Doble-2000 RTD Paper

8/12/2019 Doble-2000 RTD Paper

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67th Annual International Conference of Doble Clients, March 27-31, 2000, Watertown, MA

Page 1 of 7

RTD as a Valuable Tool in Partial Discharge Measurementson Rotating Machines

Z. Berler, I. Blokhintsev, A. Golubev, G. Paoletti, A. Romashkov

Cutler Hammer Predictive Diagnostics

Abstract : This paper presents the authors’ practical experience

in the on-line measurement of partial discharges in medium

voltage motor and generator stator windings using the RTD as a

partial discharge detector. Results of off-line calibration on

several machines are also presented.

IntroductionOn-line measurement of partial discharges (PD) has proved to be an

effective tool in evaluating the condition of stator insulation in high

and medium voltage electric motors and generators [1]. This method

is widely used in addition to the traditional off-line insulation tests

performed during scheduled outages.

Most of PD technologies available now on the market for on-linemeasurements function within the radio-frequency band of PD

signals. Such technologies have the common problem resulting from

very rapid attenuation of the high frequency signal as it travels

through the winding. Therefore, sensors commonly installed at

winding terminals have a limited zone of sensitivity and provide

valuable information for that zone only [4]. The evident solution to

this problem is the use of PD sensors imbedded into the winding to

get information on the winding itself. Some of the PD technology

vendors suggest installing specially designed sensors into a winding,

but this approach is relatively expensive and requires an extensive

machine outage and invasion into the winding assembly.

Alternatively, most of the HV machines already have RTD detectors

embedded into the winding by the manufacturer and these detectorscan be used for partial discharge measurements [2,4]. Cutler-

Hammer has over two years of experience using RTDs as PD

detectors. The special PD transducer (RFVS) was designed for

connection to the RTD wire at the RTD terminal block located on

the frame of the motor or generator. The transducer does not disturb

temperature measurements and only passes high frequency PD

signals to the PD instrument. Over 300 machines, primarily HV

motors, were tested during the past two years with good results.

RTDs were used for both the initial survey/evaluation and for on-

going periodic measurements and data trending.

RTDs are currently very effective in trending of machine PD activity

when used with an analyzer that can effectively reject noise and

process PD data. With sensor calibration the use of RTDs can be

further applied to allow comparisons between different machines.The issue of sensor calibration requires further evaluation to help

advance the technology and use of RTDs in determining the

machine’s insulation condition. Several machines have been

calibrated, but more field data is necessary for the establishment of

good quantitative data. This paper proposes a calibration procedure

and presents the results of off-line calibration

on several machines. The problems and the vision of future

improvements are also discussed.

Why do We Need the RTD as a PD Detector?The traditional approach for PD detection in rotating machines uses

sensors installed near machine line terminals. What is the value of

data obtained from such sensors and what additional information is

required to reliably assess winding insulation condition? Based on

our experience, PD sensors located near machine line terminals

provide valuable information for line terminals and, possibly, for a

ring bus, but not for the winding.

The example below presents the data obtained on-line from a

37,000kVA, 13.8kV generator and confirms this statement. The

generator has an 80pF coupling capacitor installed on each line

terminal and also 12 RTDs evenly distributed around thecircumference of the stator core. Six RTDs are placed on the exciter

and six on the turbine ends of the machine. Figure 1 presents three

sets of oscillograms taken from 80 pF coupling capacitor (Plot #1)

and from RTD#1 (Plot #2) and RTD#7 (Plot #3). All of them are on

the same phase “A”. RTDs are also located in the same slot on the

exciter and turbine ends respectively. The oscilloscope was triggered

from the PD pulse originating near the line terminals on phase A

and also from the pulse originating near each of the two RTDs. One

can see that the coupling capacitor provides no response to the PD

originating in the winding on either side of the generator. The

opposite is true as well. The attenuation of PD signal along the slot

is also very high and exceeds 10 times. Therefore, for a complete

analysis, it is necessary to install additional sensors into a winding

or to use RTDs to get information about the winding condition.

1 >1 >1 >1 >

2 >2 >2 >2 >

3 >3 >3 >3 >

1) CC_ A: 40 mVolt 200 ns2) RTD01: 40 mVolt 200 ns3) RTD07: 40 mVolt 200 ns

Triggering from lin e terminal PD.

1 >1 >1 >1 >

2 >2 >2 >2 >

3 >3 >3 >3 >


Tri ggeri ng fr om slot PD on the exciter

end.

