This paper presents the design and implementation of a power failure monitoring system for 22-kV transformer substations using the Internet of Things (IoT) technology and LoRa communication. The proposed system consists of 3 main components: Sensor nodes consist of voltage sensors and a LoRa transceiver module installed at the substation; Gateway station is composed of one LoRa transceiver module, one Wi-Fi module and one 3G/4G wireless module for transmitting data to Cloud server through internet connection and sending SMS alerts to users; and the ThingSpeak cloud server. The application of LoRa communication technology allows monitoring of grid voltage in real-time with lower operating costs than the methods of sending data over the internet and mobile phone networks. The research results can be applied to automate the monitoring and warning of power failures at the 22-kV distribution substations to help improve the stability of the power systems.