What is a high-voltage PT cabinet?

  A high-voltage PT cabinet (voltage transformer cabinet) is a core device in the power system used for voltage measurement, 

protection, and control. Its main function is to convert the high voltage of the high-voltage line into a standard low voltage for use

 by monitoring, protection, and metering devices. The following is a detailed analysis of it:

I. Core Functions

1. **Voltage Transformation**

   Through the electromagnetic induction principle of the **voltage transformer (PT)**, the high voltage (such as 10kV, 35kV) is 

converted into a standard low voltage (such as 100V or 100/√3 V) according to a fixed turns ratio (such as 1000:1), which is convenient 

for the measurement of instruments and the use of equipment.

2. **Safety Isolation**

   Achieve electrical isolation between the high-voltage circuit and low-voltage equipment, protect the safety of personnel and equipment, 

and avoid the risk of high-voltage electric shock.

 II. Main Structure

- **Core Components**:

  - **Voltage Transformer (PT)**: Usually single-phase or three-phase, divided into measurement grades (0.2/0.5 grade) and protection 

grades (3P/6P grade).

  - **Fuse**: Protect the PT from damage caused by overload or short circuit.

  - **Lightning Arrester**: Suppress the overvoltage of the busbar (such as lightning strikes, switching overvoltages).

  - **Isolation Switch**: Used to disconnect the primary circuit during maintenance.

- **Cabinet Design**:

  Adopt the **withdrawable metal-clad structure**, support the handcart-type PT unit, which can be withdrawn for maintenance while 

energized; an observation window is set on the panel for real-time monitoring.

III. Main Functions

1. **Measurement and Monitoring**

   Provide voltage signals for voltmeters, power meters, energy meters, etc., and monitor the voltage values of the busbar or line.

2. **Relay Protection**

   Provide voltage signals for overvoltage/undervoltage protection, standby power automatic switching, insulation monitoring and 

other devices, and trigger protection actions (such as tripping).

3. **Operating Power Supply**

   Provide low-voltage power supplies (such as AC 100V or DC 110V) for control circuits, intelligent instruments, etc.

4. **Overvoltage Protection**

   The lightning arrester cooperates with the PT to limit the overvoltage of the busbar and protect the insulation of the equipment.

IV. Typical Application Scenarios

- **Substation**: Monitor the busbar voltage and cooperate with the relay protection device to ensure the stability of the power grid.

- **Power Plant**: Measure the voltage of generators and transformers to support automatic control.

- **Industrial and Mining Enterprises**: Ensure the voltage stability of the power distribution system and protect motors, transformers 

and other equipment.

- **Rail Transit**: Provide high-precision voltage monitoring for the traction power supply system.

V. Differences from the Metering Cabinet

- **PT Cabinet**: Focus on voltage transformation, protection, and the supply of public voltage signals, and the accuracy is mainly based 

on the protection grade.

- **Metering Cabinet**: Specifically used for electric energy metering, equipped with high-precision metering PT (0.2 grade), and 

independently managed by the power department.

 VI. Conclusion

The high-voltage PT cabinet is the "voltage bridge" of the power system. Through safe and accurate voltage transformation, it ensures

 the reliability of measurement, protection, and control, and is an essential key device in substations, switchgear rooms, and other places.