In addition, in the Russian Federation, 75 % of oil-producing wells in operation at old fields are low- to medium-flow rate wells. One way to increase the profitability of oil production from low- to medium-flow rate wells using ESPs is to reduce the power consumption of the Submersible Electric Motor (SEM) by switching the ESP from a scalar open-loop control system to a sensorless vector control system. To implement the vector control system for ESPs, it is necessary to develop a methodology for identifying the parameters of the electrical equipment in the power channel of the ESP, as well as to implement a full-order observer of the SEM vector state variables to create a feedback channel for angular speed. One of the electrical components in the ESP power channel that affects the accuracy of the SEM vector state variable estimation is the power cable, which can reach up to 5 km in length. Such a long cable length results in the output voltage at the cable end being significantly different in amplitude and frequency from the measured input voltage, and the cable parameters themselves change as the temperature of the well varies depending on the depth. Failure to estimate the output voltage of the cable will result in incorrect estimation of the torque and angular speed of the SEM, which, in turn, may cause the angular speed of the SEM to oscillate and the ESP to trip at the bottom of the well. Due to the above factor, the development of a full-order observer for the vector state variables of the cable line with increased parametric robustness is a relevant and timely task