IEEE Recommended Practice for Partial

STANDARDS
Discharge Measurement in Liquid-Filled
Power Transformers and Shunt Reactors

IEEE Power and Energy Society

Developed by the
Transformers Committee

IEEE Std C57.113™-2023

(Revision of IEEE Std C57.113-2010)

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 IEEE Std C57.113™-2023
(Revision of IEEE Std C57.113-2010)

IEEE Recommended Practice for Partial

Discharge Measurement in Liquid-Filled
Power Transformers and Shunt Reactors

Developed by the

Transformers Committee
of the
IEEE Power and Energy Society

Approved 8 November 2023

IEEE SA Standards Board

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 Abstract: Wideband measurement of the apparent charge of partial discharges (PDs) that may
occur in liquid-filled power transformers and shunt reactors excited by ac test voltages between
40 Hz and 400 Hz are discussed in this recommended practice. The major components of the PD
measuring circuit, including the calibrator are specified in compliance with IEC 60270. The PD test
procedure is described and recommendations for the evaluation of PD test results are presented.

Keywords: apparent charge, IEEE C57.113™, partial discharge, PD, power transformer, shunt
reactor, wideband PD measurement

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 Participants

At the time this draft recommended practice was completed, the Dielectric Test on PD Measurement Working
Group had the following membership:

Ali Naderian Jahromi, Chair

Janusz Szczechowski, Vice Chair

Tauhid Haque Ansari Fernando Leal Hemchandra Shertukde

Dominique Bollinger Harry Pepe Dervis Tekin
Detlev Gross Amitabh Sarkar Ajith Varghese
David Larochelle Dan Schwartz Alexander Winter

The following members of the individual Standards Association balloting group voted on this recommended
practice. Balloters may have voted for approval, disapproval, or abstention.

Stephen Antosz Richard Jackson Poorvi Patel

Donald Ayers John John Howard Penrose
Robert Ballard Jimmy Johns Harry Pepe
Peter Balma Laszlo Kadar Charles Pestell
Thomas Barnes Gael Kennedy Sylvain Plante
Barry Beaster Zan Kiparizoski Alvaro Portillo
Wallace Binder Boris Kogan Bertrand Poulin
Thomas Blackburn Mathieu Lachance Tom Prevost
William Boettger Mikhail Lagoda Ion Radu
Jeremiah Bradshaw Chung-Yiu Lam Scott Reed
Jeffrey Britton Benjamin Lanz Johannes Rickmann
Paul Cardinal David Larochelle Oleg Roizman
Ritwik Chowdhury William Larzelere Zoltan Roman
John Crouse Moonhee Lee Rodrigo Ronchi
Kurniawan Diharja Wang Lei Ryandi Ryandi
Huan Dinh Aleksandr Levin Mahesh Sampat
Hakim Dulac Thomas Lundquist Daniel Sauer
Evgenii Ermakov Greg Luri Roderick Sauls
Jorge Fernandez Daher Balakrishnan Mani Bartien Sayogo
Namal Fernando Kumar Mani Hyeong Sim
Bruce Forsyth Richard Marek Jerry Smith
Carl Fredericks J. Dennis Marlow Bradley Staley
George Frimpong James McBride Juan Thierry
Eduardo Garcia Mark McNally Eduardo Tolcachir
Shubhanker Garg Ross McTaggart Mark Tostrud
William Griesacker Daleep Mohla James Van De Ligt
Detlev Gross Daniel Mulkey Jason Varnell
Niklas Gustavsson Ali Naderian Jahromi John Vergis
Randy Hamilton Jeffrey Nelson David Wallach
John Harley Joe Nims Joe Watson
Roger Hayes Lorraine Padden Drew Welton
Sergio Hernandez Bansi Patel Ying Zhang
Thang Hochanh Dhiru Patel Peter Zhao
Werner Hoelzl Igor Ziger

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 When the IEEE SA Standards Board approved this recommended practice on 8 November 2023, it had the
following membership:

David J. Law, Chair

Ted Burse, Vice Chair
Gary Hoffman, Past Chair
Konstantinos Karachalios, Secretary

Sara R. Biyabani Joseph S. Levy Paul Nikolich

Doug Edwards Howard Li Annette D. Reilly
Ramy Ahmed Fathy Johnny Daozhuang Lin Robby Robson
Guido R. Hiertz Gui Lin Lei Wang
Yousef Kimiagar Xiaohui Liu F. Keith Waters
Joseph L. Koepfinger* Kevin W. Lu Karl Weber
Thomas Koshy Daleep C. Mohla Philip B. Winston
John D. Kulick Andrew Myles Don Wright

*Member Emeritus

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 Introduction

This introduction is not part of IEEE Std C57.113–2023, IEEE Recommended Practice for Partial Discharge
Measurement in Liquid-Filled Power Transformers and Shunt Reactors.

The detection of partial discharges (PDs) was introduced for quality assurance tests of high-voltage (HV)
apparatus at the beginning of 1960. Originally this technique was based on the measurement of radio
interference voltages (RIV) in terms of microvolts (µV) as recommended by NEMA TR1–2000 [B114],
NEMA 107-1971[B115], and CISPR 16-1-1993 [B42]. This quantity, however, is weighted according to the
acoustical noise impression of the human ear, which is not a measure of the PD activity in the insulation of
HV apparatus. Therefore, Technical Committee No. 42 of IEC decided to prepare a separate standard for
PD measurements associated with the apparent charge, which was first published in 1968. Since that time,
this technology has been considered as an indispensable tool for the enhancement of the reliability of HV
apparatus. IEEE Std C57.113–2023 covers the wideband method for apparent charge measurements in
compliance with IEC 60270-2015.

This revision of IEEE Std C57.113–2010 is a general update of this standard to reflect the current state of
the art and has been revised to meet current IEEE Styles. Further, the old Annex on Noise identification was
deleted; Annex A and Annex B were revised and updated; and Annex F on pattern recognition was substantially
revised.

Acknowledgments

Grateful acknowledgment is made to Detlev Gross for permission to reprint Figure A.1 through
Figure A.5 from “Acquisition and location of partial discharge—esp in transformers” PhD. Thesis, TU Graz,
Austria, © 2016.

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 Contents

1. Overview��������������������������������������������������������������������������������������������������������������������������������������������������� 11
1.1 Scope�������������������������������������������������������������������������������������������������������������������������������������������������� 11
1.2 Purpose����������������������������������������������������������������������������������������������������������������������������������������������� 11
1.3 Word usage����������������������������������������������������������������������������������������������������������������������������������������� 11

2. Normative references�������������������������������������������������������������������������������������������������������������������������������� 12

3. Definitions������������������������������������������������������������������������������������������������������������������������������������������������� 12

4. Specification of PD measuring circuits������������������������������������������������������������������������������������������������������ 13

4.1 General����������������������������������������������������������������������������������������������������������������������������������������������� 13
4.2 Coupling capacitor����������������������������������������������������������������������������������������������������������������������������� 14
4.3 Measuring impedance������������������������������������������������������������������������������������������������������������������������ 15
4.4 PD measuring instrument������������������������������������������������������������������������������������������������������������������� 15
4.5 PD calibrator�������������������������������������������������������������������������������������������������������������������������������������� 17
4.6 Maintaining the specified parameters of PD measuring circuits��������������������������������������������������������� 18

5. PD test procedure�������������������������������������������������������������������������������������������������������������������������������������� 18
5.1 Calibration������������������������������������������������������������������������������������������������������������������������������������������ 18
5.2 PD measurement�������������������������������������������������������������������������������������������������������������������������������� 19

Annex A (informative) Coupling�������������������������������������������������������������������������������������������������������������������� 21

Annex B (informative) Response of PD measuring instruments�������������������������������������������������������������������� 26

Annex C (informative) Calibration of PD measuring circuits������������������������������������������������������������������������ 28

Annex D (informative) Basic sensitivity check���������������������������������������������������������������������������������������������� 29

Annex E (informative) Bushing tap ratio measurement��������������������������������������������������������������������������������� 30

Annex F (informative) PD pattern recognition����������������������������������������������������������������������������������������������� 31

Annex G (informative) Bibliography������������������������������������������������������������������������������������������������������������� 33

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 IEEE Recommended Practice for Partial
Discharge Measurement in Liquid-Filled
Power Transformers and Shunt Reactors

1. Overview
1.1 Scope
This recommended practice describes the test procedure for the detection and measurement by the wideband
apparent charge method of partial discharges (PDs) occurring in liquid-filled power transformers and shunt
reactors during dielectric tests, where applicable.

