GET 6987B
Revised, November 1991
Reformatted, September 2001
GE Power Systems
Generator
Generator Field Winding
Shorted Turn Detector
(Flux Probe – With DOS Based Acquisition Equipment)
These instructions do not purport to cover all details or variations in equipment nor to provide for every possible
contingency to be met in connection with installation, operation or maintenance. Should further information be desired or
should particular problems arise which are not covered sufficiently for the purchaser’s purposes the matter should be
referred to the GE Company.
 2001 GENERAL ELECTRIC COMPANY
GET 6987B
Generator Field Winding Shorted Turn Detector
TABLE OF CONTENTS
I. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
II. PERMANENT FLUX PROBES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A. Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Engineering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
4
5
5
III. TEMPORARY FLUX PROBES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
IV. COMPARISON OF THE TEMPORARY PROBE AND THE PERMANENT PROBE . . . . . . . . . . . . . . .
6
V. TESTING TECHNIQUES AND SHORTED TURN DETECTION SENSITIVITIES . . . . . . . . . . . . . . . . .
6
VI. ANALYSIS OF DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
VII. DATA ACQUISITION INSTRUMENTATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A. Brief History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Current Data Acquisition/Analysis System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
14
14
ILLUSTRATION LIST
Figure
Figure
Figure
Figure
Figure
Figure
Figure
1
2
3
4(A)
4(B)
5
6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure 12
Figure
Figure
Figure
Figure
Figure
13
14
15(A)
15(B)
16(A)
Figure 16(B)
2
Flexible probe design at 10 o’clock in core. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Rotor assembly-retaining ring interference requirements. . . . . . . . . . . . . . . . . . . . . . . . . . .
Cross-section of rotor with field coil nomenclature and stationary search coil A. . . . .
Installation of temporary flux probe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Design of temporary probe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Short-circuit radial flux coil waveshapes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Air-gap flux density waveforms.
(A) Zero crossing during open-circuit conditions. (B) Zero crossing during 100%
load conditions. Note: (A) and (B) show movement of the quadrature axis,
sensitizing different coils at different load test points. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Typical flux probe signal with labelling and annotation. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
(A) There is a shorted turn in coil #7, pole X. Also shows amortisseur windings.
(B) This is the same machine as in 8(A), showing shorted turn in #3 coil, pole X. . . . .
Shorted stator data showing one turn short in coil #2, pole Y (negative).
Also shows amortisseur windings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Open-circuit load point. There are three turn shorts in coil #8
(3% of winding shorted). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Example of shorted stator data with 18% to 20% turn shorts. . . . . . . . . . . . . . . . . . . . . . .
Massive turn shorts in coils #6 and #7. Example of turn shorts in coils
other than #1, #2, and #3 causing vibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data at 73% load showing magnetic wedges over coils #1, #2, #3, and #4. . . . . . . . . . .
Computer data acquisition/analysis system: Computer, printer, and flux probes. . . .
Typical load test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Three-dimensional plot for data in Figure 15(A). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Shorted stator data with corresponding signature plot and slot amplitude
table for 42% load condition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Shorted stator data with corresponding signature plot and slot amplitude
table for 50% load condition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
4
4
5
5
7
7
8
10
11
11
12
12
13
15
16
19
20
21
Generator Field Winding Shorted Turn Detector
GET 6987B
I. INTRODUCTION
Shorted turns on the field winding of a steam or gas turbine-generator rotor can restrict the output
of the generator or cause other serious operating limitations. The SHORTED TURN DETECTOR is
a system custom-designed by GE for detecting shorted turns in an operating generator’s rotating
field using a nonmagnetic flux probe. The flux probe is installed in the generator air gap where it
senses the field winding slot leakage flux. The probe produces a voltage proportional to the rate of
change of the flux as the rotor turns. This pattern of flux variation near the field is a signature
unique to each field winding. A waveform analysis technique is used to identify the location and
number of shorted turns in the field winding.
