What are the key factors for choosing an automatic transfer switch?

1. Load characteristic and capacity matching analysis

1.1 Load type identification

A detailed analysis of the load type (resistive, inductive, capacitive, or mixed) is conducted. Different types of loads have significant impacts on the current surge, starting characteristics of the ATS. For example, inductive loads such as motor starting will generate a high starting current, requiring the ATS to have stronger overload capacity and shock tolerance; capacitive loads may generate overvoltage during switching, necessitating the ATS to have corresponding protection mechanisms.

1.2 Load importance classification

The importance of the load is classified into primary (such as ICU equipment in hospitals, core servers in data centers), secondary (such as ordinary office equipment, lighting in commercial buildings), and tertiary (such as air conditioners and non-critical equipment). Different levels of importance have different requirements for the ATS in terms of switching time and reliability. Primary loads need to be prioritized for continuous power supply.

2. Switching time and switching mechanism requirements

2.1 Load allowable power-off time analysis

The maximum allowable power-off time for the load is determined based on its characteristics. For example, computer equipment typically allows a shorter power-off time, usually in the millisecond range; while some ordinary lighting equipment allows a longer power-off time.

2.2 Common switching mechanism types and characteristics

The common switching mechanisms of ATS are introduced, such as PC level (overall type transfer switch) and CB level (circuit breaker type transfer switch). PC level ATS has the characteristics of simple structure, fast switching speed, and high reliability, and is suitable for scenarios with high requirements for switching time; CB level ATS has overload and short-circuit protection functions, but its switching time is relatively longer, suitable for scenarios with higher protection requirements.

2.3 Switching time parameter selection

The key parameters of the ATS, such as total switching time (including opening and closing time) and inherent switching time, are clearly defined and ensured to meet the requirements of the load. At the same time, the synchronization between different power sources is considered. For asynchronous power sources, ATS with asynchronous switching function should be selected.

3. Reliability indicators and maintenance requirements

3.1 Mean Time Between Failures (MTBF)

MTBF is an important indicator for measuring the reliability of ATS. Choosing ATS products with a higher MTBF value can reduce the probability of failures. Understanding the MTBF data provided by manufacturers and conducting an assessment based on actual applications.

3.2 Mechanical life and electrical life

Pay attention to the mechanical life (operation times) and electrical life (load operation times) of ATS. The longer the mechanical life and electrical life, the longer the service life of the ATS, and the lower the maintenance and replacement frequency. Select ATS with sufficient life expectancy based on the expected usage frequency and years.

Source of content references

1. “Low-voltage Switchgear and Control Equipment – Part 6-1: Multi-functional Electrical Appliances – Transfer Switch Appliances” (GB/T 14048.11-2016)

2. “Code for Electrical Design of Civil Buildings” (GB 51348-2019)

3. “Design Code for Power Distribution System” (GB 50052-2009)