1 >1 >1 >1 >

2 >2 >2 >2 >

3 >3 >3 >3 >


Triggering from winding PD on the

turbi ne end.




Page 2 of 7

Figure 1. PD pulse attenuation in a winding

The effects of signal attenuation discussed above may cause

mistakes in evaluating stator winding insulation condition, if sensors

located at machine line terminals were the only ones used for

assessment. The example below at figure 2 presents PD test results

of three 13.8kV motors of a similar design at the same facility. All

describing motors have permanent RFCT sensors placed on surge

capacitor grounding conductors. The test was also provided withtemporal PD sensors connected to RTD terminals. Figure 2 (top)

shows maximum PD magnitudes recorded from RFCT sensors.

Based on these results, we can conclude that the motor1 is in a good

state and the motors 2 and 3 have moderate level of discharges. The

data from three RTD’s showed highest reading for each motor are

shown on figure 2 (bottom). Conclusions, based on this data, are the

same as above for the motors 2 and 3. But the conclusion is different

for the motor 1. It has high level of PD at the zone of RTD01 and is

the first candidate for additional testing and internal inspection.

RFCT Sensors

Motor1 Motor2 Motor3

RTD Sensors

Motor1 Motor2 Motor3

Figure 2. PD maximum magnitude by RFCT’s and RTD’s.

Why do We Need Calibration?The real need to calibrate or normalize a PD measuring circuit on a

rotating machine exists today. As the science of Partial Discharge

measurement was making its first steps, it was agreed that

calibration on rotating machine is a very difficult procedure.

Therefore, it was decided to utilize the Partial Discharge Magnitude

parameter measured in millivolts or Volts [1]. Based on that, the

only valid procedure of using PD data is through relative

comparison of PD data collected using the same vendor’s

technology over time on the same machine or between similar

machines. This situation was bearable while the number of PD

technology users was relatively small and most of sensors’

installation, data collection and interpretation were provided by a

qualified expert.

Now the situation is different. As PD technology is maturing, real-

life cases reveal the need for a standardized PD measuring circuit

calibration procedure. For instance, paper [3] reported a 19,000HP

motor failure just because the 80pF couplers were installed about

4m away from the motor line terminals. That caused signal

attenuation by a factor of 5 and resulted in misinterpretation of the

PD data. As a result the authors of [3] have now normalized all

their PD sensors with pulse generator and oscilloscope and are now

using normalized data for relative comparison between monitored

motors. This is an example of how uncalibrated sensors defeated

the original predictive expectations of the on-line PD sensors.

The reason of such a difference can be easily understood from

simplified diagram below showing typical sensors connection in a

motor terminal box. PD in a winding or near line terminals

produces small surge traveling to the feeder. In general, pulse

current induced by PD, which is really detecting by PD measuring

instrument, is split into several branches. Part of the current goes

through 80pF coupling capacitor, part of the current goes throughsurge capacitor circuit and the rest of it goes through the feeder.

The current distribution through described branches and part of PD

signal detected by any particular PD sensor depends upon

impedance of each branch including inductance of every used wire.

Therefore, the presence or absence of any element in this diagram

and their wiring, how many cables is used per phase and a surge

impedance of the single cables and many more reasons - all this will

affect PD reading from sensors.

Surge

Impedanceof Cable

5-30 Ohms 50 Ohm

Impedance

80 pF

Capacitor

Surge

Capacitor 500,000pF

RFCTRFCT

Winding

PD

Feeder

Figure 3. Sensors layout in motor terminal box

Authors, who are using universal PD analyzer, which is able to read

PD data from PD sensors installed by different PD technology

vendors, face the problem described above on everyday basis. The

example presented below on figure 4 compares PD magnitudes from

80pF couplers and RFCT’s placed on surge capacitor grounding

conductor measured on-line on 13.8 kV motor at the same time.

Both sensors were of the same manufacturer. The first three bars

present data obtained from 80pF coupling capacitors on the phases

A, B and C and three last bars are related to data obtained fron

RFCT’s. One can see two times difference in signal magnitudes.

Where is the truth?

Figure 4. PD magnitude from two different types of sensors on

13.8kV motor

1The table below summarizes our experience with different sensors,

we have used in both off-line and on-line PD tests on mediumvoltage motors. The better numbers, as a rule, can be reached at off-

line test, when all auxiliary equipment can be disconnected. In any

case, the variations in sensitivity even for the same sensor can be

very significant and confirm the necessity of a calibration.

1 The table does not cover all possible variations in measuring

circuits and sensor layouts and can be somewhat different for

PD instruments using different frequency band.




