# Development of a Digital System for Monitoring Emergency Conditions in 20 kV Distribution Networks
## 1 Introduction
### Literature Review and Problem Statement  
The literature describes various methods for measuring zero-sequence voltage, which are performed during on-site emergency maintenance of power transmission lines. Therefore, automating these procedures is a relevant task aimed at improving the speed of fault detection and eliminating costly methods that rely on expensive on-site maintenance [4]. The centralized remote monitoring of faults in the considered type of power lines can be organized using stationary measurement nodes for zero-sequence voltage installed along the power lines. These nodes are capable of transmitting measurement results via wireless communication channels of an information network to a data processing server in the Central Dispatch Service (CDS). In this form, the system will consist of a combination of measurement nodes, a wireless information network, and a data processing server. In this case, to optimize installation and maintenance costs, the use of standardized designs for measurement nodes may be optimal. Measurement nodes should be installed on sections of power lines that are most vulnerable and where the occurrence of faults is most likely. As voltage sensors, zero-sequence current transformers of the TZRL type are used, designed for installation on three-phase cables of various diameters (Figure 1) [1]. The transformer is installed on a cable with a diameter of 70 to 200 mm. In the absence of TZRL transformers, an alternative option is to use conventional current transformers connected in series with the phase conductors. The connection diagram of the windings of three conventional measuring transformers to achieve the zero-sequence voltage measurement mode (3U0) is shown in Figure 2[1]. It should be noted that in power networks, phase loads can vary significantly at different times of the day, making it challenging to achieve near-zero values of zero-sequence voltages during normal operation [1]. In the absence of emergency conditions, depending on the variation of phase loads throughout the day, these voltage values can fluctuate within a range that can be referred to as the normal operating range [2]. The occurrence of an emergency condition, such as a single-phase ground fault, significantly increases the zero-sequence voltages due to the disruption of phase symmetry, causing these values to exceed the normal operating range [4]. Therefore, this work employs a method for detecting emergency values of these voltages that significantly surpass the normal operating range. To detect such exceedances, the first proposed option is to use a digital voltage sensor, the response threshold of which is programmed for each specific case, taking into account the normal operating range present at the given location. In the event of such an exceedance, the sensor generates a signal indicating the presence of an emergency condition at its location, which is transmitted via wireless communication channels to the dispatcher's computer. In this case, the principle of operation is based on a signaling device that alerts the presence of a fault. The second option involves remote measurements of the zero-sequence voltage level performed at different points along the power transmission line using a digital voltmeter. Figure 1: External view of TZRL measuring transformers of different sizes (Description of the transformer type designations: T—current transformer; Z—for ground fault protection; R—split-core (or separable); L—with cast insulation). Figure 2: Circuit diagram for connecting windings of three conventional measuring voltage transformers in the 3U\({}_{0}\) measurement mode of phase “a”, phase “b” and phase “c”. The measurement results are then transmitted to the dispatcher's server for processing to identify the section with the highest voltage value.