Transcript 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.
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.
BASICS
What 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
Testing transformers
Presentation on DC testing
Parameters variation
CASE STUDIES
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GOOD and BAD
Diverter switch
Four resistors
Vacuum / One resistor
Arcing tap switch
Series transformer
Reactance type
Wavering trace a contact problem
Specific types
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MR type M
MR type R, T, D
MR type VRC
MR type V
MR type VV
MR type RMV
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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:
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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
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Saturation
Arcing
Regulator
Switching oscillations
Demagnetization
Presentation on removal
of remanent magnetism
Conclusions
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Not for everyone
Need to know what one is doing
Quick
Straight forward
Visible problem indication
The end