Technical Article


Selection of Power Transformer

2023-02-28 | By:admin | click

A power transformer is a static device with two or more windings that converts the AC voltage and current value of one power system to a different voltage and current value in another power system at the same frequency to transmit electric energy. In the process of transmission and distribution of electric energy, the power transformer is the core of energy conversion and transmission. Its performance and quality are directly related to the reliability and operational benefits of power system operation. Power transformers are widely used in various fields such as industry, agriculture, transportation, and urban communities, and their losses account for about 40% of transmission and distribution power losses. For transformers that operate every day and consume a lot of power, improving power efficiency, reducing energy consumption, and saving power are the indicators that users care about. So how to choose a power transformer with high efficiency and energy saving?

According to the insulating medium, power transformers can be divided into oil-immersed transformers, dry-type transformers and gas-filled transformers. 

Oil-immersed transformers include mineral oil-impregnated transformers and high-flammable-point oil (synthetic oil and natural ester) impregnated transformers. Mineral oil-immersed transformers are widely used in various places, but the fire protection and safety requirements of the installation place should be fully considered. High ignition point oil has higher safety performance because of its flash point and ignition point higher than mineral oil. Therefore, high ignition point oil-immersed transformers are often used in places with relatively high safety requirements, or places with insufficient fire protection distance from buildings. 

Dry-type transformers usually have epoxy resin cast insulated dry-type transformers and impregnated insulated dry-type transformers. The transformer should meet the requirements of the combustion class specified in IEC60076-11, and is usually used in indoor substations built together with buildings or underground substations with good waterproof and moisture-proof performance.

Gas-filled transformers use non-combustible gases such as sulfur hexafluoride or mixed gas as insulation and cooling medium. The main body has the characteristics of non-explosive and non-flammable, and is usually used in places with higher fire protection and safety requirements.

The following factors should be considered in the selection of transformers:
1. Select the transformer according to the use environment: under normal medium conditions, you can choose an oil-immersed transformer or a dry-type transformer. In multi-storey or high-rise main buildings, non-combustible or flame-retardant power transformers should be selected; in places where dusty or corrosive gases seriously affect the safe operation of transformers, closed or sealed power transformers should be selected; without flammable oil High-voltage and low-voltage power distribution devices and non-oil-immersed distribution transformers can be installed in the same room. At this time, the distribution transformer should be equipped with an IP2X protective shell to ensure the safety of electricity use. the
2. Select the transformer according to the power load: usually select according to the capacity of the power transformer recommended in IEC60076-8 "Guidelines for the Application of Power Transformers". Dry-type transformers should generally be based on IEC905 "Guidelines for Dry-type Power Transformer Load" and calculate the load to determine its capacity. the
3. According to the insulation level: The insulation level refers to the heat resistance level of the insulating materials used in electrical equipment. The insulating materials can be divided into 7 levels according to their heat resistance, and their temperature rise limits are also different. The insulation class of commonly used power transformers is between A and H, the insulation class of oil-immersed transformers is generally A class, and the insulation class of dry-type transformers is generally F class or H class. the
4. No-load loss: No-load loss refers to the active power consumed by the winding line terminal when the rated voltage at the rated frequency is applied to the terminal of a winding and other windings are open. Load loss refers to the active power consumed at rated frequency and reference temperature when the rated current flows through the line terminals of one winding and the other winding is short-circuited.

Factors to consider when purchasing a transformer:
Confirm the standards that the product meets. When selecting a transformer, the standards that the transformer meets should be specified. Generally, oil-immersed power transformers should meet the requirements of IEC60076 and other standards, and dry-type power transformers should meet the requirements of IEC905 and other standards. If the product has other needs, it should be indicated in the inquiry or bidding documents and specified in the contract. In principle, it is a basic requirement for power transformer products to comply with national standards and the standards of the IEC International Electrotechnical Commission.

China Quality Certification Center identifies and evaluates the energy-saving indicators of power transformers through product certification methods. The qualified equipment is energy-saving products, which is one of the important references when purchasing.
Comprehensively consider the various indicators of the product. When selecting a transformer, it should be based on the overall reliability of the transformer, comprehensively consider the rationality, economy and environmental friendliness of technical parameters, and combine load development, safety requirements, operating environment, operating mode, operating conditions and loss evaluation methods, etc. , put forward reasonable technical and economic indicators and performance evaluation indicators. At the same time, the possible impact on the safe operation of the system, environmental protection, transportation, installation space and operation and maintenance must also be considered.