1.2 Purpose
PD measurements in transformers and shunt reactors should preferably be made on the basis of measurement
of the apparent charge. Relevant measuring systems are classified as narrowband or wideband systems.
Both systems are recognized and widely used. Without giving preference to one or the other, it is the object
of this document to describe the wideband method. General principles of PD measurements, including the
narrowband method, are covered in IEC 60270-2015 and IEC 60076-3-2013 [B72].6,7

1.3 Word usage

The word shall indicates mandatory requirements strictly to be followed in order to conform to the standard
and from which no deviation is permitted (shall equals is required to).8,9

The word should indicates that among several possibilities one is recommended as particularly suitable,
without mentioning or excluding others; or that a certain course of action is preferred but not necessarily
required (should equals is recommended that).

The word may is used to indicate a course of action permissible within the limits of the standard (may equals
is permitted to).

The word can is used for statements of possibility and capability, whether material, physical, or causal (can
equals is able to).

6
Information on references can be found in Clause 2.
7
The numbers in brackets correspond to those of the Bibliography in Annex G.
8
The use of the word must is deprecated and cannot be used when stating mandatory requirements; must is used only to describe
unavoidable situations.
9
The use of will is deprecated and cannot be used when stating mandatory requirements; will is only used in statements of fact.

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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

2. Normative references
The following referenced documents are indispensable for the application of this document (i.e., they must
be understood and used, so each referenced document is cited in text and its relationship to this document is
explained). For dated references, only the edition cited applies. For undated references, the latest edition of the
referenced document (including any amendments or corrigenda) applies.

IEC 60270-2015, High-voltage test techniques—Partial discharge measurements.10,11

IEEE Std 4™, IEEE Standard Techniques for High Voltage Testing.12,13

IEEE Std C57.12.00™, IEEE Standard General Requirements for Liquid-Immersed Distribution, Power, and
Regulating Transformers.

IEEE Std C57.12.90™, IEEE Standard Test Code for Liquid-Immersed Distribution, Power, and Regulating
Transformers.

IEEE Std C57.19.00™, IEEE Standard Requirements and Test Procedures for Power Apparatus Bushings.

3. Definitions
For the purposes of this document, the following terms and definitions apply. The IEEE Standards Dictionary
Online should be consulted for terms not defined in this clause. 14

apparent charge level: Mean value of the apparent charge of partial discharge (PD) pulse trains measured in
terms of picocoulomb (pC) by means of PD instruments.

NOTE—As specified in 4.5.15

calibrating charge: Charge of artificial partial discharge (PD) pulses generated by PD calibrators.

NOTE—As specified in 4.5.

PD calibrating circuit: Interconnection of the partial discharge (PD) calibrator with the test object and the PD
measuring circuit intended for the determination of the scale factor, Sf.

NOTE—As specified in 4.5.

PD measuring circuit: Interconnection of the partial discharge (PD) measuring instrument with the measuring
impedance and the coupling capacitor intended for measuring the apparent charge level.

pulse train response: Reading of the partial discharge (PD) measuring instrument versus the repetition
frequency of injected calibrating pulses.

NOTE—As specified in 4.5.

10
IEC publications are available from the International Electrotechnical Commission (http://​www​.iec​.ch/​) and the American National
Standards Institute (https://​www​.ansi​.org/​).
11
This is the consolidated version of IEC 60270:2000+AMD1:​2015.
12
IEEE publications are available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, Piscataway, NJ 08854, USA
(http://​standards​.ieee​.org).
13
The IEEE standards or products referred to in Clause 2 are trademarks owned by the Institute of Electrical and Electronics Engineers,
Incorporated.
14
IEEE Standards Dictionary Online is available at: http://​dictionary​.ieee​.org. An IEEE account is required for access to the dictionary,
and one can be created at no charge on the dictionary sign-in page.
15
Notes in text, tables, and figures of a standard are given for information only and do not contain requirements needed to implement this
standard.

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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

specified apparent charge level: Apparent charge level permitted for the test object if subjected to the partial
discharge (PD) test procedure and conditioning stated in IEEE Std C57.12.90 and IEEE Std C57.19.00.

4. Specification of PD measuring circuits

4.1 General
To measure the apparent charge, the following major circuit components are required:

— Coupling unit, which captures the PD signal from the terminals of the test object
— Measuring instrument, which processes the captured PD pulses and evaluates the apparent charge
level
— Associated high-voltage (HV) and low-voltage (LV) leads and measuring cables, which connect the
individual components

Generally, the coupling unit contains a coupling capacitor, CC, which is connected in series with measuring
impedance, Zm. If the test object is equipped with capacitive graded bushings, the capacitance between HV
conductor and bushing tap, C1, may substitute the coupling capacitor, CC, as illustrated in Figure 1. Refer to
Annex A for details of coupling capacitor different designs and circuits.

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IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

C0 Calibrating capacitor
C1 Capacitance between HV conductor and bushing tap
C2 Capacitance between bushing tap and grounded bushing flange
Ca Virtual capacitance of the test object
Dc Coupling device
Fi Noise rejection filter
Hv Connection to the HV test supply
Mc Measuring cable
Mi Measuring instrument
Pc PD calibrator
To Test object
V0 Step pulse generator
Zm Measuring impedance

Figure 1—PD measuring circuit using the bushing tap coupling mode

The HV connection leads between the test object and coupling capacitor should be PD-free up to the highest
applied ac test voltage level. The ground connection leads should be kept as short as possible in order to
reduce the inductance and thus to reduce the impact of electromagnetic interferences disturbing sensitive PD
measurements. Optional HV and LV filters may also be utilized to reduce the influence of environmental
disturbances.

4.2 Coupling capacitor

The coupling capacitor, CC, is intended for the decoupling of the high-frequency PD signal from the terminals
of the test object at low attenuation, due to the high-pass filter characteristics of this unit. Additionally, the ac

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IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

test voltage level appears extremely reduced at the output of CC. This response is also achieved, if instead of
the coupling capacitor, CC, the capacitance between HV conductor and bushing tap, C1, is utilized. To reduce
the impact of stray capacitances on PD test results, the capacitance of CC and C1 are normally larger than
300 pF. However, with the appropriate quadrupole, smaller values of coupling capacitance can be feasible.
Moreover, the coupling capacitor should be PD-free up to the maximum applied ac test voltage level.

4.3 Measuring impedance

The measuring impedance, Zm, is intended for the conversion of PD current pulses into equivalent voltage
pulses. Using the classical coupling mode by means of a separate coupling capacitor, the measuring impedance,
Zm, is generally formed by a parallel connection of a resistor, Rm, with an inductor, Lm; see Annex A.

If the bushing tap coupling mode according to Figure 1 is used, the measuring impedance, Zm, consists of
the parallel connection of a resistor, Rm, and an inductor, Lm. Both elements are additionally shunted by the
capacitance between bushing tap and grounded bushing flange, C2; see Annex A.

Moreover, passive and active elements could be utilized for PD signal filtering and overvoltage protection. All
these elements are usually integrated in a terminating box, referred to in IEC 60270 as a coupling device, Dc.

Due to the high-pass filter characteristics of the series connection of either Cc or C1 with the measuring
impedance, Zm, care should be taken that the specified lower limit frequency, f1, of the complete PD measuring
circuit is not substantially affected by the parameters of the PD coupling unit; see Annex A.

WARNING
In order to reduce any danger for the operator and the instrumentation, as well as to help ensure an optimum
signal transmission, the coupling device should always be located inside the HV test area. The coupling
device shall be attached physically as close as possible to the bushing tap or to the coupling capacitor.

