The low-voltage side voltage of the transformer in operation should not differ by ± 5% from the rated voltage.
2. The unbalanced current (neutral line current) of the transformer shall not exceed 25% of the rated current on the low-voltage side.
3. Generally, the transformer screen does not operate at full load, as its economic operating load rate is 40%~70%. Therefore, the current in each phase must not exceed the rated current.
4. The upper oil temperature of the transformer shall not exceed 85 ℃.
5. The insulation strength of transformer oil must be qualified: for transformers above 35kV, the new oil is 40KV/2.5mm, and the operating oil is 35KV/2.5mm; For transformers with a voltage range of 6-10kV, the new oil is 30kV/2.5mm, while the operating oil is 25kV/2.5mm. Those who fail to meet the standards should be replaced or filtered in a timely manner.
6. Transformers must not have oil leakage or seepage, and the transformer body must be clean without oil scale or dust. The oil level in the oil gauge should be normal.
7. For transformers equipped with explosion-proof tubes, the glass at the end of the explosion-proof tube should be intact and free of cracks.
8. The moisture absorbent (silicone) inside the transformer respirator should be checked regularly and replaced promptly if found to be damp.
9. Transformers equipped with pressure type thermometers must have a connecting line (capillary tube, hollow inside) from the temperature sensing component (temperature sensor) to the meter head, without any flattening or breakage.
10. The transformer casing and neutral point shall be connected to the outdoor grounding electrode, and the grounding resistance shall not exceed 42 Ω.
11. The transformer protection device should meet the selective requirements, that is, when the low-voltage side busbar is short circuited, the low-voltage side short-circuit protection device should reliably act first, cut off the low-voltage side main power supply, and the high-voltage side short-circuit protection device should not act. But when a short circuit occurs in the low-voltage coil of the transformer and the section of the line from the low-voltage porcelain bottle to the low-voltage circuit breaker protection device, the high-voltage short-circuit protection device should quickly act to cut off the high-voltage power supply.
12. For small capacity transformers, high-voltage side short circuit protection devices generally choose high-voltage fuses, while low-voltage side short circuit protection devices may choose fuses or automatic air switches. The rated current of the high-voltage side fuse is calculated by multiplying the high-voltage rated current of the transformer by a certain multiple. For general 6-10kV transformers, 100kVA and below shall be calculated based on 2-3 times their rated current; For those with a rated current of over 100kVA, the calculation shall be based on 1.5 to 2 times the rated current. The rated current of the low-voltage side fuse is calculated based on the rated current of the low-voltage side of the transformer or slightly higher.
13. When the transformer is running, its sound should be normal and there should be no "squeaking" discharge sound or popping sound. If any abnormal sound is found, the cause must be checked in a timely manner and handled properly. If necessary, it should be replaced in a timely manner.
The height of the transformer room is related to the height of the transformer, the incoming method, and the ventilation method. According to ventilation requirements, the transformer floor can be divided into two types: raised and not raised. The former is a transformer installed on a raised floor, with a wind tunnel left below. Generally, there are three types of floor elevations: 0.8m, 1.0m, and 1.2m. The height of the transformer room is 4.8-5.7m; When the floor is not raised, the transformer is installed on a concrete ground, and the height of the transformer is generally 3.5-4.8m. Whether the floor needs to be raised is determined by calculation based on ventilation conditions.
The requirements for transformers in 10kV substations are as follows:
It is strictly prohibited to install transformer substations containing electrical equipment containing combustible oil in a type of high and low rise main building. It is not advisable to set up transformer substations with electrical equipment containing combustible oil in Class II high and low rise main buildings. If restricted by conditions, flame-retardant oil transformers can be used and installed on the first floor near the exterior wall or basement. They should not be located above or below crowded areas, adjacent to or on both sides of exits. Corresponding fire prevention and oil drainage measures should also be taken.
Except for pole mounted transformer substations in residential communities, outdoor or semi outdoor substations are used in civil buildings in large and medium-sized cities. If it is necessary to set it up, it is advisable to choose a complete set of substations with protective shells. It is advisable to install two or more transformers for distribution transformers. When there is a large amount of primary load, or when it is a secondary load but is set according to security needs (such as fire protection), and when there are significant seasonal load changes or concentrated loads, two or more power transformers are often used.