The flux signature waveform is obtained from either a permanent or temporary flux probe. A permanent flux probe is installed during manufacture or as a retrofit. A temporary probe must be installed
on-site.
The shorted turn test data can be acquired either when the generator is operating under varying
real and reactive load conditions (no load to full load) or when the generator is off line and connected
in a shorted stator configuration. This latter method, involving considerable system reconfiguration, is a test condition that provides a waveform having more definitive characteristics than that
of the on-line test data. A one-per-revolution signal is desired for data acquisition of two-pole generators for proper pole identification. For four-pole machines, a one-per-revolution signal is necessary for correlating the data across different load points.
With the machine condition set and stable, the flux probe signal is recorded for at least one revolution of the generator rotor field. Using this record, the analyst can compare the individual voltage
amplitudes in the flux probe signal to determine the condition of the generator field coils.
The amplitude of each cycle in the flux probe signal is a function of the slot leakage flux and is proportional to both the active turns in the slot and the magnitude of the air-gap flux density. Maximum
flux density is at the leading edge of each pole and progressively decreases toward the quadrature
axis. As a result, the amplitude of coil 1 is larger than the rest. There is an exception when magnetic
wedges are installed between the probe and the coil. In such a case, the peak-to-peak voltage induced by this coil is much smaller because magnetic wedges shunt a large portion of the leakage
flux.
II. PERMANENT FLUX PROBES
Figures 1 and 2 show a typical permanent probe design and probe location. Figure 3 provides typical
field coil nomenclature. The flexible probe design allows the probe to be mounted from a nominal
3/ inch to 13/ inches from the field body. As shown in Figure 2, the permanent probe design per4
4
mits field installation without probe interference.
Magnetic wedges, sometimes used in the #1 and #2 slots, reduce the slot leakage flux in the air gap.
The permanent probe should be located in an axial position of the air gap over nonmagnetic field
wedges wherever possible.
The shorted turn data may be taken during either load testing or stator short-circuit testing.
The application of permanent probes with their inherent easy signal accessibility and attractive
testing techniques has greatly reduced the troubleshooting tasks of unusual operating conditions,
such as:
Higher field current requirements for the same load than previously experienced.
Thermal sensitivity rotor balance problems (rotor vibration amplitudes change with field current
changes). Since slots with turn shorts operate at cooler temperatures than slots without turn
3
GET 6987B
Generator Field Winding Shorted Turn Detector
shorts, rotor bowing may occur. Rotor bowing caused by coils 1, 2, and sometimes 3 has more
effect on vibration than that caused by the higher numbered coils.
A. Installation
Machines manufactured after 1990 may have permanent flux probes installed during manufacture.
Machines manufactured after 1976 may have temporary probe access ports. All other machines
will require on-site retrofit.
Rotor Assembly
Retaining Ring
1″
Rotor
In
Position
Rotor Surface
Figure 1. Flexible Probe Design
in Core
Pole
Lead
Slots
Figure 2. Rotor Assembly-retaining
Ring Interference Requirements
Rotation
“A”
1
Pole X
1
2
Coil and
Slot Numbers
2
End Turns
3
3
End Turns
4
4
Coils
5
5
6
6
6
Quadrature Axis
6
Wedges
I
End Turns
5
5
4
4
“A”
Probe
Coil
3
3
2
2
Pole Y
1
Pole Axis
1
Slot
Leakage
Flux
Pole
Lead
Slots
Figure 3. Cross-section of Rotor with Field Coil Nomenclature and Stationary Search Coil A
4
Generator Field Winding Shorted Turn Detector
GET 6987B
Installation of the permanent flux probe is accomplished on-site in one workday or less. Each
permanent probe is custom made to fit the particular machine. Probes for General Electric machines are engineered from the existing drawings. Non-GE machines require a pre-installation
trip to the site after the generator rotor field has been removed. This trip is necessary to acquire
machine physical dimensions for flux probe design.
B. Engineering
Probe design is based on air-gap, retaining ring diameter, stator wedge depression, etc. Axial
probe locations are specified so that wherever possible the probe is placed over nonmagnetic
field wedges, thereby enhancing the probe sensitivity.
