Tab.6 Main parameters of HTS transformer

Extracts from the Article

The basic routine tests of the HTS transformer were performed in the Xinjiang Transformer Factory, TBEA, Changji, Xinjiang. All of the tests were managed by experts from the China National Transformer Quality Supervision Testing Center, Shenyang. The routine tests include DC resistances of windings, transformation ratio, symbol identification of vector group, insulation resistance of windings, insulation resistance of iron core, no-load current, no-load loss, external withstand voltage, inductive withstand voltage, short circuit impedance and load loss. Real tests include a temperature rise in the amorphous core. Special tests include null impedance in the three-phase transformer, and a load test with loading up to 1.1 times the rated level for an extended period. The DC resistances of windings are summarized in Table 5, while other results are listed in Table 6. After considering heat-leakage of the cryostat, current lead and various losses which are converted to loss value at room temperature, the efficiency of the HTS transformer is 98.5%, higher than the 98.1% in the conventional dry transformer with the same scale. Since HTS windings operate in liquid nitrogen temperature at 77 K all the time, the temperature rise tests mainly include temperature rise of the iron core and lead terminals. In the no-load test, the temperature of the LV lead terminal is almost constant, but that of the HV lead terminal approached room temperature and was not affected by the temperature of the iron core. However, the temperature of the iron core increased with time at first and stably reached 50oC. In the load test, load loss was constant; a stable temperature rise of 32oC of iron core was achieved after operating for 16 hours; the temperature of the HV current terminal was 21oC, slightly higher than the 18oC of the environment. However, temperature rise of the LV lead terminal rapidly increased in the first two hours, then increased slowly and finally reached equilibrium with temperature of 27.5oC. For the lightning impulse test, an HV winding mode exactly the same as that of the 630 kVA HTS transformer was fabricated and tested by Shenyang Transformer Group, Tebian Electric Apparatus Stock Co., Ltd (TBEA). The results show that the lightning impulse withstand voltage reached 155 kV time more than the Chinese National Standards of 75 kV with the related scale. For the sudden short circuit test, a 45 kVA single-phase HTS transformer based on the same technology of 630 kVA HTS windings was developed and tested at the China National Transformer Quality Supervision Testing Center, Shenyang [ 16]. All of the results lay the foundation and accumulate valuable knowledge on the target 630 kVA HTS transformer, which also ensure the safety and reliability of the transformer operation. Consequently, the developed 630 kVA HTS transformer meets the requirements of test operations in a live grid.

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