Analytical transformer lightning protection method

The transformer uses the principle of electromagnetic induction to change the AC voltage. The main components are the primary coil, the secondary coil and the core (core). In electrical equipment and wireless circuits, it is often used as lifting voltage, matching impedance, safety isolation and so on. Transformers can be divided into: distribution transformers, power transformers, fully sealed transformers, combined transformers, dry transformers, single-phase transformers, electric furnace transformers, rectifier transformers, reactors, anti-interference transformers, lightning protection transformers, box-type transformers. Electrical appliances, test transformers, corner transformers, high current transformers, and excitation transformers.

Transformers are divided into large transformers and small transformers according to different requirements. The step-up transformers (capacity <1000kVA) of small power stations that are connected to the grid are generally replaced by distribution transformers with connection group Y/Y0.

(1) It is forbidden to apply salt to grounded soil to reduce soil resistivity. Because salt has serious corrosiveness to the grounding body, after adding salt, the grounding resistance may meet the requirements, even small, but the time is long, and the grounding resistance is far greater than the specified value. When lightning strikes, the transformer is burned due to a counterattack.

(2) Test the grounding resistance. Before the thunderstorm season (2~3 months), test the grounding resistance of the transformer. If it does not meet the specified value, take timely measures and check the lightning protection facilities. Pay special attention to the inspection of the down conductor at the soil junction and all joints. To make it meet the requirements. In order to reduce side error and ensure personal safety, the grounding resistance should be measured with the grounding down conductor disconnected.
(3) Set the arrester correctly. The overvoltage of the forward and reverse converted waves may appear on the distribution transformer. In order to prevent the transformer from being damaged by the lightning strike 10kV line, the distribution transformers for Y/Y0 or Y/Y wiring shall be installed on the high and low voltage sides. Valve type arrester. Practice has proved that the closer the arrester is to the distribution transformer, the better the lightning protection effect. The high and low voltage side arresters can be installed on the side of the transformer top cover, and then the transformer casing, the arrester down conductor and the transformer neutral line are connected together, and the three are grounded together. The grounding down conductor should be a copper stranded wire (or steel strand) with a cross-sectional area of ​​25mm2, and the length should be the shortest, so that the lightning overvoltage applied to the distribution transformer approximates the residual voltage of the arrester, reducing the breakdown transformer. The danger of insulation.

(4) Regularly test the arrester. In order to protect the transformer from lightning strikes, for 100kVA and earth-based distribution transformers, the arrester should be tested once a year, and the grounding resistance should not exceed 4Ω; the arrester below 100kVA should be tested every two years, and the grounding resistance The value shall not be greater than 10 Ω; for those who are unqualified, it shall be processed in time.