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)
Parameters | Selection Requirements | Typical Models |
Protection level | IP54 or above (dustproof and splash proof) | GW16-126D (W) |
Creepage distance | ≥ 31mm/kV (Class III polluted area) | GW7-252 type (Polymeric insulator) |
Ice breaking power | ≥ 300N (in severe cold regions) | GW6-1100 (with ice breaking mechanism) |
>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
Scenario | Selection Plan | Technical Basis |
Photovoltaic/Wind Power Boosting Station | GW4-126 Type with Grounding Switch (Double Grounding Guarantee Maintenance) | NB/T 31045-2021 |
Chemical explosion-proof zone | Stainless steel shell+climbing umbrella skirt (corrosion-resistant) | GB 3836.1 explosion-proof certification |
High speed railway traction substation | High mechanical strength (withstand over 1000 cycles of opening and closing) | TB/T 3324-2023 |
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
Type | Operability | Applicable Scenarios |
Manual | 250N · m | Low voltage distribution room (≤ 40.5kV) |
Electric | Remote Control | Unmanned Boosting Station |
Hydraulic | >8000N | Ultra high voltage (≥ 550kV) |
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.
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