Page 3 of 7

Table 1Sensor Type Sensitivity

Range [V/nC]

Comments

Capacitor

(1nF loaded

50Ohm)

2.0 – 0.5 Depends upon surge impedance of

auxiliary devices and feeder or bus.

Capacitor

(80pF loaded50Ohm)

1.0 – 0.2 Same as above and inductance of

measuring circuit.

RFCT(5 Ohm)

on surge capacitor

ground

0.3 – 0.1 Depends upon surge impedance of

auxiliary devices and feeder or bus.

RFCT(12.5 Ohm)

on surge capacitor

ground

0.8 – 0.2 Same as above.

RTD 0.3 – 0.05 Depends upon machine design and

less upon leads length.

Another issue that further promotes the need for sensor

normalization, or calibration, is the increasing flow of practical datacollected by different vendors. For instance, the author of [5]

reported the analysis of over 13,000 test samples. This data is not

very useful for other users since normalization to conventional

measurement units was not done. The above clearly indicates the

need to establish a field calibration procedure to allow for the future

advancement of the benefits of the varying PD technologies

available today. Without such flexibility, the end user is limited to

possibly outdated technology, and will not be able to benefit from

advancements in the future.

Calibration Procedure and UnitsThe approach described below is offered as a possible and useful

solution to the development of an acceptable field calibration

procedure for various PD sensors.

It is well known that the partial discharge transient wave, which is

detected by a PD sensor, experiences very high attenuation and

shape modification while travelling through the stator winding. This

causes a difference in the response of a sensor to a signal originating

in different points in the winding and therefore, becomes the main

problem complicating sensor calibration. The ideal solution is in

calibration of every sensor to all possible PD locations. This

approach is impractical due to the extreme complexity and unknown

PD source location during on-line testing. Two terms are proposed

to establish a uniform calibration standard, and provide a basis for

consistent calibration between various PD sensors and sensing

technologies.

Sensiti vity to PD at Sensor Location (Sensitivi ty) - we can calibrate

a sensor by injecting a known charge close to a sensor and

determining its sensitivity in terms of nC/Volt. Such sensitivity

applies primarily for partial discharges originating close to a sensor.

Signal attenuation is not taken into consideration in this factor. On

the other hand, attenuation is a very important factor for PD signals

distant to a sensor. Therefore, if sensitivity defined as it is described

above is used, data obtained on-line from a sensor in terms of nano-

Coulombs presents the lower limit estimation of an apparent charge

for discharges originating close to a sensor. In other words, a

discharge value can be greater for PD near the sensor, but it can not

be less. In spite of the approximate character of this approach, it is

still more accurate than millivolts alone. It creates the opportunity to

compare data taken from different sensors, taken from different

machines and even for machines of different rated voltages. All of

the above is true, to the same extent of approximation, for all

quantities which can be derived from “raw” PD data. These

quantities could be PD power or PD current and so on. Thequestion left without an answer is the applicability of such

approximation or, in other words where is the limit, beyond which a

comparison looses any practical sense? The answer to this question

is in the term described below and called the “Zone of Sensor

Sensitivity”.

Zone of Sensor Sensit ivi ty - This term is more qualitative than

quantitative. It limits the boundaries of a spatial zone that can be

assessed using a particular sensor. We use 20dB attenuation of a

signal as the criterion to determine the border of the Zone of Sensor

Sensitivity. One can not evaluate PD data reliably beyond that zone

of a particular sensor. From the example given above, we can

evaluate the line terminal insulation condition based on the 80 pF

capacitor readings, but we can not seriously discuss the winding

condition due to the inability of the line terminal PD sensors to

detect winding related PD signals. Any conclusions beyond the

Zone of Sensor Sensitivity would be just a guess based on previous

experience on similar machines with similar operating conditions,

but not on the real data. The knowledge obtained based on the Zone

of Sensor Sensitivity, for various PD sensor technologies, allows for

better planning concerning the number and location of sensors for a

particular application and provides a check on the reliability of the

information obtained. The Zone of Sensor Sensitivity can be

determined during off-line calibration.

