dielectric response power cable system

8/17/2019 Dielectric Response Power Cable System

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Dielectric Response Measurement as DiagnosticTool for Power Cable Systems

Bolarin Oyegoke, Petri Hyvönen, Martti Aro Report TKK-SJT-47

Literature review

ISSN 1237-895XISBN 951-22-5396-8


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2 Dielectric respose as diagnostic tool for power cable systems

Preface

This report summarises a particular part of literature review of research on diagnostic testing

and measurements of power cable systems on-site. The two basic topics partial discharge

measurements and dielectric response measurements are reviewed in separate reports. The

survey on dielectric response theory in Finnish language is based mainly on course given by prof

Roland Eriksson and his colleagues at KTH Sweden in August 2000. The space charge

measurement methods are reviewed as a possible diagnostic tool for high-voltage DC cablesystems in future.

An experimental part with tests and measurements on medium voltage cables on-site is

planned to follow still in 2001.

In addition to the University, this study was funded by the National Technology Agency

(TEKES) and Foundation for development of electric power engineering. Risto Harjanne

(Helsinki Energy) acted as chairman of the project board. The other members were Jarmo

Elovaara (Fingrid), Jari Eklund (TEKES), Kari J Heinonen (Fortum Service), Olli Lindgren

(Fortum Technology Centre), Erkki Kemppainen (ABB Transmit), Jukka Leskelä (Finergy),

Kirsi Nousiainen (TUT), Lauri Nyyssönen (Pirelli Cables and Systems) and Antti Vähämurto

(Empower).

Summarising Report

TKK-SJT-49: Advanced diagnostic test and measurement methods for power cable systems

on-site

Partial Reports

TKK-SJT-45: Partial discharge measurements as diagnostic tool for power cable systems

TKK-SJT-46: Basic theory for dielectric response measurements (in Finnish).

Dielektrisen vasteen mittausmenetelmien teoreettinen perusta.

TKK-SJT-47: Dielectric response measurements as diagnostic tool for power cable systems


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Dielctric response as diagnostic tool for power cable systems 3

Table of Contents

Preface...........................................................................................................................................................2

Table of Contents..........................................................................................................................................3

Summary.......................................................................................................................................................4

1 Introduction.............................................................................................................................................4

1.1 Background....................................................................................................................................41.2 Frequency and time domain methods............................................................................................5

1.3 Comparing time and frequency domain DR measurements ..........................................................5

2 Off-line methods .....................................................................................................................................6

2.1 Measurement of tanδ and total harmonic distortion in the loss current at power frequency.........62.2 Measuring dissipation factor tanδ..................................................................................................62.3 Measuring DC leakage current ......................................................................................................7

2.4 Measuring the polarisation current and DC transient response current.........................................8

2.5 Measuring depolarisation current ..................................................................................................82.6 Measuring return voltage...............................................................................................................8

2.7 Measuring potential decay after charging......................................................................................9

3 On-line methods....................................................................................................................................10

3.1 Measuring DC component in AC charging current .....................................................................10

3.2 Measuring DC superposition current...........................................................................................11

3.3 Measuring the insulation resistance.............................................................................................11

3.4 Measurement of dielectric dissipation factor and DC component...............................................12

3.5 Method of locating water treeing deterioration in XLPE cable insulation on-site ......................12

4 Commercial dielectric response measuring systems.............................................................................13

4.1 Insulation diagnostic system IDA 200.........................................................................................13

4.2 Cable diagnostic system KDA 1..................................................................................................13

4.3 Cable diagnostic system CD30/31...............................................................................................14

4.4 Cable testing and diagnostic system PHG TD.............................................................................15

5 Examples of measurement of dissipation factor in function of frequency..........................................15

6 Discussion.............................................................................................................................................19

References...................................................................................................................................................21

Annex 1. Measurement of Dielectric Response..........................................................................................23


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SummaryDielectric response (DR) is an advanced tool for insulation diagnosis. Insulation deterioration

and degradation change the DR. Measurement of DR at different frequencies or, in time domain

with different time parameters, give some picture of insulation condition.

