On-line monitoring of mechanical unbalance/ misalignment troubles in ship alternators by direct measurement of split-phase currents

Synchronous generators (SGs) are vital ganglia of the ship. SGs supply survival/defense/attack systems, propulsion, etc., so deserving on-line monitoring. Rotor unbalances shorten bearing lifetime, with overheating and stator-rotor rubs. No technique is definitely established for on-line evaluation of rotor eccentricities (REs) in working SGs. Actual manual air gap checks are time-consuming, and require unit shut-down and dismounting. This paper shows a method based on measurement of split-phase currents in stator windings with parallel branches. A symmetrical component transformation reverts the split-phase currents in rotating space vectors. The (p±1)-order vectors provide an affordable estimation of REs in 2p-pole machines. Rogowski coils or current transformers can be installed in the terminal box, or on winding front-ends, for current measurement. A LabView virtual instrument (VI) was developed for method application. This paper also describes some tests carried out on board an Italian Navy's ship for on-line monitoring of shaft misalignments in a loaded 2MVA SG. Loads on board ships are usually unbalanced and may change suddenly. However, it is shown that the load-related unbalance can be separated from the eccentricity-related unbalance in the split-phase currents. Good assessment of air gap percentage reduction in the tested 2MVA machine was finally obtained.

[1]  P. Talas,et al.  Dynamic Measurement And Analysis Of Air Gap Variations In Large Hydroelectric Generators , 1983, IEEE Transactions on Power Apparatus and Systems.

[2]  Z. Daneshi-Far,et al.  Review of failures and condition monitoring in wind turbine generators , 2010, The XIX International Conference on Electrical Machines - ICEM 2010.

[3]  Alberto Tessarolo,et al.  Time-Stepping Finite-Element Analysis of a 14-MVA Salient-Pole Shipboard Alternator for Different Damper Winding Design Solutions , 2012, IEEE Transactions on Industrial Electronics.

[4]  Damir Zarko,et al.  Calculation of unbalanced magnetic pull in a salient-pole synchronous generator , 2010, Proceedings of 14th International Power Electronics and Motion Control Conference EPE-PEMC 2010.

[5]  Gojko Joksimovic,et al.  Harmonic Signatures of Static Eccentricities in the Stator Voltages and in the Rotor Current of No-Load Salient-Pole Synchronous Generators , 2011, IEEE Transactions on Industrial Electronics.

[6]  C. Bruzzese,et al.  Ship brushless-generator shaft misalignment simulation by using a complete mesh-model for machine voltage signature analysis (MVSA) , 2009, 2009 IEEE Electric Ship Technologies Symposium.

[7]  J. F. Lyles,et al.  Vertical hydraulic generators experience with dynamic air gap monitoring , 1992 .

[8]  C. Bruzzese,et al.  DIEM project's outcomes: An automated air-gap monitoring approach for Italian Navy's on-board low-voltage generators , 2012, 2012 Electrical Systems for Aircraft, Railway and Ship Propulsion.

[9]  Luis Romeral,et al.  Modeling of Surface-Mounted Permanent Magnet Synchronous Motors With Stator Winding Interturn Faults , 2011, IEEE Transactions on Industrial Electronics.

[10]  T. Habetler,et al.  An Impedance Identification Approach to Sensitive Detection and Location of Stator Turn-to-Turn Faults in a Closed-Loop Multiple-Motor Drive , 2011, IEEE Transactions on Industrial Electronics.

[11]  C. Bruzzese.  Rotor eccentricity evaluation in an alternator with parallel pole-phase-groups in the stator: FEM simulations and experimental proofs , 2012, 2012 IEEE International Energy Conference and Exhibition (ENERGYCON).

[12]  Leila Parsa,et al.  Recent Advances in Modeling and Online Detection of Stator Interturn Faults in Electrical Motors , 2011, IEEE Transactions on Industrial Electronics.

[13]  C. Bruzzese,et al.  New Rotor Fault Indicators for Squirrel Cage Induction Motors , 2006, Conference Record of the 2006 IEEE Industry Applications Conference Forty-First IAS Annual Meeting.

[14]  C. Bruzzese,et al.  Static and dynamic rotor eccentricity on-line detection and discrimination in synchronous generators By No-Load E.M.F. space vector loci analysis , 2008, 2008 International Symposium on Power Electronics, Electrical Drives, Automation and Motion.

[15]  F.C. Trutt,et al.  Condition monitoring of brushless three-phase synchronous generators with stator winding or rotor circuit deterioration , 2001, Conference Record of the 2001 IEEE Industry Applications Conference. 36th IAS Annual Meeting (Cat. No.01CH37248).

[16]  C. Bruzzese,et al.  Synchronous generator eccentricities modeling by improved MWFA and fault signature evaluation in no-load E.M.F.s and current spectra , 2008, 2008 International Symposium on Power Electronics, Electrical Drives, Automation and Motion.

[17]  Geoff Klempner,et al.  Handbook of Large Turbo-Generator Operation and Maintenance , 2008 .

[18]  Claudio Bruzzese.  Study of cardioid-shaped loop current space vector trajectories for rotor eccentricity detection in power synchronous machines , 2011, 8th IEEE Symposium on Diagnostics for Electrical Machines, Power Electronics & Drives.

[19]  L. Wang,et al.  Finite-Element Analysis of Unbalanced Magnetic Pull in a Large Hydro-Generator Under Practical Operations , 2008, IEEE Transactions on Magnetics.

[20]  H. Henao,et al.  Load influence on induction machine torque and stator current in case of shaft misalignment , 2009, 2009 35th Annual Conference of IEEE Industrial Electronics.

[21]  Dimitri Torregrossa,et al.  Prediction of Acoustic Noise and Torque Pulsation in PM Synchronous Machines With Static Eccentricity and Partial Demagnetization Using Field Reconstruction Method , 2012, IEEE Transactions on Industrial Electronics.

[22]  Claudio Bruzzese.  A virtual instrument for on-line evaluation of alternator's shaft misalignments through ICSVA (internal current space-vector analysis) , 2011, 8th IEEE Symposium on Diagnostics for Electrical Machines, Power Electronics & Drives.