detecting internal FAUlTS IN A TRANSFORMER WINDING
Presented by
RAKHI.M.S
EEE
College Of Engineering, Trivandrum
2007-11 batch

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CONTENTS
Objectives
Introduction
Causes and Effects
Existing methods
Ratiometer method
Advantages and Limitations
Conclusion
Reference

OBJECTIVES

To detect the internal faults in a transformer winding
Detection of faults to take corrective measures to prevent interruption during operations
To improve the life expectancy of the transformer

INTRODUCTION
Faults in transformer windings
External fault
Internal fault
Turn to Earth
Turn to Turn
Detection methods
MAGNETIC BALANCE TEST
BUCHHOLZ RELAY OPERATION
RATIOMETER TEST


TURN TO EARTH FAULT





N1 – Number of turns in the primary
N2 – Number of turns in the secondary
na - number of turns in the upper part
nb – number of turns in the lower part




TURN TO TURN FAULTS

REASONS FOR FAULTS
Due to vibrations initiated by the electromechanical forces at service current and over currents.
Erosion of winding
Erosion of conductor insulation

ADVERSE EFFECTS DUE TO FAULTS
Severe hot-spots
Oil heating
Winding deformation
Damage to clamping structure
Core damage
Explosion

MAGNETIC BALANCE TEST
Carried out on three phase transformers
Energize one of the phases with a voltage lower than rated voltage
Keeping all the other phases open-circuit
Compare voltage of this winding with open circuited winding
A fault in the winding can be detected by the induced voltage variation

BUCHHOLZ RELAY
Gas actuated relay
Used in oil immersed transformers having a voltage rating more than 500 KVA
Detect incipient fault
It provides protection only against transformer internal faults and does not respond to external bushing or cable connection faults

RATIOMETER
Transformer ratiometer will measures the transformation ratio of transformers in a ratiometric circuit.
Measurement is conducted at low flux density
Measurement is equivalent to the turns ratio of the transformer.
V1/V2 = N1/N2
Measures phase angle deviation between the tested windings






PRINCIPLE OF OPERATION
Excite the HV winding of the test transformer
With signal ,line frequency.
Output of the LV winding is measured in a ratiometric circuit with respect to its magnitude and phase.
In addition to ratio , polarity of the winding also it indicates
Measurement is done over a no. of power frequency cycles in order to eliminate power frequency interference

FEATURES
Designed for power transformers, VTs, PTs & CTs.
Displays Turns Ratio, Polarity & Excitation Current simultaneously.
Display warnings of incorrect lead connections, reverse polarity, open & short circuits.
Easy connection & test setup.

RATIOMETER TEST
Determine inter turn short circuit in the winding
Sensitive to accuracy & calibration of bridge resistor
Required phase angle adjustments for accurate measurement
Increased no load losses indicates the faults in the winding

PRACTICAL IMPLEMENTATION



Remove the time consuming decision making process (return to service or replace) to determine if the transformer is faulted.
Simpler and safer to handle
Reduce the system interruption duration index(can get the faulty signal with in short time).
It detects the slow developing faults at a stage much earlier than other forms

LIMITATIONS
Mechanical failure of equipments can occur.
Unable to detect with high confidence multiple faults which occur concurrently within transformers.
Faults affecting magnetic circuits cannot be detected by electrical devices and can only be detected by mechanical devices

CONCLUSION
Get the overview of faults and how it can be detected in a transformer winding.
We can improve the overall safety associated with transformer failures.
Investigation has been on two-winding single-phase transformer but this method is also useful for three-phase transformer and can be extended to use in all part of transformer winding

REFERENCE

Subhasis Nandi “A Novel Frequency Domain Based Technique to Detect Transformer Inter-turn Faults” IEEE Trans. Power Del; Vol .24 pp. 569-584,feb 2008
Peter Palmer-Buckle, Karen L. Butler, PE,N. D.R.Sarma, Alvin Kop ”Simulation of Incipient transformer fault” IEEE Trans. Power Del; Aug 2008
Mr.Bharsigharan” Detecting the position of winding Short Circuit Faults in Transformer Using High frequency Analysis” EURO journels; (2008), pp.644-6Vol.23 No.4