C. Components
The components for each retrofit detector are hand carried by the installer at the time of the
installation and are not available in kit form. These components are as follows:
• Probe and wire
• Circular sealing gland (similar to a thermocouple gland) including a BNC-type connector and
a PVC-Schedule 80 type cover. (If a non-PVC cover is requested, the customer must provide
per our drawings.)
• Materials to secure and cover the flux probe lead-out wire.
In addition to removing the generator rotor and the upper, turbine-end end shields, plant personnel will be required during probe installation to drill holes for the wire routing and to weld
the circular gland (7018 weld rod is preferred, however individual plant practices will prevail).
It is preferred that all turbine-end end shields be removed.
III. TEMPORARY FLUX PROBES
The temporary probe is a removable transducer, 84 or 90 inches long, that is inserted through an
exit gland in the machine. This probe is inserted to approximately one inch of the field body. Flux
data can then be obtained. The probe is removed after data acquisition. Figure 4 shows typical
installation and design of a temporary probe. A comparison of permanent and temporary probes
follows.
Field Body O.D.
Wrapper
Core
I.D.
Probe
1″ Nom.
Figure 4(A). Installation of Temporary Flux Probe
Probe Stop
Entrance Seal
Ball Valve
Figure 4(B). Design of Temporary Probe
5
GET 6987B
Generator Field Winding Shorted Turn Detector
IV. COMPARISON OF THE TEMPORARY PROBE AND THE PERMANENT PROBE
TEMPORARY PROBE
PERMANENT PROBE
Dimensions
3/16″ or 1/4″ O.D. by 84″ or 90″
Overall length 0.3″ to 6″
Installation
Hardware permanently mounted
per drawing from generator drafting
based on core inlet locations. Field
in place, generator degassed. Probe
may be inserted while generator is
on-line or with field at standstill.
Hardware installed by GE District
Office. Probe inserted then removed
after testing.
Custom mounted on stator wedge
at 10 o’clock or 2 o’clock position,
turbine end. Mounted to avoid magnetic field wedges whenever possible. Field must be removed. Exit
gland through outside wrapper plate
affords easy connection and personnel protection. One workday installation time.
Sensitivity
Equal
Equal
Location
Accuracy of test is decreased if
probe installed over field magnetic
wedges.
Accuracy of test is increased greatly
where field magnetic wedges are a
problem because possible to install
probe over nonmagnetic wedges.
Convenience
Must be inserted prior to each test.
Requires only connection to data
acquisition equipment.
Versatility
Load or shorted stator testing.
Load or shorted stator testing.
V. TESTING TECHNIQUES AND SHORTED TURN DETECTION SENSITIVITIES
The technique of detecting shorted turns is to measure variations in the air-gap search coil waveforms of non-turn-short and turn-short conditions. These waveform signatures are the time-rateof-change of the rotating radial air-gap flux density. This waveform accentuates the flux density
variations at the rotor slots and teeth. The amplitude of the slot voltage spikes is a function of the
active turns in the slots (slot leakage flux) and distortion factors due to the air-gap flux density magnitudes across the slots. To obtain the greatest shorted turn detection sensitivity, the data is read
at the slots where the distortion effects are minimal.
Stator short-circuit test data, Figure 5, have the least amount of distortion effects in this generator
load configuration when the armature reaction flux almost completely cancels out the field flux.
Thus, the slot voltage spike magnitudes in the raw test data are directly proportional to the active
turns in each slot. Note the clarity of the turn-short condition (coils 4, 6, and 8 on one pole) in Figure
5(A) when compared to the no-turn-short condition in Figure 5(B). The symmetry of the waveform
on either side of a pole and the inverted symmetry of each pole provides comparative data for shorted
turn analysis without previous signature data. Stator short-circuit data provide the least distorted
test results. However, to set up this test requires considerable planning and work to isolate the generator from the system, short the high side of the transformer, deactivate relays, and set up special
excitation supplies or controls.