The major problem associated with medium voltage XLPE cables is deterioration by water

trees, and it sometimes is the main reason for insulation failures in XLPE cables in long service.

For high voltage XLPE cables the major problem is electrical trees. Increased moisture content

will be harmful to the oil-paper insulated cables.

Existing diagnostic methods for detecting water tree deterioration and for evaluation of

moisture content are reviewed. Diagnostic criteria are based on the non-linearity of the DR with

respect to the charging voltage. Measurement of one parameter e.g. tanδ alone, even in functionof frequency, may not be sufficient to reveal the status of the cable insulation. Therefore, its

measurement is often combined with measurement of another parameter e.g. DC leakage current.

Measurement of return voltage alone may not, either, reveal the status of the cable insulation

sufficiently enough. In this respect its combination with some other diagnostic parameters such

as self decay voltage and/or polarisation and deparisation current are proposed and used.

Dielectric response gives an overview of average condition of the insulation system under

study, but no localisation of the possible degraded areas. Further research is needed for more

detailed conclusions regarding the status of a particular insulation. Predicting the remaining life

of the insulation system requires still further research.

1 Introduction

This report deals with dielectric response measurements on insulation of medium voltage

power cable systems.

1.1 Background

One of the major problems associated with the medium voltage XLPE cables is deterioration

by water trees, and it sometimes is the main reason for insulation failures in XLPE cables in long

service. Increased moisture content will be harmful to the oil-paper insulated cables.


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polarisation current behaviour in application of DC voltage on cable system, and as returnvoltage and depolarisation current behaviour after disconnecting and short-circuiting the cable

for a certain time periods.

Measurement of DR is an advanced non-destructive tool for diagnostic testing of different

insulation systems, such as paper-oil and polymeric insulation. DR gives an indication of

insulation condition e.g. of high-voltage cable systems. Changes in insulation such as water trees

and electrical trees or other deterioration change the DR.

1.2 Frequency and time domain methods

Dielectric response can be measured in different ways. Relevant parameters of DR shall be

known when considering and comparing the DR’s of different insulations or DR’s of the same

insulation after certain periods in service. Preferably, certain parameters should be kept constant.

In time domain the DR appears as depolarisation current [5, 9, 10], return voltage (also called

residual, recovery and build-up voltage) [2, 3, 9, 10], polarisation current, discharge voltage [11,

12] and isothermal relaxation current [3, 4]. In frequency domain the DR appears as dissipation

distortion in the loss current at power frequency [13, 16, 17].

Diagnostic criteria are based on the non-linearity of the dielectric response in the time and

frequency domain with respect to the charging voltage. In frequency domain non-linearity is

characterised by a voltage dependent dissipation factor, whereas in the time domain an over

proportional increase of the response with higher charging voltage occurs. Non-linearity in the

dielectric response has been subject of study in many doctoral theses [9, 18, 19, 20].

For on-site application very low frequency (0.1 Hz) voltage tests in combination with tanδmeasurement have proved as a good diagnostic tool for service aged XLPE cables [1, 21].

Measurement of tanδ at 50 Hz was without information about the condition of polymer-insulatedcables under investigation [2]. Furthermore, tanδ measurement at 50 Hz will involve largecapacitive currents compared to VLF (0.1 Hz). Major problem with tanδ measurement at 0.1 Hzwas the sensitivity of the measuring device. However, improved 0.1 Hz tanδ measurementsystem are commercially available [1].


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2 Off-line methods

Dielectric response measurements as diagnostic method to detect deterioration of insulation

can be performed off-line or on-line. Some methods may be used both off-line and on-line.

2.1 Measurement of tan and total harmonic distortion in the loss current at

power frequency

The method deals with the 50/60 Hz insulation loss current measurements in high voltagecable insulation containing water trees. In order to isolate the small insulation loss current from

the significantly larger, quadrature (capacitive) current, a current-comparator-based (CCB) high

voltage capacitance bridge is needed (Fig. 1). The loss current waveform is measured and the

harmonic distortion of the loss current is correlated with the length of water trees. This method is

still at the laboratory research level.

