Which type of transformer is used to step voltage down to a safe value, typically 120 volts?

Which type of transformer is used to step voltage down to a safe value, typically 120 volts?

• A. Potential
• B. Instrument
• C. Current
• D. Distribution

Answer: (A)

Instrument transformers are used to read high-voltage systems safely. A potential transformer specifically scales the line voltage down to a safe, standardized secondary level for meters and protection relays. The secondary voltage is chosen to be within the input range of measurement equipment—typically around 120 V—so technicians can monitor voltage without exposing instruments to the full HV on the line. Current transformers do the analogous job for current, stepping down the current to a safe level for meters and relays, but they don’t decrease voltage. Distribution transformers, on the other hand, reduce high distribution voltages to service voltages (like 120/240 V) for customers, which is a different purpose from measurement and protection.

Instrument transformers are used to read high-voltage systems safely. A potential transformer specifically scales the line voltage down to a safe, standardized secondary level for meters and protection relays. The secondary voltage is chosen to be within the input range of measurement equipment—typically around 120 V—so technicians can monitor voltage without exposing instruments to the full HV on the line.

Current transformers do the analogous job for current, stepping down the current to a safe level for meters and relays, but they don’t decrease voltage. Distribution transformers, on the other hand, reduce high distribution voltages to service voltages (like 120/240 V) for customers, which is a different purpose from measurement and protection.