What is an Automatic Transfer Switch?
An automatic transfer switch , or ATS, is a switch that automatically switches the power supply from the primary source to a backup power source when the primary source experiences a power outage.
When a power outage occurs in the primary power system, this switch activates a backup power source, such as a UPS (or) uninterruptible power supply.
Types of Automatic Transfer Switch (ATS)
1). Change-over Switch Type
2). Breaker Interlocked Type
3). Parallel Operation ATS
4). Bypass Breaker ATS
1). Change-Over Switch Type
Mechanism: Motorized changeover (or) contactor-based.
Logic: Only one source (Q1 or Q2) is active at a time.
Use Case: Simple systems with clear source priority.
2). Breaker Interlocked Type
Mechanism: Two ACBs or MCCBs interlocked electrically & mechanically.
Logic: Q1 and Q2 controlled with failover response.
Use Case: High-current systems needing robust protection and selectivity.
3). Parallel Operation ATS
Mechanism: Syncs both incomers via a bus coupler (BC).
Logic: Can run both sources in parallel under specific conditions.
Use Case: Critical loads where seamless transfer or load sharing is required (Ex: hospitals, data centers).
4). Bypass Breaker ATS
Mechanism: Four breakers – two mains (Q1/Q2) and two bypass (QB1/QB2).
Logic: Allows maintenance on ATS without power interruption.
Use Case: Tier-1 critical systems where zero downtime is mandatory.
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