Line

60 Hz 2048 x 60 Hz

C s C x

Phase-Lock Loop

(P.L.L.)

DigitalWaveform

Generator

High V oltage

AmplifierV=0-20 kV

f=0-15 kHz

Detector/ Recorder

FilterHigh V oltage

CCB Capac itance

Bridge

Digital

Scope

Fig. 1. Block diagram of the measurement set-up.


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Current

Transformer

Current

VoltageConverter

Current

Voltage

Converter

90o

Phaseshift

Circuit

Automatic

Balanced

Circuit

tanδ %%0.25

C nF

38.5

isi

Voltage Divider tanδ Measurement sectionTestCable

Fig. 2. Schematic representation of the principle of dielectric dissipation factor measurement.

2.3 Measuring DC leakage current

DC test voltage is applied between the conductor and insulation shield of a cable (Fig. 3).

Magnitude of the DC leakage current is used to judge the situation of the insulation. The

undeteriorated section of cable does not affect the value of DC leakage current, but local

deterioration can be known as an absolute quantity[7]. This implies that since sound part of the

cable insulation do not contribute much to the measured value of DC leakage current, then the

degree of cable insulation deterioration can be estimated by measuring the DC leakage current.

he local deterioration causes a current significantly larger than the sound insulation. This method

involves application of high DC voltage, and it is applicable for on-site off-line measurement.

The combination of the methods of DC leakage current and dielectric dissipation factor

provides an effective means for diagnosing insulation deterioration of cable off-line.

Current limitingresistor


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2.4 Measuring the polarisation current and DC transient response current

Current that is flowing through the cable during charging is measured in time domain. This

current is called as polarisation current. During the charging period the cable is charged with

direct voltage. Different mechanisms of polarisation and conduction that are of great importance

are activated during this period. Polarisation current is not measured during transient period after

applying charging voltage. Variable parameters during the measurements include the charging

voltage and period and the period for polarisation current measurement. Values of the

polarisation current during the measurement and voltage nonlinearity of polarisation current

carries information about the insulation condition.

The peak of the current that is flowing through the cable immediately after applying charging

voltage is called as DC transient response current. Its value carries information about the

insulation condition as well.

Measurement of polarisation current Ip and DC transient response current is performed during

the charging period (Fig. 4).

2.5 Measuring depolarisation current

The procedure of measurement of depolarisation or discharge current can be divided into two

parts (Fig. 4). During the charging period the cable is charged with direct voltage. Different

mechanisms of polarisation and conduction of great importance are activated during this period.

After the charging period the cable is disconnected from the direct voltage source and short-

circuited with current measuring system. Different mechanisms of depolarisation are activated.During this period the depolarisation (discharge) current Idp is measured and integrated to obtain

the absorption charge Q. Ratio of Q to capacitance C of the cable is used as index of the

deterioration. Variable parameters include the charging voltage and period, and the period for

discharge current measurement.

Usually, the large transient discharge current immediately after the short-circuit is not

measured, although it also may include some information on insulation condition.

2.6 Measuring return voltage

Four different terms are used in literature on the same quantity, i.e. return, residual, recovery

and build-up voltage. The procedure can be divided into three parts (Fig. 4). During the charging

period the cable is charged with direct voltage. After that, the cable is disconnected from the


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dp

Time (s)

p

ch

Short circuit

Return voltage periodCharging period

Return voltage

o l t a g e ( V )

u r r e n t ( A )

Fig. 4. Polarisation, depolarisation and return voltage method.

2.7 Measuring potential decay after charging

The voltage discharge rate, i.e. the initial steepness of the self-discharge voltage is used as the

parameter for the diagnosis. In this method only the decay voltage Ud is measured (Fig 5).

In the combined method (voltage response method), also the return voltage is measured

(Fig. 5). By measuring the initial steepnesses of the two voltage curves the two dielectric

processes, conduction and polarisation, can be investigated separately.

