doble M4110 User manual

Doble Engineering Company
85 Walnut Street
Watertown, Massachusetts 02472-4037
(USA)
PN 500-0396 72A-2243-01 Rev. B 9/04
September 17, 2004
M4110 Leakage Reactance
Interface User Guide

Copyright © 2004
By Doble Engineering Company
All Rights Reserved.
This Manual is the sole property of the Doble Engineering Company (Doble)
and is provided for the exclusive use of Doble Clients under contractual
agreement for Doble Test Equipment and Services.
In no event does the Doble Engineering Company assume the liability for any
technical or editorial errors of commission, or omission; nor is Doble liable for
direct, indirect, incidental, or consequential damages arising out of the use or
inability to use this Manual.
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and (c)(2) of the Commercial Computer Software - Restricted Rights Clause at
FAR 52.227-19.
This manual is protected by copyright, all rights reserved, and no part hereof
may be photocopied or reproduced in any form without prior written consent
of the Doble Engineering Company.
Copyright
© 2004
By Doble Engineering Company
All Rights Reserved.

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September 17, 2004
Preface
Structure of this Manual
This manual consists of 4 chapters and two appendixes.
Chapter 1 “Introduction To Leakage Reactance Testing”
introduces the M4110 Leakage Reactance Interface.
Chapter 2 “Understanding Leakage Reactance Testing” provides
an overview of Leakage Reactance theory.
Chapter 3 “Leakage Reactance Test Procedures” describes
procedures for executing Leakage Reactance tests.
Chapter 4 “Interpretation Of Test Results” explains how to
analyze test results.
Appendix A “Voltage Selection” describes how to change the test
set input voltage from 115 volts to 220 volts.
Appendix B “Part Numbers” lists the parts of the M4110 Leakage
Reactance Interface.

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Conventions Used in this Manual
The following terms and typographical conventions are used in the manual:
Convention Description
Windows Refers to the Microsoft Windows operating system,
Version 95 or later.
Click Quickly press and release the left mouse button.
Double-click Quickly press and release the left mouse button twice
without moving the mouse.
Select Position the cursor on the desired option and click the
left mouse button once. Or, highlight the desired
option using the arrow keys and press ENTER. Or, press
ALT and the underlined letter.
Press Type a single keyboard key. For example, press ENTER.
FN+(appropriate key) Press and hold the FN key, and press (appropriate
key).
Bold Courier Text Indicates characters to be typed.

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1. Introduction To Leakage Reactance Testing
M4110 Leakage Reactance Interface ................................................................................................. 1-1
Installing the Software........................................................................................................................ 1-2
What You will Need for the Test........................................................................................................ 1-2
2. Understanding Leakage Reactance Testing
Introduction ........................................................................................................................................ 2-1
Failure Modes..................................................................................................................................... 2-3
How Results are Calculated................................................................................................................ 2-5
Three-phase Equivalent Test........................................................................................................ 2-5
Per-phase Test .............................................................................................................................. 2-5
Single-phase Two-winding Test...................................................................................................2-5
3. Leakage Reactance Test Procedures
Test Considerations ............................................................................................................................ 3-1
Information Needed Before Running a Test....................................................................................... 3-1
Test Voltages...................................................................................................................................... 3-2
Selecting the Test Method.................................................................................................................. 3-2
Special Considerations................................................................................................................. 3-3
Test Connections.......................................................................................................................... 3-3
Test Procedures for a Two-winding Three-phase Unit ...................................................................... 3-4
Three-phase Equivalent Test........................................................................................................ 3-5
Per-phase Test .............................................................................................................................. 3-5
Test Procedures for a Two-winding Single-phase Unit...................................................................... 3-5
Test Procedures for a Multi-winding Unit.......................................................................................... 3-5
Test Setup Using the M4110 or the M4130 ..................................................................................... 3-11
Setup for a Single-Phase Transformer Test, M4110.................................................................. 3-11
Setup for a Single-Phase Transformer Test Using the M4130................................................... 3-12
Setup for a Three-Phase Transformer Test Using the M4110 ................................................... 3-12
Setup for a Three-Phase Transformer Test Using the M4130 ................................................... 3-13
Setup for a Transformer with Three or More Windings ............................................................ 3-14
Running a Test.................................................................................................................................. 3-14

