How to select a static transfer switch?

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In many important occasions, the reliability of electricity supply is crucial. To improve the reliability of power supply for loads, most power supply systems employ dual-power sourcing. Examples include two separate utility power feeds, one utility power feed combined with a UPS, and even the more reliable setup involving two UPS units. It has many applications, such as in computer systems of factories and mines, comprehensive commercial IDC data centers, bank branches, as well as numerous critical loads within the telecommunications, mobile, and power systems. With the application and development of power electronics technology, factory power supply and distribution systems often face such a situation in their operation: on one hand, there are an increasing number of factors that affect power quality, and on the other hand, there is a growing number of electrical devices that are sensitive to power quality. How to design a power supply and distribution system with fast switching capabilities to ensure continuous and reliable power supply has become a key consideration for industry professionals. As a result, the application of static transfer switches is gradually expanding from commercial settings to industrial environments. What kind of product is a Static Transfer Switch (STS)? Many customers are not very clear about this, especially those who are using it for the first time and think it is just an ordinary switch. Here, we will explain the functions and uses of static transfer switches, and we will also cover the key points to consider when selecting such switches. A static transfer switch is a switch with two input circuits; normally one circuit is connected while the other is disconnected, with power supplied to the load from one of the AC inputs. When a fault occurs in one of the power supply circuits, the GSS static transfer switch automatically disconnects the currently active circuit and connects the other circuit, thereby transferring the load to the other power source without any interruption. The notable features of static transfer switches are as follows. 1) The switch utilizes semiconductor devices (thyristors, IGBTs) to achieve rapid switching between primary and backup power sources. The switching speed is much faster than that of mechanical switches, being less than 5 ms. 2) It enables fully digital control and has strong anti-interference capabilities. 3) Each power supply circuit is equipped with a bypass maintenance module, ensuring convenient and safe maintenance of the equipment. Each static switch has three isolation switches to guarantee safe isolation from both the power source and the load. 4) The control unit continuously monitors all system parameters in real time (including the two power supplies, the load, and the status of the static switches), and it features alarm and protection functions against overvoltage/undervoltage at the input, overvoltage/undervoltage at the output, overheating, and overload. What points should be considered when selecting a static transfer switch? 1) Depending on the application scenarios and loads, there are two types. One is single-phase with a voltage of 220V; it is mainly used in commercial settings. One type is three-phase, with a voltage of 380V; it is mainly used for industrial load equipment. 2) The core semiconductor devices are mainly thyristors. Currently, the two best brands on the market are Infineon and Sevcon. When making a selection, it’s worth checking whether the manufacturer offers products compatible with these two brands. 3) Switches come in two types: single-pole and double-pole. You might have some questions here: what exactly is a single-pole switch? What is double cut? Actually, single cutting can be understood as switching only the live wire during the transition, while the neutral wire remains unchanged; the two incoming wires can share the same neutral connection. And double cutting? It means switching both the live wire and the neutral wire at the same time. The choice between single-switch or double-switch operation depends on the situation of the two power supplies. If both mains supplies come from the same upstream station, then single-switch operation with common neutral is possible; otherwise, double-switch operation must be chosen ； In cases where there is one mains power line and one UPS line, the UPS typically comes with an isolation transformer; in such situations, common-neutral single-pole switching can be used ； Similarly, for two UPS systems equipped with isolation transformers, they can also share a common neutral and be switched individually. 4) When selecting a static switch, it is also important to consider whether the device has the capability for rolling switching or synchronous switching, as this depends on the type of load. If the load is a single-phase device but is connected to different phases of three-phase power supply, such as computers and lighting equipment, then rolling switching can be used. However, if the load itself is a three-phase device, such as frequency converters or motors, synchronous switching is necessary; otherwise, an alarm for three-phase imbalance will occur. It is believed that through the above introduction, everyone now has a basic understanding of STS static switchgear. The GSS series of static converters has been successfully used in various applications. The current current ratings available include 200A, 400A, 800A, 1000A, 1200A, etc. Different capacity configurations come with distinct cabinet units, offering advantages such as flexible configuration, high reliability, seamless switching, and easy maintenance. These features provide reliable core functionality support for large-scale industrial applications in the future.