Combined measurement of the potential decay after charging (Fig. 5) together with the

depolarization (discharge) current (Fig. 4) is also used for diagnosis.

UchUd

Voltage (V)

Sd

Return voltage

S


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3 On-line methods

Water trees has long time been recognised as the most hazardous factor in life of XLPE

distribution cables and the major cause of insulation failure. The existing methods for cable

diagnosis such at the measurement of the DC leakage current and or tanδ require an interruptionin electrical service and needs extensive installation work. For these reasons, in Japan some hot-

line diagnostic methods are developed and used to detect water tree deterioration.

These methods include the DC current in AC charging current method, the DC superposition

method, a method to measure insulation resistance, and a method of detecting electrical tree

deterioration in XLPE cable insulation on-site. Accuracy of the DC component current method

and the DC superposition method is compared in [8].

3.1 Measuring DC component in AC charging current

When high AC voltage is applied to cable insulation, a DC component may be detected in theAC charging current within a short time. It is known that the magnitude and polarity of the DC

component are closely related to deterioration of the cable insulation. Accordingly, the degree of

cable insulation deterioration can be estimated by measuring the DC component [6, 7].

A switch is connected between the other end of the metal shield for the purpose of

disconnecting it from the ground during the measurement [6]. For the DC component

measurement the switch is opened (Fig. 6). A closed circuit is formed by connecting thegrounding potential transformer, distribution line, cable under measurement, measuring device

and ground in series.

Source

To load

High voltage (6.6 kV)

distribution line


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3.2 Measuring DC superposition current

In this method a DC voltage is superimposed over the AC operating voltage (Fig. 7). The

superimposed voltage is applied between nodes 1 and 2. The DC superposition current Ids is

obtained by calculating the difference between two current values measured with a superimposed

voltage of different polarity applied between nodes 1 and 2 (Ids = Ids+ - Ids-). The DC current

component Idc is also measured without DC superimposed voltage [8].

2

1

Cable

AC Supply

Capacitor

50 µF

DC Supply

MeasuringDevice

Transformer

Fig. 7. Set-up for the DC current component method and DC superimposed method.

3.3 Measuring the insulation resistance

The method is applicable to a distribution system with a grounding potential transformer GPT

(Fig. 8). A DC source of about –50 V is connected between the neutral point and the ground

through a blocking coil and switches for applying the negative DC voltage to an AC cable

without turning off the AC. The measuring system is mainly composed of a measuring circuit forthe resistance and a device for discriminating the stray ground current. The resistance value

measured with this method has close correlation with the insulation resistance obtained by

measuring the DC leakage current as a conventional method [6].

Source


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4 Commercial dielectric response measuring systems

4.1 Insulation diagnostic system IDA 200

Insulation Diagnostic System IDA 200 is a system measures the complex impedance of a

cable at a variable voltage and frequency (capacitance and tanδ at 0.0001-1000 Hz). A digitalsignal processing unit (DSP) generates a test signal with the desired frequency (Fig. 10).

Imag(Ch 0)

Real(Ch 0)

Real(Ch 1)

Imag(Ch 1)

Ch0

cost

Asint

Sinewave

generator sintA

Test

object

Lo

Hi

Ground

Guard

A

V

∫

∫

∫

∫

X

X

X

X

A

Ch1

Principle of the sine correlation technique. Schematic block diagram of the IDA 200-system.

Fig. 10. Schematic block diagram of the IDA 200-system and the principle of the sine

correlation technique.

The signal is amplified with an internal amplifier and then applied to the cable. The voltage

over and the current through the specimen are measured with high accuracy using a voltage

divider and an electrometer.

For the measuring input, IDA 200 uses a DSP unit that multiplies the input (measurement)

signal with a reference sine voltage, and then integrates the results over a number of cycles. With

this method, noise and interference is rejected-allowing IDA 200 to work with voltage levels up

to 200 V and still achieve high accuracy and detail of analysis. (Programma).

