<p>Power&nbsp; quality&nbsp; is&nbsp; becoming&nbsp; a&nbsp; major&nbsp; problem&nbsp; of&nbsp; modern&nbsp; power&nbsp; systems.&nbsp; Harmonics,&nbsp; which&nbsp; are&nbsp; the most&nbsp; significant&nbsp; power&nbsp; quality&nbsp; term,&nbsp; can&nbsp; have&nbsp; substantial&nbsp; effects&nbsp; on&nbsp; electrical&nbsp; devices.&nbsp; Nonlinear loads&nbsp; as&nbsp; electric&nbsp; arc&nbsp; furnaces,&nbsp; power&nbsp; electronic&nbsp; devices&nbsp; cause&nbsp; harmonic&nbsp; problems&nbsp; on&nbsp; power&nbsp; systems, due&nbsp; to&nbsp; their&nbsp; voltage-current&nbsp; characteristics.&nbsp; Passive&nbsp; Power&nbsp; Filters&nbsp; (PPF)&nbsp; are&nbsp; used&nbsp; effectively&nbsp; for harmonic&nbsp; mitigation&nbsp; in&nbsp; power&nbsp; systems.&nbsp; In&nbsp; this&nbsp; study,&nbsp; harmonic&nbsp; measurement&nbsp; data&nbsp; of&nbsp; a&nbsp; steel-iron plant&nbsp; which&nbsp; are&nbsp; obtained&nbsp; from&nbsp; National&nbsp; Power&nbsp; Quality&nbsp; Project&nbsp; supported&nbsp; by&nbsp; The&nbsp; Scientific&nbsp; And Technological&nbsp; Research&nbsp; Council&nbsp; Of&nbsp; Turkey&nbsp; (TUBITAK)&nbsp; are&nbsp; used.&nbsp; A&nbsp; passive&nbsp; harmonic&nbsp; filter&nbsp; is designed&nbsp; for&nbsp; a&nbsp; nonlinear&nbsp; load&nbsp; which&nbsp; is&nbsp; measured&nbsp; within&nbsp; the&nbsp; context&nbsp; of&nbsp; the&nbsp; project.&nbsp; In&nbsp; the&nbsp; case&nbsp; of distorted&nbsp; power&nbsp; quality&nbsp; conditions&nbsp; such&nbsp; as&nbsp; voltage&nbsp; variations,&nbsp; frequency&nbsp; fluctations,&nbsp; unsteady&nbsp; loads and&nbsp; changes&nbsp; in&nbsp; phase&nbsp; angles,&nbsp; behaviour&nbsp; of&nbsp; the&nbsp; designed&nbsp; passive&nbsp; filter&nbsp; is&nbsp; analyzed&nbsp; with&nbsp; simulation studies and&nbsp; obtained results are&nbsp; presented.&nbsp;<br></p>