Harmonic Analysis of Arcing Faults and Impacts on System Protection: Copyright Material IEEE, Paper No. PCIC-2018-46

Transformer protection schemes commonly use percentage restrained differential elements for winding protection, often delayed or desensitized by 2nd and 4th harmonic elements during inrush of LV and MV transformer banks. Differential relays are now commonly applied to smaller transformers and the zone of protection can now include cables, bus duct, circuit breakers, and other components. Harmonic controlled differential relays are seeing wider use for arc flash mitigation, and other harmonic-controlled schemes have also been proposed. Preliminary observations suggest that the harmonic spectra of arcing fault currents can differ substantially, which begs the question - when can harmonic-supervised protection be employed with harmonic restraints set to avoid operation for inrush while still operating quickly for arcing faults? This paper explores this topic by analyzing relay responses to real arcing faults using relays from multiple vendors that employ different harmonic detection algorithms.

I. Introduction

In recent years there has been a trend toward applying selective high speed protection schemes on low voltage (LV) power distribution equipment. This trend has been driven by an increased focus on equipment reliability and mean time to repair as well as an increased emphasis on arc flash incident energy reduction. High speed protection schemes have been applied to LV transformers [1], LV switchgear buses [2], [3], and LV motor control centers [4]. While high speed protection can provide several benefits, it may involve some drawbacks such as additional hardware requirements, additional instrument transformer requirements, increased power distribution equipment size, increased complexity during testing, increased difficultly developing protection settings, and higher cost.