Phase angle drift detection method for loss of mains/grid protection

Abstract

The invention concerns a phase angle drift method for loss of mains / grid protection, wherein the accumulated electrical phase angle drift derived from the difference between the current measured local frequency and the estimated frequency using historical data is compared to a angle threshold with the phase angle draft a n being such that : Formula (3), where : n: sample index, [alpha]n: updated phase angle, [alpha]n-12: previous phase angle, fn<est>: estimated frequency, fn: measured frequency, T 12samples: time interval between algorithm executions, the estimated grid frequency being calculated using the following equation in which the key parameters are the historical delay, D cycles, and the window, W cycles, over which the estimated frequency is calculated : Formula (4), where : fn-D-w : oldest frequency value, fn-D: newest frequency, TD: historical time delay, TW: estimation window, wherein the addition / substration of the phase angle increase / decrease calculated for the half cycle in equation (3) is not carried out unless the frequency difference between the estimated frequency fn<est> and the measured frequency fn is greater or equal to a first determined value.

Description

technical field [0001] The present invention relates to phase angle shifting / PAD / methods for de-loading protection. Background technique [0002] The term LOM ("off-load") is used to describe a situation where a generator is inadvertently isolated from the grid and continues to supply local demand. This situation is unacceptable for several reasons, including: risk of DNO ("distribution network controller") operation when reconfiguring the network, reverse reclosing, potential active ungrounded network, and local demand Poor quality power supply is provided. [0003] Existing passive methods to find commonly applied LOM detection include ROCOF ("Rate of Change of Frequency") and VS ("Vector of Change"). However, concerns have increased over their stability in response to network failures and, to a lesser extent, the degree of sensitivity provided. These two performance criteria are closely related, and sensitivity is often sacrificed for higher levels of stability by incr...

AI Technical Summary

Problems solved by technology

[0047] Third, the choice of W must be based on the realization that small values ​​will expose the estimate to overshoots due to short-term perturbations in the output of the frequency tracker caused by transient phenomena such as phase transitions

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