4.4 PD measuring instrument

For measuring the apparent charge, either analog or digital signal processing can be utilized. Independent from
the measuring principle applied, the instrumentation is generally equipped with the following major units:

— Attenuator or programmable gain amplifier, to adjust the magnitude of the input PD pulses
— Band-pass filter amplifier, to amplify and integrate the captured PD pulses
— Peak detector, to evaluate the apparent charge level

To help ensure comparable and reproducible PD test results, both the frequency response and the pulse
train response of PD measuring instruments should be specified and in accordance with the latest edition of
IEC 60270.

4.4.1 Frequency response

To measure the apparent charge level the captured PD current pulses are integrated. For this purpose, usually a
band-pass filter is utilized, characterized by the lower and upper limit frequency, f1 and f2, and the bandwidth,
∆f, given by Equation (1):

f2​  ​​ − ​f1​  ​​​

​Δf = ​ (1)

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IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

To keep the integration error as low as possible, the PD measurement is performed in a frequency range where
the amplitude-frequency spectrum of the PD pulses is nearly constant; see Annex B.

From a practical point of view the lower limit frequency, f1, should be located around 100 kHz. Lower values
may reduce the impact of attenuation of PD pulses propagating along transformer windings. However, this
may also lead to serious disturbances, such as iron core related noises as well as harmonics from the ac test
facility. To reduce the impact of interferences in the low-frequency range the high-pass filter characteristics
should be such that the attenuation is about 40 dB for frequencies around 25 kHz and at least 60 dB for
frequencies below 15 kHz.

To reduce the integration error, the upper limit frequency, f2, should be chosen around 300 kHz. To reduce
interferences of radio broadcast stations, the attenuation should exceed 20 dB for frequencies above 500 kHz
and at least 40 dB for frequencies above one MHz.

From the specified frequencies, f1 and f2, it follows that the bandwidth, ∆f, has a value of 200 kHz. A wider
bandwidth would be useful for the localization of PD sites, but this may lead to an increasing measuring error,
because the PD pulses may not be integrated as desired; see Annex B.

4.4.2 Pulse train response

To evaluate the apparent charge level of random distributed PD pulse trains, the pulse magnitudes should be
weighted in compliance with the IEC 60270.

NOTE 1—To eliminate stochastically appearing noise pulses at comparatively low repetition rate, for instance one pulse
per cycle of the applied ac test voltage, some PD detectors are equipped with special features for noise suppression which
may reject pulses having a repetition rate below 100 Hz. Care should be taken when using this instrumentation because
PD pulses of high magnitude may not be recognized if they do not ignite in each half-cycle of the applied ac test voltage.
To avoid such erroneous measurements, a visualization of the phase-resolved PD pulses is strongly recommended using a
suitable display unit, such as a scope or a computer.

NOTE 2—The specified pulse train response is appropriate only for ac test voltages where the frequency may range
between 40 Hz and 400 Hz. For dc test voltages or test voltages composed by ac and dc voltages, it is recommended to
evaluate the number versus the magnitude of PD pulses.

4.4.3 Display unit

In addition to the measurement of the apparent charge level by means of analog or digital meters it is strongly
recommended to display the phase-resolved PD patterns by means of a suitable display unit, such as an
oscilloscope or a computer. This may assist not only the identification and classification of harmful PD defects
but also the discrimination of disturbing electromagnetic interferences, which are often not phase-correlated.
Current instruments offer both phase-resolved PD pattern and time-domain display in parallel multi-channel
configuration.

4.4.4 Basic sensitivity

The basic sensitivity should be determined by means of calibrating pulses specified in 4.5, which are injected
into the input of the measuring impedance connected to the PD measuring instrument via the associated
measuring cable. A calibrating charge of 50 pC should cause a minimum deflection of 50% of the full reading
of the indicating instrument or of the optional display unit.

4.4.5 Linearity

The linearity should be determined by means of calibrating pulses specified in 4.5, which should be injected
in the measuring impedance connected via the associated measuring cable to the PD measuring instrument.
The measuring sensitivity should be adjusted such that the full reading (100%) is obtained for an injected

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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

calibrating charge of 500 pC. After that the magnitude of the calibrating charge should be reduced stepwise by
100 pC. Under this condition the values indicated by the PD measuring instrument should not deviate by more
than ±10% from the true magnitudes of the injected pulse charges.

NOTE—Injecting calibration signals with magnitudes close to the noise floor produces an apparent non-linearity due to
the so-called noise modulation—the calibration pulse “rides” on the noise and appears larger.

4.5 PD calibrator
The PD calibrator is intended for the simulation of the charge transfer from the PD source to the terminals
of the test object; see Annex C. To generate artificial PD pulses required for this purpose, the calibrator is
generally equipped with a pulse generator connected in series with a calibrating capacitor, C0; see Figure 1.
The pulse generator produces fast rising step voltages of known magnitudes, V0. Therefore, the calibrating
charge is given by Equation (2):

​​q​ 0​​  =  ​V0​  ​​  ×  ​C0​  ​​​ (2)

The PD calibrator should meet the requirements of IEC 60270. To adjust the desired magnitude of the
calibrating charge, q0, the magnitude of the voltage step, V0, and the capacitance of the calibrating capacitor,
C0, can be tuned accordingly. Current calibrators use a fixed C0 and an adjustable V0 instead. The calibrating
charge should be adjustable between 50 pC and 1000 pC. These magnitudes should not differ by more than
±10% from the rated values.

To reduce the measuring error caused by non-controlled distortions of the pulse shape, care has to be taken
that the conditions C0 < 200 pF and C0 < 0.1 Ca are satisfied. A simplified approach for the evaluation of Ca
is presented in Annex D. To avoid any superposition errors and thus to reduce the impact of the pulse train
response on the reading of the PD measuring instrument, the repetition frequency of the calibrating pulses
should be in the range of 50 Hz to 1000 Hz, inclusive.

The output impedance of the step pulse generator should not exceed 100 Ω. The rise time of the step pulse,
which refers to the 10% and 90% values of the maximum pulse magnitude, should be less than 100 ns. After
the peak is obtained the voltage magnitude should not differ more than ±5% from the mean value for a time
span not shorter than 50 µs. The decay time, which refers to the 90% and 10% values of the pulse magnitude,
should either be the same as the rise time, if bipolar calibrating pulses are created, or it should exceed 200 µs if
pulses of only positive or negative polarity are created.

To display the calibrating pulses when the actual PD test under high voltage is running, the calibrating
capacitor, C0, which is usually designed only for low voltages, should be substituted by an HV calibrating
capacitor; this should be PD-free up the maximum ac test voltage level. The measuring cable between the
step pulse generator and the terminating box connected to the input of the HV calibrating capacitor should be
matched with the characteristic cable impedance in order to avoid disturbing pulse reflections. Generally, the
HV calibrating capacitor should be located as close as possible to the HV terminal of the test object.

The objective of the calibration procedure is to determine the scale factor, Sf, which represents the ratio
between the calibrating charge, q0, injected between the terminals of the test object, and the reading, R0, of the
PD measuring instrument. With current instruments, this scale factor is typically calculated automatically and
often not user accessible [see Equation (3)].

​​Sf​  ​​    =  ​q​ 0​​   /   ​R0​  ​​​ (3)

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IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

To evaluate the apparent charge level, qa, under HV test conditions the reading, Ri, of the PD instrument is
multiplied by the scale factor, Sf [see Equation (4)].

​​qa​  ​​  =  ​Ri​  ​​  ×  ​Sf​  ​​    =  ​q​ 0​​  ×  ​Ri​  ​​  / ​​R0​  ​​​    ​​  ​ (4)

This means the apparent charge level can be determined if the calibrating charge, q0, is multiplied by the
reading, Ri, due to PD events, and divided by the reading, R0, caused by the calibrating charge.

4.6 Maintaining the specified parameters of PD measuring circuits

To verify the specified technical parameters of the PD measuring circuits including the PD calibrator,
performance checks should be performed at least once a year and after repair. The scale factor, Sf, of the PD
measuring circuit and the values of the pulse charges, q0, created by the PD calibrator should be kept in a record
of performance established and maintained by the user. Additionally, type tests, routine tests, and performance
tests should be performed in compliance with the recommendations of IEC 60270.

