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. BASICS What 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

10. Basic test issues Types of regulation Static vs. dynamic
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

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

12. Presentation on DC testing Parameters variation
Testing transformers
Presentation on DC testing
Parameters variation

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

14. Specific types 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

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

16. Presentations on various problems and issues when testing

17. 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)

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

19. Presentation on removal of remanent magnetism
Demagnetization
Presentation on removal
of remanent magnetism

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

21. The end