We calibrate the PD measuring circuit in terms of apparent charge

using the procedure similar to that described in ASTM D1868 or

IEC 270 Standards. Therefore, we inject a known charge through a

differentiating (dosing) capacitor into a known point and record theresponse of all sensors in Volts. Consequently, sensitivity of a

sensor in terms of nano-Coulomb per Volt for a particular injection

point can be calculated. Zone of Sensor Sensitivity can also be

determined. Figure 5 presents the example of the calibrating circuit

for a radio frequency current transformer placed on the surge

capacitor-grounding conductor on a motor. The same circuit is used

to calibrate any type of PD sensor. Aluminum foil is wrapped

around the accessible part of the winding or the bus bar near the

calibrated sensor. The foil capacitance to the HV conductor is

commonly in the order of several hundreds to one thousand of pico-

Farads. This exceeds the capacitance of the dosing capacitor by

about 10 times. This capacitance is connected in series with the

dosing capacitor. As a consequence, the dosing capacitor limits the

injected charge. Therefore, an injected charge can be calculated as

the product of pulse magnitude and the dosing capacitance. A small

RFCT is additionally inserted into the charge injecting circuit and

measures injected current. This is an additional method to obtain an

injected charge. An injected charge is calculated as the area under

the oscillogram of the injected current. The first peak of the

oscillogram is used for injected charge calculation. In all cases, we

have had within 20% agreement between the injected charges

measured in both ways. This proves that either of the two methods

can be used.




Page 4 of 7

Response from all available sensors is measured for every point of

pulse injection. Therefore, cross-coupling coefficients between

different sensors can additionally be determined while obtaining the

sensitivity of any particular sensor. In order to detect the Zone of

Sensor Sensitivity, a pulse is injected into different points distant

from a calibrated sensor and a distance resulting in 20dB attenuation

is determined. Figures 6 “a” and “b” show photographs of the in-

field calibration on a 800MW 2-pole generator.

Figure 5. Calibration Circuit.

Figure 6a. Pulse Injection into the Endwinding Area.

Figure 6b. Pulse Injection into Line Terminals Area.

Sample Calibration ResultsThe results of calibration on small generator and two HV motors are

presented below.

12.5 MW, 13.8 kV Generator

This 42-slot generator is equipped with 12 RTDs distributed evenly

around the circumference of the stator core. Two RTDs are placed in

a slot, one on the exciter and another on the turbine end. RTDs 1-6

are placed on the exciter end and RTDs 7-12 are placed on the

turbine one. Therefore, 6 slots are equipped with a RTD. The

distance between the two nearest slots containing a RTD is 6 slots.

Fourteen signals were recorded simultaneously for every injection

point

• 12 RTDs were connected to the instrument through our

specially designed RFVS sensors and PD analyzer’s signal

conditioning module;

• T1 line terminal was connected to the instrument through a

1,000pF, 20kV coupling capacitor sensor and our PD

analyzer’s signal conditioning module;

• RFCT measuring injected current was loaded with 50 Ohms at

the oscilloscope end.

Figure 7 shows the RTD response in terms of Volts per nano-

Coulomb for pulse injection into four different points. Three of them

are related to slots containing RTDs and one to the Slot 22, which is

between RTD9 and RTD10. The other two related to RTDs were

placed in the Slot 18, which is at RTD # 10, and Slot 25, which is at

RTD # 9. All three RTDs showed approximately the same

sensitivity. The response drops by about 10 times if the pulse is

injected 3 slots away from the RTD. The attenuation of a signal

along a slot is about 5 times.

Figure 8 presents the coupling capacitor response to a PD injection

into different slots on both the exciter and the turbine ends. The

response drops very rapidly while moving the injection point away

from the line Slot 18. At the same time, this sensor is insensitive toany pulse injected at the turbine end.

Both Figures 7 and 8 indicate that a different level of criteria is

required for evaluation of PD located internal to the winding versus

at the line terminals. To detect PD near a winding RTD, using the

RTD as the PD sensor, a sensitivity of ~ 0.06V/nC would be applied

whereas PD occurring at the line terminals is detected with a

sensitivity of ~ 1V/nC. Using only a line-terminal PD sensor would

mask the low level of internal PD, which is detectable using the

RTD. For example, equal partial discharges at the line terminals

versus internal to the winding near an RTD would yield a

measurement of 1 volt for the PD at the line terminal and less than

0.1V for the same magnitude of PD internal to the winding. Such a

wide range of voltage measurements, at the line terminal, makes it

almost impossible to detect partial discharges internal to the winding

using only line-terminal PD sensors. With separate measurementsobtained using RTD’s, these internal partial discharges can now be

detected using the sensitivity of ~ 06V/nC; therefore a measurement

of 0.1 Volts at the RTD can be properly evaluated without the

masking of higher voltage measurements associated with having

only the line terminal type of PD sensor.

