Selection Guide for High Voltage Isolation Switches: Precise Matching from Parameters to Scenarios

2025-07-05 13:08:52

Selection Guide for High Voltage Isolation Switches: Precise Matching from Parameters to Scenarios

1、 Core parameter analysis: Data determines security

1. Rated voltage (Ur)

-Definition: The maximum system voltage that an isolation switch can withstand for a long time (such as 12kV, 40.5kV, 126kV).   

-Selection rule: Ur ≥ maximum operating voltage of the system × 1.1 (margin factor).   

-Case: The 35kV system requires the selection of Ur=40.5kV isolating switches (such as the minrong GW4-40.5 type).   

2. Rated current (Ir)

-Definition: The current value that can be sustainably carried at room temperature, which needs to be matched with the system load.   

-Selection rule: Ir ≥ maximum load current × 1.3 (overload factor).   

-Impact: Current overload will cause the contact temperature to exceed the standard (national standard limit: 65K).   

3. Thermal stability current (Ith)

-Definition: The ability to withstand thermal effects during a short circuit (usually 3s/4s).   

-Calculation formula: Ith ≥ system short-circuit current × √ (short-circuit time/standard time).   

-Case: For a short-circuit current of 20kA/3s, a switch with Ith ≥ 20kA (such as GN30-12 type) should be selected.   

4. Dynamic stability current (Ipk)

-Definition: The ability to withstand the peak electric force impact of short-circuit current (instantaneous value).   

-Relationship: Ipk ≈ 2.5 × Ith (GB/T 1985 mandatory correlation).   

-Consequences of failure: deformation of the conductive rod and fracture of the insulator.   

2、 Environmental adaptability: scene definition and selection

?  Outdoor environment (sandstorm/salt spray/ice and snow)

>Case: State Grid Qinghai Chaidamu Converter Station uses GW7-252 type with a climbing distance of 54mm/kV to resist sandstorms.   

?  Indoor environment (high voltage switchgear/distribution room)

-Selection focus: Compact size, maintenance free (such as minrong GN30-12 Rotary isolation switch).   

-Safety distance:

-12kV Power distribution cabinet: phase to phase ≥ 125mm (GB 3906)

-40.5kV PLC control cabinet: phase to phase ≥ 300mm

-Required option: Mechanical interlocking (to prevent operation under load).   

?  Special Scene

3、 Structural selection: Function matching requirements

1. According to the fracture form

-Horizontal rotary (GW4 Switch Disconnector): Large footprint, suitable for outdoor substations.   

-Vertical fracture type (GW7): Strong ice breaking ability, preferred for high altitudes.   

-Double column telescopic (GW16): saves longitudinal space and is preferred for urban substations.   

2. Grounding switch configuration

-Maintenance grounding: Both sides of the main circuit need to be configured (such as the "double grounding" structure of GW4-100IVD).   

-Fast grounding: Suppress VFTO (very fast transient overvoltage), used for 550kV GIS (such as ZH10-550 type).   

3. Selection of operating mechanism

4、 Fatal selection error case

1. Insufficient thermal stability: The 35kV line of a steel plant used Ith=25kA switch (actual short circuit was 31.5kA), and the short circuit explosion damaged the entire busbar.   

2. Low climbing distance: The 40.5kV isolation switch of the coastal wind farm did not increase climbing (standard 25mm/kV), and salt spray caused flashover and power outage.   

3. Neglecting ice breaking: Inner Mongolia substation GW4-126 is not equipped with an ice breaking mechanism, and the knife switch is stuck and cannot be opened due to freezing rain.   

Conclusion: Four step precise selection

1. Parameter rigidity meets the standard: Ur, Ir, Ith, Ipk must be strictly calculated;   

2. Environmental adaptation upgrade: outdoor heavy climbing distance/ice breaking, indoor heavy size/interlocking;   

3. Function on-demand configuration: Maintenance grounding is required, and quick grounding is based on voltage level;   

4. Institutional matching operation and maintenance: For unmanned stations, choose electric and hydraulic for ultra-high pressure.