Urgent problems of the power industry of the 21st century require the creation of smart energy systems, providing high efficiency in the generation, transportation, and consumption of electricity as well as increased requirements for the manageability of energy systems and environmental and resource-saving characteristics. One of the solutions to the many problems of the power industry is the creation of new high-efficiency electrical equipment for intelligent power systems based on superconducting technologies to ensure a qualitatively new level of functioning of the electric power industry. In most industrialized countries, superconducting power cables are one of the most advanced developments of superconducting devices. Taking into account the obvious advantages of superconducting cable lines for the transmission of large power flow through an electric network, compared with conventional cables, the Federal Grid Company of Unified Energy System (PJSC "FGC UES") initiated an R&D program that includes the creation of high-temperature superconducting ac and dc cable lines. Two cable lines and accessories on the transmitted power of 50 MW at 20 kV were made. Tests of both types of cables were conducted in the R&D Center at FGC UES JSC in Moscow. The test results are presented in the report.