RFCT and Dosing

Capacitor

Aluminum FoilAluminum Foil




Page 5 of 7

Sensors Response to Injected Charge

0

0.02

0.04

0.06

0.08

0.1

0.12

RTD1 RTD2 RTD3 RTD4 RTD5 RTD6 RTD7 RTD8 RTD9 RTD10 RTD11 RTD12

Sensor Name

S e

n s i t i v i t y [ V / n C l ]

Sl18 RTD10_Tr Sl22_Tr Sl25 RTD9_Tr Sl32 RTD8_Tr

Figure 7. RTD Response to Injected Pulse

Coupling Capacitor Response to Injected Charge

0

0.5

1

1.5

2

2.5

T1 Line Sl18 Sl20 Sl25 Sl29 Sl32 Sl18 Sl22 Sl25 Sl32

Injection Point

S e n s i t i v i t y [ V / n C ]

Figure 8. Coupling Capacitor Response to Injected Pulse.

7550 HP 13.2 kV Synchronous Motor

The motor has 72 slots and is equipped with 12 RTDs placed at the

ring bus side of a slot. RTDs are distributed evenly along the

winding, every six slots. The sensitivity of different RTDs variesfrom 0.05V/nC to 0.07V/nC with an average value of 0.06V/nC.

RTDs located at a greater distance from the RTD terminals showed

sligthly less sensitivity, possibly related to the RTD wire routing..

The signal attenuation from the opposite end was very stable for all

RTDs and varies from 4.5 to 5.3 times.

8000 HP 13.2 kV I nduction M otor

This 4 pole motor has 96 slots and is equipped with 12 RTDs. Two

RTDs are located in the same slot approximately in the center of the

core. Six slots in total are equipped with RTDs. Wires from both

RTDs placed in the same slot come out of the slot in opposite

directions. This motor has a large diameter and a relatively short

core of about 1.5 m. In spite of the short core and approximately

centrally located RTD, they show 6 – 7 times better response to pulses injected from the side of the RTD wires.. A wire works as a

RF antenna as well and therefore the effective length of antenna is

greater for a pulse injected from a RTD wire side of the core. The

motor also showed moderate scatter in RTD sensitivity for different

RTDs. It varies from 0.2 to 0.28 Volt per nano-Coulomb, which is

about +15 to 20%. RTDs located closer to the RTD terminals at the

motor showed higher sensitivity. Higher signal attenuation as a

result of longer wires is the most probable reason for the observed

scatter. The effect of signal attenuation from the RTD to the RTD

terminals is most significant for RTD wires protected by a spiral

steel shield. Sensitivity for such RTDs is commonly in the range

from 0.015 to 0.02 Volt per nano-Coulomb.

The above results of RTD calibration confirm that RTDs can be

used as PD detectors in PD technologies based on high frequency

pulse recording.

The difference in sensitivity between different machines may behigh, therefore, a calibration is recommended for quantitative

comparison between different machines or between sensors of

different design. Note that relative comparison over time or between

machines of the same design is not a problem without any

calibration. Several examples of PD tests using RTDs presented

below also confirm that RTDs are a very valuable tool in PD

technology.

Off-line Test

This off-line test was performed on a 12.5MW, 13.8 kV generator

described above. Test voltage of 8 kV (phase to ground rated

voltage) was applied to one phase at a time. The other two phaseswere grounded. PD data was collected in the form of traditional

phase-resolved PD distribution with phase resolution of 2 degrees

and magnitude resolution of 0.5dB by Cutler-Hammer “Twins” PD

analyzer [6]. The sensitivities obtained from the calibration for

RTD’s and the 1,000pF coupling capacitor were used when

processing PD data. The flat projection of the Phase-Resolved PD

Distribution (PRPDD) on the phase-magnitude plane (top view)

obtained during “B” phase test is presented on Figure 9.

Figure 10 shows integral quantities calculated for data taken from all

of the PD sensors in three subsequent tests. In spite of significant

difference in signal magnitude (in terms of millivolts) obtained from

sensors of different types (Fig. 9), one can see the reasonable scatter

in integral quantities calculated from the coupling capacitor and

RTD data using the sensitivity of the sensor.

Figure 9. Phase B PD data.

Exciter End Turbine End




Page 6 of 7

Phase 1 Phase 2 Phase 3

Figure 10. Charts show PD Intensity, Maximum Apparent

Charge and Pulse Repetition Rate Respectively.(All Calculated from PD data above 0.1 nC.)

