What are the mechanical characteristics and electrical performance of vacuum circuit breakers?

Mechanical Characteristics

Mechanical characteristics mainly refer to the motion characteristics of the operating mechanism and transmission system of a circuit breaker. They are related to whether the circuit breaker can accurately and reliably complete the "opening" and "closing" actions, and they form the basis of its reliability. Tests are usually carried out offline and without power.

The core parameters include:

1.Rated voltage (Ur) and insulation level:

The highest system voltage at which the circuit breaker can operate continuously, along with the corresponding power frequency withstand voltage and lightning impulse withstand voltage, determine its insulation strength.

2. Rated Current (Ir):

The maximum current that the circuit breaker is permitted to carry under long-term operating conditions. It is related to the heating and temperature rise of the contacts and the conducting circuit.

3. Rated short-circuit breaking current (Isc):

One of the most important parameters. It represents the maximum effective value of short-circuit current that a circuit breaker can reliably interrupt at its rated voltage. It directly reflects the circuit breaker's capability to eliminate the most severe faults in the power system.

4. Rated short-time withstand current (Ik) and peak withstand current:

Short-time withstand current: The effective value of short-circuit current that a circuit breaker can withstand without damage within a short period of time (such as 1s, 3s, 4s). It tests its thermal stability.

Peak withstand current: The peak value of the first half-wave of the short-circuit current that can be endured. It tests its dynamic stability (the ability to resist the impact of electromagnetic force).

5. Rated short-circuit making current:

The maximum peak current at which a circuit breaker can successfully close without welding or exploding when a short-circuit fault exists in the system. It is usually 2.5 times the rated short-circuit breaking current (peak factor).

6. Breaking Characteristics:

Residual Current: The tiny current remaining at the moment when the current crosses zero after the arc is extinguished during the breaking process. The residual current of vacuum circuit breakers is extremely low (usually below a few amperes), which is one of its advantages.

Reignition and Restriking: The ability to withstand the recovery voltage without restriking after breaking. Vacuum circuit breakers perform exceptionally well in this aspect.

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7. Electrical life:

The ability to operate normally without replacing the arc extinguishing chamber contacts after a certain number of short-circuit current interruptions at the rated current. It is divided into:

Full capacity electrical life: The number of times the rated short-circuit current can be interrupted (usually relatively small, such as several dozen times).

Rated current electrical life: The number of times the rated load current can be interrupted (usually very high, up to tens of thousands of times).

Electrical Performance

Electrical performance mainly refers to the breaking, carrying and interrupting capabilities of a circuit breaker in a circuit, which is the core of its function. Tests are usually conducted in high-voltage and high-current test stations.

The core parameters include:

Rated voltage (Ur) and insulation level:

Rated Current (Ir):

The maximum current that the circuit breaker is permitted to carry under long-term operating conditions. It is related to the heating and temperature rise of the contacts and the conducting circuit.

Rated short-circuit breaking current (Isc):

Rated short-time withstand current (Ik) and peak withstand current:

Rated short-circuit making current:

Breaking Characteristics:

Reignition and Restriking: The ability to withstand the recovery voltage without restriking after breaking. Vacuum circuit breakers perform exceptionally well in this aspect.

Electrical life:

The ability to operate normally without replacing the arc extinguishing chamber contacts after a certain number of short-circuit current interruptions at the rated current. It is divided into:

Full capacity electrical life: The number of times the rated short-circuit current can be interrupted (usually relatively small, such as several dozen times).

Rated current electrical life: The number of times the rated load current can be interrupted (usually very high, up to tens of thousands of times).

The Close Relationship Between Mechanical Characteristics and Electrical Performance

Speed vs. Breaking Capacity: The initial separation speed directly affects the diffusion and extinction speed of the arc. Insufficient speed may cause the arc to linger on the contact surface for too long, leading to severe burning of the contacts and even failure to break the circuit.

Bouncing vs. Electrical Life: The closing bounce (the short-term rebound of the moving and stationary contacts after contact) is a mechanical characteristic parameter, but excessive bouncing can generate multiple arcs, severely burn the contact material, and significantly reduce the electrical life of the circuit breaker.

Simultaneous breaking of loads: If the three-phase asynchronism is too large, one phase will undertake all or most of the breaking task first, causing it to bear electrical stress beyond its design capacity, which is likely to lead to damage of the arc extinguishing chamber of that phase.

Mechanical stability and electrical reliability: The deterioration of mechanical characteristics (such as poor lubrication, component wear, and spring fatigue) can lead to changes in parameters such as opening and closing times and speeds. Eventually, when an action is required (especially during the interruption of short-circuit faults), it may cause electrical performance failure, resulting in major accidents.

Summary

Therefore, for the selection, acceptance and operation and maintenance of vacuum circuit breakers, strict tests and monitoring must be carried out simultaneously on both mechanical characteristics and electrical performance to ensure they are always in the best condition and guarantee the safe and stable operation of the power system.

The ZND-12X permanent magnet vacuum circuit breaker

The ZND-12X permanent magnet vacuum circuit breaker is a widely applicable vacuum circuit breaker with a rated voltage of 12kV and AC 50/60Hz. It adopts a magnetic control operating mechanism, has a very small size, and can be used to open and close various electrical loads. It is widely used in urban power grids, rural power grids, and other power grid construction and product upgrading projects, and is especially suitable for frequent operation applications.

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