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