On-line Test

This on-line test was performed on a 7500 HP 13.8 kV motor. Themotor is equipped with three permanent radio-frequency current

transformers (RFCT) placed on the surge capacitor grounding

conductor in the motor terminal box and with 6 RTDs embedded

into the winding. RTD 1 & 4, RTD 2 & 5 and RTD 3 & 6 are

installed on the phases A, B and C respectively. RFVS sensors were

used to obtain temporary connections to RTD terminals in the RTD

connection box on the motor frame.

The flat projection of PRPDD from all available sensors is presented

on Figure 11, and maximum apparent charge is on Figure 12. It is

very important to mention that data presented for each sensor is

unique for a particular sensor. Any possible crosscoupling from

sensor to sensor was rejected by the “Twins” analyzer. As one can

see, both magnitudes from the RFCT and RTD are in approximately

Figure 11. Phase-Resolved PD data.

the same magnitude range and C-phase showed higher PD activity at

the line terminals as well as inside the winding. This is evident by

correlating the Maximum Apparent Charge for Phase C, shown in

Figure 12, with the higher Maximum Apparent Charges also shown

for RTD #3 and #6, both of which are installed at Phase C. This is

also visually evident by reviewing the PRPDD of Figure 11 below.

Phase C (CC_C) indicates more PD activity, and this is also evident

for RTD 3 and RTD 6 below.

Figure 12. Maximum Apparent Charge.

Conclusions

1. The attenuation of high frequency signals in rotating machine

windings is the main factor which complicates PD

measurements on such equipment. Sensors commonly placed

near machine line terminals are insensitive, as a rule, to distantPD originated internal to the machine winding. Additional

sensors placed in the winding are required to reliably detect

partial discharges. Resistive Temperature Detectors (RTDs)

already placed in a winding by the machine manufacturer can

be used as high frequency antennas to collect partial discharge

pulses from the depth of the winding. The use of RTDs allows

PD data to be obtained without an outage to install invasive

sensors into winding slots.

2. RTDs commonly have good sensitivity to PD originating

nearby. Therefore, if used complimentary to conventional PD

detectors, these provide better information on partial discharges

in the entire stator winding and yield a more reliable winding

insulation assessment.

3. Calibration is recommended to scale PD data taken from RTDs,

and other types of PD sensors, of different machines, to the

same base. This calibration correlates the characteristics of the

various PD sensors which may have different characteristics for

high frequency applications. Such calibration would also

correlate different responses from similar RTD’s, or other PD

sensors, to the same discharge on machines of different

designs. Note that relative comparison over time or between

machines of the same design is not a problem without any

calibration. In this case, the use of RTD’s can be trended,

similar to sensors which would require an outage for invasive

installation.

4. The calibration procedure was designed with the aim to scalesensors of different design to the same basis. Two terms

“Sensiti vity to PD at Sensor location” and “Zone of Sensor

Sensitivity ” is suggested to perform sensor calibration in terms

of apparent charge.

5. Over two years of practical experience confirms that RTDs can

be used as a very valuable tool for on-line and off-line PD

measurements on a rotating machine (with an adequate PD

analyzer that can process data and efficiently reject all types of




Page 7 of 7

noise). The key advantage is that the use of PD predictive

technologies can be easily implemented with existing RTDs.

References

1. Draft of the IEEE P1434 “Guide to Measurement of Partial

Discharges in Rotating Machinery, 1998.

2. K. Itoh, Y. Kaneda, S. Kitamura et al. “New Noise RejectionTechnique on Pulse-by-Pulse Basis for On-Line Partial

Discharge Measurements of Turbine Generators”, IEEE PES

Paper # 96WM 154-5-EC

3. Osman M. Nassar, Thani S. Al-Anizi. “Saudi Aramoco

experience with partial discharge on-line motor monitoring

equipment”, IRIS Rotating Machine Technical Conference,

March 10-13, 1998, Dallas, TX USA.

4. I. Blokhintsev, M. Golovkov, A. Golubev, C. Kane “Field

Experiences on the Measurement of Partial Discharges on

Rotating Equipment”, IEEE PES’98, February 1-5, Tampa, FL

5. V. Warren “On-Line Partial Discharge Monitoring: Where do

We Stand and What Next?” EPRI Utility Generator and

Predictive Maintenance & Refurbishment Conference,

December 1-3, 1998, Phoenix, Arizona.

6. Z. Berler, A. Golubev, A. Romashkov, I. Blokhintsev “A New

Method of Partial Discharge Measurements”, CEIDP-98

Conference, Atlanta, GA, October 25-28, 1998.

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