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Dynamic Resistance Measurement

Dynamic Resistance Measurement. As a tool for OLTC Condition assessment. The dynamic LTC function provides. Graphical results on a PC that makes easy identification of LTC faults in contact resistance, contact timing, make before break mechanism timing and diverter issues, etc.

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Dynamic Resistance Measurement

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  1. Dynamic Resistance Measurement As a tool for OLTC Condition assessment

  2. The dynamic LTC function provides • Graphical results on a PC that makes easy identification of LTC faults in • contact resistance, • contact timing, • make before break mechanism timing and • diverter issues, etc. The LTC does not have to be drained or opened up to achieve this diagnostics.

  3. Content of this presentation • Introduction • History + WG • Tap changers + failures + why test • Test method • Case studies • Good OLTC • Bad OLTC • Demagnetization

  4. What is an OLTC? Standard defines OLTC as • 3.14 load tap changer (LTC): A selector switch device, which may include current interrupting contactors, used to change transformer taps with the transformer energized and carrying full load.

  5. BASICSWhat is DRM? Dynamic vs Static

  6. Static – dynamic : golf ball Click for video

  7. Dynamic resistance measurement principles Fast sampling record of the test current Transition time

  8. The result is a graph

  9. Basic test issues • Types of regulation • Types of switching cycle • Static vs. dynamic • Continuous vs. step by step • Why a sudden jump in step by step mode • Instrument and computer • Presentation of RMO TD

  10. History and purpose History and purpose History and purpose Presentation on References and Working group activities

  11. Testing transformers Presentation on DC testing Parameters variation

  12. CASE STUDIES • GOOD and BAD • Diverter switch • Four resistors • Vacuum / One resistor • Arcing tap switch • Series transformer • Reactance type • Wavering trace a contact problem

  13. MR type M MR type R, T, D MR type VRC MR type V MR type VV MR type RMV ABB UZ ABB type VUCGRN ASEA UZB Fuller UK type? English Electric UK type? Waukesha type UZD Specific types

  14. Interesting cases • ELPROM Bulgaria, see > motor current issue • SMUD • PG&E • Bellehaven • Gill • Malaysia discontinuitybad spring • UK change over switch mis-adjustment • MR type RMV gassing

  15. Issues Presentations on various problems and issues when testing

  16. This section deals with: • Simulation of defects in Ireland • Testing OLTC w/o transformer • Motor current analysis • Neutral operation (2+2/3+1 positions) • Open or shorted secondary • Main contact vs. Main switching contact • Powering the instrument (motor influence)

  17. Various problems • Runaway – stabilization • Small ripple • High interference signal • The ratio of the two • Saturation • Arcing • Regulator • Switching oscillations

  18. Demagnetization Presentation on removal of remanent magnetism

  19. Conclusions • Not for everyone • Need to know what one is doing • Quick • Straight forward • Visible problem indication

  20. The end

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