Selection of Vacuum Circuit Breaker

Selection of a vacuum circuit breaker is a crucial step in electrical engineering, directly impacting the safety, reliability, stability, and economy of the power supply system. Improper selection can lead to false tripping, ineffective protection, and even safety accidents.

The following are the core points for circuit breaker selection, following a systematic process from system to parameters:

I. Defining Core Basic Parameters (Starting Point of Selection of Vacuum Circuit Breaker)

Rated Voltage (Ue): Must be greater than or equal to the system's nominal voltage at the installation point (e.g., 380V AC, 690V AC).

Rated Current (In): Must be greater than or equal to the calculated load current of the line or equipment. Load type (continuous, short-time, intermittent), ambient temperature (derating is required for high temperatures), and installation method must be considered.

Number of Poles: Selected according to power supply system type:

Single-phase system: 1P or 1P+N

Three-phase three-wire system: 3P

Three-phase four-wire system: 3P+N or 4P (Whether the N pole has protection function depends on the system grounding method)

II. Determine Breaking Capacity (Safety Critical of Selection of Vacuum Circuit Breaker)

This refers to the maximum fault current that the circuit breaker can safely interrupt, which must meet the expected short-circuit current at the installation point.

Rated Ultimate Short-Circuit Breaking Capacity (Icu)

Rated Operating Short-Circuit Breaking Capacity (Ics)

Selection Principle: Icu and Ics must be greater than the expected maximum short-circuit current at the installation point (short-circuit current calculation is required). A certain margin is usually allowed (e.g., 20-30%).

III. Select Protection Characteristics and Trip Curve (Functional Core)

Selection of Vacuum Circuit Breaker with corresponding protection functions and tripping characteristics according to the different protected objects.

Protection Function Types:

Overload Long-Delay Protection (L)

Short-Circuit Instantaneous Protection (I)

Short-Circuit Short-Delay Protection (S)

Ground Fault Protection (G)

Trip Curves (for Miniature Circuit Breakers (MCBs):

B Curve (3-5In)

C Curve (5-10In)

D Curve (10-20In)

K Curve (10-14In)

A Curve (2-3In)

IV. Consideration of Selectivity Coordination (System Coordination of Selection of Vacuum Circuit Breaker)

Full Selectivity: Within the entire current range of overlapping protections, the tripping time of the upstream circuit breaker is greater than that of the downstream circuit breaker, ensuring absolutely no cascading tripping.

Local Selectivity: Achieves selectivity within a certain short-circuit current range; exceeding this range may result in cascading tripping. Calculation verification is required.

Implementation Method: Primarily achieved by adjusting the current setting value (Is) and time delay (ts) of the short-delay (S) circuit breaker to create a time difference between upstream and downstream circuit breakers. Typically, a time difference ≥ 0.1s-0.2s is required.

V. Considerations for Usage Category and Application Environment

Usage Category:

Class A (Non-selective): Typically only provides L and I protection, mainly used at the end of branch lines.

Class B (Selective): Provides L, S, and I protection, used for main lines or applications requiring selective coordination.

Application Environment:

Installation Location: Altitude: Ambient Temperature:

VI. Other Important Factors

Installation and Wiring Method;

Auxiliary Function Requirements;

Communication Function;

Measurement Function;

Alarm Contacts;