Protection of motors with incomplete or minimal motor data

Abstract

Many times, the Engineer responsible for setting motor protection for existing motors has very little documentation on the motor itself. Very few documents discuss how to adequately protect motors when proper motor documentation is not available. This paper will present an overview of fundamental motor protection concepts and then proceed to perform various setting examples for motors with and without complete motor data. An ideal case with a fully documented (all information such as thermal limit curves, safe stall times, locked rotor amps) motor will be analyzed first. Subsequently cases where only typical nameplate data available will be analyzed. Techniques on how to estimate various parameters using the power of modern microprocessor relays will also be discussed. An iterative approach to determining proper settings will be discussed. Several setting examples covering a wide range of driven equipment will be presented.