5. PD test procedure
5.1 Calibration
5.1.1 PD measuring circuit

Before starting the first HV test, the complete PD measuring circuit according to Figure 1 should be calibrated
to establish the scale factor, Sf; see 4.5. For calibration, all equipment should be set up exactly as used during
the PD test. If the test object is a three-phase transformer, the calibration should be performed at each terminal
in turn, while making sure that the PD measuring instrument is always connected to each phase using either the
bushing tap coupling mode or a separate coupling capacitor.

The calibrating pulses should be injected between the top of the HV bushing and the transformer tank, as
evident from Figure 1. Generally, a portable battery powered PD calibrator should be used. If desired, a
suitable pulse generator along with a terminating box connected to a suitable HV calibrating capacitor may
also be used in order to display the calibrating pulses during the running HV test, and to adjust the magnitudes
of the calibrating charge from the control room.

The connecting leads between the calibrator and test object should be kept as short as possible in order to
avoid pulse distortions that may cause calibration errors. Therefore, the portable calibrator or the terminating
box in connection with the HV calibrating capacitor should be placed as close as possible to the HV terminals
of the test object. At least four separate calibrating charge levels should be injected to check the linearity of
the PD measuring instrument. For a specified apparent charge level of qa = 500 pC, the calibration should be
performed with the values q01 = 100 pC, q02 = 200 pC, q03 = 500 pC, and q04 = 1000 pC.

5.1.2 AC test voltage measuring circuit

The ac test voltage measuring circuit should be calibrated in accordance with the requirements of IEEE Std 4™
as well as in compliance with IEC 60060-1 [B70] and IEC 60060-2 [B71]. If an ac voltage measuring
instrument is connected to the voltage output of the coupling device or to the bushing tap, either the capacitive
divider ratio should be determined as reported in Annex E, or the complete ac measuring circuit should be
calibrated using a reference measuring system.

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IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

5.2 PD measurement
5.2.1 PD test circuits

Figure 2 shows a circuit recommended for PD tests under induced voltage, i.e., the HV winding of the single-
phase power transformer is excited through the LV winding. The LV test voltage source should be designed
as specified in IEEE Std C57.12.00™ and IEEE Std C57.12.90™, which requires simulations of the actual
operating configuration.

An optional LV filter may be required to reduce interferences coming from the ac power supply. The HV and
LV connection leads should be kept as short as possible in order to reduce the inductance and thus to reduce the
impact of electromagnetic noises.

The coupling device, which is generally equipped with the measuring impedance and additional elements for
signal filtering and over-voltage protection as well as with the LV arm of the voltage divider, should be placed
as close as possible to the bushing tap. The signal outputs of the coupling device for the PD pulses and the ac
test voltage are connected via measuring cables to the PD measuring instrument and to an ac voltmeter.

Figure 2—PD measuring circuit for power transformers using induced test voltage

In addition to the reading instrument of the PD measuring instrument a display unit, such as a scope or a
computerized PD measuring system should be utilized, which may be useful not only for the identification and

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IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

classification of harmful PD sources (CIGRE TF 15.11/33.03.02[B34], CIGRE WG 21-03 [B40], CIGRE WG

D1.33 [B41], Fuhr [B52], Fuhr et al. [B53], Fryxell et al. [B54]), but also for the discrimination of disturbing
noises in the surroundings.

Figure 3 shows a test circuit recommended for PD tests of power transformers and shunt reactors excited by a
step-up transformer. In the past few years, efforts were made on the qualification of static frequency converters
to generate test voltages fulfilling the requirements of the applicable standards for induced voltage test as well
as other tests required a three-phase power supply. The static frequency converters are used for measurement
of partial discharge during induced voltage tests. Most of the new and modernized transformer test facilities
for factory testing or mobile test applications are often equipped with static frequency converters. An optional
HV filter may be required on the HV side in order to reduce the impact of disturbing interferences coming from
the step-up transformer. Additionally, a filter may be helpful for noise rejection if positioned on the LV side of
the step-up transformer.

5.2.2 Test procedure

The PD test procedure and the ac test voltage level applied should be as specified in IEEE Std C57.12.00,
IEEE Std C57.12.90, and IEEE Std C57.19.00™.

Figure 3—PD measuring circuit for shunt reactors energized by a step-up transformer

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IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

Annex A
(informative)

Coupling
A.1 Introduction
As partial discharge testing requires applying high voltage to the test object, a safe method is needed to separate
the high voltage potential and the high frequency partial discharge signal. Hence, such circuits are often called
power separation filters.

Generally, different techniques are applicable and in use. They all have two main tasks in common to first
reduce the remains of the power frequency to magnitudes that do not harm the user or subsequent equipment
and, second, to efficiently de-couple the high frequency signals. In a typical 50 Hz or 60 Hz testing
environment, power frequency and the lower cutoff frequency of the partial discharge measurement are just
three decades apart, while it is only approximately two decades separation in case of the upper permissible
power frequency of variable frequency resonant test sets. Thus, in general, high-pass filters of higher order are
needed to achieve the desired attenuation.

A.2 Capacitive coupling

The capacitive coupling is the most efficient coupling technique. Here, a coupling capacitor is connected in
parallel to the test object and, hence, provides the high frequency return path for the partial discharge impulses.
A measuring impedance or quadrupole is fitted into this circuit. Concerning the high frequency behavior, it
doesn't matter whether the quadrupole Q is put into the ground lead of the coupling capacitor (Figure A.1, a) or
into the ground lead of the test object (Figure A.1, b). However, as the capacitance of the test object Ca is often
larger than the capacitance of the coupling capacitor CC, the quadrupole is usually put into the coupling branch
to benefit from the smaller capacitive load current. Moreover, in the event of test object failure, the quadrupole
would suffer from the short circuit current, if placed in the test object branch.

NOTE—Reprinted with permission from Detlev Gross, “Acquisition and location of partial discharge—esp. in
transformers” PhD. Thesis, TU Graz, Austria, © 2016.

Figure A.1—Capacitive coupling—quadrupole underneath coupling capacitor (a) or test

object (b)

A basic measuring impedance or quadrupole consists of an inductor and a damping resistor to form a second
order high pass filter (Figure A.2). The corner frequency should be selected to be below the lower cutoff of

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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

the partial discharge detectors. Thus, the inductance of the quadrupole is matched to the coupling capacitor to
match the detector's bandwidth, i.e., its lower cutoff frequency [Equation (A.1)].
_

√
1 _
_ 1
​f = ​  ​ ​ ​  ​ ​​ (A.1)
2π LC

Additionally, a damping resistor is needed to avoid oscillatory behavior of the circuit (Figure A.2). Typically,
the damping of this second order filter [Equation (A.2)] is aperiodic (D = 0.707). However, damping values
between 0.3 and 1.0 produce suitable response. A stronger damping, i.e., a smaller resistor, reduces the overall
sensitivity, while a weaker damping does cause oscillations, which at least reduce the pulse repetition rate16
that can be processed by the partial discharge detector.
_

√
L
1 _
_
​D = ​   ​ ​ ​  ​ ​​ (A.2)
2 C

Whereas C, L, and R are the components as shown in Figure A.2.

NOTE—Reprinted with permission from Detlev Gross, “Acquisition and location of partial discharge—esp. in
transformers” PhD. Thesis, TU Graz, Austria, © 2016.

Figure A.2—Basic RLC coupling circuit and its step function response

The step function response of such a damped series resonance circuit is shown with (Figure A.2) for different
damping factors. For a typical 1 nF coupling capacitor the inductance of the quadrupole is about 15 mH to
meet 40 kHz, for instance. Hence, for this example, the damping resistor is about 2.7 kΩ.

Obviously, such circuit would be inappropriately loaded, if connected to a detector using a cable of any style.17
Using a cable with 50 Ω impedance and termination would cause a damping of > 100 and shift the corner
frequency to 3.18 MHz with a first order decay of 20 dB/dec. Thus, an impedance matching is needed directly

16
The repetition rate that can be processed by a partial discharge detector is more prominently influenced by the reciprocal of the
processing circuit's bandwidth. For 9 kHz narrow band detection, for example, this rate will be few thousand pulses per second, only.
17
However, although not very elegant, a coupling capacitor can be terminated with a 50 Ω (power) resistor. 11 nF into 50 Ω creates a first
order filter with a corner frequency of 290 kHz.

