Selection Guide for High and Low Voltage Switchgear Assemblies

Release time:

2025-06-20

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Abstract

High and Low Voltage Switchgear Selection Guide

I. Core Selection Principles

  1. Compliance First Comply with national standards (such as GB 7251 series, GB/T 11022) and industry standards (such as DL/T standards in the power industry). High-voltage cabinets require 3C certification, and some scenarios need to meet IEC international standards.
  2. Demand Matching Determine the technical parameters and structural form based on the power load, installation environment, and application scenario (industrial/civil/municipal).
  3. Safety and Reliability Focus on short-circuit breaking capacity, protection level, insulation level, and interlocking mechanism.

II. Classification and Application Scenarios of High and Low Voltage Cabinets

Type Voltage Level Typical Application Scenarios Common Cabinet Models
High-voltage switchgear 3kV-35kV Substations, high-voltage power distribution systems in large factories KYN28A-12、XGN15-12、GG-1A
Low-voltage switchgear 0.4kV (380V/220V) Residential buildings, commercial places, industrial equipment terminal power distribution GGD、GCK、GCS、MNS、XL-21

III. Key Elements for High-Voltage Cabinet Selection

(I) Technical Parameter Matching
  1. Rated Voltage and Frequency
    • Must be consistent with the grid voltage (e.g., 12kV rated voltage cabinet for 10kV system), frequency 50Hz (domestic standard).
  2. Rated Current
    • The main busbar current is calculated according to the transformer capacity (e.g., for a 1000kVA transformer, the rated current on the 10kV side is ≈57.7A, and the current in the cabinet ≥100A).
  3. Short-Circuit Breaking Capacity
    • Must meet the system short-circuit current requirements (e.g., if the 10kV system short-circuit current is 25kA, then the circuit breaker breaking capacity in the cabinet ≥25kA).
(II) Cabinet Structure and Protection
  1. Structural Form
    • Armored withdrawable type (such as KYN28A) High reliability, used for important loads, with five-proof interlocking (to prevent misoperation).
    • Fixed type (such as XGN) Low cost, suitable for small substations or scenarios with stable loads.
  2. Protection Level
    • Indoor cabinets ≥IP3X (protection against solid foreign object ingress), outdoor cabinets ≥IP54 (dust and waterproof).
(III) Core Component Configuration
  • Circuit Breaker Vacuum circuit breakers (ZN63 series) are preferred. Oil circuit breakers are prohibited for voltages above 10kV.
  • Isolation Switch Must be interlocked with the circuit breaker to ensure the "open before close" operating sequence.
  • Lightning Arrester Used for lightning protection; selection must match the system voltage (e.g., HY5WS-17/50 for a 10kV system).

IV. Key Elements for Low-Voltage Cabinet Selection

(I) Load Calculation and Parameter Design
  1. Calculating Rated Current
    • Determine the main busbar current according to the total load power (P=UIcosφ) (e.g., for a 1000kVA transformer, the 0.4kV side current is ≈1443A).
  2. Short-Circuit Withstanding Capacity
    • Low-voltage cabinets must meet the short-time withstand current (e.g., 30kA/1s), and the cabinet frame must be able to withstand the electromagnetic force impact.
(II) Cabinet Type Selection
Type Structural Features Applicable Scenarios Advantages
GGD Fixed type, steel plate welded structure Small and medium-sized factories, residential buildings Low cost, easy maintenance
GCK/GCS Drawer type, modular design Frequent operation or need for quick component replacement Strong breaking capacity, maintenance does not affect other circuits
MNS Imported technology, horizontal busbar rear installation Large commercial centers, data centers High space utilization rate, protection level IP54
(III) Component and Function Configuration
  • Main Circuit Breaker Use molded case circuit breakers (such as ABB Emax, Schneider MT), rated current ≥1.2 times the calculated current.
  • Branch Circuit Breaker Miniature circuit breakers (MCB) or molded case circuit breakers (MCCB), must have overload/short-circuit protection.
  • Reactive Power Compensation Configure capacitor banks (power factor needs to be improved to 0.9 or higher), intelligent compensation controllers are optional.

V. Environmental Adaptability Selection Points

  1. Temperature and Humidity
    • For high-temperature environments (≥40℃), a heat-dissipating enclosure and additional fans are required; for humid environments, a heater and moisture-proof coating are needed.
  2. Special Scenario Requirements
    • Explosion-proof environment ：Explosion-proof enclosures (Ex d certified) and components that meet explosion-proof standards must be selected.
    • Dusty environment ：Protection level ≥IP65, regular cleaning of dust nets.
  3. Altitude
    • At altitudes >1000m, the insulation distance must be adjusted according to GB/T 11022 (insulation strength decreases by 1% for every 100m increase in altitude).

VI. Scalability and Maintenance Design

  1. Reserved Circuits
    • Low-voltage cabinets require 10%-20% reserved circuits, while high-voltage cabinets require reserved bays (such as PT cabinets, connecting cabinets).
  2. Maintenance Space
    • ≥800mm maintenance access must be provided in front and behind the cabinet; removable high-voltage cabinets require space for circuit breaker removal.
  3. Intelligent Requirements
    • Optional intelligent instruments (monitoring voltage/current/power), communication modules (supporting Modbus protocol), and integration into the power monitoring system.

VII. Selection Process and Precautions

(1) Basic Process
  1. Determine the system voltage level, load capacity, and distribution.
  2. Calculate the short-circuit current and protection level requirements.
  3. Select cabinet models and component configurations that meet the standards.
  4. Compare manufacturer solutions (such as cabinet materials, interlocking design, and quotations).
  5. Sign a technical agreement (specifying parameters, certifications, and delivery time).
(2) Pitfalls to Avoid
  • Avoid "using lower-rated equipment instead of higher-rated equipment" (such as using a 16kA short-circuit breaking capacity circuit breaker instead of a 25kA one), which may cause safety accidents.
  • For high-voltage cabinets, confirm the "five-prevention interlocking" function (to prevent incorrect switching, live grounding, etc.).
  • For low-voltage drawer cabinets, test the drawer insertion and removal life (≥5000 times) and contact reliability.

VIII. Brand and Price-Performance Ratio Reference

  • Mainstream Brands of High-Voltage Cabinets ：Schneider (MVnex), ABB (UniGear ZS1), domestic brands (such as Taikai, Pinggao).
  • Mainstream Brands of Low-Voltage Cabinets ：Schneider (Blokset), ABB (MNS3.0), domestic brands (such as Zhengtai, Delixi).
  • Cost-Effective Strategy ：For large projects, prioritize imported brand core components + domestic cabinets; for small projects, you can choose complete sets of equipment from leading domestic brands.

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Intelligent Development Trends of Switchgear

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