Harmonic Filter Analysis

Harmonic Filter Analysis and Redesign for a Modern Steel Facility with Two Melt Furnaces Using Dedicated Capacitor Banks
Thomas J. Dionise, PE
Eaton Electrical Power Systems Engineering Warrendale, PA Senior Member, IEEE
Abstract—This modern steel making facility relies on reactive compensation at the substation level in the form of harmonic filtering to support voltage for casting operations,and at the melt furnace level in the form of capacitor banks to support LMF operations. A history of harmonic filter failures at the substation, and intermittent capacitor unit failures at the melt furnace banks, culminated in a recent catastrophic failure of the filter reactor. This paper describes the analytical methods used to redesign the harmonic filter to achieve the desired level ofcompensation yet avoid future failure of the filter components. Field measurements showed the harmonic filter provided a low impedance path for harmonic currents produced during arcing of either or both melt furnace transformer resulting in overload of the filter reactor. Preliminary harmonic analysis enabled temporary detuning of the harmonic filter in the field to avoid this damaging resonancecondition permitting steel making operations to continue while redesigning the filter. Detailed harmonic analysis and filter design considered a wide range of normal and emergency system conditions, especially the effects of extended line outages by the utility for reconductoring. Recommendations included specifications for the redesigned harmonic filter as well as changes to improve performance of themelt furnace capacitor banks.) Keywords-Power Quality meaasurements, harmonic analysis, harmonic filtering, IEEE 519-1992, IEEE 18-1992.

Visuth Lorch
Eaton Electrical Power Systems Engineering Warrendale, PA

TABLE I.

HISTORY OF FILTER FAILURES

Date 1995 1997 1997 April 2003 July 2003 Sept 2003

Failure filter bank commissioned cap oil fire and reactor failure rebuilt reactors andreplaced failed caps reactor failure phase-B, others damaged new and rebuilt reactors installed severe reactor failures

In addition to the filter failures, other problems included 1) capacitor failures at the Rounds Caster Filter, #1LMF and #2LMF, 2) low voltage problems at the Vine St. Sub, and 3) voltage problems at the Bloom Caster EMS and Boiler House. Fig. 1 shows the damage to the reactorfollowing the September 2003 failure. Clockwise from upper left, the damage to the Phase-B reactor included: a) iron core hot enough to melt varnish and blacken paint, b) nuts came off the bolts that “sandwich” the windings to the core, c) the entire reactor frame slipped ¼ inch or more, and d) Arcing between Phase-B and ground (Phase-B faulted to ground).

I. INTRODUCTION The reactivecompensation of interest for this steel making facility was the Rounds Caster Filter (12.6 MVAc at 14.4 kV, three 1-phase iron core reactors of 1.5 mH rated 600 A), and its interaction with the melt furnaces and melt furnace capacitors (#1LMF 14.4 MVAc at 13.8 kV and #2LMF 16.2 MVAc at 14.4 kV). All three capacitor banks are wye-ungrounded. A history of harmonic filter failures at the substation, andintermittent capacitor unit failures at the melt furnace banks, culminated in a recent catastrophic failure of the filter reactor. Table I shows the history of the repeated failure of the Rounds Caster Filter reactor.

Figure 1. Damage to Filter Reactor Following September 2003 Failure

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