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IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

at this point. This can be a matching transformer, such as a balun or an active impedance converter, i.e., a
voltage follower or amplifier as shown in Figure A.3.18,19

NOTE—Reprinted with permission from Detlev Gross, “Acquisition and location of partial discharge—esp. in
transformers”, PhD. Thesis, TU Graz, Austria, © 2016.

Figure A.3—Impedance matching: (a)transformer, (b)balun, and (c)amplifier as voltage

follower

On the other hand, leaving the coaxial cable not terminated becomes an option for comparably short coaxial
connecting cables. Given the upper corner frequency of 1 MHz, as specified with IEC 60270, an RG58 coaxial
cable of 10 m length, for instance, would cause only a frequency dependent attenuation of 5% at 1 MHz due
to the reflection. Additionally, the cable's capacitance has to be taken into consideration—the mentioned 10 m
cable poses a capacitance of about 1 nF, which would reduce the signal to 50% for a 1 nF coupling capacitor.

As partial discharge signals are comparably faint, early amplification helps to reduce pickup of ambient
noise on the signal path to the detector. Moreover, as the signal cable’s sheath is preferably grounded on both
sides, transient sheath currents can easily add to the faint signal. Here, clip-on ferrites act as sheath-current-
transformers and reduce such effects. 20

If the capacitance C1 of a transformer bushing is used instead of the afore discussed separate coupling
capacitors, additionally the bushing's stray capacitance C2 to ground has to be taken into account (see
Figure A.3 and Figure A.4).
_

√
1 _
_ 1
​f = ​  ​ ​ ​   ​ ​​ (A.3)
2π L​(​C1​  ​​ − ​C2​  ​​)​

18
Here, the critical property of such matching transformers is their winding and stray capacitance, which would introduce self-resonance
and strong damping at higher frequencies. Thus, old-fashioned low-capacitance basket weave coils, as known from early radio sets offer
the lowest winding capacitance and a sufficiently high self-resonance frequency.
19
Balun stands for balanced-unbalanced and their main application is to match single-ended (unbalanced) lines, such as coaxial cables
to parallel (balanced) lines, such as twisted pair. In lower frequencies, baluns are commonly constructed using bifilar or tri-filar isolated
wires on ferrite ring cores, while in higher frequencies, short coaxial cable can cover the task. In case of quadrupoles, baluns serve to
transform the impedance. For instance, a four-to-one balun transforms the impedance by a factor of 16 (42). Hence, with such 4:1 balun,
the 50 Ω of a conventional coaxial cable translates into 800 Ω.
20
Such clip-on-ferrites are commonly used to reach EMI requirements for commercial electronic equipment. The relevant EMI standards
cover well the frequency bands needed for partial discharge testing (40 kHz to 1000 kHz).

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IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

For composite bushings and bushings with the so-called test tap, this stray capacitance is in the same range as
the main capacitance C1, while it can reach comparably high values for ANSI bushings with voltage tap and,
hence, dominates the overall circuit. 21

NOTE—Reprinted with permission from Detlev Gross, “Acquisition and location of partial discharge—esp. in
transformers”, PhD. Thesis, TU Graz, Austria, © 2016.

Figure A.4—(a) Basic coupling circuit at a bushing tap and (b) with additional voltage divider

The quadrupole can be additionally equipped with a divider capacitor CD to provide the PD detector with
a voltage signal for synchronizing the PD acquisition and to measure the phase-to-ground voltage of the
bushing, as shown with Figure A.4, b. Although in most cases negligible, both the signal cable capacitance and
C2 contribute to the overall divider capacitance.

To avoid damage of the components of the quadrupole as well as the connected PD detector, adequate measures
are taken to limit over voltages due to test object failure or flashover, for instance. Gas-filled spark gaps offer
both effective limiting and a low capacitance.

Likewise, instead of a dedicated coupling capacitor, a second (preferably identical) test object can provide the
high frequency return path. Especially in a balanced circuit, i.e., with a balanced quadrupole, or a quadrupole
in each branch, such configuration can greatly improve the circuit's noise immunity and overall sensitivity.

21
The test tap is connected to the last layer of the stack of n capacitive layers that are separated with aluminium-coated paper. Thus,
for the voltage tap, the capacitance C2 = n×C1 can reach 20 nF and above. Additionally, this high C2 hampers the sensitivity of PD
(and RIV) measurements.

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IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

NOTE—Reprinted with permission from Detlev Gross, “Acquisition and location of partial discharge—esp. in
transformers”, PhD. Thesis, TU Graz, Austria, © 2016.

Figure A.5—Balanced circuit using a test object and a coupling capacitor or two test objects

With the balanced circuit (Figure A.5), the common mode noise signal is in phase at the two quadrupoles,
while the partial discharge signal is in anti-phase.22 Thus, a differential amplifier cancels the noise signal, while
it adds the two partial discharge signals. However, care should be taken to have identical corner frequencies
and damping in order to reach an identical pulse decay and undershoot, as differences between the branch
responses make the remains of noise signals survive the cancellation.

Besides the obvious capacitors, stray capacitances of construction elements, such as internal shields of
gas-insulated equipment, can be used for capacitive coupling, for example. Of course, the same rules for
quadrupoles, as discussed before, apply.

Traditional balanced circuits made use of a manually balanced bridge (Kreuger Bridge, [B90]), where the measurement
22

impedances were inside the detector. The bridge was then adjusted for minimum noise, and subsequently calibrated.
Nowadays, the differential amplification is done electronically, while the adjusting procedure remains the same, in principle.

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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

Annex B
(informative)

Response of PD measuring instruments

B.1 Frequency response
Due to the high-pass filter characteristics of the PD coupling unit, see Annex A, the voltage jump appearing
across the terminals of the test object as a result of a PD event is differentiated. Therefore, this signal should be
integrated again in order to evaluate the apparent charge of the captured PD pulses. Subclause 4.4.1 provides
recommendations for f1 and f2 values. The integration can be performed at sufficient accuracy if the measuring
frequency is chosen below 500 kHz, where the amplitude frequency spectrum of the PD pulses is nearly
constant (Schon [B134], [B135], [B136]); see Figure B.1. Under this condition the output signal of the PD
measuring instrument is a pulse whose magnitude is a measure of the charge of the input pulse. It should be
noted that the duration of the output pulse to be evaluated is much longer than those of the input PD pulse.

A Amplitude-frequency spectrum of PD pulses

B Band-pass filter characteristics of the PD measuring instrument

Figure B.1—Selection of the band-pass filter characteristics for PD instruments

B.2 Pulse train response

PD events occurring under ac test voltages are characterized by pulse sequences whose magnitudes may
randomly be distributed over an extremely wide range. To ensure comparable and well-reproducible PD test
results, it seems therefore feasible to average the randomly distributed PD pulse magnitudes. As a consequence,
in IEC 60270 the evaluation of the “largest repeatedly occurring PD magnitude” is recommended. This PD
quantity is equivalent to the “apparent charge level” as defined in this recommended practice; see specified
apparent charge level in Clause 3.

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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

As can be seen from Figure B.2, after the maximum PD magnitudes are averaged, the apparent charge level
can well be quantified by a value of approximately 2800 pC. This approach is based on a specified pulse train
response of the PD measuring instrument shown in Figure B.3, where the tolerance band is well fitted for the
condition τ1 << τ2 < 440 ms. Here is τ1 the charging time constant and τ2 the discharging time constant of the
peak detector as part of the PD measuring instrument. It should be mentioned that CISPR 16-1-1993 [B42]
also recommends an averaging of random distributed noise pulses where the characteristic time constants are
specified by τ1 < 1 ms and τ2 < 160 ms.

