A PMU should be considered as a set of modern digital electrical grid technologies, which provide measuring information for control systems of electrical modes at a high new level. The number of measuring devices in the power system, as well as the list of tasks solved with their use, depends on the technology availability. One of the promising areas for PMU introduction is relay protection, which opens up new opportunities for improving its functions and revising the existing principles for detecting and tripping faults. The article includes a review of the main areas related to providing new additional properties of the existing algorithms for protecting power system elements, expanding the protection area with a differential operation principle to protect feeders and sections of electrical grids, creating new fault detectors that react to a change in the shape of one or several mode parameters at the same time. The key advantages are associated with the acquisition of adaptability properties, speed, increased sensitivity, the ability to create absolutely selective protection without communication channels. Along with the overview of trends, the article provides their classification according to their use as a part of existing protection algorithms and as part of algorithms based on new fault detection principles. The level of software and hardware development in modern intelligent electronic devices provides the PMU integration to the existing methods of obtaining measurements and signals, and, in particular, with their processing algorithms. Despite the obvious advantages, the features of the PMU implementation based on distributed sensors and digital communication channels significantly narrow the application area for modern relay protection with PMU and other control systems in electric power grids.