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4. Interpretation of Test Results
Initial Test...........................................................................................................................................4-1
Subsequent Test..................................................................................................................................4-2
Appendix A. Voltage Selection
Altering the Voltage Rating from 115 Volts to 230 Volts................................................................. A-1
Appendix B. Part Numbers

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1. Introduction to Leakage Reactance Testing
M4110 Leakage Reactance Interface
This optional interface contains the circuitry necessary to convert the voltage
and current, measured during a Leakage Reactance test on a transformer, into
a form that can be measured by the M4100 Instrument. It also contains a
variac so that the proper test voltage can be obtained. The Leakage Reactance
test cannot be made without either this Interface or the M4130 Leakage
Reactance Module, and the accompanying software. It also requires an M4000
Insulation Analyzer.
When using this interface, the standard M4000 safety switch and safety strobe
are used. The necessary current and voltage cables are provided for connection
to the transformer, along with the necessary software, so that this becomes a
self-contained kit for this test. The user is only limited by the size of the variac
provided.
Figure 1.1 M4110 Leakage Reactance Interface

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Installing the Software
The Leakage Reactance test requires additional software, and is installed in the
same directory as the M4000 software. Run the installation program from the
Setup command. Once you have picked the directory, the software installs
itself with no dialog boxes. You will be able to run the Leakage Reactance test
from the M4000 software, or, if available, from the DTA software.
Advantages of using the DTA software include:
1. Your test data is stored in the same file with your power factor, exciting
current, turns ratio, oil quality and DGA, and other test data.
2. DTA has forms specifically designed for Leakage Reactance tests.
3. You can store your Leakage Reactance test data in the DTA Office
database for future reference.
4. You can easily pull up one file with the entire history of Leakage
Reactance tests for a given transformer.
For more information on using the Leakage Reactance test with DTA, see the
DTA manual.
What You will Need for the Test
Besides the M4110 Leakage Reactance Interface and its cables, you will need:
1. M4100 and its cables, including the M4100 and either the M4200c
Controller or a laptop computer with the M4000 and Leakage Reactance
software loaded.
2. Heavy jumper cables, needed to short-circuit the secondary for each test.
You will be injecting anywhere from a fraction of an ampere to 3 or so
amperes on the High Voltage side, so you must take into account the
transformer’s turns ratio and use jumpers that can withstand the expected
current on the Low Voltage side.
3. To match the nameplate impedance, the transformer must be tested on the
same tap positions as were used to obtain the nameplate value. This
information must be obtained from the nameplate, and the transformer
must be set to those tap positions before the test.
NOTE To switch between 115 volt and 220 volt operation, see Appendix A.
What follows in this manual is information on the theory involved, and what
exactly is being measured, test connections and test procedure, and finally, test
results analysis.

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2. Understanding Leakage Reactance Testing
Introduction
Winding deformation which leads to an immediate transformer failure may be
the result of several overcurrent events. The probability of overcurrent
conditions is not very high and, as a result, a transformer can remain in service
with partially deformed windings, although the reliability of such a
transformer is reduced. Many transformer failures begin with mechanical
deformation but eventually occur for electrical reasons. Consequently,
determining mechanical deformation should be given very serious
consideration. Even small changes in measured parameters should be treated
with the utmost respect.
Several methods have been used to detect winding deformation. They are:
• frequency response analysis
• Iow-voltage impulse test
• capacitance measurement
• leakage reactance measurement
Methods one and two have inherently very promising searching capabilities.
The relative sophistication of the instruments and the expertise required for
these measurements has yet to allow them to become “household tools” at
many utilities.
Capacitance measurements are performed as a part of the routine
AC-insulation tests and normally include all three phases. Capacitance
between the windings, and between each winding and the core/tank, is a
function of their geometric relationships, as well as the dielectric constants of
the intervening insulation. It is known that capacitance may exhibit minor
variations due to temperature changes or serious contamination.
Leakage reactance measurements are performed by short-circuiting the low
voltage winding. During that test, the reluctance encountered by the magnetic
flux is determined predominantly by the leakage channel (Figure 2.1).

