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This post was last edited by yunrun on 2020-1-29 at 22:58. The ATSE dual-power automatic transfer switch is essential for switching between two power sources. Changhui Instruments provides a professional overview of the concept and characteristics of ATSEs, as well as the issue of neutral line overlap during power source switching, and the applications of ATSEs, in accordance with the GB14048.11-2008 standard. 1. The concept of ATSE: ATSE stands for Automatic Transfer Switching Equipment, which refers to automatic transfer switches. The **standard for ATSE is GB/T 14048.11; let’s take a look** at the definition of ATSE in this standard: Standard number: GB 14048.11-2008; Standard title: Low-voltage switchgear and controlgear – Part 6-1: Circuit-switching apparatus with multiple functions. Entry: 2.1.2; Content: 2.1.2 Automatic transfer switching equipment (ATSE) consists of one (or several) circuit-switching apparatuses along with other necessary components, and it is used to monitor the power supply circuits and to automatically transfer one or several load circuits from one power source to another. ①There are two power supply inputs; during normal operation, one of the power supplies remains connected at all times. ②It features power supply status detection, enabling the simultaneous measurement of the status parameters (voltage, frequency) of two power supplies. ③When the regular power supply fails (due to voltage loss, overvoltage, undervoltage, phase loss, or frequency deviation), it can automatically transfer the load from the regular power supply to the backup power supply. According to the national standard GB/T 14048.11-2008, an ATSE includes its main unit and controller. The ATSE unit can be divided into two grades: PC grade or CB grade. The PC-grade ATSE is a single unit that can connect and carry current, but cannot be used to interrupt short-circuit currents ； A CB-rated ATSE consists of two sets of interlocked circuit breakers. Since the circuit breaker is equipped with an overcurrent trip device, a CB-class ATSE can be turned on and used to interrupt short-circuit currents. 2. Main features of ATSE: Rated current: up to 5000A. Number of poles: 3-pole and 4-pole types. Structural principle and components: Type 1: Contactor-type ATSE ； Type 2: Circuit breaker type ATSE ； Type 3: Compliant with switch-type ATSE ； Type 4: PC-grade integrated ATSE. Types of use: AC-31 or AC-33. Operating positions: two-stage ATSE or three-stage ATSE. 3. The issue of neutral line overlap when the ATSE switches power sources. As we know, there are three types of TN systems: TN-C, TN-S, and TN-C-S. Among them, TN-C connects PE and N together to form a PEN conductor for protective grounding or protective neutral connection. Let’s take a look at Figure 1. http://yunrun.com.cn/upload/202001/27/202001271250417631.png Figure 1: Explanation of the neutral wire overlap issue in ATSEs. The power supply in Figure 1 is a TN system: it includes generators and power transformers as power sources, as well as ATSEs and three-phase lighting loads. Suppose the original low-voltage power grid was powered by mains electricity, but now it needs to be switched to being powered by generator G for some reason, and generator G has already been started up. During the ATSE switching process, if line N1 disconnects first and then the phase lines disconnect one after another, there will be a moment when the neutral point on the load side deviates, resulting in a high voltage on line N on the load side, which may damage lighting fixtures or electrical equipment. This phenomenon often occurs during grid switching. The reason for this is that the ATSE switches the N wire before the phase wires, resulting in a high voltage being applied to the N wire on the user side; in severe cases, this can even lead to injury to people. The same phenomenon will occur if, when the ATSE switches from the generator power supply to the mains power supply, it switches the N wire before switching the phase wires. To avoid the aforementioned phenomenon, ATSE delays the disconnection of the phase wires relative to the N wire when performing the disconnection operation ； When performing the closing operation, ATSE delays the closing of the phase wires relative to the N wire. The time difference between the two is not less than 20 minutes. Note: The time difference referred to here is the operating time difference of the ATSE switch itself, not the time difference between the start-up of the generator and the occurrence of a mains voltage loss fault. For CB-class ATSEs, since they are composed of two circuit breakers along with a controller, it is impossible to resolve the issue of neutral line overlap. However, since CB-rated ATSEs are constructed using circuit breakers, they possess the capability to interrupt overcurrents, which is their greatest advantage. Some PC-grade ATSE switches allow the timing for connecting or disconnecting the phase wire with respect to the N wire to be set in 5-minute intervals. For example, the opening operation can be set such that the phase wire contact acts 25 minutes ahead of the N wire contact, while the closing operation can be set so that the N wire contact acts 45 minutes ahead of the phase wire contact; this ensures that there is no issue with overlapping neutral wires. Some ATSE switches can also perform switching at the voltage zero point; at this time, no surge voltage occurs because the grid voltage is at its lowest. 4. Application scenarios of ATSE: Applications that place high demands on ATSE switches are typically high-end building projects, airports, exhibition centers, as well as the mobile and telecommunications industries. These environments feature a large number of lighting and communication devices, which cannot withstand sudden high voltage spikes on the N wire. ATSE switches are available in three-pole and four-pole versions, and the applications for these two versions are as follows: ① One application scenario: switching between mains power and generator supply via an ATSE. If the low-voltage distribution network uses a TN-S grounding system, and the low-voltage incoming circuit breaker is equipped with ground fault protection, then both the ATSE and the circuit breaker must be of the four-pole type ； If the low-voltage distribution network uses a TN-C grounding system, since the N conductor must not be disconnected, both the ATSE and circuit breakers must be of three-pole type. ②Application scenario 2: Dual-power switching in the feeding circuit. If the feeding circuit requires switching between two power sources, and those sources come from two different busbars, a three-stage ATSE switch can be used. Source: Changhui Instruments http://yunrun.com.cn/