Generator load test data can provide shorted turn sensitivities close to that obtained by the stator
short-circuit test. The data, however, is somewhat more difficult to analyze because of air-gap flux
density distortion factors which exist during load conditions. At load conditions, the air-gap flux
density is a multiharmonic wave resulting from the interaction of the stator winding armature reaction and the field trapezoidal fluxes. Figure 6 provides air-gap flux density waveforms at two differ-
6
Generator Field Winding Shorted Turn Detector
GET 6987B
ent loads. Note the raw test data in Figure 6 has large slot voltage spikes where the air-gap flux density is high and smaller voltage where the air-gap density is low (zero crossing). Experience has
shown that at the zero crossing of the air-gap flux density, the slot leakage flux distortion factors
are minimal. This phenomenon is similar to the condition previously discussed during stator shortcircuit testing.
8 6
4
POLE Y
POLE X
4
POLE Y
POLE X
6 8
(A) Turn-short Condition
(B) No-turn-short Condition
Figure 5. Short-circuit Radial Flux Coil Waveshapes
ZERO
CROSSING
ZERO
CROSSING
.00
.00
(A)
(B)
Figure 6. Air-gap Flux Density Waveforms. (A) Zero Crossing During Open-circuit Conditions. (B) Zero Crossing During 100% Load Conditions. Note: (A) and (B) Show Movement of the Quadrature Axis, Sensitizing Different Coils At Different Load Test Points.
7
GET 6987B
Generator Field Winding Shorted Turn Detector
To obtain optimum sensitivities under load conditions, it is necessary to observe search coil waveforms at several load points. At different loads, the air-gap flux density zero crossing rotates in relationship to the rotor surface. This rotation defines the generator power angle which is a function
of the real and reactive loads. At full speed, no load, the air-gap zero crossing is at the quadrature
axis (90 degrees from the pole axis near the highest numbered coils). At full load and zero reactive
load, the zero crossings are close to the #1 and #2 slots leading the poles. At intermediate loads,
the zero crossings are at the intermediate slots (leading the poles). This machine operating feature
explains why satisfactory shorted turn sensitivities can be obtained under load conditions.
An additional benefit of a load test is that rated field current and temperatures and the associated
expansion stresses may produce turn shorts that are not experienced at low field currents. This
sensitivity enhancement is analogous to shorted turns that may exist at speed but not at standstill.
VI. ANALYSIS OF DATA
Analysis of the flux probe data has been refined over the years to handle both two- and four-pole
machines. The analysis technique provides a methodology for comparing slot characteristic data
for different poles, and utilizes a signature plot which is characteristic of the machine and its operating load condition. Although all the examples that will be used to illustrate the analysis technique
are for two-pole machines, the techniques developed have been used successfully for four-pole machines.
The typical flux probe output shown in Figure 7 is for a six-slot, two-pole machine. It can be seen
that the number of peaks corresponding to each pole is twice the number of coils per pole. Under
load conditions, only the data of coils leading the pole face provide sensitive detection information.
The peaks corresponding to the coils are appropriately labelled as shown in Figure 7. The amplitudes of each coil are normalized to the largest coil amplitude of all the poles. Using the slot/coil
numbers as a common axis, these normalized amplitudes are plotted for all the poles. This overlay
plot is called a signature plot (shown on right-hand side of Figures 8, 9, 10, etc.).
ONE PER REV
S1
S2
RATE OF
CHANGE
OF FLUX
S5 S3
S4
S6
LEGEND
POLE X
T3
T5
T1
T4
.00
T5
T6
FLUX
DENSITY
T2
T2
P
T6 T4
T1
S=Slot
T=Tooth
P=Pole Face
P
POLE Y
T3
S6
S5
S4
S3
S2
S1
Figure 7. Typical Flux Probe Signal with Labelling and Annotation
8
Generator Field Winding Shorted Turn Detector
GET 6987B
Any turn shorts will show up as deviations in the corresponding signature of a pole. If a baseline/
template signature for the machine type and load conditions is available in our database, the deviation will always be obvious. Even in the absence of baseline data, however, the signature plot provides comparisons between corresponding slots of the poles, and therefore can detect the location
and number of turns shorted.