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Figure 2.1 Leakage Channel
The leakage channel is the space confined between the inner surface of the
inner winding, the outer surface of the outer winding, and the bottom and the
top yokes. When winding distortion occurs, it changes the reluctance of the
magnetic flux path, resulting in a change of the measured leakage reactance.
The leakage reactance measurement is the simplest of all four tests. During
routine transformer test investigations, it is useful to perform both leakage
reactance and capacitance tests. The changes in both parameters will serve as a
reliable indicator of the winding distortion. Case studies comparing the results
of both measurements are presented in Minutes of the Sixty-First Annual
International Conference of Doble Clients, 1994, sec. 6-5.
It should be noted that the leakage reactance test does not replace the exciting
current measurement; the two are complementary. Leakage reactance is
influenced by the reluctance in the leakage channel, magnetizing current is
influenced by the reluctance in the transformer core and can detect shorted
turns in the windings, shorted core laminations, multiple core grounds and
problems with the LTC and NLTC.

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Failure Modes
When a system short circuit causes high current to flow through a large power
transformer, the windings and internal leads are subjected to extremely high
mechanical forces. The total radial force on a winding can be multiple millions
of pounds and total axial force can be between one and two million pounds.
The extremely high current during the fault conditions is a major source of
mechanical displacements and subsequent transformer failures.
The current flowing in transformer winding conductors sets up an
electromagnetic field in and around the windings, as shown in the simplified
sketches of Figure 2.2 and Figure 2.3. Any current-carrying conductor (I)
which is linked by this field (B) experiences a mechanical force (F) which is
perpendicular to the direction of the current and the field.
In a core form transformer, the forces act radially outward on the outer
winding and radially inward on the inner winding, but because of the radial
fringing at the ends of the windings, there are also axial force components
which tend to compress the windings (Figure 2.2).
Figure 2.2 Generated Forces in a Core Form Transformer

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The common failure modes for a core form transformer are as follows:
• Inward radial hoop buckling
• Outward radial hoop stretching
• Conductor beam bending from generated axial force
• Conductor tilting from cumulative axial force
• Coil end support instability produced by axial force.
Whereas the principal forces in the core form design were radially directed,
the principal forces in the shell form are axially directed (Figure 2.3). They
tend to separate the low-voltage winding from the high-voltage winding,
which pushes the low-voltage winding against the core. The high-voltage
wincing is being crushed inward upon itself. There are modest radial force
components as well. These tend to compress the pancake winding sections
radially.
Figure 2.3 Generated Forces in a Shell Form Transformer
The common failure modes for a shell form transformer are as follows:
• Conductor tilting from cumulative axial force
• Conductor beam bending from generated axial force
• Radial instability of the winding pancakes
• End support collapse (forces transmitted into the core).
The described windings deformations can affect the leakage flux path, which
in turn may result in the change of the measured leakage reactance.

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How Results are Calculated
Three-phase Equivalent Test
The resulting leakage reactance in % is calculated as follows:
%X = [(1/60)ΣΧM][S3ϕ(in kVA)/V2L-L(in kV)]
where
ΣΧM– sum of the individual reactances of each phase, measured in
ohms
S3ϕbase three-phase power of the winding where the measurements
are performed, obtained from the transformer nameplate
V2L-L – base line-to-line voltage of the winding where the
measurements are performed, obtained from the nameplate
Per-phase Test
The resulting leakage reactance in % is calculated as follows:
• For test performed from a delta-connected winding
%X = [(1/30)][S3ϕ(in kVA)/ V2L-L (in kV)]
• For test performed from a wye-connected winding
%X = [(1/10) ΧM][S3ϕ(in kVA)/ V2L-L (in kV)]
where:
ΧM– measured reactance in ohms
S3ϕ– base three-phase power of the winding where the measurements
are performed, obtained from the transformer nameplate
VL-L – base line-to-line voltage of the winding where the
measurements are performed, obtained from the transformer
nameplate.
• For the test performed from the zig/zag-connected winding, the results
are analyzed in ohms without conversion into %
Single-phase Two-winding Test
The resulting leakage reactance in % is calculated as follows:
%X = [(1/10) ΧM][S(in kVA)/V2(in kV)]
where ΧMis the measured reactance ohms, and S and V are the base
power and voltage of the winding where the measurements are performed,
obtained from the transformer nameplate.

