What is a static contact? What are its principles and characteristics?

Core Definition
As the name suggests, a stationary contact refers to the fixed, non-mechanically moving conductive contact part of a switching device (such as a circuit breaker, disconnector, contactor, relay, etc.).

It pairs with the moving contact to form the contact system, a key component of the device.

Working Principle and Function

Closed State: When a switch needs to connect a circuit, the moving contact, driven by an operating mechanism (such as a spring, electromagnet, or manual lever), moves toward the stationary contact and makes firm contact. At this point, current flows from the stationary contact to the moving contact (or vice versa), forming a conductive path.

Open State: When a switch needs to disconnect a circuit, the moving contact separates from the stationary contact, creating a gap (arc) between the two, thus interrupting the current.

Core Functions:

Conducting Current: In the closed state, the moving contact carries the normal operating current along with the moving contact.

Breaking Circuit: In the open state, the moving contact works with the moving contact to establish an insulation gap, ensuring reliable circuit disconnection.

Arc Withstanding: When disconnecting inductive or high-current circuits, an arc is generated between the contacts. The stationary contact (usually in conjunction with an arc extinguishing system) must be able to withstand the erosion caused by the arc.

Key Features

Stationary: This is the most fundamental difference between stationary contacts and moving contacts. They are typically securely mounted on an insulated base or bracket of the appliance.

Strong Structurally: Because they serve as a mounting base, their mechanical structure is typically designed to be more robust.

Connecting to External Circuits: Stationary contacts are typically equipped with terminals for connecting to external, fixed wires or busbars. For example, in a circuit breaker, the power-side contacts are typically stationary contacts.

Potentially Acting as Arcing Contacts: Some large-capacity switchgear utilize a pair of arcing contacts designed to make contact first and then separate during the opening and closing process, protecting the main contacts from arc erosion. Stationary arcing contacts are a type of stationary contact.

Stationary Contact vs. Moving Contact

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For a clearer understanding, please see the comparison table below:

Practical Application Examples

Home air switch (miniature circuit breaker):

When you flip the switch, you operate an internal mechanism that drives the moving contact to or from the stationary contact.

The upper and lower terminals are usually connected to the stationary contact.

High-voltage disconnector:

In power systems, we often see large knife switches.

The two clamped metal plates fixed to the insulator are the stationary contacts.

The conductive rod in the middle that can move up and down is the moving contact (also called the knife switch).

AC contactor:

When the coil is energized, a magnetic field is generated, attracting the armature, which drives the moving contact into contact with the stationary contact, connecting the main circuit.

When the coil is de-energized, the spring forces the moving contact to separate from the stationary contact.

Summary

The stationary contact is an essential component in any switch. Although stationary, it serves as the guiding star for the entire contact system, providing a reliable reference point for the precise opening and closing of the moving contact, thereby ensuring safe and reliable connection and disconnection of circuits. Understanding the difference between stationary and moving contacts is fundamental to understanding the operating principles of most switchgear.

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