Each slot has an optimal range of load points where it is most sensitive. The zero crossing of the
flux density signal when overlaid on the flux probe signal clearly indicates the coil with the maximum sensitivity. Thus, it is necessary to vary the load to examine different coils for shorted turns.
For example, the full-load condition sensitizes coil #1. Figure 8 presents data that demonstrate the
variation of sensitivity at different loads. At the 10% load condition, the zero crossing is near the
#6 slot and the one shorted turn (coil #7) is definitive. At the 80% load condition, the zero crossing
is close to the #3 coil and the turn short condition in the #3 coil is well defined.
Figure 9 shows shorted stator data for a two-pole machine with a short in coil #2 of the negative
pole. Figures 10, 11, and 12 indicate the wide range of turn shorts that may occur. Figure 10 shows
a machine with three turn shorts in coil #8. Vibration is unlikely in such cases when shorts are
detected in the higher numbered coils. Figure 11 is an example of a machine with approximately
20% of its total turns shorted. The shorted turns are distributed across both poles and exist in several slots.
9
GET 6987B
Generator Field Winding Shorted Turn Detector
10% load condition
1.
10% load condition
0.8
Shorted
Turn
0.6
0.4
.00
0.2
0.
1
2
POLE X
3
4
COIL NUMBER
5
6
7
POLE Y
(A)
80% load condition
80% load condition
1.
Shorted
Turn
0.8
0.6
.00
0.4
0.2
0.
1
2
POLE X
3
4
COIL NUMBER
5
(B)
Figure 8. (A) There is a Shorted Turn in Coil 7, Pole X. Also Shows Amortisseur Windings.
(B) This is the Same Machine as in 8(A), Showing Shorted Turn in #3 Coil, Pole X. Note: Turn
Short in Coil #7, Pole X has Disappeared Due to Movement of the Quadrature Axis.
10
6
7
POLE Y
Generator Field Winding Shorted Turn Detector
GET 6987B
50% sh. stator
50% sh. stator
1.
0.8
0.6
.00
0.4
0.2
0.
1
2
3
POLE X
4
5
6
COIL NUMBER
7
4
5
6
COIL NUMBER
7
8
POLE Y
Figure 9. Shorted Stator Data Showing One Turn Short in Coil
#2, Pole Y (Negative). Also Shows Amortisseur Windings
THREE
TURNS
SHORT
1.
0.8
0.6
.00
0.4
0.2
0.
AMORTISSEUR WINDINGS
1
2
3
POLE X
8
POLE Y
Figure 10. Open-circuit Load Point. There are Three Turn
Shorts in Coil #8 (3% of Winding Shorted)
11
GET 6987B
Generator Field Winding Shorted Turn Detector
1
2
3
POLE X
4
5
6
COIL NUMBER
7
POLE Y
Figure 11. Example of Shorted Stator Data with 18% to 20% Turn Shorts
MASSIVE SHORTS
IN COILS 6 AND 7
.00
Figure 12. Massive Turn Shorts in Coils #6 and #7. Example of
Turn
Shorts in Coils Other Than #1, #2, and #3 Causing Vibration
12
8
A
9
10
Generator Field Winding Shorted Turn Detector
GET 6987B
Even though most cases of vibration correspond to turn shorts in coils #1, #2, and #3, severe shorts
in the higher numbered coils can cause vibration. Figure 12 shows a two-pole machine (with seven
coils) with vibration problems due to massive shorts in coils #6 and #7 within the same pole. Presence of magnetic wedges can reduce the slot leakage flux in the air gap. An extreme case of turn
short sensitivity reduction is shown in Figure 13 where there are magnetic wedges over coils #1,
#2, #3, and #4.
