TDS 146
A diagnostic tool for on-site diagnosis of power transformers with on-load tap changer.

The Transformer Diagnostic System is developed for testing power transformers with an on-load tap changer. The transformer diagnostic system is suitable for pre-failure detection of major degradation mechanisms and defects of different types of on-load tap changers. Winding defects can also be found with this diagnostic system.

The TDS146 is used for:
Monitoring the contact condition: Condition-based maintenance requires diagnostic measurements to determine when and what kind of maintenance is necessary.
Diagnoses of the power transformer windings and OLTC in case protective devices have switched off the transformer.
Measurements after tap changer maintenance or repair:
Pre-failure detection of maintenance errors
Finding defects that remained undiscovered during inspection (for example contact misalignment).
Measurements after tap changer maintenance or repair:
Measuring OLTC contact degradation and winding defects inside the transformer tank which are not visible during inspection.
Detection of defects:
The TDS146 checks the main functionality of the tap changer and is able to find such as:
Contact deterioration of (for example due to coking or overheating)
Selector switch contacts
Diverter switch contacts
Tap-selector contacts
Change-over selector contacts
Reversing switch contacts
Coarse change-over selector contacts
Fixed-connection contacts
Interrupted or damaged transition resistors
Mechanical friction in motor drive and transmission
Broken or weakened springs
Winding damage
Maintenance errors
Safety contactor for switching time protection
Weak or damaged drive axis
Synchronization problems between phases

Main functionality of the TDS146:
Tap changer:
Dynamic resistance measurement (DRM)
Check contactor for switching time control (if equipped)
Position measurement on the OLTC drive axis (for rotor-type OLTCs with accessible drive axis)
Motor power measurement on the OLTC drive mechanism
Transformer windings:
Transformer turn ratio measurement
DC winding resistance measurement

Relevant standards and recommendations:
ANSI/IEEE C57.12.90-1987: American national standard / IEEE Standard TestCode for Liquid- Immersed Distribution, Power and Regulating Transformers.
IEEE Std 62-1995: IEEE Guide for Diagnostic Field Testing of Electric Power Apparatus. Part 1: Oil Filled Power Transformers, Regulators and Reactors.
IEEE Std C57.12.37-2006: IEEE Standard for the Electronic Reporting of Distribution Transformer Test Data.
IEEE Std C57.140-2006: IEEE Guide for the Evalua- tion and Reconditioning of Liquid Immersed Power Transformers.
IEC 60214: Tap-changers - Performance require- ments, test methods and application guide.
IEC 60076-1: Power Transformers - Part 1: General

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