MV Vacuum Circuit Breaker Applications & Technology for Modern Power

Medium voltage vacuum circuit breakers are integral to the functionality of modern electrical networks. Despite their widespread use, operational hiccups like switching surges and vacuum interrupter leaks can occur, underscoring the continuous drive for better product quality. To address these concerns head-on, this article will delve into effective maintenance strategies for medium voltage vacuum circuit breakers, with the goal of boosting their application technology and safeguarding the stability and security of power infrastructure.

Initial Use and Technical Attributes of Vacuum Circuit Breaker

The UK led the way in deploying vacuum switchgear within high-voltage electrical networks. Their pioneering units, rated at 132 kV and 13500 MVA, enjoyed a long and reliable service life, continuing to operate until the late 1990s. Nevertheless, their higher economic cost meant that these initial 132 kV grade high-voltage vacuum circuit breaker necessitated the use of eight interrupters in series for each phase. Moreover, the electrostatic field design of these high-voltage vacuum circuit breakers came with certain drawbacks, including intricate mechanisms and inconsistent voltage sharing across the break contacts.
However, in comparison to SF6 circuit breakers (a common type for both high and medium voltage levels), vacuum circuit breakers generally offer a higher RRRV withstand capability, attributed to the strong dielectric properties of vacuum. Also, vacuum switchgear typically has shorter contact travel and lower moving mass than SF6 units, leading to lower mechanical energy consumption and potentially a longer mechanical life.

Advancing Power with MV & HV Vacuum Circuit Breaker Technology

The past few years have witnessed a surge in interest surrounding vacuum circuit breakers (VCBs) across both medium and high voltage power sectors, fueled by technological leaps and a growing emphasis on environmental responsibility. Especially within medium voltage applications, VCBs are progressively displacing traditional SF6 circuit breakers due to their ecological benefits and reduced maintenance requirements. Progress in manufacturing has continually pushed the voltage limits of individual vacuum interrupter, opening doors for their use in elevated voltage tiers, including segments of the high voltage spectrum. Presently, 72.5 kV vacuum circuit breakers are a common sight in medium voltage systems, while higher-rated VCBs, like the 145 kV models, are starting to make their mark in high voltage scenarios. China has made significant strides in the development and deployment of medium voltage vacuum circuit breaker and is focused on creating more dependable and smarter solutions for the evolving needs of modern power grids.
The primary factors contributing to insulation incidents in medium voltage vacuum circuit breakers are suboptimal insulation design within the circuit breaker assembly and non-standard installation protocols. Therefore, meticulous attention to the installation process and comprehensive testing of vacuum circuit breakers are crucial to prevent insulation failures and ensure the dependable operation of medium voltage vacuum circuit breakers. Reflecting on industry exhibitions from several years ago, European countries had already showcased their commercially viable 72.5 kV vacuum circuit breaker products. Currently, China has made significant strides in the research and development of VCBs for both medium and high voltage applications, with a strong contingent of researchers continuously focused on innovation and application in high voltage switching apparatus.
While SF6 gas plays a significant role in medium voltage circuit breakers due to its superb thermal characteristics, strong electron-attracting properties, and high dielectric strength, enabling effective arc quenching and voltage handling, its environmental impact is a major drawback. Conversely, vacuum circuit breakers are environmentally sound, leading to their increasing prevalence in power systems, particularly in 72.5 kV level networks where they are already operational. The trend suggests that higher voltage grades of VCBs, including 72.5 kV and 145 kV, will gain even wider acceptance in the foreseeable future.

MV Vacuum Circuit Breaker: Technical Challenges & Design

The core of medium voltage vacuum circuit breaker technology lies in the vacuum interrupter’s electrostatic field and high voltage integrity. The non-linearity of vacuum breakdown voltage, especially with larger gaps, necessitates size compromises for high voltage applications. Contact gap and grading shield annular gaps impact insulation; early designs used series interrupters for higher voltage.
Balancing size and performance requires managing macro and micro field strengths. Macro-control uses multi-shielding to optimize electric field distribution, reducing geometric concentration (e.g., central shield for arc products, auxiliary shields for electrode edges, composite shields for annular gaps), aided by modern electrostatic analysis. Micro-control addresses particle and roughness-induced field enhancement via material purification and precision machining.
Vacuum arcs are controlled by axial magnetic fields (AMF) for diffusion and quenching. Gap center field strength is critical, weakening with distance. Conflicting gap size needs for voltage withstand and current interruption require electromagnetic design optimization. To avoid AMF decay during opening, moving contacts need rapid initial movement followed by deceleration.
Applying medium voltage vacuum circuit breakers involves technical hurdles requiring careful management. Pre-operation checks are vital. Inductive load switching causes overvoltages; capacitive current interruption is challenging, solved by controlled switching leveraging the small stroke.
Online monitoring of interrupters is developing; periodic power-frequency withstand tests are key for insulation assessment during maintenance. Medium voltage research focuses on new contact materials. High voltage breakers need specialized bellows due to longer strokes, impacting lifespan. Increasing rated current requires addressing heat dissipation.

Mastering MV Vacuum Circuit Breaker Technology

Electrical Endurance: Definition, Influences, and Improvement

Medium voltage vacuum circuit breaker electrical endurance is the specified and tested number of full-capacity breaking operations. Long endurance is vital due to the typical non-replacement of contacts. Modern interrupters use copper-chromium contacts and axial magnetic field (AMF) electrodes; AMF reduces arc voltage, copper-chromium minimizes erosion via even arc distribution, extending lifespan. Technology continuously enhances performance and stability in China.

Temperature Rise Control: Heat Source Analysis and Dissipation

Main heat source is loop resistance, significant in the interrupter. Contact resistance heat dissipates via conductive rods. Internal contact system cooling relies on moving and stationary rods; stationary end, connected to support, dissipates better. Conducting excess heat from the contact gap via the stationary end is effective.

Vacuum Interrupter Leakage: Materials, Causes, and Prevention

Bellows are typically 0.15mm stainless steel. Harsh environments can corrode them, causing leaks at the cover plate seal. Prevention involves precise alignment and proper storage.
Mechanical Parameter Adjustment: Impact on Lifespan and Performance Optimization
Chinese MV VCB mechanical lifespan is typically 10-20k operations, with a 30-40k target. Electromagnetic mechanisms are common for reliability and simplicity; some prefer spring mechanisms. Mechanisms are complex; quality improvements involve split assembly with specialized manufacturing. Proper mechanical parameter settings improve lifespan and utility, e.g., increased buffer distance and optimized characteristics limit tripping stroke and rebound via energy absorption.
Enhancing Operational Reliability: Technical Personnel Roles

To improve MV VCB reliability, technicians should:

• Thoroughly understand structure and parameters, communicate with manufacturers, and learn advanced technologies.
• Manage mechanical parameter commissioning and adjustment for proper operation.
• Ensure spare part performance meets requirements.
• Share experience and collaborate with manufacturers for enhanced reliability.

Conclusion: The Significance of MV Vacuum Circuit Breaker

To sum up, medium voltage vacuum circuit breakers, thanks to their many intrinsic benefits, have established themselves as crucial and irreplaceable components in today’s power delivery infrastructure. The superior dielectric strength of vacuum as an insulating medium points towards substantial future advancements for vacuum switching technology in the high voltage sector. Although the application of medium voltage vacuum circuit breakers currently involves specific technical challenges, the development and implementation of effective solutions, along with precise parameter optimization by experienced technical professionals, will undoubtedly lead to improved product quality and a wider spectrum of applications.