The term "fixed" is used to distinguish it from "withdrawable" switchgear. In fixed switchgear, the main switch and other functional units are installed inside the cabinet and are not mounted on a removable trolley.

In fact, many types of switchgear are fixed. For instance, most ring main units are fixed, as well as C-GIS gas-insulated switchgear, which is also primarily fixed.

In contrast, withdrawable switchgear allows functional units like the vacuum circuit breaker to be removed from the cabinet for maintenance or testing. It also enables the insertion of replacement breakers of the same specification to quickly restore power. This was especially useful in the early days of circuit breaker applications, when quality was less stable, making maintenance and quick replacements essential. Withdrawable switchgear also allows easy replacement of voltage transformer fuses, which are mounted on the trolley.

In applications like electric arc furnaces, where frequent operations are required, the annual operation count may reach the circuit breaker's mechanical lifespan limit of 10,000 operations. The switchgear itself may still be in good condition, but replacing the entire switchgear would be costly and time-consuming. In these cases, it is more practical to swap out the withdrawable breaker unit with a new one of the same specification and configuration.

Advantages of Fixed Switchgear

The fixed installation design reduces the space needed for a withdrawable breaker, which requires front operational space. Typically, withdrawable breakers are removed by transporting the trolley past the cabinet door, needing about 1.5 to 2 meters of space. In contrast, fixed switchgear requires only about 1 meter in front of the cabinet for operation, saving space, especially in prefabricated switchgear rooms, where a smaller footprint is beneficial.

Fixed switchgear uses an isolating switch as the medium-voltage isolation point for breaker maintenance. The disconnection point is visible, and the isolating switch, mounted on a common base, ensures precise positioning, avoiding the misalignment issues in withdrawable switchgear that can lead to overheating or even damage due to poor contact alignment.

Fixed switchgear also supports higher current capacities more easily. The conductive path in a fixed cabinet is shorter, reducing heat generation, and the switchgear’s vertical layout aids in airflow and heat dissipation. It’s challenging to achieve the same current capacities (e.g., 5000/6300A) in withdrawable switchgear due to limitations with the contacts.

Fixed installations handle short-circuit currents better. For instance, generator output breakers in fixed switchgear can achieve a short-time withstand current capacity of 63/80kA.

For very large or heavy equipment, withdrawable installations are generally unsuitable. High-current, 40.5kV circuit breakers, which are sizable and weigh nearly half a ton, are challenging to move and align on a trolley. In switchgear with auxiliary transformers, operating large transformers and high-voltage fuses on a trolley is difficult. Trolley-mounted systems also generate significant heat and require substantial secondary connectors for the transformer's output current. Fixed installations avoid these issues, especially for auxiliary transformers, where the currents are low, allowing operation with a small-current isolating switch that is both reliable and easy to operate.

Additional Benefits of Fixed Switchgear

Fixed switchgear offers easier secondary wiring, eliminating the need for secondary connectors, making connections more reliable, and supporting high-current secondary circuits. The shorter control and protection circuit distances reduce line length, saving materials and reducing energy loss.

The mechanical interlock between circuit breakers, isolating switches, and grounding switches is simpler and more reliable. In withdrawable switchgear, complex interlocking mechanisms are required to prevent the breaker from moving into position while the grounding switch is closed, whereas fixed switchgear only requires a simple interlock. If the isolating switch is not closed, it blocks the breaker’s closing mechanism, preventing the breaker from closing.

Additionally, fixed switchgear installations are more flexible and not limited by movement requirements, allowing configurations like side-mounted or horizontal breaker layouts, making it easier to meet system functionality needs.