padmounted transformer
Padmounted Transformer in Construction Work The pad mounted transformer is widely used in electrical engineering
10 kv Oil Filled Transformer is a key equipment for power distribution, and its failure will have a serious impact on the safe and stable operation of the power grid. This paper takes a 10 kv Oil immersed transformer fault as an example, through insulation resistance, winding DC resistance, transformer oil withstand voltage and oil dielectric loss and other test tests, and combined with lifting core disassembly to analyze the cause of the fault, to provide reference for strengthening the analysis and treatment of 10 kv Oil Filled Transformer fault.
Through insulation resistance, winding DC resistance, oil breakdown and other tests, and combined with lifting core inspection, a typical fault of 10 kv Oil filled transformer caused by insulation failure of insulation pad was analyzed, and preventive measures were proposed for the cause of the fault.
At 10:58 on June 29, 2020, the 10 kv Oil filled transformer was put into operation, and when closing the drop fuse operation, everything was normal when closing the A-phase drop fuse, but when closing the C-phase drop fuse, the transformer made a strange sound, accompanied by the pressure release valve spraying oil. Immediately pull open the drop fuse, found that the A-phase drop fuse fuse burned out, judged that this equipment may be damaged, can not be put into operation.
Fault 10 kv Oil filled transformer model S13-M-50/10, capacity of 50 kVA, coupling group Dyn11, voltage combination and tap range of 10 ± 2 × 2.5% / 0.4kV, no-load loss of 96.4W, no-load current of The rated current is 0.41%, the load loss is 893.8W, the short-circuit impedance is 4.15%, and it will be put into operation in December 2019.
Before lifting the core for inspection, the faulty 10 kv Oil filled transformer was tested and tested according to the maintenance test procedure.
A digital insulation resistance tester was used to measure the insulation resistance of the windings to ground and between the windings. The test data is shown in Table 1. The test result shows that the insulation resistance of high-voltage winding to ground is zero, the insulation of high-voltage winding to ground has been seriously damaged, and the insulation resistance of high-voltage winding to low-voltage and low-voltage winding to ground is in good condition.
Test position | Insulation resistance／ＧΩ |
High-voltage winding to ground／GΩ | 0 |
High-voltage winding to low-voltage | 1.2 |
Low-voltage winding to ground | 2.2 |
According to the requirements of the regulations, for the Oil filled transformer with the capacity below 1600 kVA, the deviation between phases should be no more than 4% and the deviation between lines should be no more than 2%. From the test data, it can be seen that the DC resistance data of the high-voltage winding and low-voltage winding of the Oil filled transformer meet the requirements, indicating that there is no large area of inter-turn short circuit inside the 10 kv Oil filled transformer.
The oil breakdown voltage of the 10 kv Oil filled transformer is not less than 35 kV according to the requirements of the regulation.
Number of tests | Breakdown voltage/kV／ｋＶ |
1 | ４４．８ |
2 | 54.2 |
3 | 43.6 |
4 | 51.2 |
5 | 37.2 |
6 | 37.6 |
Mean | 44.4 |
The 10 kv Oil filled transformer was tested for oil dielectric loss and the test data is shown in Table 5. According to the requirements of the regulation, the dielectric loss factor of the Oil filled transformer of 220 kV and below should be not more than 4.0%. From the test results, it can be seen that the oil filled transformer meets the requirements of the regulation.
In summary, the fault Oil filled transformer high-voltage winding to ground insulation is seriously damaged, winding DC resistance, oil sample breakdown voltage and dielectric loss test data are to meet the requirements of the regulation, inter-turn insulation should not have a large area short circuit, the preliminary judgment of the fault location in the high-voltage winding to ground insulation parts location.
The overall winding appearance is good, no obvious deformation, no discharge traces in the tank shell, but there are carbonization traces in the C-phase insulation pad and bottom iron yoke of the high-voltage winding, as shown in Figure 1.
Further disassembly and inspection revealed that the insulating pad had obvious traces of carbonized discharge, as shown in Figure 2.
The insulation resistance of the insulation pad alone was zero, and the test voltage could not be established normally. It is known that the cause of this failure was the decrease of the insulation strength of the bottom pad and the discharge of the high-voltage winding to the ground, which led to the carbonization of the insulation pad and the loss of insulation capacity, and finally led to the destruction of the 10 kv Oil filled transformer.
According to the test data and the results of the core disassembly inspection, the failure of the Oil filled transformer was caused by the decrease of the insulation strength of the bottom pad and the discharge of the high-voltage winding to the yoke, resulting in the destruction of the Oil filled transformer. In order to avoid the occurrence of similar failures, it is recommended that the following measures be taken in the manufacturing process of the transformer: strengthen the quality control supervision of the manufacturing process, the electrical insulation strength of the relevant insulation parts of the Oil filled transformer should be carried out in a complete test to prevent the failure of insulation parts leading to failures; the withstand voltage test can well investigate the insulation capacity of the 10 kv Oil filled It is suggested that the acceptance of Oil filled transformer should pay enough attention to this item to ensure the safe and stable operation of 10 kv Oil filled transformer.
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