As a typical branch and contact node in the 10kV distribution network, the positioning of the ring main unit is very clear: it only needs to achieve the opening and closing of normal load current, line isolation, fault grounding protection, and does not need to frequently cut off short-circuit high current. The core logic of selection is sufficient, cost-effective, and compact footprint.
Vacuum circuit breaker is more commonly deployed on the main grid side, substation outgoing lines, or power supply incoming lines, serving as the "all-round bodyguards" of the power grid. It has reliable short-circuit breaking capability, which can not only open and close load currents, but also quickly cut off huge short-circuit fault currents, isolate faults in the first time in case of serious faults, and protect upstream main equipment. The powerful breaking ability comes at a cost: the arc extinguishing structure, operating mechanism, and supporting protective devices are more complex, the equipment cost is higher, the overall dimensions of the machine are larger, and more installation space needs to be reserved, which also requires higher requirements for civil engineering and operation and maintenance conditions.
I. Completely Different Functional Roles
Load breaker switch (LBS): only responsible for the opening and closing of normal load current, cannot cut short circuits; A fuse must be installed for short-circuit protection.
Vacuum circuit breaker (VCB): It can cut off loads and short circuits directly, with built-in protection (overcurrent, quick break, grounding), and can automatically reclose.
II. Five Key Reasons for Using Load breaker Switch in Ring Main Units
1. Low Cost (Most Critical)
A load breaker switch with a fuse is approximately 50% cheaper than a vacuum circuit breaker with a comprehensive protection unit; the price difference is significant for large-scale projects.
2. Compact Size and Space-Saving Design
The ring main unit should be compact and modular design, with a simple load switch structure and small size; Vacuum circuit breaker+handcart+comprehensive protection has a large volume and requires more space.
3.No Operating Power Supply Required; Simple Wiring
The load breaker switch can be operated manually and do not require a DC power supply or control power ; Circuit breaker must be equipped with an operating power supply and relay protection,making the system complex.
4.Suitable for specific applications: distribution branch circuits with fewer faults
Ring main unit is used for end/branch lines in residential areas, shops, small factories, etc., with low load and low probability of short circuit; There is already a circuit breaker protection on the upper power supply side, so there is no need for the lower level to repeat the high configuration.
5.Fuses provide faster and more reliable short-circuit protection
The fuse melts in milliseconds during a short circuit, with good current limiting effect and minimal impact on the power grid; Although circuit breakers are fast, their cost and maintenance are high.
III. When Should Vacuum Circuit Breakers Be Used?
Substation incoming lines/main transformer cabinets, large capacity (>1250kVA) terminals, important loads (data centers, hospitals), and situations requiring frequent operation/automatic reclosing.
Conclusion
Priority is given to using load switches at the nodes of the ring network branch line, which is both economical and compact, without the need for supporting operating power supplies; The main network and heavy-duty circuit are suitable for vacuum circuit breaker, which can achieve multi-dimensional fault protection and higher safety.