Professional Technology for Seismic Performance Testing and Optimization Design of Circuit Breakers

2025-10-01 17:31:27

In a strong earthquake of magnitude 7, multiple old Circuit breakers in a 110kV substation failed to operate or accidentally operated due to the breakage of the supporting insulator roots, exacerbating the power grid paralysis. The new type of circuit breaker, which has undergone seismic strengthening design, remains intact and 

successfully cuts off multiple faulty lines. This painful lesson highlights the extreme importance of seismic design and testing for circuit breakers.

1、 The hazards and failure modes of circuit breakers caused by earthquakes

Earthquakes impact equipment with complex horizontal, vertical acceleration, and frequency components, causing two main effects on circuit breakers (especially tall porcelain supported circuit breakers):

1. Inertial force effect: The equipment mass generates a huge inertial force under acceleration, forming bending moments and shear forces, which act on the root (such as the connection between the porcelain bottle and the base) and the top (such as the arc extinguishing chamber).

2. Resonance effect: If the dominant frequency of an earthquake is close to the natural frequency of the circuit breaker itself, resonance will occur, causing the dynamic response (stress, displacement) to be rapidly amplified several times to tens of times.

The main failure modes include:

Structural damage: fracture of supporting porcelain bottles (the most common and fatal), deformation of operating mechanism housing, and cracking of brackets.

Functional failure: deformation and jamming of the transmission link, abnormal contact pressure leading to a surge in contact resistance, false signals from auxiliary switches, and even false tripping.

2、 Seismic Performance Testing: From Standards to Practice

The core purpose of seismic testing is to verify whether the circuit breaker can maintain structural integrity and function normally under simulated earthquake conditions.

2.1 Testing Standards

The International Electrotechnical Commission (IEC) standard IEC 61463 "Seismic Requirements for High Voltage Switchgear and Control Equipment" is an authoritative guide. Its core is the response spectrum method (RRS), which specifies the minimum acceleration amplitude that equipment must withstand at different frequency points. Domestic standards such as GB/T 13540 also provide detailed regulations.

2.2 Testing method: Vibration table test

This is the most direct and reliable verification method.

1. Installation: Rigidly fix the prototype circuit breaker on a large vibration table according to the actual installation conditions.

2. Input waveform: The vibration table generates simulated seismic waves (such as artificial waves or historical seismic waves) according to the response spectrum required by the standard.

3. Experimental process:

White noise scanning: First, input low-level white noise and test its dynamic characteristics such as natural frequency and damping ratio.

Seismic resistance test: Input seismic waves of specified magnitude in the X, Y, and Z directions in sequence. Usually multiple (e.g. 5) cycles are required.

4. Monitoring and judgment:

Structural integrity: After the test, check for cracks and damage in the porcelain bottles, brackets, etc.

Functional verification: Before, after, and during the experiment, it is necessary to measure the resistance of the main circuit and conduct mechanical operation tests (including no-load operation and opening and closing tests under rated current) to ensure that the operating characteristics are normal.

The rigor of the experiment: The assessment level usually corresponds to the Safety Shutdown Earthquake (SSE), which means that the equipment still needs to ensure safe shutdown after experiencing this earthquake.

3、 Optimization design: an engineering method to enhance seismic resistance

Based on testing and simulation analysis, the optimization design revolves around a core objective: to increase the natural frequency of the equipment, move it away from the dominant frequency range of earthquakes (usually 1-10 Hz), and enhance the strength of key components.

Its complete optimization design process is a closed-loop system from analysis to verification, as shown in the following figure:

```mermaid

flowchart TD

A [Seismic Load Analysis]

Determine input conditions] -->B [Dynamic modeling and simulation

(Finite Element Analysis FEM)

B -->C {Simulation result evaluation

Natural frequency and stress distribution

C - Low natural frequency

There is a risk of resonance ->D [optimization design measures]

C - Stress exceeds the allowable value

There is a risk of intensity ->D

C -- Meet requirements -->E [Manufacturing prototype]

D -->D1 [Increase natural frequency

(Shock absorption design)

D -->D2 [Enhance structural strength

(Seismic Design)

D1 & D2 --> B

E -->F [Vibration table test verification]

F - Test passed ->G [Design finalized]

F -- Test failed -->B

```

3.1 Increase natural frequency (shock absorption design)

This is the most effective method aimed at avoiding resonance.

Reduce equipment height: adopt a low center of gravity design. For example, the new type of floor standing tank circuit breaker has much better seismic performance than traditional porcelain column circuit breakers due to its low center of gravity and high natural frequency.

Increase structural stiffness:

Optimize bracket design: Adopt a triangular stable structure bracket to replace the thin four column bracket.

Add support: Install pull rod support or damping support in the middle or top of the equipment to effectively change the vibration mode and improve stiffness.

Using composite insulation materials: Replace traditional porcelain materials with high-strength composite materials (such as silicone rubber composite sleeves). Composite insulators have the characteristics of light weight, good elasticity, and high bending strength, and their seismic performance is significantly better than that of ceramic insulators.

3.2 Enhancing Structural Strength (Seismic Design)

When it is impossible to completely avoid the resonance zone, strength must be ensured.

Strengthening of key areas:

Ceramic bottle and metal flange adhesive joint: This is the weakest link. Adopting improved cement adhesive, adding clamping springs, and optimizing flange structure to improve stress distribution.

Connection between operating mechanism and bracket: Use high-strength bolts and increase the thickness of the connecting plate to prevent loosening and deformation.

Application of damping technology:

Install tuned mass dampers at the top or center of gravity of the equipment. When the equipment vibrates, the dampers generate reverse force, consume vibration energy, and significantly reduce dynamic response.

4、 Summary: Philosophy of Seismic Design for Modern Circuit Breakers

1. Simulation first: Finite element analysis is widely used in the design phase for dynamic simulation, predicting natural frequencies and stress concentration points, achieving "virtual testing", and reducing the risk of failure in the later stage.

2. Material innovation: Composite insulators are the future trend, and their excellent tensile and bending properties provide greater space for seismic design.

3. Structural optimization: Developing from tall porcelain columns to low center of gravity tank or GIS (gas insulated Metal enclosed switchgear). GIS enclosing all components in grounded metal shells is the optimal solution for seismic performance.

4. Testing and verification: Vibration table testing is an indispensable final verification step, which is the key to obtaining authoritative certification for products and entering the market of high-risk earthquake areas.

Conclusion: The seismic performance of circuit breakers is no longer an additional item for post remediation, but a core competitiveness that runs through the entire process of product design, material selection, simulation verification, and experimental assessment. For the construction of power grids in earthquake prone areas, choosing circuit breakers that have undergone strict seismic verification is an important investment for power grid safety and social stability.