Determining the course of action when shorted turns are discovered is a complicated subject depending on many factors. The following considerations are used to evaluate the alternatives:
1. Isolated shorted turns normally do not cause additional turn shorts. The turn short resistance is low and no significant heating occurs at the short.
2. If turn shorts result from end turn or slot winding distortion, a progressive increase in the
number of turn shorts can be expected.
3. Low rated generators have 200 to 400 total turns while high rated units may have only 90
to 120 turns. Thus, the effect of a shorted turn in a given coil on a high rated unit will be
greater than a similar shorted turn in a low rated unit.
4. Field electrical losses at a specific load will increase proportionally to the percentage of total
field windings shorted.
5. Manufacturers of generators typically supply excitation systems with current capability
margins that will accommodate a modest number of shorted turns.
6. Shorted turn corrective action should only be made if significant improvement in performance can be expected or if there are indications that additional turn shorts will develop,
which could cause an unplanned maintenance outage.
FOUR
MAGNETIC
WEDGES
1.
0.8
0.6
.00
0.4
0.2
0.
1
2
POLE X
3
4
5
COIL NUMBER
6
7
POLE Y
Figure 13. Data at 73% Load Showing Magnetic Wedges Over Coils #1, #2, #3, and #4
13
GET 6987B
Generator Field Winding Shorted Turn Detector
VII. DATA ACQUISITION INSTRUMENTATION
A. Brief History
The earliest sets of flux probe data were recorded on Polaroid oscilloscope photographs from
an analog oscilloscope. Peak-to-peak amplitude measurements were taken from these
photographs using a centimeter scale. Calculations and signature plots were done by hand.
Test time at each load was 15 to 40 minutes.
The digital oscilloscope and plotter were the next generation of data analysis instrumentation.
Peak-to-peak amplitude measurements were taken using the cursors on the digital oscilloscope. Calculations and signature plots were done by hand. The maximum number of test
points was limited by the oscilloscope’s memory.
B. Current Data Acquisition/Analysis System
The data acquisition/analysis system currently being used is an IBM PC-AT compatible loaded
with custom software and hardware. This system may be backed up by a digital oscilloscope,
which can also be utilized when inserting a temporary flux probe with the generator on-line.
Data acquisition and analysis have been revolutionized by the user-friendly software and hardware. Capturing data is now accomplished in seconds. The memory capabilities are unlimited,
thus allowing several machines to be tested at a single power station during the same trip. Numerical tables, waveform plots, and signature analysis data may be generated before the data
for the next load test point is acquired. The preliminary (on-site) analysis is more precise because data can be taken at any load desired.
The system software operates on all DOS-based IBM PC-AT compatible computers (running version DOS 3.0 and above). The software recognizes all graphics adapters, and can print to most
printers and HPGL plotters. The software can display the flux probe waveform in real-time and
in color. The database archives all the data with a time and date stamp. Utilities are provided
for saving the database contents onto floppy diskettes, and also for retrieving prior jobs from
secondary storage media.
The software has an option to receive and transmit data via modem. GE Mechanical Systems
Service Support maintains an on-line computer with an extensive database of all machines
tested. Any data sent by the customer is added to our database. On user request, specialists
will examine the data and provide a report and analysis.
Data reduction using the software is extremely easy. The user can interactively generate all the
information or plots desired. In order to reduce the data, the user must identify the pole face
for each pole in the flux probe signal. The rest of the measurements are then automatically generated. The software handles the presence of magnetic wedges, though the sensitivity of shorted
turn detection is affected. There are other instances when noise or interference may cause errors. In such cases, the raw data may be edited or filtered interactively.
14
Generator Field Winding Shorted Turn Detector
GET 6987B
Figure 14. Computer Data Acquisition/analysis System:
Computer, Printer, and Flux Probes
Figure 15 shows a complete load test on a two-pole machine with five coils per pole. The data
in this case was taken at load decrements of 10% as shown in Figure 15(A). Figure 15(B) shows
a composite of all the signature plots.
Figure 16 shows waveforms, signature plots, and tables generated for a typical shorted stator
test.
