In this note, we are going to learn a topic called “What is PT in Electrical or Potential Transformer?“, as its Construction, Working Principles, Specifications, and Applications as well. Welcome to Poly Notes Hub, a leading destination for Engineering notes syllabus-wise.
Author Name: Arun Paul.
What is PT in Electrical?
In electrical engineering, PT is an abbreviation for “Potential Transformer.” A potential transformer is a sort of instrument transformer that converts high voltage to a lower, safer voltage appropriate for measuring and protecting electrical systems. It is often used in power systems alongside measuring equipment and protective relays to correctly detect voltage levels and supply voltage inputs to protective devices without exposing them to the system’s full voltage.
Construction of Potential Transformer
Below we listed some important parts of PT in Electrical System –
- High Voltage (HV) Terminal: This is the terminal to which the high voltage of the electrical system is attached. It is intended to safely handle high voltages while providing adequate insulation to prevent electrical arcing or leakage.
- Porcelain Insulator: The porcelain insulator protects and supports the HV terminal and other internal components of the PT. Porcelain is widely utilized because of its superior electrical insulating characteristics and capacity to tolerate high temperatures and mechanical stress.
- Tank: The tank encloses the PT’s internal components and protects them from environmental variables like moisture, dust, and physical damage. It is often composed of metal and is intended to be strong and durable.
- Secondary Terminal Box: This box houses the PT’s secondary terminals, which provide stepped-down voltage for external connections to measuring equipment or protective relays. It is often situated on the side or top of the PT tank and is outfitted with terminals or connectors for convenient access.
Working Principle of PT
The Potential Transformer (PT) works on the same principle of electromagnetic induction that a standard transformer does. It reduces high voltages in power systems to lower, safer values for monitoring and safety. The PT is made up of two windings: primary and secondary. The primary winding connects to the high voltage supply, while the secondary winding is connected to measuring equipment or protective relays. The voltage transformation is determined by the turn ratio of the windings.
The application of voltage to the main winding creates a magnetic field in the transformer’s core, triggering voltage induction in the secondary winding. One important aspect of PTs is their capacity to offer electrical isolation between the primary and secondary circuits, which ensures the safety of linked instruments and relays. PTs also provide precise and accurate voltage measurements.
The load impedance connected to the PT’s secondary winding has an impact on measurement accuracy, hence low secondary impedance designs are recommended to reduce voltage drop while maintaining accuracy. Overall, potential transformers serve an important role in power systems by allowing for reliable voltage measurements, which are required for monitoring and protecting electrical equipment and networks.
Specifications of Potential Transformers (PTs)
Below we listed some specifications of Current Transformers or CTs –
- Voltage Ratio: This indicates the ratio of the primary voltage to the secondary voltage, indicating how much the voltage is reduced by the PT.
- Accuracy: PTs are classed according to their accuracy in voltage transformation. Common accuracy classes are 0.1, 0.2, 0.5, and 1.0, which indicate the percentage error allowed in voltage measurement.
- Primary Voltage Rating: This represents the highest voltage that the PT can handle on the primary side without exceeding its insulating capacity.
- Secondary Voltage Rating: Indicates the voltage output on the PT’s secondary side, which is usually standardized to a lower level for protection and measurement.
- Frequency: Defines the frequency range, commonly standardized to the system frequency (e.g., 50 Hz or 60 Hz), over which the PT is intended to function.
- Temperature Range: Specifies the temperature range at which the PT can operate consistently without losing performance or causing damage.
Applications of Potential Transformer
Below we listed some uses of PT in electrical systems –
- Voltage measurement
- Protective relaying and Instrumentation
- Control systems
- Testing and commissioning
- Transformer tap changer control
- Substation automation