Which banks step down transmission system voltage from 138 kV or 230 kV to 34.5 kV?

• A. Subtransmission banks
• B. Distribution banks
• C. Intertie banks
• D. Power banks

Answer: (A)

A subtransmission bank is designed to take high transmission voltages, like 138 kV or 230 kV, and step them down to the subtransmission level around 34.5 kV. This sets up the next stage of the network to deliver power through the subtransmission system and toward distribution. In a substation, you’ll see transformers arranged as banks for each voltage path, with the high-side tied to the transmission circuits and the low-side feeding the 34.5 kV subtransmission feeders.

Distribution banks, by contrast, take 34.5 kV and step further down to lower distribution voltages for customers. Intertie banks are intended for tying together different power systems and are generally configured for interchange at higher voltages rather than stepping down to distribution levels. The term power banks isn’t a standard designation for this voltage-stepping role.

So the bank that converts 138 or 230 kV down to 34.5 kV is the subtransmission bank.