Figure B.2—Evaluation of the apparent charge level, recording time 300 s

Figure B.3—Maximum and minimum reading, Rmax and Rmin, of PD instruments versus the
pulse repetition rate, N, recommended in IEC 60270

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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

Annex C
(informative)

Calibration of PD measuring circuits

The objective of the calibration is to determine the scale factor, Sf, required for evaluating the apparent charge
level, qa, from the reading of the PD measuring instrument, Ri, as shown in Equation (C.1):

​​qa​  ​​ − ​Ri​  ​​  × ​S​ f​​​ (C.1)

This procedure is in principle based on a simulation of the charge transfer from the PD source to the terminals
of the test object. For this purpose, artificial PD pulses are injected between the terminals of the test object by
means of a calibrator (Lemke [B94], Lemke et al. [B96]); see Figure D.1. The scale factor, Sf, is determined
from the ratio between the calibrating charge, q0, and the reading of the PD measuring instrument, R0.
Therefore, Sf is expressed either in terms of pC/scale of the reading instrument or in terms of pC/div of the
display unit.

For better understanding, consider the following practical example:

Calibrating charge injected between the terminals of the test object: q0 = 200 pC
Reading of the PD instrument: R0 = 50 scales
Resulting scale factor: Sf = q0 / R0 = 4 pC /scale
Reading of the PD instrument during the actual PD test: Ri = 20 scales

Based on these values, the apparent charge can be calculated as shown in Equation (C.2):

​​qa​  ​​  = ​R​ i​​  × ​S​ f​​  = ​(20 scales)​ × ​(4 pC/scale)​  = 80 pC​ (C.2)

It should be noted that advanced computerized PD measuring instruments are equipped with a feature to scale
the PD data in terms of pC automatically after the calibration procedure has been performed.

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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

Annex D
(informative)

Basic sensitivity check

To check the basic sensitivity of the PD measuring instrument, the circuit shown in Figure D.1 could
be utilized. Here the virtual test object capacitance, Ca, is simulated by an LV capacitor having a value of
10 000 pF. Furthermore, the capacitance between the HV conductor and the bushing tap, C1, and the
capacitance between the bushing tap and the grounded bushing flange, C2, are simulated by an LV capacitors
having values of, for instance, C1 = 500 pF and C2 = 2500 pF, respectively. The measuring impedance, Zm, of
the PD measuring circuit is connected to the junction of C1 and C2, which represents the bushing tap coupling
mode.

The sensitivity should be such that when a calibrating charge of 25 pC is injected into Ca the reading of the
PD measuring instrument exceeds at least twice the internal amplifier noise level. This basic sensitivity check
needs only to be performed when installing a new PD measuring system and at specified time intervals, i.e.,
after each year and after repair or modification of the components of the PD measuring circuit.

Figure D.1—Circuit recommended for the basic sensitivity check

The circuit illustrated in Figure D.1 could also be utilized for an estimation of the virtual test object capacitance,
Ca, if the internal capacitance of the calibrator, C0, is known. This can be done by the following three steps:

a) With all the equipment configured exactly as it should be during the PD test, a calibrating charge of
approximately 500 pC should be injected into the terminals of the test object, which is represented in
Figure D.1 by Ca. The reading, R1, of the PD measuring instrument should be noted.
b) After connecting an additional capacitor, Cp, of 1000 pF in parallel to the output of the calibrator, the
appearing reading, R2, should also be noted.
c) A reading ratio of R2 / R1 > 0.8 indicates that Ca is fairly high, and the procedure should be repeated
with the parallel capacitance, Cp, increased 10 times, i.e., from originally 1000 pF up to 10 000 pF.

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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

Annex E
(informative)

Bushing tap ratio measurement

To display phase-resolved PD patterns, a low ac voltage component should be available having the same phase
angle as the applied ac test voltage in order to synchronize the display unit. The most convenient way is to
capture the ac signal from the bushing tap. To evaluate the appearing output voltage magnitude, the ratio of
the capacitive divider formed by the capacitance between the HV conductor of the bushing and the bushing
tap, C1, and the capacitance between the bushing tap and grounded bushing flange, C2, should be known. From
this it can be determined whether the maximum ac voltage magnitude appearing at the bushing tap can be
accepted for the measuring purpose or if it should be reduced by means of an additional measuring capacitor,
C3, connected in parallel to C2.

The capacitive divider ratio of the bushing may also be measured directly for the applied ac test voltage by
means of a suitable ratio bridge. The value usually ranges between 1:10 000 and 1:50 000. As an option, an
appropriate device specified in IEEE Std 4 for alternating voltage measurement can also be connected directly
to the HV bushing terminal. For this case the bushing tap output voltage should be measured by means of an ac
voltmeter having an input impedance of more than 1 MΩ. After energizing the transformer up to the desired ac
test voltage level, the output voltage is measured. The bushing tap ratio can then be calculated by dividing the
magnitude of the low voltage through the magnitude of the applied ac test voltage.

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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

Annex F
(informative)

PD pattern recognition
F.1 General
Characteristic signatures of PDs in liquid-filled power transformers and shunt reactors have been published
in many papers, for instance in (CIGRE TF 15.11/33/03/02 [B34], CIGRE WG 21-03 [B39], CIGRE 21-03
[B40], Fuhr [B52], Fuhr et al. [B53], CIGRE WG D1.29 [B157]). Phase resolved partial discharge (PRPD)
pattern visualizes the occurrence of PD activities in reference to the phase of ac voltage and commonly used to
identify the source of discharges during PD measurements. The PRPD pattern displays PD pulses (pC values
in the calibrated test circuit) measured during a pre-set acquisition time. The PRPD are normally displayed
in a two-dimensional graph, where the amplitude of apparent charge is in vertical axis and the phase angle is
the horizontal axis. The PRPD pattern can be displayed in a three-dimensional graph, where the amplitude of
the apparent charge (vertical axis), the phase position (horizontal axis) and the number of counts (color) are
visible.

F.2 Influence of the measuring circuit and instrument settings

The polarity of the cluster of PD pulses that appears on each half of the ac voltage cycle is influenced by a host
of factors unrelated to the physics of partial discharges and its propagation from the discharge site to the point
of the detection. Many of these influences are from the measuring circuit and instrument settings and have a
significant influence on the PRPD patterns. Their effect should be understood before recognition of discharge
sources are attempted.

F.3 Cross-talk in PD responses and source differentiation

When all three phases of the transformer are energized, the measured PD pattern will reveal the single-phase
PD response together with PD responses from the other phases due to an effect known as cross-talk or cross-
coupling. Their effect should be understood before recognition of discharge sources are attempted. If the
transformer low voltage or tertiary bushings are equipped with bushing tap, it is possible to perform a multi-
terminal calibration table including all available PD measurement terminals which could be helpful for PD
source identification. The cross-coupling matrix can be used for a preliminary PD source localization in the
case where a PD signal occurs. Table F.1 shows an example of cross-coupling calibration matrix that is created
by injecting calibration signal to each terminal and measuring the response in all other terminals.

Table F.1—Example of cross-coupling calibration matrix

H1 H2 H3 H0 X1 X2 X3 X0
H1 100% 1.5% 1.9% 2.5% 22% 1.5% 2.0% 1.5%
H2 49.9% 100% 72% 56% 35% 33% 35% 35%
H3 2.0% 2% 100% 2.5% 1.5% 1.5% 22% 1.3%
H0 62% 33% 63% 100% 28% 28.5% 27% 25%
X1 15% 2.5% 2.5% 1.7% 100% 3.0% 2% 1.9%
X2 2.5% 2.3% 2.5% 1.5% 3.0% 100% 2.5% 2.0%
X3 2.5% 2.0% 14% 2.0% 1.5% 2.5% 100% 1.5%
X0 20% 14% 20% 11.5% 20% 17.5% 18% 100%

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IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

F.4 Interferences
During PD tests of power transformers and shunt reactors, excessive electromagnetic interferences or
disturbances may be encountered, which is often called noise. The term noise refers to all sources of unwanted
PD pulse like interference having its origin outside the evaluated area of interest in the transformer which
usually refers to the region within the walls of the transformer tank and inside transformer bushings.

