss of life, it needs to be discussed is to allow the loss of life control should be in what Park, and under-load compensation of her husband when the role of compensation.
The actual situation is that most of the transformers are not allowed to overload, but to under-load insulation aging compensation as a margin to consider. This makes the choice of product capacity tends to imitate large, invisible increase investment and loss. Of course, there are other extreme cases, for example, users consider the economic benefits of bone Many electric furnace transformers and small distribution transformers use small capacity to make it long-term overload of the state of operation.
Neither of these two cases should be a scientific method, and the determination of the rated load should be based on the principle of not excessively reducing the life of the transformer. Overloaded parts should be calculated daily loss of life.
Most of the domestic transformer capacity selection is not carried out when the dynamic load analysis, so the capacity selection is generally large, many transformers run for many years, the insulation is very new, very few aging phenomenon, which fully demonstrates the importance of a reasonable choice of capacity.
Especially in rural areas with distribution transformers, it is not always possible to run in the economic operation zone, so the choice of the capacity of such transformers should be at least determine the power loss of the transformer.
