The Role of the PT Cabinet in the Power Grid

The PT cabinet (potential transformer cabinet) undertakes core functions such as **voltage monitoring, 

signal transmission, equipment protection, and safe operation** in the power grid, and it is a crucial and 

indispensable device in the power system. The following are its specific functions:

### I. Voltage Transformation and Signal Provision

1. **Voltage Reduction and Standardization**

   - **Core Component**: Potential Transformer (PT)

   - **Function**: It reduces the high voltage of the power grid (such as 10kV, 35kV) proportionally to a 

standard secondary voltage of **100V or lower**, providing safe and available voltage signals for **relay 

protection devices, electric meters, and monitoring systems**.

   - **Multi-winding Design**:

     - **Measuring Winding**: Used by monitoring devices such as voltmeters and power meters;

     - **Metering Winding**: Provides accurate voltage signals for electric energy meters for electric energy

 metering;

     - **Auxiliary Winding**: Monitors the insulation status of the system (such as single-phase grounding faults)

 through **open delta connection**.

### II. System Protection Functions

2. **Overvoltage Protection**

   - **Component**: Lightning Arrester (Zinc Oxide Lightning Arrester MOA)

   - **Function**: Quickly discharges abnormal energy such as lightning strikes and switching overvoltages, 

protecting the busbar and the PT itself from high voltage impacts and preventing equipment insulation breakdown.

3. **Short-circuit and Overload Protection**

   - **Components**: High-voltage Fuse, Low-voltage Circuit Breaker

   - **Function**:

     - When a short-circuit/overload occurs in the PT or the primary circuit, the fuse blows or the circuit breaker 

trips to cut off the fault current and prevent the accident from expanding.

     - The high-voltage fuse (such as the RN2 type) has a strong interrupting capacity and can protect the PT

 from being damaged by large currents.

### III. Safety Isolation and Maintenance Guarantee

4. **Electrical Isolation and Clear Disconnection Point**

   - **Component**: Isolating Switch (or Draw-out Type Isolation Structure)

   - **Function**:

     - Disconnects the primary circuit during maintenance, providing a **visible physical disconnection point*

* to ensure the safety of personnel;

     - The draw-out type PT cabinet supports **live plugging and unplugging**, allowing the PT to be replaced

 without power outage, enhancing the flexibility of the system.

5. **Grounding Protection**

   - **Component**: Grounding Switch

   - **Function**: Reliably grounds the primary circuit during maintenance, releases residual charges, and 

prevents electric shock accidents caused by mis-energization.

### IV. Suppression of Special Operation Problems

6. **Ferromagnetic Resonance Suppression**

   - **Component**: Primary Resonance Suppressor

   - **Function**: In an ungrounded neutral system (such as a 10kV distribution network), it suppresses the *

*ferromagnetic resonance overvoltage** caused by the saturation of the PT core, avoiding equipment 

damage or misoperation caused by resonance.

### V. Status Monitoring and Operation Assistance

7. **Live Line Indication and Five-prevention Interlocking**

   - **Components**: Live Line Indicator + Electromagnetic Lock

   - **Function**:

     - Displays the live status of the busbar in real-time, reminding operators to operate safely;

     - Interlocks with the isolating switch and the grounding switch to achieve the **"Five-prevention" function*

* (preventing mis-opening and mis-closing, entering the live compartment by mistake, etc.).

### VI. Typical Application Scenarios

- **Substation**: Monitors the busbar voltage and provides voltage signals for line protection and main

 transformer protection;

- **Distribution Substation**: Cooperates with the switchgear to achieve metering, protection, and insulation

 monitoring of the distribution system;

- **Industrial Power Consumption**: Provides a voltage reference for the relay protection of large 

equipment (such as motors).

### Conclusion: The PT Cabinet is the "Sensory Organ" and "Protector" of the Power Grid

Through the above functions, the PT cabinet ensures the **safe, stable, and efficient operation** of the power 

system and serves as a bridge connecting the primary high-voltage system and the secondary control and

 protection system.