In electrical power systems, CT (Current Transformer) and PT (Potential Transformer) are essential instruments used for safe measurement and protection.
⚡ What is CT (Current Transformer)?
A CT reduces high current to a lower, safe value (usually 1A or 5A) so it can be measured by instruments. It is always connected in series with the line.
✅ Benefits of CT:
Ensures safe current measurement
Provides isolation from high current lines
Improves protection system accuracy
Commonly used with ammeters and protective relays
Where CT is used:
Power stations, substations, industrial panels, and energy metering systems.
Critical Safety Note: The secondary side of a CT must never be open-circuited while the primary is energized.
⚡ What is PT (Potential Transformer)?
A PT reduces high voltage to a lower, standard value (like 110V or 63.5V) for measurement and protection. It is always connected in parallel with the line.
✅ Benefits of PT:
Ensures safe voltage measurement
Provides isolation from high voltage lines
Helps in accurate monitoring and control
Used with voltmeters and relays
Where PT is used:
Transmission lines, substations, switchyards, and monitoring systems.
⚠️ Critical Safety Note: The secondary side of a PT must never be short-circuited.
| Feature | Current Transformer (CT) | Potential Transformer (PT) |
| Primary Connection | Connected in Series | Connected in Parallel |
| Function | Steps down current | Steps down voltage |
| Secondary Value | Typically 1A or 5A | Typically 110V or 100V |
| Working State | Near short-circuit | Near open-circuit |
| Danger Zone | Open circuit causes high voltage | Short circuit causes high current |