15
GET 6987B
Generator Field Winding Shorted Turn Detector
Full/Full (100%, Full MVARS out)
Full/Full (100%, Full MVARS out)
1.
0.8
0.6
0.4
.00
0.2
0.
1
2
Full/Zero (100%, Zero MVARS)
3
COIL NUMBER
POLE X
4
5
POLE Y
Full/Zero (100%, Zero MVARS)
1.
0.8
0.6
0.4
.00
0.2
0.
1
2
90%/Zero MVARS
3
COIL NUMBER
POLE X
4
5
POLE Y
90%/Zero MVARS
1.
0.8
0.6
0.4
.00
0.2
0.
1
2
80%/Zero MVARS
3
COIL NUMBER
POLE X
4
5
POLE Y
80%/Zero MVARS
1.
0.8
0.6
.00
0.4
0.2
0.
1
2
POLE X
3
COIL NUMBER
Figure 15(A). Typical Load Test
16
4
POLE Y
5
Generator Field Winding Shorted Turn Detector
GET 6987B
70%/Zero MVARS
70%/Zero MVARS
1.
0.8
0.6
0.4
.00
0.2
0.
1
2
60%/Zero MVARS
3
COIL NUMBER
POLE X
4
5
POLE Y
60%/Zero MVARS
1.
0.8
0.6
0.4
.00
0.2
0.
1
2
50%/Zero MVARS
3
COIL NUMBER
POLE X
4
5
POLE Y
50%/Zero MVARS
1.
0.8
0.6
0.4
.00
0.2
0.
1
2
40%/Zero MVARS
3
COIL NUMBER
POLE X
4
5
POLE Y
40%/Zero MVARS
1.
0.8
0.6
.00
0.4
0.2
0.
1
2
POLE X
3
COIL NUMBER
4
5
POLE Y
Figure 15(A). Typical Load Test (Continued)
17
GET 6987B
Generator Field Winding Shorted Turn Detector
30%/Zero MVARS
30%/Zero MVARS
1.
0.8
0.6
0.4
.00
0.2
0.
1
2
20%/Zero MVARS
3
COIL NUMBER
POLE X
4
5
POLE Y
20%/Zero MVARS
1.
0.8
0.6
0.4
.00
0.2
0.
1
2
Minimum Load
3
COIL NUMBER
POLE X
4
5
POLE Y
Minimum Load
1.
0.8
0.6
0.4
.00
0.2
0.
1
2
Open Circuit
3
COIL NUMBER
POLE X
4
5
POLE Y
Open Circuit
1.
0.8
0.6
0.4
.00
0.2
0.
1
2
POLE X
3
COIL NUMBER
Figure 15(A). Typical Load Test (Continued)
18
4
POLE Y
5
Generator Field Winding Shorted Turn Detector
GET 6987B
Pole X
Pole Y
Amplitude
A
B
C
D
Coil #
1
2
3
4
5
E
F
G
H
I
J
K
L
A:
B:
C:
D:
E:
F:
G:
H:
I:
J:
K:
L:
100%–Full
100%–Zero
190%
180%
170%
160%
150%
140%
130%
120%
1MIN LOAD
1OPEN CKT
Load #
Figure 15(B). Three-dimensional Plot for Data in Figure 15(A)
19
GET 6987B
Generator Field Winding Shorted Turn Detector
42% sh. stator
1.
0.8
0.6
.00
0.4
0.2
0.
