What are CT and PT in the transformer

In the context of transformers, CT and PT are abbreviations for Current Transformer and Potential Transformer, respectively. They are both types of instrument transformers used for different purposes in electrical power systems.

Current Transformer (CT)

Purpose:

• CTs are used to measure high currents in power systems by reducing large currents to a smaller, more manageable value for metering and protection devices.

Function:

• A CT works by having a primary winding with a few turns carrying the high current and a secondary winding with many turns connected to the measuring instruments. The current in the secondary winding is a scaled-down version of the current in the primary winding.

Applications:

• Metering: Accurate measurement of current for billing and monitoring purposes.
• Protection: Providing current input to protective relays, which can disconnect power in the event of a fault.

Types:

• Bar-type CT: The primary conductor passes through the core.
• Wound-type CT: The primary winding consists of multiple turns wound on the core.

Potential Transformer (PT)

Purpose:

• PTs, also known as Voltage Transformers (VTs), are used to measure high voltages by reducing them to a lower, more manageable value for metering and protection devices.

Function:

• A PT works by having a primary winding connected across the high-voltage line and a secondary winding connected to the measuring instruments. The voltage in the secondary winding is a scaled-down version of the voltage in the primary winding.

Applications:

• Metering: Accurate measurement of voltage for billing and monitoring purposes.
• Protection: Providing voltage input to protective relays for over-voltage, under-voltage, and other protection schemes.

Types:

• Electromagnetic PT: Uses a magnetic core and windings.
• Capacitive PT: Uses a capacitive voltage divider to reduce the voltage before it is further reduced by an electromagnetic transformer.

Key Differences Between CT and PT

• Measurement Parameter:

• CT: Measures current.
• PT: Measures voltage.

• Connection:

• CT: Connected in series with the power line.
• PT: Connected in parallel with the power line.

• Output:

• CT: Provides a current proportional to the primary current.
• PT: Provides a voltage proportional to the primary voltage.

Usage in Power Systems

• Current Transformers (CTs) and Potential Transformers (PTs) are integral components in electrical power systems, ensuring accurate measurement and protection. They help in the safe and efficient operation of the system by providing essential data for monitoring and control.

Jul 31,2024