Surges and transients from electrical switching operations, transient and pulses from power electronics, radio
frequency noises radiated from broadcast stations, and poor grounding or shielded system are examples of the
source of PD noises. In this context it should be noted that one of the greatest advan0tages of the wideband
method is the ease with which the electromagnetic disturbances can be displayed and thus be discriminated
from the PD signal. For the identification and localization of electromagnetic noises, the following general
rules may be helpful:

a) External noises appear often independent from the applied ac test voltage level and thus do not
disappear if the test voltage level is lowered, as the PD events do.
b) Pulse-shaped noises may appear unsynchronized with the applied ac test voltage, whereas PD pulses
occur always phase-correlated.

In this context it should be noted that advanced computer-based PD measuring systems are equipped with
powerful features for the recognition and rejection of disturbing noises.

PRPD patterns are powerful diagnostics tools to identify transformer defects as well as interferences such
as power supply noise, radio noise, and poor grounding or shielding. The PRPD patterns reflect the physical
phenomena of the specific PD sources. CIGRE Brochures 662 and 676 provides examples of PRPD patterns
that can be used to identify internal defects and external noises (see [B163] and [B157]).

The occurrence of partial discharges is a stochastic process, and PD detection is influenced by several factors,
so the PRPD patterns may appear in several variations. As such, experience and interpolation ability are
required for correct interpretation and screening of the PD type based on the measured PRPD pattern.

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IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

Annex G
(informative)

Bibliography
Bibliographical references are resources that provide additional or helpful material but do not need to be
understood or used to implement this standard. Reference to these resources is made for informational use
only.

[B1] Ahmed, A. S. and A. A. Zaky, “Calibration of Partial Discharge Detectors for Pulse-Height Distribution
Analysis,” IEEE Transactions on Electrical Insulation, vol. EI-14, no. 5, pp. 281–284, October 1979.

[B2] ANSI C63.2–1987, American National Standard Specifications for Electromagnetic Noise and Field-
Strength Meters, 10 Hz to 40 GHz.23

[B3] ANSI C68.3–1976, American National Standard Recommended Practice for the Detection and
Measurement of Partial Discharges (Corona) During Dielectric Tests.

[B4] Arman, A. N., and Starr, A. T., “The Measurement of Discharges in Dielectrics,” J.IEE 79 (1936), pp.
67–81, 88–94.

[B5] AS 1018-1970, Recommendations for Partial Discharge Measurements, Standards Australia.

[B6] Aschwanden, T., et al., “Development and Application of New Condition Assessment Methods for Power
Transformers,” CIGRE paper 12–207, Session Paris, Aug. 1998.

[B7] ASTM D 1868–73, Detection and Measurement of Discharge (Corona) Pulses in Evaluation of Insulation
Systems.24

[B8] Austin, J. and R. E. James, “On-Line Digital Computer System for Measurement of Partial Discharges in
Insulation Structures,” IEEE Transactions on Electrical Insulation, vol. EI-11, no. 4, pp. 129–139, December
1976.

[B9] Baehr, R. et al., “Diagnostic Techniques and Preventive Maintenance Procedures for Large Transformers,”
CIGRE paper 12–13, Sept. 1–9, 1982.

[B10] Bartnikas, R., “Effect of Pulse Rise Time on the Response of Corona Detectors,” IEEE Transactions on
Electrical Insulation, vol. EI-7, no. 1, pp. 3–8, March 1972.

[B11] Bartnikas, R., “Use of a Multichannel Analyzer for Corona Pulse-Height Distribution Measurements on
Cables and Other Electrical Apparatus,” IEEE Transactions on Instrumentation and Measurement, vol. IM-22,
no. 4, pp. 403–407, December 1973

[B12] Bartnikas, R. and E. J. McMahon, “Corona Measurement and Interpretation,” Eng. Dielectrics, Vol. 1.
American Society for Testing and Materials, 1979, STP 669.

[B13] Barutti, A., “Measurements and Localization of Partial Discharges: A Step Forward,” Technol. Elettrica,
no. 11, pp. 76–79, November 1976 [Italy].

23
ANSI publications are available from the Customer Service Department, American National Standards Institute (https://​www​.ansi​.org/​
).
24
ASTM publications are available from the American Society for Testing and Materials, (https://​www​.astm​.org/​).

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IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

[B14] Beer, G. et al., “Contribution expérimentale à l’étude de la dégradation produite par des décharges
partielles dans le papier isolant imprégné à l’huile,” CIGRE paper 15-02, Aug. 24 – Sept. 2, 1970.

[B15] Bellaschi, P. L., “Power Transformer Corona Testing—The Long-Time Test,” Transmission and
Distribution, June, pp. 40-41, 1972.

[B16] Berg, G., L. E. Lundgaard, and L. Machazek, “Discharge Signatures from a Wedge Geometry in
Transformer Insulation,” 13th International Symposium on High Voltage Engineering, Paper O.26.06, Delft,
Aug. 2003.

[B17] Bertula, T., V. Palva, and E. Talvio, “Partial Discharge Measurement on Oil-Paper Insulated
Transformers,” CIGRE paper 12–07, June 10–20, 1968.

[B18] Bertula, T., Y. Saunamaki, and N. Ostman, “Vieillissement de l’isolation papier huile vue plus
spécialement sous l’angle de l’influence du champ électrique sur les impuretés contenues dans l’huile,”
CIGRE paper 15–06, Aug. 24–Sept. 2, 1970.

[B19] Black, I. A., “A Pulse Discrimination System for Discharge Detection in Electrically Noisy
Environments,” International High-Voltage Symposium, Zurich, Switzerland, Sept. 1975.

[B20] Black, I. A. and N. K. Leung, “The Application of the Pulse Discrimination System to Measurement
of Partial Discharges in Insulation under Noisy Conditions,” IEEE International Symposium on Electrical
Insulation, Boston, MA, pp. 167–170, June 1980.

[B21] Bohdanowicz, A. and S. Palmer, “Some Results of Partial Discharge Measurements by Means of Charge
Detectors and Radio Voltage Meter of Simulated Corona Pulses Injected into a Power Transformer,” Canadian
Electrical Association Apparatus Meeting, Montreal, Canada, Mar. 17, 1982.

[B22] Borsi, H., et al., “Enhanced Diagnosis of Power Transformers Using On- and Off-line Methods—
Results, Examples and Future Trends,” CIGRE paper 12–204, Session Paris, Aug. 2000.

[B23] Borsi, H. and E. Gockenbach, “Partial Discharge Measurement and Evaluation Techniques for
Transformers,” 13th International Symposium on High Voltage Engineering, paper O.24.05, Delft, Aug. 2003.

[B24] Boyles, C. R. and R. A. Hinton, “Seven Years of Corona Testing,” Paper no. 70 CP120-PWR, IEEE
Winter Power Meeting, New York, NY, Jan. 25–30, 1970.

[B25] Brand, U. and M. Muhr, “New Investigations on the Measurement of Partial Discharge (PD) and Radio
Interference Voltage (RIV) on High-Voltage Engineering,” Paper no. 63.13, Fourth International Symposium
on High Voltage Engineering, Athens, Greece, Sept. 5–9, 1983.

[B26] Brown, R. D., “Corona Measurement on High-Voltage Apparatus Using the Bushing Capacitance Tap,”
IEEE Transactions on Power Apparatus and Systems, vol. PAS-84, pp. 667–671, August 1965.

[B27] Carter, W. J., “Practical Aspects of Apparent Charge Partial Discharge Measurements,” IEEE
Transactions on Power Apparatus and Systems, vol. PAS-101, no. 7, pp. 1985–1989, July 1982.

[B28] Channakeshava, G., B. I., and Jayaram, B. N., “Possibilities of Estimating the Energy of Partial
Discharge at Site in Transformer Windings,” Paper no. 63.08, Fourth International Symposium on High-
Voltage Engineering, Athens, Greece, Sept. 5–9, 1983.

[B29] Channakeshava, G., B. I., and Jayaram, B. N., “Studies on Partial Discharge Measurement in
Transformer Windings,” CIGRE paper 12–09, Sept. 1–9, 1982.

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IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

[B30] Cesari, S. and S. Yakov, “Partial Discharge Inception Tests on Oil Immersed Insulation Structures,”
Paper 22.09, Fourth International Symposium on High-Voltage Engineering, Athens, Greece, Sept. 5–9, 1983.

