Reverse attack of vacuum isolation switch: a key breakthrough in the engineering application of 126kV products

2025-09-29 13:43:23

The 126kV vacuum isolation switch, which was piloted for the first time by a provincial power grid company, has delivered a stunning performance after three years of rigorous testing. It has an operating life of over 10000 times without maintenance, a current transfer capacity of 1600A for disconnecting busbars, and zero greenhouse gas emissions. This marks the official upgrade of vacuum isolation switches from "laboratory samples" to "main equipment for the power grid".

1、 Why do we need a vacuum isolation switch? The bottleneck of traditional technology

Under the trend of dual carbon targets and equipment miniaturization, the drawbacks of traditional isolation switches are becoming increasingly prominent

1. Environmental dilemma of SF6 gas: SF6 is a strong greenhouse gas explicitly restricted by the Kyoto Protocol, with a global warming potential (GWP) 23500 times that of CO ?. The risk of leakage and the cost of future carbon taxes have become the 'Damocles sword' of the power grid.

2. The complexity of compressed air systems: There are numerous auxiliary equipment such as air compressors, dryers, pipeline valves, etc., with multiple failure points, a large maintenance workload, and noise and energy consumption issues.

3. Limitations in breaking capacity: Traditional isolation switches do not have active arc extinguishing capabilities, which can easily generate difficult to extinguish arcs when breaking off no-load bus capacitor currents and small inductor currents, leading to contact erosion and even insulation faults.

The natural advantages of vacuum technology:

Absolute environmental protection: The interior of the vacuum arc extinguishing chamber is high vacuum (≤ 10 ?? Pa), without any greenhouse gases.

Extremely high electrical lifespan: The vacuum arc extinguishes instantly when the current crosses zero, and the contact burns extremely lightly.

Truly maintenance free: The vacuum arc extinguishing chamber is sealed and maintenance free for life, significantly reducing the total lifecycle cost.

2、 Three key breakthroughs in engineering applications

The successful application of vacuum technology to 126kV high-voltage isolating switches is not a simple technical replacement, but crosses three huge engineering gaps.

Breakthrough 1: High voltage insulation and long stroke sealing technology

This is the primary physical barrier for vacuum isolation switches to transition from 40.5kV to 126kV.

Challenge:

1. Vacuum fracture insulation: The fracture insulation level of a single vacuum arc extinguishing chamber needs to be increased from the 95kV power frequency withstand voltage of 40.5kV level to 230kV (to ground) and above of 126kV level.

2. Long travel dynamic sealing: In order to achieve visible isolation of the fracture surface, the moving contact needs to have a linear motion stroke of more than 1 meter. How to achieve such a long stroke absolute seal in a high vacuum environment is a world-class challenge.

Solution:

1. Composite insulation design: Adopting a composite insulation method of "vacuum fracture+dry air/nitrogen external insulation". The vacuum arc extinguishing chamber is responsible for arc extinguishing and core insulation, while the external dry air gap provides additional insulation strength and forms visible isolation fractures, meeting safety requirements.

2. Magnetic fluid sealing and corrugated tube series connection technology:

Precision bellows: Using multi-layer stainless steel bellows as the core expansion element, it has been verified through millions of fatigue tests to ensure long service life.

Magnetic fluid sealing: Introducing magnetic fluid sealing technology in key areas of dynamic sealing, using a magnetic field to fix nanoscale magnetic liquid in the axial gap, forming a "liquid O-ring", achieving zero leakage dynamic sealing.

Breakthrough 2: Mechanical Life and Reliability in Vacuum Environment

The vacuum arc extinguishing chamber is a precision component, but its mechanical life must match the M2 level (10000 times) operation requirements of the isolation switch.

Challenge:

1. Mechanical impact: The huge impact force generated by high-power spring operating mechanisms can easily cause microcracks in fragile ceramic metal sealing parts.

2. Precise positioning: The positioning accuracy under long-distance transmission directly affects the contact resistance and closing stability of the contacts.

Solution:

1. Flexible transmission and buffering design: Elastic buffering elements and flexible Connectors are added between the operating mechanism and the vacuum arc extinguishing chamber moving guide rod to effectively absorb and attenuate impact energy.

2. High precision guidance system: The guidance system adopts linear bearings and precision guide rails to ensure the straightness and positioning accuracy of the moving contact during long stroke motion (error<0.5mm).

3. Online monitoring: Integrated displacement sensors and contact pressure sensors, real-time monitoring of opening and closing positions and contact pressure, achieving status visualization and predictive maintenance.

Breakthrough Three: Active Fast Vacuum Breaking and Intelligent Control

This is the core of the vacuum isolation switch to achieve a "functional counterattack", enabling it to have the active breaking ability that traditional isolation switches do not have.

Challenge:

1. Disconnecting strategy: How to quickly and reliably disconnect capacitive (no-load bus) and inductive (transfer current) loads without generating reignition or overvoltage.

2. Intelligent linkage: How to achieve reliable electrical and logical interlocking with Grounding switches and Circuit breakers.

Solution:

1. Permanent magnet operation and phase control technology:

Permanent magnet mechanism (VMC): adopts a bistable permanent magnet operating mechanism to drive the vacuum arc extinguishing chamber. Its action speed is fast (full opening time<50ms), the structure is simple, and the reliability is high.

Phase selection control: When breaking capacitive current, the control system accurately issues a disconnection command before the natural zero crossing of the current, causing the contacts to separate precisely at the zero crossing of the current, achieving arc free disconnection and fundamentally suppressing overvoltage.

2. Deeply integrated intelligent control unit:

The controller not only receives remote instructions, but also has a built-in disconnection logic library that can automatically identify the load type (capacitive/inductive) and call the optimized disconnection strategy.

By double locking with hard contacts and fiber optic communication with circuit breakers and grounding switches, the absolute reliability of the "five prevention" logic is ensured.

3、 Engineering Value and Future Prospects

The successful engineering of 126kV vacuum isolation switch has brought significant value enhancement:

Future prospects:

The success of vacuum isolation switches has opened up the way for environmentally friendly switchgear with higher voltage levels (such as 252kV). With further cost reduction and improved standards, it is expected to become the mainstream technology route for medium and high voltage power grid isolation switches in the next decade, completely ending the history of SF6 gas in the field of high voltage isolation switches.

Conclusion: The reversal of 126kV vacuum isolation switch is a systematic innovation driven by materials science, precision machinery, power electronics, and intelligent control. It is not only an upgrade of a single product, but also an important milestone in the evolution of power grid equipment towards environmental protection, intelligence, and maintenance free.