Isolation transformers are special transformers, which are used to isolate the AC network from the DC leakage currents caused by DC rails in close proximity of AC rails. These transformers are typically 25/25 kV or 16/16 kV single-phase transformers, and the power ratings run up to 10 MVA. Due to the DC immunity requirements, an air gapped core design is needed in the isolation transformers.

Therefore, strong test system is required in the factory. A lightning impulse test is always done as a routine test. Overvoltages are higher than normally, due to the air gapped core and the DC currents, which are present at switching when the train passes cut-off sections.

Posted in Uncategorized