Dynamic Resistance Measurement As a tool for OLTC Condition assessment
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.
The LTC does not have to be drained or opened up to achieve this diagnostics.
Content of this presentation
• Introduction– History + WG– Tap changers + failures + why test– Test method
• Case studies– Good OLTC– Bad OLTC
• Demagnetization
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.
BASICSWhat is DRM?
Dynamic
vs
Static
Static – dynamic : golf ball
Click for video
Dynamic resistance measurement principles
Fast sampling record of the test current
Transition time
The result is a graph
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
History and purpose
Presentation on References
and
Working group activities
History and purposeHistory and purpose
Testing transformers
Presentation on DC testing
Parameters variation
CASE STUDIES
• GOOD and BAD• Diverter switch• Four resistors• Vacuum / One resistor• Arcing tap switch• Series transformer• Reactance type• Wavering trace a contact problem
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
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
Issues
Presentations on various problems and issues when testing
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)
Various problems
• Runaway – stabilization
• Small ripple– High interference signal– The ratio of the two
• Saturation
• Arcing
• Regulator
• Switching oscillations
Demagnetization
Presentation on removal
of remanent magnetism
Conclusions
• Not for everyone
• Need to know what one is doing
• Quick
• Straight forward
• Visible problem indication
The end