According to the the GB/T17468-1998 power transformer selection guide and the State Power Corporation Guodian farmers [1999] No. 191 "rural power grid construction and transformation of the technical principles" document the principle of selection is as follows:

    1) selection of the technical specifications and parameters of the transformer should be consistent with national standards and industry standards, should in general be GB/T6451 (oil-immersed transformer) GB/T10228 (dry-type transformers) JB/T2426 (station transformer) to select . Selection should be a clear step-up transformer, step-down transformers, distribution transformers, auxiliary transformers, interconnecting transformer, single phase, three-phase transformers, load tap changer, excitation voltage, self-cooled transformers, or air-cooled transformer. Should be chosen by the provincial and ministerial level, or level of identification equipment, preferred products recommended by the State Economic and Trade Commission and the State Power Corporation.

    2) the rural power line power supply radius should meet the following requirements: 400V line ≤0. 5km; 10kV line is ≤15km; 35kV line ≤40km; 110kV line ≤150km.

    The capacity of rural power main transformer and distribution transformer capacity should adopt the ratio of 1:2.5, distribution transformers and power capacity ratio should be 1:1.5 to 1.8.

    3) the construction of rural substation should adhere to the principle of "dense point, short radius" to "outdoor type, small, low cost, safe and reliable, technologically advanced", designed with unattended. Design standards may be considered the 10-year load requirements of the development generally in accordance with the two main transformers to consider.

4) new and modified the distribution network, according to small-capacity, point clouds, short radius of the original column construction and renovation should be used in low-loss distribution transformers, the key is the use of S9 and S9, and a small amount of non- alloy transformers. Distribution transformer capacity choice, according to the local economy and life consumption level, and consider the level of development identified in more than five years. 64,73 series of high-energy distribution transformers to replace them all out.

    Prefabricated box substation district to plan distribution to determine a reasonable range of power supply, power distribution transformer capacity is calculated according to the scope of supply of electricity load, the city may be large-capacity step program, generally household 4. 5-7. 5kW or household 60W / m² calculation.

    5) distribution transformer high side should be the national stereotypes of the new fuse and the metal oxide surge arresters. The wire cross-sectional area of ​​low pressure side of the outlet shall be not less than 35mm ² (aluminum], the total switch air circuit breaker, and install leakage protection.

    6) supply voltage tolerances can G812325-1990 (voltage tolerances) SD325-1989 "reactive guide", GB50052-1992 power supply specifications provided, namely:

    Voltage of 220V user allowable deviation value of the rated voltage of ± 5% -10%; 380V user ± 7%; the 10kV user ± 7%; 35kV users 10%.

    Power lines less than the current economic current density (state regulations: steel in less than 3,000 annual maximum load utilization hours for 3A/mm ², 3000-5000 2.25A/mm ²> 5000 ² 1.75A/mm; aluminum 1. 65A/mm ², 1. 15A/mm ², 0. 9A/mm ²). If the high voltage line over a voltage drop of 5%, the low voltage line more than 4 percent, according to the provisions of the overhead distribution lines, "Technical Specification should be used in load tap.

    Configuration OLTC regulator magnitude of up to ± 10% - ± 15%, even greater. And series more than the non-excitation voltage, high precision voltage regulator, the regulator operation also monitoring side. After the installation of line drop compensation equipment, inverse voltage regulator to reduce the voltage fluctuations.

    35-110/10kV, 5000-31500kVA price is higher than the excitation voltage transformer load tap changer is about 15% -20% more expensive, the 5000kVA following an increase of about 10%, this is due to them were equipped with a modular and composite OLTC and to increase the number of turns, wire, increasing the fuel tank and fuel due to the index. For 10kV Distribution Transformer, Yi regulating transformer excitation voltage of about 1-2 million more expensive.