Accounting for the longitudinal regimes of asymmetry to designing the backup protection of power distribution grid

Urgency of the problem. Higher probability of the transverse asymmetry (short-circuit (SC)) in the 6-110 kV distribution grids as compared to the longitudinal-transverse and longitudinal asymmetry on overhead lines (phase wire breaks, breaks with SC) has led to less attention to it [1-8]. It should be noted, breaks of phase wires of overhead transmission lines (overhead lines), even at a short circuit in a network with effectively grounded neutral in many cases, are not accompanied by an increase in current comparable with the short-circuit currents [3-8]. In most cases, relay protection (RP) of the overhead lines with branch and intermediate substations is not sufficiently sensitive to these regimes [1-7], despite the fact that it can not only lead to loss of electricity in the distribution grid, but also cause damage of power transformers due to prolonged current exceeding the nominal current by 2-4 times [4-6], motors, overvoltage in the ungrounded power transformers, possible unwanted tripping by the RP on the adjacent parallel line [9-12]. We propose the following solutions of these problems: expansion of the information base of relay protection and the use of adaptive principles of its designing [13-17], which will increase sensitivity of the backup relay protection to the regimes of the longitudinal asymmetry. This approach is discussed by an example of relay protection of electrical networks including overhead lines and transformers. Using multivariable principle of designing backup protection with control of absolute and relative values of the signal parameters ensures detection of fault regimes and increase sensitivity of the RP.