[B31] CIGRE JWG 15.01.04, “Characterization of Partial Discharges in Transformer Insulation,” Paper
15.01.04, Session Paris, Aug. 2000.

[B32] CIGRE JWG 15/21/33–20, “Progress on High-Voltage Monitoring Systems for In-service Power
Apparatus,” Session Paris, Aug. 1996.

[B33] CIGRE SC 12, “Measurement of Partial Discharges in Transformers,” Electra, no. 19, pp. 13–65, Nov.
1971.

[B34] CIGRE TF 15.11/33.03.02, “Knowledge Rules for Partial Discharge Diagnosis in Service,” Electra
Brochure 226, 2003.

[B35] CIGRE TF 33.03.05, “Calibration Procedures for Analog and Digital Partial Discharge Measuring
Instruments,” Electra, no. 180, pp. 123–124, Oct. 1998.

[B36] CIGRE WG 03, “Elimination of Interference in Discharge Detection,” Electra, no. 21, pp. 55–72.

[B37] CIGRE WG 12-01, “General Report of Group 12-01, Electra, no. 37, pp. 64–74, Dec. 1974.

[B38] CIGRE WG 12.01, “Measurement of Partial Discharges in Transformers,” Electra, no. 47, pp. 37–47,
July 1976.

[B39] CIGRE WG 21-03, “Significance of Discharge Detection,” Electra, no. 11, pp. 53–60, Dec. 1969.

[B40] CIGRE WG 21-03, “Recognition of Discharges,” Electra, no. 11, pp. 61–98, Dec. 1969.

[B41] CIGRE WG D1.33, “Guide for Electrical Partial Discharge Measurements in compliance to IEC
60270,” Technical Brochure 366, Electra, vol. 60, no. 241, Dec. 2008.

[B42] CISPR 16-1-1993, Comité International Spécial des Perturbation Radioélectrique.25

[B43] Corvo, A. M., “Diagnostic Technique and Proceedings of Preventive Maintenance of Large
Transformers,” CIGRE paper 12–11, Sept. 1–9, 1982.

[B44] Dakin, T. W., C. N. Works, and R. L. Miller, “Utilization of Peak-Reading Voltmeters and Recorders for
Corona Measurement,” IEEE Transactions on Electrical Insulation, vol. EI-2, no. 2, pp. 75–82, August 1967.

[B45] Dembinski, E. M. and J. L. Douglas, “Calibration and Comparison of Partial Discharge and Radio-
Interference Measuring Circuits,” IEE Proceedings, vol. 115, no. 9, pp. 1332–1340, Sept. 1968.

[B46] Dietrich, W., “An International Survey on Failures in Large Power Transformers in Service,” Electra,
no. 88, pp. 21–48, May 1983.

[B47] Dolezal, I. F., “Dielectric Test Requirements and Factory Test Experiences on High Voltage Power
Transformers,” Paper no. C75–147–4, IEEE PES Winter Meeting, New York, NY, Jan. 26–31, 1975.

CISPR documents are available from the Central Office of the International Electrotechnical Commission (http://​www​.iec​.ch/​). They
25

are also available in the United States from the Sales Department, American National Standards Institute (https://​www​.ansi​.org/​).

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IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

[B48] Douglas, J. L., “Calibration of Circuits for Measuring Partial Discharges in EHV Transformers,”
IEE Conference on Diagnostic Testing of HV Power Apparatus in Service, London, England, pp. 40–47,
Mar. 1973.

[B49] Douglas, J. L., F. C. Pratt, and F. Rushton, “A Critical Assessment of Methods of Measuring Partial
Discharges in EHV Transformers,” CIGRE Conference paper 12–03, Paris, France, 1974.

[B50] Dix, J. W., G. H. Hickling, and B. P. Raju, “Partial Discharge Measurement and its Impact on Alternating
Over-Potential Tests on Transformers,” IEE Conference on Diagnostic Testing of HV Power Apparatus in
Service, London, England, Conference Digest, pp. 31–39, Mar. 6–8, 1973.

[B51] Fu, M., G. Chen, and S. Wang, “Practical Application of On-line Partial Discharge Monitoring
Techniques for 500 kV Shunt Reactors,” International Symposium on High Voltage Engineering, paper
O.26.04, Delft, Aug. 2003.

[B52] Fuhr, J., “Non-Standard PD-Measurements-Tool for Successful PD-Source Identification in the
Laboratory,” International Symposium on High Voltage Engineering, paper P.02.07, Delft, Aug. 2003.

[B53] Fuhr, J. et al., “Detection and Localization of Internal Defects in the Insulation of Power Transformers,”
IEEE Transaction on Electrical Insulation, vol. 28, no. 6, 1993.

[B54] Fryxell, J. et al., “Performance of Partial Discharge Tests on Power Transformers,” CIGRE paper
12–04, June 10–20, 1968.

[B55] Gailhofer, G., Kury, H., and Rabus, W., “Partial Discharge Measurements on Power Transformer
Insulation, Principles and Practice,” CIGRE paper 12–15 June, 10–20, 1968.

[B56] Gänger, B. and H. J. Vorwerk, “Ionization Measurements on Transformers,” Brown Boveri Review, vol.
54, no. 7, pp. 355–367, July 1967.

[B57] Gao, W., K. Tan, and Q. Zheng, “Study on Quantification Method of Partial Discharge in Winding of
Power Transformer,” International Symposium on High Voltage Engineering, paper P.02.07, Delft, Aug. 2003.

[B58] Gemant, A. and W. Philippoff, “Die Funkenstrecke mit Vorkondensator,” Zeitschrift für Technische
Physik, vol. 13, pp. 425–430, 1932.

[B59] Guidelines for partial discharge detection using conventional (IEC 60270) and unconventional methods,
CIGRE Brochure 662, 2016.

[B60] Guuinic, P. and L. E. Lundgaard, “Partial Discharges in Power Transformers,” 13th International
Symposium on High Voltage Engineering, paper O.22.03, Delft, Aug. 2003.

[B61] Harrold, R. T., “Voltage Vector Analysis for Corona Location in Transformers,” IEEE Transactions on
Power Apparatus and Systems, vol. PAS-90, pp. 2339–2348, 1971.

[B62] Harrold, R. T. and T. W. Dakin, “The Relationship Between the Picocoulomb and Microvolt for Corona
Measurements on HV Transformers and Other Apparatus,” IEEE Transactions on Power Apparatus and
Systems, vol. PAS-92, no. 1, pp. 187–193, January/February 1973.

[B63] Harrold, R. T. and A. M. Sletten, “Corona Location in Transformers by Radio Frequency

Spectrum Analysis, Parts I and II,” IEEE Transactions on Power Apparatus and Systems, vol. PAS-82,
no. 7, pp. 1584–1602, September/October 1970.

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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

[B64] Hartill, E. R., et al., “Some Aspects of Internal Corona Discharges in Transformers,” CIGRE paper no.
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[B65] Hessen, P. and W. Lampe, “Partial Discharges Triggered by Switching Surge in Power Transformers,”
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[B70] IEC 60060-1, High-voltage test techniques—Part 1: General definitions and test requirements.26

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26
IEC publications are available from the Central Office of the International Electrotechnical Commission (https://​www​.iec​.ch/​). IEC
publications are also available in the United States from the Sales Department, American National Standards Institute (https://​www​.ansi​
.org/​).
27
IEEE publications are available from the Institute of Electrical and Electronics Engineers (http://​standards​.ieee​.org).

37
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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

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38
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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

[B96] Lemke, E. et al., “Experience in the Calibration Technique for PD Calibrators,” 3rd European
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39
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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

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28
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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

[B130] Russwurm, D. and M. Boltze, “Combined RIV and PD Measurements to Satisfy the Various Needs of
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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

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 IEEE Std C57.113-2023
IEEE Recommended Practice for Partial Discharge Measurement in Liquid-Filled Power Transformers and Shunt Reactors

[B162] Zaengel, W. S. and P. Osvath, “Correlation between the Bandwidth of PD-detectors and its Inherent
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