ABB 671B287A09 B High Speed Under Frequency Relay

ABB 671B287A09 Type KF High Speed Under Frequency Relay is a protective relay that rapidly trips circuits when system frequency drops below a preset threshold, helping protect generation assets and critical loads from under-frequency events. The 671B287A09 variant is a 120 VAC coil device in ABB’s KF family, specified for standard 60 Hz networks with an under-frequency trip window commonly cited as 55 to 59.5 Hz by distributors. In ABB protection schemes, the KF relay can actuate an auxiliary relay such as a WL-type switch, and the documentation describes a 0.2 A pick-up tap configuration used to drive that auxiliary contact in certain wiring arrangements. The part is listed under the manufacturer part number 671B287A09; distributor listings show it as a 120 VAC high-speed under-frequency relay, with some sources noting it has been discontinued by the manufacturer. Typical applications include protection of generators, feeders, and critical power infrastructure where fast under-frequency response is required to maintain stability and prevent cascading outages.