What are the categories of low-voltage switchgear? What is its structure?

Low-voltage switchgear: A combination of one or more low-voltage switchgear and related control, measurement, signal, protection, regulation and other equipment, with the manufacturer being responsible for completing all internal electrical and mechanical connections, and assembled together with structural components.

Classification of Low-Voltage Switchgear

Low-voltage switchgear can be classified in various ways, the most common being based on structural form and intended function.

 

1. Classification by Structural Form (the most mainstream classification)
This classification, derived from the international standard IEC 61439, primarily distinguishes between types based on the design of the cabinet frame and compartments.

Fixed-Type Switchgear

Features: All electrical components (circuit breakers, disconnectors, instrument transformers, etc.) are fixed to the cabinet frame and cannot be moved or removed. Maintenance or replacement must be performed with the power off.

Advantages: Simple structure, easy manufacturing, low cost, high reliability, and a large internal cabinet space.

Disadvantages: Inconvenient inspection and maintenance, long power outages, and reduced power supply continuity.

Common models: GGD (the most commonly used fixed cabinet in China) and distribution boxes (such as the PZ30) can also be considered small fixed-type switchgear.

Withdrawable/Drawer-type Switchgear

Features: Key electrical components (especially circuit breakers) are housed in a withdrawable drawer. The drawer has multiple positions, including operating (connected), test (disconnected but adjustable), disconnected (completely disconnected), and withdrawn.

Advantages:

High power supply reliability: If a circuit fails, the drawer for that circuit can be directly removed and replaced, quickly restoring power without affecting other circuits.

Safe and convenient maintenance: Comprehensive isolation and locking functions ensure high maintenance personnel safety.

Compact layout and small footprint.

Disadvantages: Complex structure, demanding manufacturing processes, high cost, and high requirements for mechanical precision and interchangeability of the drawers.

Common models: MNS (introducing ABB technology), GCS (domestically developed), GCK, and Blokset (Schneider). This is the mainstream product in the mid-to-high-end market.

 

2.Classification by Function
♦Power Distribution Cabinet: Primarily used for power distribution, it divides a single power source into multiple outputs to supply various power-consuming areas or equipment. This is the most common type, found in a building's main distribution room and floor distribution boxes.

♦Motor Control Center (MCC): Specialized for controlling and protecting motors. These cabinets typically contain contactors, thermal relays, soft starters, or inverters.

♦Capacitor Compensation Cabinet: Used for reactive power compensation, improving power factor, and reducing power loss. These cabinets primarily contain power capacitors, switching switches (contactors or thyristors), and reactors.

♦Incoming/Outgoing Cabinet: In a power distribution system, the cabinet that connects to the transformer or upstream power source is called an incoming cabinet; the cabinet that distributes power to downstream circuits is called an outgoing cabinet.

♦Tie Cabinet: In a dual-way or multi-way power supply system, it is used to connect two busbars to achieve switching between power sources.

 

3.Other Classification Methods

By installation location: indoor, outdoor.

By enclosure protection rating: IP30 (protection against solid objects larger than 2.5 mm), IP54 (dustproof and splashproof), etc.

 

Low-voltage switchgear structure

Regardless of the classification, the basic structure is similar, primarily designed to ensure safety, reliability, and ease of operation and maintenance. Taking the most common withdrawable switchgear as an example, we'll explain its typical structure, which typically consists of the following components:

 

1.Enclosure

This is the frame and outer shell of the switchgear. It is typically constructed by bending and assembling high-quality cold-rolled steel sheets. The surface is spray-coated or galvanized for corrosion resistance, aesthetics, and mechanical strength.

The enclosure's protection rating (e.g., IP40) is primarily determined by the enclosure's structure.

 

2.Horizontal and Vertical Busbars

Horizontal busbars: Installed at the top of the cabinet, they are the main power lines running through all cabinets, responsible for distributing power. They are typically made of high-conductivity copper or aluminum busbars.

Vertical busbars, also known as branch busbars, extend from the horizontal busbars and are installed at the rear of each functional unit (drawer). They distribute power to each drawer unit.

Busbars are typically covered with heat-shrinkable insulation tubing or secured with insulating brackets to ensure safe insulation distances between phases and to ground.

 

3.Functional Unit (Compartment/Drawer)

This is the core area that implements specific control and protection functions. A single panel can contain multiple functional units.

Functional units are typically divided into several independent compartments by metal partitions. This design is called a Form, such as Form 2, 3b, 4, etc. The more compartments, the higher the safety level and isolation.

Circuit Breaker Compartment: The space where the circuit breaker is installed.

Busbar Compartment: The space where the horizontal and vertical busbars are housed.

Cable Compartment: Located at the bottom of the panel, it is used for connecting and disconnecting power cables.

Secondary Equipment/Instrument Compartment: Typically located at the upper front of the panel, it houses secondary control components such as relay protection devices, instruments, indicator lights, push buttons, and transfer switches.

 

4.Circuit Breaker

The heart of the switchgear, it's responsible for connecting and disconnecting circuits and protecting against faults like overloads and short circuits.

In a drawer-type switchgear, the circuit breaker is mounted on the drawer and can be moved with it.

 

5.Secondary terminal blocks (Terminal Blocks)

Typically installed on the sides or bottom of a cabinet, they connect internal secondary devices (such as relays and instruments) with external control signals and measurement circuits, serving as a bridge between internal and external control circuits.

 

6.The grounding system (Earthing System)

Includes the grounding busbar (PE busbar) and grounding conductors, ensuring reliable grounding of the cabinet, door panels, and electrical component housings, preventing electric shock accidents and playing a crucial role in safety.

 

7.Mechanical interlock

A crucial safety device used to prevent improper operation. For example:

A circuit breaker can only be closed in the "test" or "disconnected" position (preventing power from being supplied under load).

A drawer cannot be withdrawn when in the "operating" position.

A circuit breaker cannot be operated when the cabinet door is open.

 

Summary

Features	Fixed switchgear (e.g., GGD)	Withdrawable switchgear (e.g., MNS, GCS)
Core Features	Components are fixedly installed	Main components housed in removable drawers
Power Continuity	Low (maintenance requires power outage)	High (fast replacement of faulty units)
Safety	Medium (maintenance requires contact with live parts)	High (complete isolation and interlocking)
Structural Complexity	Simple	Complex
Cost	Relatively low	High
Application Scenarios	Applications requiring low power continuity, small distribution systems, and terminal distribution	Applications requiring high power supply reliability and safety, such as large factories, data centers, hospitals, and main distribution rooms in high-rise buildings

 

If you have specific low-voltage switchgear needs, such as:

Project Selection and Configuration: You need to select and configure the appropriate switchgear model (such as MNS, GCS, GGD, etc.) for your data center, factory, building, or other project.

Technical Consultation and Solutions: You would like to receive more detailed technical specifications, product catalogs, system diagrams, or primary/secondary solutions.

Quotation and Delivery: You would like to receive a quote tailored to your specific needs, along with information on production lead times and delivery details.

Please contact us through the following methods:

Email:pannie@hdswitchgear.com.

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