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The core role of medium-voltage switchgear (1 kV–35 kV) in substations.

Release time:

2026-01-19

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Abstract

In the complex network of power systems, substations serve as critical hubs connecting power generation, transmission, and distribution, and they assume the core tasks of voltage transformation, power distribution, and system protection. As the key control and protection components in substations, medium-voltage switchgear (1 kV–35 kV) directly determine the safety and power supply quality of the grid through their performance. This article systematically analyzes the pivotal role of medium-voltage switchgear in substations from four perspectives: functional positioning, technical characteristics, typical application scenarios, and development trends.

I. Functional Positioning of Medium-Voltage Switchgear: The “Nervous Center” for Power Transmission and Distribution Interconnection

Medium-voltage switchgear serves as the critical link in substations, connecting the high-voltage transmission system to the low-voltage distribution system. In a 35kV substation, after the main transformer steps down the high voltage from the upstream grid (such as 110kV) to 35kV, the medium-voltage switchgear further distributes this power either to the 10kV distribution network or directly supplies industrial users. Its core functions include:

1. Power Distribution and Control: By combining components such as circuit breakers and disconnect switches, flexible switching among multiple outgoing lines is achieved, thereby meeting the electricity demands of different areas or users. For example, a 35kV substation in a coastal city employs KYN28-12-type metal-clad switchgear. Through modular design, 10 outgoing lines are allocated to the industrial park, commercial complexes, and rail transit system.

2. Fault Isolation and Protection: When a short circuit or overload occurs in the circuit, the circuit breaker can cut off the fault current within milliseconds, preventing the fault from spreading throughout the entire system. Taking the LW8-35 SF6 circuit breaker as an example, its pneumatic arc-extinguishing structure can withstand a short-circuit current of up to 31.5 kA, ensuring the safety of the equipment.

3. Safety Maintenance Assurance: The interlocking design of the isolating switch and earthing switch creates a clear disconnection point during maintenance and ensures reliable grounding, thereby preventing personal accidents caused by misoperations. For example, the GN19-12 isolating switch features a blade-type contact design that guarantees sufficient contact gap after disconnection to meet the IP4X protection rating requirements.

II. Technical Features of Medium-Voltage Switchgear: The Integration of Modularity and Intelligence

The technological evolution of medium-voltage switchgear has consistently revolved around the principles of “safety, reliability, and efficiency,” with its core features reflected in the following three aspects:

1. Modular Structure: Modern medium-voltage switchgear typically adopts a standardized design, integrating components such as circuit breakers, current transformers, and busbars into metal-enclosed or insulated, sealed cabinets. For example, ABB’s SafeRing series uses epoxy-resin-encapsulated pole units, reducing the equipment’s footprint by 40% compared to conventional air-insulated devices and offering a maintenance-free period of up to 10 years.

2. Diversification of Arc-Extinguishing Technologies: Depending on voltage levels and application scenarios, medium-voltage switchgear employs vacuum, SF6, or air arc-extinguishing technologies. Among these, vacuum circuit breakers have become the mainstream choice for 10kV systems due to their oil-free nature and zero emissions of SF6 greenhouse gases; their electrical life can exceed 30 operations. In contrast, 35kV systems typically use SF6 circuit breakers, which leverage their superior insulation performance—having an arc-extinguishing capability 100 times greater than that of air—to achieve high reliability.

3. Intelligent Upgrades: With the widespread adoption of integrated automation systems, medium-voltage switchgear is gradually incorporating electronic operating mechanisms and sensors to enable condition monitoring and remote control. For example, intelligent synchronizing switches detect voltage zero-crossing points, limiting inrush currents to no more than twice the rated current and significantly extending equipment lifespan.

III. Typical Application Scenarios for Medium-Voltage Switchgear: From Urban Distribution Networks to Industrial Loads

Medium-voltage switchgear is widely used in the “last mile” of power systems, and typical applications include:

1. Urban Distribution Network: In 10kV ring main units, medium-voltage switchgear achieves rapid fault isolation and load transfer through a “hand-in-hand” wiring configuration. For example, a new district has adopted the Acrel-1000 integrated automation system, which monitors in real time the number of switch operations, power quality, and short-circuit currents, thereby boosting power supply reliability to 99.99%.

2. At the industrial user end: Impact loads from large motors, rectifiers, and other equipment place stringent demands on the short-circuit breaking capacity of switching devices. A certain steel enterprise selected the ZN63A-12 vacuum circuit breaker, which has a rated current of up to 3,150 A and can withstand a short-circuit current of 40 kA, thereby meeting the frequent start-and-stop requirements of electric arc furnaces.

3. Special Scenarios: In locations with extremely high requirements for power continuity, such as data centers and hospitals, medium-voltage switchgear must be equipped with an automatic transfer switch (ATS) for dual power sources. For example, a Grade-III hospital uses a three-position load switch to achieve seamless switching between utility power and a diesel generator, ensuring zero interruption of critical loads such as operating rooms.

IV. Development Trends in Medium-Voltage Switchgear: A Dual Impetus Driven by Greenization and Digitalization

In response to the “dual carbon” goals and the growing demand for building a new-type power system, medium-voltage switchgear is evolving in the following directions:

1. Environmental-friendly medium substitution: Due to its high global warming potential, SF6 gas is gradually being replaced by mixed gases (SF6/N2) or solid insulation materials. For example, Siemens has launched the 8DJH environmentally friendly switchgear, which uses dry air insulation and reduces the global warming potential (GWP) by 99%.

2. Digital Twin Technology: By deploying IoT sensors and edge computing, we can achieve full-lifecycle management of equipment. A provincial power grid company has piloted a digital twin platform, increasing the accuracy of switchgear fault prediction to 85% and reducing maintenance costs by 30%.

3. Flexible DC Technology: In new-energy grid integration scenarios, medium-voltage DC switchgear utilizes power electronic devices to achieve rapid disconnection, thereby supporting the integration of a high proportion of renewable energy sources. For example, the Zhangbei Flexible DC Grid Project employs DC circuit breakers that reduce the disconnection time to within 3 milliseconds.

As the “nerve center” of substations, medium-voltage switchgear’s technological advancements directly drive the power system toward greater safety, efficiency, and sustainability. In the future, as new materials and technologies continue to break through, medium-voltage switchgear will play an even more critical role in building a new-generation power system.

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Hunan Chengyuan Electrical CO.,LTD

The core role of medium-voltage switchgear (1 kV–35 kV) in substations.