How To Choose A Power Transformer
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 are most concerned about. So how to choose an efficient and energy-saving power transformer?
1. Energy Efficiency Standards for Power Transformers
At present, there are two main national mandatory standards for power transformer energy efficiency indicators, namely GB 20052-2013 "Energy Efficiency Limits and Energy Efficiency Grades of Three-phase Distribution Transformers" and GB 24790-2009 "Power Transformer Energy Efficiency Limits and Energy Efficiency Grades" . These two standards have been implemented for a long time, and the performance parameters stipulated in the standards are no longer in line with the current technical requirements. In order to better promote the energy saving and consumption reduction of power transformers, the new mandatory standard GB 20052-2020 "Power Transformer Energy Efficiency Limits and Energy Efficiency Grades" was officially released on May 29, 2020, and will be released on June 1, 2021. officially implemented.
2. Naming method of power transformer
JB/T 3837-2016 "Transformer Product Model Compilation Method" stipulates the naming rules of power transformers, and enterprises can voluntarily name power transformers according to this standard. Generally, the model specification includes information such as the structure type, core material, voltage level, and rated capacity of the power transformer. Usually, the power transformer will also add the label "-NX1" (first-level energy efficiency) or "-NX2" (second-level energy efficiency) at the end of the model to clarify the energy efficiency level of the product.
For example: oil-immersed power transformer, specifications: high-voltage side voltage 10kV, rated capacity 2000kVA, core material is silicon steel sheet, core structure is three-dimensional wound core, energy efficiency level is 1. Use the following method to name the model specification:
S-M·RL-2000/10-NX1
3. Key indicators for purchasing power transformers
1. Select the transformer according to the use environment
Under normal medium conditions, oil-immersed transformers or dry-type transformers can be selected. In multi-storey or high-rise main buildings, non-combustible or non-combustible power transformers should be selected. Closed or sealed power transformers should be selected in places where dusty or corrosive gases seriously affect the safe operation of transformers. High and low voltage power distribution devices without flammable oil 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 casing to ensure safety.
2. Select the transformer according to the power load
Usually, it is selected according to the capacity of the power transformer recommended in GB/T 17468-2019 "Guidelines for the Selection of Power Transformers". Dry-type transformers should generally be selected according to GB/T 1094.12-2013 "Guidelines for the Load of Dry-type Power Transformers" and the calculated load. Determine its capacity.
3. Know the insulation class
Insulation grade refers to the heat resistance grade of insulating materials used in electrical equipment. Insulation materials can be divided into 7 grades 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.
4. No-load loss
No-load loss refers to the active power consumed by the winding line terminals when the rated voltage at rated frequency is applied to the terminals of one winding and the 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.
4. Main product categories and application places
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 comply with the combustion level requirements specified in GB/T 1094.11, and is usually used in indoor substations built jointly 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.
