Selection and Coordination in VCB

The selection and coordination of vacuum circuit breakers are directly related to the safety, reliability, and selectivity of power systems. Below, we will elaborate on these aspects in detail from the perspectives of "selection" and "coordination".

When selecting vacuum circuit breakers, a comprehensive consideration should be made based on their application scenarios (such as incoming lines in substations, distribution outgoing lines, motor protection, etc.) and system parameters. The following key parameters are mainly relied upon:

1. Core Electrical Parameters

Rated Voltage: It must be greater than or equal to the highest operating voltage of the installed power grid.

Rated Current: It must be greater than the maximum long-term working current of the circuit and take into account a certain overload capacity and future development margin.

Rated Short-Circuit Breaking Current: This is one of the most critical parameters. It must be greater than or equal to the expected short-circuit current at the installation location. This current needs to be calculated through power system short-circuit analysis.

Rated Short-Time Withstand Current: It refers to the effective value of the short-circuit current that the circuit breaker can withstand in the closed state within a specified time (such as 1s, 4s). It tests the dynamic and thermal stability of the circuit breaker.

Rated Short-Circuit Making Current: It refers to the maximum current peak that the circuit breaker can successfully close when a short-circuit fault exists (usually 2.5 times the breaking current), testing its ability to withstand electrical dynamic impact.

2. Mechanical and Operating Mechanism Parameters

Mechanical Life: Vacuum circuit breakers have a very long mechanical life, typically over 10,000 operations. The selection should be based on the frequency of operation.

Operating Mechanism Type: Spring operating mechanism (most commonly used), electromagnetic operating mechanism, etc. Spring mechanisms are highly reliable and have low requirements for operating power.

3. Environmental and Other Factors

Installation Environment: Indoor or outdoor? Environmental temperature, humidity, altitude (parameters need to be corrected for high altitudes), etc.

Installation Method: Fixed type or handcart type (withdrawable type)? Handcart type is convenient for maintenance and is widely used.

Brand and Quality: Choose a reputable brand to ensure product quality and after-sales service.

Coordination, also known as "matching", is the ability to ensure that vacuum circuit breakers work in coordination with other protective devices in the system (such as upper-level circuit breakers, lower-level circuit breakers, fuses, etc.) to achieve selective protection. The ultimate goal is to limit the impact of faults to the minimum and ensure continuous power supply to non-fault areas. Coordination mainly includes the following aspects:

1. Coordination with Fuses

In some cases (such as transformer protection, capacitor protection), a combination of "vacuum circuit breaker + fuse" is adopted.

Objective: For large current short circuits, the fuse provides rapid protection by melting; for overcurrent, the vacuum circuit breaker trips with a delay.

Coordination requirements: It is necessary to ensure that within a specific current range, the operating characteristic curve of the fuse and the operating characteristic curve of the circuit breaker have good coordination to avoid over-level tripping.

2. Coordination with the withstand capability of load-side equipment (lateral coordination)

Objective: Ensure that when the vacuum circuit breaker cuts off the short-circuit current, the arc energy and current interruption effect it generates do not cause damage to the circuit breaker itself or other equipment in the system (such as transformers, motors).

Implementation method: Select vacuum circuit breakers with low current interruption values, especially when used to switch inductive loads (such as motors, transformers), to suppress operation overvoltage.

Selection is the foundation: Equip each point with the appropriate "soldier" (circuit breaker).

Coordination is the tactic: Let these "soldiers" work in coordination to form a deep defense line, rather than charging blindly or fighting alone.

In actual engineering, the selection and coordination analysis of vacuum circuit breakers is a systematic project, usually requiring the use of professional short-circuit current calculation software and protection coordination curve analysis software to complete, to ensure that the power system is both safe and reliable.

ZW32-12 Outdoor Vacuum Circuit Breaker (hereinafter referred to as "circuit breaker") is a three-phase AC 50Hz outdoor high voltage switchgear mainly used in 10kV outdoor distribution systems of rural and urban networks, as a means of breaking and closing load currents, overload currents, and short-circuit currents; It can also be used in other similar places;Structural features: The circuit breaker consists of three-phase pillars and an operating mechanism, with a simple structure. The pillar adopts epoxy resin solid insulation, which has the advantages of high and low temperature resistance, UV resistance, and aging resistance;Circuit breaker performance: E2-C2-M2.