What is the working principle of the ATS device in a dual power supply cabinet?

Release time:

2025-04-30

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Abstract

The ATS (Automatic Transfer Switch) device in a dual power supply cabinet is the core component that enables automatic switching between two power sources (such as mains power and a generator, or mains power and a backup mains power). Its operating principle is based on three core mechanisms: power status monitoring, fault detection, and mechanical/electrical interlock switching, combined with knowledge base information, as detailed below:

 

I. Basic Components of the ATS Device

The ATS device is mainly composed of the following parts:

  1. Switch Body:
    • PC-level: Integrated structure, without built-in short-circuit protection, requires external circuit breaker.
    • CB-level: Composed of two mechanically interlocked circuit breakers, with built-in short-circuit protection.
  2. Controller:
    • Detects voltage, frequency, and phase loss parameters of the two power sources.
    • Issues a switching command based on preset logic (such as undervoltage, power failure, phase loss).
  3. Actuator:
    • Electromagnetic coil drives the mechanical contact action.
    • The contact part ensures safe switching through an arc extinguishing device.
  4. Auxiliary Components:
    • Mechanical and electrical interlock devices ensure that only one power source is connected.

 

II. Step-by-Step Analysis of the Operating Principle

1. Power Status Monitoring

  • Controller Functions:
    • Continuously monitors voltage, frequency, and phase parameters of the two power sources.
    • Determines if the main power source has failed (such as undervoltage, phase loss, power outage).
  • Typical Fault Trigger Conditions:
    • Voltage below the set threshold (e.g., below 85% of rated voltage).
    • Phase loss in any phase.
    • Frequency deviation exceeds the allowable range (e.g., 50Hz ±5%).

2. Automatic Switching Logic

When the main power source fails:

  1. Cut off the main power source:
    • The controller sends a command to the ATS, the electromagnetic coil is energized, and the mechanical mechanism disconnects the main power contacts.
  2. Close the backup power source:
    • The mechanical interlock ensures that the backup power contacts are closed, achieving power switching.
    • Switching time: Usually ≤2 seconds (items 1, 3), PC-level is faster (≤0.2 seconds).
  3. Backup Power Source Startup:
    • If the backup power source is a generator, the ATS needs to start the generator set:
      • After the generator starts, a stable voltage is output in about 3 seconds, and the ATS switches the power supply after confirmation.
      • After the mains power is restored, switch back to the mains power after a 30-second delay (to prevent repeated switching due to instantaneous fluctuations in the mains power).

3. Mechanical and Electrical Interlocking Mechanisms

  • Mechanical Interlock:
    • The contact design ensures that the main power and backup power contacts are physically interlocked to prevent simultaneous conduction.
  • Electrical Interlock:
    • Through controller logic locking, manual operation is prohibited from conflicting with automatic mode.

4. Maintaining the State After Switching

  • Backup Power Supply:
    • The ATS continuously monitors the status of the backup power source; if it also fails, an alarm is triggered.
  • After the main power source is restored:
    • After the controller detects that the main power source has returned to normal, it switches back to the main power source after a certain delay (e.g., 30 seconds).

 

III. Key Features and Type Differences

PC-level vs. CB-level:

  • PC-level:
    • Advantages: Simple structure, fast switching speed (≤0.2 seconds), high safety (high contact pressure, strong short-circuit resistance).
    • Relies on external protection: Requires an external circuit breaker to provide short-circuit protection.
    • Applicable scenarios: Fire systems, occasions with high switching speed requirements.
  • CB-level:
    • Advantages: Built-in circuit breaker, with short-circuit protection function.
    • Limitations: Longer switching time (over 100ms), mechanical structure may have a slip risk due to circuit breaker tripping.

Intelligent Control:

  • Modern ATS integrates an intelligent controller that can monitor electrical parameters (voltage, current, power factor) in real-time and achieve remote control.

 

IV. Typical Application Scenarios

  • Switching between mains power and generator (as in item 1):
    • When the mains power fails, the ATS starts the generator and switches the power supply within 3 seconds.
    • After the mains power is restored, switch back to the mains power after a 30-second delay to ensure stability.
  • Dual Mains Power Switching:
    • When one mains power is interrupted, seamlessly switch to the other mains power, suitable for places with high requirements for power continuity (such as hospitals, data centers).

 

V. Summary

The ATS device ensures seamless switching to the backup power source in case of main power failure by means of real-time monitoring, quick judgment, and mechanical/electrical interlock switching, guaranteeing power continuity. Its core advantages are:

  • Reliability: Mechanical and electrical double interlock to prevent power paralleling or switching failure.
  • Safety: PC-level design is suitable for high short-circuit current scenarios (such as fire systems).
  • Intelligence: Modern ATS integrates parameter monitoring and remote control functions.

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