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3. Leakage Reactance Test Procedures
Test Considerations
There are two options being offered for measuring leakage reactance using the
M4000. The M4130 Leakage Reactance Module requires the use of an
external user-supplied variac and user-supplied current cables. The M4110
Leakage Reactance Interface includes all controls, cables, and safety
interlocks, and the Leakage Reactance Module in a single package. Following
are instructions for use of the M4110.
In addition to the M4000, it is necessary to have the following equipment for
Leakage Reactance Testing:
• Doble Leakage Reactance Interface, including
• Set of M4110 Voltage Source Cables
• Set of M4110 Voltage Sense Cables
• M4110 Ground Cable
• A set of heavy jumper cables for short-circuiting the Low Voltage
winding
• The M4110 leakage reactance software module for the M4000
If using the M4130 Leakage Reactance Module, a variac and three cables are
required to connect the variac autotransformer to the transformer bushings and
the Leakage Reactance Module. The size of the cable must be in accordance
with the variac rating. Note that the M4130 Leakage Reactance Module is
rated 400 volts, 50 amperes. The M4130 is supplied with voltage sense cables
and a DC power supply cable.
Information Needed Before Running a Test
Although it is possible to run a test without any transformer nameplate
information or benchmark data, % Reactance and % Impedance cannot then be
calculated. Transformer nameplates include the following information which
should be entered into the M4000 program prior to running a test:
• Percent Impedance
• Base VoltAmperes (in MVA) for this impedance
• Base Line-to-Line voltage (in kV) for this impedance
• Tap positions for which the nameplate values were obtained

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NOTE For Single Phase transformers only, the Base Voltage in kV should be the
Line-to-Ground, and not the Line-to-Line, kV.
If available from previous testing the following additional benchmark
information should be entered:
• Benchmark percent impedance
• Benchmark percent reactance
If not, use the nameplate impedance in these fields.
Test Voltages
The objective is to select a voltage sufficient to allow an accurate
measurement of the leakage reactance. The source can be a 120 or 240 volts
outlet. The M4000 Leakage Reactance Interface can deliver a maximum test
current of 25 amperes for 3-5 minutes before tripping the output circuit
breaker. Its maximum continuous output current rating is 9.5 amperes. It is
equipped with a thermal shutdown circuit that prevents the output from being
energized in the event the variac autotransformer temperature has exceeded
the safe operating limit. The red overload light indicates overload.
If using the M4130 Leakage Reactance Module, choose a variac with the
ratings of the M4130 in mind (50 A, 400V).
Once you enter the transformer nameplate information (Percent Impedance,
and kV, MVA, and tap positions on which this number is based) and the
benchmark information, the M4000 calculates and suggests a test current. You
can then adjust the variac to the recommended test current.
If transformer nameplate information reference information is not available, a
test may still be run. However, if using the M4110, you must adjust the variac
so as to achieve at least 15 volts on the winding.
CAUTION Take care to assure all connecting cables are rated for the expected test
current. Since one of the windings will be short-circuited for this test, the
jumper cables must be rated for the expected current in the
short-circuited winding. Although the current cables used to energize
a winding will need to carry 25 amperes or less, the jumpers used to
short-circuit the opposite winding may be required to carry many times
this current.
Selecting the Test Method
The following approach to selecting the test type is recommended.

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On a new or rebuilt three-phase transformer or during the initial test on a used
transformer, a three-phase equivalent test and per-phase tests should be
performed. This allows comparison with the nameplate value (the three phase
equivalent test), between the phases (per-phase tests) and provides a
benchmark for future tests (per-phase tests). On a single-phase unit, only one
test can be performed (Figure 3.3 M4110 Setup (a)). For comparison, tests
should be performed on the same LTC positions as the nameplate values.
Once the comparison with the nameplate is verified, follow-up tests can
include per-phase tests only. Besides being a more searching test, it allows
comparison not only with the previous test results but between the phases
as well.
The initial tests should be performed on all the de-energized tap changer
positions. It is conceivable that throughout its service life a transformer
may be energized in several DETC positions. When units trip off-line, the
service personnel may be reluctant to change the DETC positions solely to
perform a test in positions in which the initial leakage reactance measurement
was performed
Special Considerations
The test performed from the high-voltage winding at a given voltage requires a
lower current from the source than the test performed at the same voltage from
the low-voltage winding.
It is recommended to perform the test at the highest possible voltage to
minimize the effects of the magnetizing reactance. For further information, see
Proceedings of the Sixty Second Annual International Conference of Doble
Clients, 1995, sec. 8-12.1. When nameplate data is available and input to the
M4000 software, these test settings are selected for you.
For certain winding configurations, the results of the per-phase will not
compare with the nameplate value or results of the three-phase equivalent test.
For further information see Proceedings of the Sixty-Second Annual
International Conference of Doble Clients, 1995, sec. 8-13.1.
Test Connections
Test connections for use with the M4110 are shown in Figure 3.3 M4110
Setup (a) and Figure 3.4 M4110 Setup (b). Test connections for use with
the M4130 are shown in Figure 3.5 M4130 Setup (a) and Figure 3.6 M4130
Setup (b).

