In applications such as switching power supplies, motor current load detection, lighting and instrumentation, current mutual inductance transformers are generally used as control, circuit protection and monitoring devices. With the increasing number of current transformers in stock, how to choose a suitable current transformer requires consideration of many factors. This article introduces a simple selection method, which is very useful for selecting suitable cost-effective devices in many applications. helpful. Although off-the-shelf devices are cheap and immediately desirable, there are some functional limitations in their use. Certain applications may require special products or even complete customization. The selection of current mutual inductance transformer should consider many factors, such as size, frequency, function and current range.