How to select the structural components of the incoming line cabinet?

   The selection of the structural components of the incoming line cabinet needs to be comprehensively

 considered according to the requirements of the power distribution system, the characteristics of the 

load, the installation environment, and safety specifications. The following are the selection methods

 and key points for the key components:

### I. Selection of Main Circuit Components

#### 1. Power Inlet Terminals

- **Basis for Selection**:

  - Current Rating: Select according to the current-carrying capacity of the incoming cable (for example,

 a 1000A cable is matched with a 1000A terminal).

  - Material: Copper terminals are preferred (with good electrical conductivity), and aluminum terminals 

need anti-corrosion treatment.

  - Interface Type: Bolt-type terminals are suitable for multi-core cables, and copper nose terminals need

 to match the cable specifications.

#### 2. Isolating Switch (QS)

- **Key Points for Selection**:

  - Rated Current: ≥ Rated current of the main circuit breaker (for example, if the main circuit breaker is 

1000A, select an isolating switch of 1250A).

  - Function: It needs to have a **visible break point**, support opening the circuit without load, and a

 manually operated type is often selected.

  - Number of Poles: Select 3 poles for a three-phase system and 2 poles for a single-phase system.

#### 3. Main Circuit Breaker (QF)

- **Type Selection**:

  - **Molded Case Circuit Breaker (MCCB)**: Used for small-power systems with a current below 630A.

  - **Air Circuit Breaker (ACB)**: For currents above 630A, an electric operating mechanism is required 

(such as a 2500A air circuit breaker).

- **Protection Function**: It needs to include overload inverse-time, short-circuit instantaneous, and 

zero-sequence leakage protection.

- **Breaking Capacity**: It needs to be ≥ the system short-circuit current (for example, if the short-circuit 

current is 50kA, select a circuit breaker with a breaking capacity of 65kA).

#### 4. Current Transformer (CT)

- **Accuracy Selection**:

  - For Measurement: Class 0.5 (matched with an ammeter).

  - For Protection: Class 5P10 (matched with a microcomputer protection device).

- **Ratio Matching**: The primary side current ≥ the maximum load current of the line (for example, 

if the line current is 800A, select a 1000/5A CT).

#### 5. Busbar

- **Material and Specification**:

  - Copper busbar (TMY) is preferred, which has a large current-carrying capacity and is corrosion-resistant; 

for aluminum busbar (LMY), pay attention to the temperature rise.

  - Calculation of Cross-sectional Area: For a current of 1000A, select a 100×10mm copper busbar (with a 

current-carrying capacity of 1350A).

- **Insulation Treatment**: The surface is sprayed with plastic, and there are phase color marks (yellow for

 L1, green for L2, and red for L3).

### II. Selection of Control and Protection Components

#### 1. Microcomputer Protection Device

- **Functional Requirements**:

  - It needs to support the monitoring of current, voltage, and zero-sequence current, and have RS485 

communication (Modbus protocol).

  - The setting values are adjustable: The overload delay and short-circuit instantaneous trip values need to

 cooperate with the lower-level protection.

#### 2. Surge Protector

- **Parameter Selection**:

  - Nominal Discharge Current: 10kA (for general scenarios) to 40kA (for high lightning areas).

  - Rated Voltage: ≥ System voltage (for example, select a 420V surge protector for a 380V system).

#### 3. Electric Energy Meter

- **Type**: Three-phase electronic energy meter with 485 communication (supporting remote meter

 reading).

- **Accuracy**: Class 0.5S (for billing) or Class 1 (for monitoring).

### III. Selection of Auxiliary Components

#### 1. Control Buttons and Indicator Lights

- **Design Requirements**:

  - Buttons: Red for opening the circuit and green for closing the circuit, with mechanical anti-misoperation

 (for example, the button needs to be pressed and rotated).

  - Indicator Lights: Power (green), closing (red), and fault (yellow), which need to be resistant to

 temperatures above 105°C.

#### 2. Terminal Block

- **Specification**: Rail-mounted terminal block, select 10A terminals for the current circuit and 5A 

terminals for the voltage circuit.

- **Identification**: Clearly mark the terminal numbers (such as 101, 102), and arrange the strong and

 weak current terminals in separate slots.

### IV. Selection of Structural Components

#### 1. Cabinet Frame

- **Material**: Cold-rolled steel plate (thickness 1.5-2.0mm), select stainless steel or IP54 plastic 

spraying for outdoor use.

- **Protection Level**: IP30 for indoor use and IP54 for outdoor use. A moisture-proof heater needs

 to be added in a humid environment.

- **Size**: Determine according to the number of components, and reserve 20% of the space for

 expansion.

#### 2. Openable Cabinet Door

- **Type**:

  - **Front Door**: With an observation window (acrylic material), install instruments and buttons.

  - **Back Door/Side Door**: Designed as a double-door for convenient wiring and maintenance, and it 

needs to be equipped with grounding bolts.

- **Lockset**: Select an anti-pry lock, and there needs to be a grounding jumper between the cabinet 

door and the cabinet body.

#### 3. Wire Ducts and Cable Ties

- **Wire Ducts**: Separate strong and weak current ducts (with a spacing of ≥100mm), select flame-retardant 

PVC as the material, and the thickness is ≥1.5mm.

- **Cable Ties**: Made of nylon, resistant to temperatures from -40°C to 105°C, and the bundling force is ≥50N.

### V. Precautions

1. **Component Matching**:

   - The rated current of the circuit breaker ≥ the current-carrying capacity of the incoming cable, and 

the CT ratio ≥ the maximum current of the line.

2. **Protection Coordination**:

   - The surge protector of the incoming line cabinet needs to cooperate with the superior lightning

 protection device, and the protection level decreases step by step.

3. **Grounding Design**:

   - The cabinet body, busbar, and metal wire ducts need to be connected to the grounding copper busbar

 through a 4mm² yellow-green grounding wire, and the grounding resistance ≤4Ω.

4. **Environmental Adaptation**:

   - Select a high-temperature-resistant busbar (such as a tinned copper busbar) in a high-temperature 

environment, and add a dust filter in a dusty environment.

### Typical Selection Example

- **Scenario**: 10kV/0.4kV power distribution system, incoming line current of 1000A, indoor installation.

- **Main Circuit**: Air Circuit Breaker (ACB 1000A) + Isolating Switch (1250A) + Copper Busbar (100×10mm).

- **Control and Protection**: Microcomputer Protection Device (including three-stage overcurrent protection)

 + Surge Protector (40kA).

- **Structure**: IP30 cabinet body, with a digital display meter on the front door, separate strong and weak

 current wire ducts, and the cross-sectional area of the grounding copper busbar ≥50mm².

Through the above methods, it is possible to ensure that the incoming line cabinet achieves a balance 

among safety, reliability, and economy, meeting the long-term stable operation requirements of the 

power distribution system.