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NOTE These test connections represent common transformer winding vector
relationships. Always check your transformer nameplate drawing to be
sure the phase short-circuited corresponds to the phase energized! The
consequence of short-circuiting the wrong winding will be that the tester
will not be able to obtain the recommended current to run the test. For
example, for a Per-Phase Wye test, a transformer with the following
vector representation of its winding relationship would require the
different connections shown:
Figure 3.1 Example of Transformer Winding Vector Diagram Requiring
Modified Leakage Reactance Test Connections
Test Procedures for a Two-winding Three-Phase Unit
With the M4000 insulation analyzer, which uses single-phase excitation, the
leakage reactance of a three-phase unit can be measured using two methods:
the three-phase-equivalent test and the per-phase test.
Table 3.1 Example of Modified Connections for Leakage Reactance
Per-Phase Wye Test
Connections Shown In
Manual For Per-Phase Wye
Test
Connections Required by
Per-Phase Wye Test For
Wye-Delta Vector Diagram
Shown Below
Energize Short Energize Short
H1-H0 X1-X3 H1-H0 X2-X1
H2-H0 X2-X1 H2-H0 X3-X2
H3-H0 X3-X2 H3-H0 X1-X3

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Three-phase Equivalent Test
One test is performed on each phase, by connecting the voltage source and
sense leads from the Leakage Reactance Interface to each pair of line
terminals. All three line terminals on the opposite winding are connected
together with jumpers, as shown on Figure 3.4 M4110 Setup (b) (if using the
M4110), and Figure 3.6 M4130 Setup (b) (if using the M4130).
Per-phase Test
One test is performed on each phase, by connecting the voltage (source and
sense) leads from the Leakage Reactance Interface to a line and the neutral
terminals on wye and zig/zag windings or to a pair of line terminals on a delta
winding. The terminals on the opposite winding should be short-circuited, as
shown in Figure 3.3 M4110 Setup (a) (if using the M4110), and Figure 3.5
M4130 Setup (a) (if using the M4130).
NOTE For the Per-Phase tests, use the vector diagram on the transformer
nameplate to assure that the phase being short-circuited corresponds to
the phase being energized. The examples in the above-mentioned figures
may not always correspond to the vector diagrams representing your
transformer.
Test Procedures for a Two-winding Single-phase Unit
The test connections for a single-phase unit are shown in Figure 3.3 M4110
Setup (a) or Figure 3.4 M4110 Setup (b) (if using the M4110), and Figure 3.5
M4130 Setup (a) or Figure 3.6 M4130 Setup (b) (if using the M4130).
CAUTION Be aware of the transformer turns ratio, and the high currents that may
result on the short-circuited winding. Be sure the jumper cables are rated
for that current!
Test Procedures for a Multi-winding Unit
In a multi-winding (more than two windings) unit, the leakage reactance
associated with each pair of windings should be tested. Pick two windings
between which you wish to measure the Leakage Reactance, and (after
entering the nameplate data corresponding to that winding pair) energize the
higher-voltage one while shorting the lower-voltage one in accordance with
the connection instructions. The line terminals of the other windings should be

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left floating. In a three-winding unit, the test procedures described above are
applied to three pairs of windings. In a four-winding unit, they are applied to
six pairs of windings. The figure below shows the Per-Phase leakage reactance
test on one phase between the H and X windings of a three-winding
transformer. Tests would then be made between H and Y windings (X
floating), and between X and Y (H floating).
Figure 3.2 Leakage Reactance Test on a Three-Winding Transformer