Abstract : This paper introduces a simple device for testing and adjusting thermal relays, and elaborates on its characteristics, working principle, debugging method, and usage precautions. Keywords : Current transformer, thermal relay, debugging, setting 1. Problem Statement The thermal relays used in Dongqu Coal Preparation Plant frequently malfunction, seriously affecting normal production. Analysis revealed that during use, the characteristics of the relay's thermal element often change, causing the thermal relay's operating value to deviate significantly from the setting value. This results in ineffective protection or malfunctions when the motor experiences overcurrent or overload. Therefore, it is necessary to conduct regular preventative testing and adjustment of the thermal relays to ensure normal production. According to the thermal relay test regulations, the setting test requires a current of 1.0 to 6.0 times the rated current. However, the power of motors varies, requiring a test device with a large current variation range (from a few amps to several hundred amps). Devices with this capability are expensive. Therefore, through repeated practice, we have developed a reasonable, simple, and feasible testing method. Using the commonly used LQJ series current transformer as the current-increasing element, we constructed a simple debugging device for testing and adjusting thermal relays. [b]2 Working Principle of the Debugging Device 2.1 Reverse Application of Current Transformer[/b] The common usage of a current transformer is shown in Figure 1(a). The primary winding w of the transformer is connected in series in the power line, and the secondary winding w is connected to the load RI, where RI is an ammeter or current relay with very low impedance. [b][align=center]For more details, please click: Simple Debugging Device for Thermal Relays[/align][/b]