INNOVATIVE AIRGAP MONITORING SYSTEM

摘要

Airgap is a measure of the distance between the rotor poles and the stator bore. This distancernis specific to each machine and is dependant on the associated electrical parameters resultingrnfrom the design of the generator. The centrifugal, thermal, and magnetic forces occurringrnduring unit operation can affect the shape and relative positioning of the rotor and stator,rnparticularly on larger machines where the rotor and stator can be quite flexible and the airgap isrnsmall relative to the diameter of the generator.rnUnbalanced airgap conditions can cause stator and rotor pole circulating currents, mechanicalrnstresses on the rotor, stator and bearings, local overheating, machine vibration and otherrnproblems which decrease the unit's efficiency and lead to premature aging/failure of the unit.rnOn-line monitoring of the airgap provides a continuous, true picture of the generator's structuralrncondition and dynamic behavior thereby affording the opportunity for informed diagnostics andrninformed decisions on how to remedy or improve any undesirable operating conditions beforernserious damage occurs.rnAn airgap monitoring system is expected to report on the airgap variation, but it must also bernable to report on the rotor and stator shapes. Historically, commercially available airgaprnmonitoring installations have consisted of numerous (8-24) sensors mounted on the stator borernat equally spaced intervals. With all sensors being stator mounted, a significant number mustrnbe installed to provide the required data/information, and any algorithm used to determine thernrotor and stator shapes must not interpolate in such a way that pertinent data/information is lost.rnBritish Columbia (BC) Hydro reviewed the three commercially available systems and hasrninstalled a "hybrid" configuration, consisting of both stator and rotor mounted sensors, on arnnumber of generators. This setup is superior in delivering technical data about the rotor andrnstator shapes, is capable of trending changes in shapes, can be used for alarm and/or trip unitrnprotection and is much less expensive, particularly when an existing vibration monitor isrnconfigured to accept the airgap sensor signals.