1
2
3
POLE X
LOAD CONDITION 42% SH. STATOR
MW
4
5
COIL NUMBER
MVARS
6
7
8
POLE Y
Amps
NORMALIZED SLOT AMPLITUDE MEASUREMENTS
POLE X
LEFT SIDE
Location
Amplitude
T1-S1
0.887
T2-S2
POLE Y
RIGHT SIDE
Location
LEFT SIDE
Amplitude
Average
Location
Amplitude
S1-P
1.000
0.943
T1-S1
0.887
0.981
S2-T1
0.990
0.986
T2-S2
T3-S3
0.906
S3-T2
0.858
0.882
T4-S4
0.877
S4-T3
0.821
T5-S5
0.849
S5-T4
T6-S6
0.830
T7-S7
T8-S8
RIGHT SIDE
Location
POLE X
Average
S1-P
1.000
0.943
1.000/(0.0%)
0.877
S2-T1
0.868
0.873
1.130/(13.0%)
T3-S3
0.924
S3-T2
0.896
0.910
0.969/(–3.1%)
0.849
T4-S4
0.868
S4-T3
0.821
0.844
1.006/(0.6%)
0.811
0.830
T5-S5
0.849
S5-T4
0.811
0.830
1.000/(0.0%)
S6-T5
0.802
0.816
T6-S6
0.840
S6-T5
0.802
0.821
0.994/(–0.6%)
0.830
S7-T6
0.811
0.821
T7-S7
0.840
S7-T6
0.811
0.825
0.994/(–0.6%)
0.821
S8-T7
0.821
0.821
T8-S8
0.821
S8-T7
0.830
0.825
0.994/(–0.6%)
Figure 16(A). Shorted Stator Data with Corresponding Signature Plot and
Slot Amplitude Table for 42% Load Condition. Note: There is One Turn
Short on the #2 Coil, Pole Y. (Continued on next page.)
20
POLE Y
Amplitude
Generator Field Winding Shorted Turn Detector
GET 6987B
50% sh. stator
1.
0.8
0.6
.00
0.4
0.2
0.
1
2
3
POLE X
LOAD CONDITION 50% SH. STATOR
MW
4
5
COIL NUMBER
MVARS
6
7
8
POLE Y
Amps
NORMALIZED SLOT AMPLITUDE MEASUREMENTS
POLE X
LEFT SIDE
Location
Amplitude
T1-S1
0.888
T2-S2
POLE Y
RIGHT SIDE
Location
LEFT SIDE
Amplitude
Average
Location
Amplitude
S1-P
1.000
0.944
T1-S1
0.879
0.981
S2-T1
1.000
0.991
T2-S2
T3-S3
0.907
S3-T2
0.850
0.879
T4-S4
0.869
S4-T3
0.822
T5-S5
0.850
S5-T4
T6-S6
0.841
T7-S7
T8-S8
RIGHT SIDE
Location
POLE X
POLE Y
Amplitude
Average
S1-P
0.991
0.935
1.010/(1.0%)
0.879
S2-T1
0.869
0.874
1.134/(13.4%)
T3-S3
0.925
S3-T2
0.897
0.911
0.964/(–3.6%)
0.846
T4-S4
0.879
S4-T3
0.832
0.855
0.989/(–1.1%)
0.813
0.832
T5-S5
0.860
S5-T4
0.813
0.837
0.994/(–0.6%)
S6-T5
0.804
0.822
T6-S6
0.832
S6-T5
0.804
0.818
1.006/(0.6%)
0.832
S7-T6
0.813
0.822
T7-S7
0.841
S7-T6
0.813
0.827
0.994/(–0.6%)
0.822
S8-T7
0.822
0.822
T8-S8
0.822
S8-T7
0.822
0.822
1.000/(0.0%)
Figure 16(B). (Continued from Previous Page.) Shorted Stator Data With
Corresponding Signature Plot and Slot Amplitude Table for 50% Load
Condition. Note: There is One Turn Short on the #2 Coil, Pole Y.
21
For more information and quotations contact your local GE Power Generation Services office.
Or Contact:
GE Installation & Service Engineering
James A. Williams, (518) 385-0128
Gregory J. Goodrich, (518) 385-0118
Mechanical Systems Service Support
Building 55, Room 253
Schenectady, N.Y. 12345
When a permanent probe is purchased from GE, a contract describing limited liability will be agreed to with
the customer.
GE Installation and
Service Engineering
General Electric Company
One River Road, Schenectady, NY 12345
518 • 385 • 2211 TX: 145354