These are stepped up to the transmission voltage level, and power is transmitted to transmission substations where the voltages are stepped down to the subtransmission level (typically, 69 to 138 kV).

这些都加大了对传输的电压水平，并且动力被传递给传输站，其中的电压呈阶梯状下降到变速级(通常为69到138千伏)。

youdao

To send power miles away without huge line losses demanded that electricity be stepped up to a high voltage, then stepped down again at the receiving end.

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