How to select high voltage switchgear？

Selecting high-voltage switchgear is a systematic process that requires comprehensive consideration of multiple key factors.

1. Core Selection Principles

When selecting high-voltage switchgear, three core principles must be adhered to:

Safety: The safety of operators and maintenance personnel, as well as the stable operation of the power system, must be ensured. This is the most important prerequisite.

Reliability: The switchgear must be able to consistently and stably perform its intended functions under specified operating conditions and within specified timeframes, with a low failure rate.

Applicability and Cost-Effectiveness: The switchgear must meet current and foreseeable future development needs, taking into account initial investment, operating and maintenance costs, and overall lifecycle costs.

 

2. Clarify Basic Usage Conditions (Selection Basis)

Before selecting a specific model, the following basic conditions must be determined:

Voltage level: Such as 3.6kV, 7.2kV, 12kV, 24kV, 40.5kV, etc. This is the most basic parameter and determines the insulation level of the switchgear.

Main busbar rated current: Calculated based on the total system capacity. Common values ​​include 630A, 1250A, 1600A, 2000A, 2500A, 3150A, etc.

Short-circuit breaking current: The maximum short-circuit current that the switchgear can safely interrupt. Examples include 16kA, 20kA, 25kA, 31.5kA, 40kA, etc. This needs to be determined based on system short-circuit calculations.

Installation environment:

Indoor or outdoor? Outdoor applications require a higher IP rating and corrosion resistance.

Ambient temperature, humidity, and altitude? High-altitude areas require revisions to insulation and current-carrying capacity.

Are there any special environments, such as those with explosive, corrosive, or dusty conditions?

 

3. Detailed Explanation of Key Selection Factors

Type Selection (Based on Main Insulation Medium and Structure)
This is the core of the selection process. Currently, the mainstream types are as follows:

♦Metal-clad Removable Switchgear (such as the KYN28A-12)

Structure: The circuit breaker is mounted on a removable trolley, which can be pulled out to the "test position" or completely removed for safe and convenient maintenance.

Advantages: High safety (complete "five-protection" interlocking), easy maintenance, high reliability, and the most widely used.

Disadvantages: Relatively large size and high price.

Applications: Almost all 10kV-35kV power distribution systems in industrial and mining enterprises, substations, and large buildings, serving as incoming and outgoing lines, busbars, and transformer protection.

 

♦Gas-Insulated Switchgear

Structure: High-voltage components such as vacuum circuit breakers, disconnectors, and busbars are sealed in a stainless steel gas tank filled with low-pressure SF6 or environmentally friendly gas.

Advantages: Extremely compact, unaffected by environmental influences (condensation, dirt, dust), long maintenance-free cycles, and extremely high reliability.

Disadvantages: Expensive, environmentally friendly requirements for SF6 gas (leakage and recovery), and long repair times after failures.

Applications: Extremely space-constrained locations (such as urban substations, high-rise buildings, and rail transit), harsh environments, and users with extremely high reliability requirements.

 

♦Solid-Insulated Switchgear

Structure: High-voltage live components are integrally cast or encapsulated with solid insulating materials such as epoxy resin.

Advantages: Completely SF6-free and environmentally friendly; size is between air-insulated and gas-insulated; and excellent resistance to harsh environments.

Disadvantages: Relatively new technology, high cost, and demanding production processes.

Applications: Locations with strict environmental requirements, limited space, and a reluctance to use SF6 gas.

 

♦Ring Main Unit (Load Switch Cabinet)

Structure: Typically uses SF6 or vacuum arc interrupter load switches, is compact, and is mostly fixed.

Note: Load switches cannot interrupt short-circuit currents, only rated load currents.

Applications: Primarily used for switching and sectionalizing distribution lines, such as 10kV ring main systems, small distribution rooms, and incoming and outgoing lines in box-type substations. If transformer protection is required, high-voltage fuses must be used in conjunction with these switches.

 

Summary:

For most industrial projects, the preferred choice is Metal-Clad Removable Switchgear (KYN series), featuring mature technology and a high cost-performance ratio.

For extremely limited space or harsh environments, Gas-Insulated Switchgear (C-GIS) is recommended.

For branch distribution networks, Ring Main Units are recommended.

 

Core Component Selection
Circuit Breaker Type:

Vacuum Circuit Breaker: Currently the absolute mainstream, with strong arc extinguishing capability, long life, maintenance-free, and environmentally friendly features. The preferred choice.

SF6 Circuit Breaker: Primarily used in voltage levels of 40.5 kV and above, it has been largely replaced by vacuum circuit breakers in the 12 kV range.

Protection and Control Devices:

Relay Protection Device (Microcomputer-Based Integrated Protection): The "brain" of modern switchgear. Select a model with appropriate protection functions (instantaneous trip, overcurrent, overload, differential, zero-sequence, etc.) based on the circuit function (incoming and outgoing lines, transformers, motors, etc.). Also consider whether the communication capabilities (such as RS485 and Ethernet) meet the automation system requirements.

Transformers:

Current Transformer: Pay attention to the accuracy class (e.g., 0.5 for measurement, 5P10/10P10 for protection) and the transformation ratio.

Voltage Transformer: Provides voltage signals for measurement and protection.

 

Verify Key Technical Parameters
Based on the basic requirements determined in step 1, strictly verify the following parameters in the manufacturer's catalog:

Rated voltage

Rated current

Rated short-circuit breaking current

Rated short-time withstand current (thermal stability current)

Rated peak withstand current (dynamic stability current)

Power frequency withstand voltage and lightning impulse withstand voltage

Protection level: Minimum IP3X (protection against tool intrusion), IP4X (protection against cable intrusion) recommended. Inter-cabinet protection must meet IP2X.

 

Final reminder:
Always adhere to the "Five Preventions" requirements! This is the minimum safety standard:

Prevent accidental opening or closing of circuit breakers.

Prevent opening or closing of disconnectors under load.

Prevent hooking or closing grounding wires (grounding switches) while energized.

Prevent closing a circuit breaker while the grounding wire (grounding switch) is on.

Prevent entering a live compartment while energized.

 

Contact Us 

 

As a high-voltage switchgear manufacturer, Shaanxi Huadian's product quality, reliability and technical standards are generally at the leading level in China, and are used in many national key projects.For most industrial and power projects, it is a domestic brand that is trustworthy and preferred.If you are intrested,please contact us:pannie@hdswitchgear.com.