In electrical diagrams, what do CT and PT stand for and what are their functions?

• A. CT = Current Transformer, PT = Potential Transformer; CT measures voltage for metering and protection.
• B. CT = Capacitor Transformer, PT = Potential Transformer; both measure voltage.
• C. CT = Current Transformer, PT = Potential Transformer; CT measures current; PT measures voltage for metering and protection.
• D. CT = Current Transformer, PT = Power Transformer; PT measures power.

Answer: (C)

In electrical diagrams, instrument transformers are used to make big electrical quantities safe to measure. A current transformer is placed in series with a circuit and provides a reduced current that mirrors the actual circuit current; this scaled current feeds meters and protective relays. A potential transformer, often called a voltage transformer, is connected across the line and delivers a reduced voltage that mirrors the line voltage; this scaled voltage also feeds meters and protection relays. The key idea is that both preserve the proportional relationship to the actual values, so devices can read and react without being exposed to high currents or high voltages.

So the correct understanding is that CT stands for Current Transformer and PT stands for Potential Transformer (voltage transformer), with CT measuring current and PT measuring voltage for metering and protection.