4.2 Cable diagnostic system KDA 1


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Sheath

i(t)

Conductor

3

2

1

RC Rd RM

UFA A

D

Computer

Cable jacket

1: DC Charging 2: Discharging 3: Measurement

inner/outer

semiconductor

Fig. 11. Basic measurement circuit for the IRC-Analysis.

An empirical ageing factor (A-factor) is calculated to classify the ageing condition of the

cable. This factor is calculated from depolarisation current ID at time constants τ3 and τ2 as

( )( ) 22D33D

.I

.IAτ τ

τ τ =

4.3 Cable diagnostic system CD30/31

The Cable Diagnostic System CD30 is for evaluation of the ageing degree and the damage

condition of 1 kV to 30 kV PE and XLPE cables. The model CD31 is for oil-paper cables. The

devices base upon measurement of return voltages at different charging voltages (Fig. 12).The tested cable is charged with DC voltages (0.5, 1, 1.5, 2U0) for 5 minutes (switch S1).

Then, the high voltage source is turned off and the switch S2 closed for two seconds to discharge

the cable capacitance over a resistor RD. (Hagenuk)


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After this time the return voltage is measured for 10 to 40 minutes, depending on the cable

length. For that, the cable is connected to the high input impedance measurement receiver U(switch S1). The measured value of return voltage is digitised and forwarded to the PC.

The maximum values of the return voltages are plotted as a function of the charging voltage.

This relationship can be linear or non-linear. The linearity factor is calculated as the ratio

between the maximum values of the return voltage at 2U0 and U0 and used as an indicator of the

ageing condition. The factor grater than 2 is considered as a non-linear response and signifies

ageing of the cable and the factor 3 indicates a strongly aged cable.

4.4 Cable testing and diagnostic system PHG TD

The instrument PHG TD measures tanδ at different sine voltage levels maintained at 0.1 Hz.The tanδ at 2U0 and the difference between 2U0 and U0 values are used as diagnostic criteria. Atanδ value larger than 3102.1 −× at 2U0 or the difference of tanδ at 2U0 and U0 largerthan 4106 −× signifies water tree deterioration. If the cable is very long, it is possible to reduce the

measuring frequency to 0.01 Hz in order to reduce the capacitive current generated by the highvoltage source. However, as a consequence the measuring time will increase. (Baur)

5 Examples of measurement of dissipation factor in

function of frequency

Three oil impregnated paper insulated cables were measured in laboratory. Measurement of

dissipation factor as a function of frequency was performed with IDA-200 measuring system.

TanD elta Cable1

0,1

1

D e l t a Phase-A

Phase-B


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Cable 1 is a 20 kV single-phase cable with aluminium conductor and sheath. Phase A con-

tained a joint. Phases B and C were without joints. Samples of cable were removed from servicedue to external mechanical failure. During the measurement of the dielectric response of the ca-

ble, its metallic sheath was connected to ground. Voltage supply and measurement was con-

nected to the phase conductor. Current measurement was connected to the ground conductor.

Guard connector of the IDA-200 termination box was left open. (Fig 13).

All three phases of cable 1 show different responses. Comparing the responses of phase A to

the phases B and C one will notice the influence of the joint that is present in phase A. The main

difference between response of phases B and C is that the response of phase B is shifted slightly

towards higher frequencies.

The minimum value of the response is believed to carry information about the moisture

content in the cable. In this regard for phase B and C the tanδ minimum can be seen to occur at50 Hz and 10 Hz, respectively. For phase B the magnitude of tanδ is slightly lower than that forphase C. Based on this finding one may conclude that phases B and C are practically under the

same condition in terms of moisture content.On the other hand, the minimum of tanδ measured in phase A is not clearly indicated. The

presence of a joint in this phase is the most likely factor that is affecting the response measured

on this phase. It would be interesting to see the contribution of the joint on the measured result

before taken decision on the condition of the cable especially on phase A.

TanD elta C able2

0,01

0,1

1

T a n D e l t a Phase-A

Phase-B

Phase-C


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Cable 2 is a 20 kV three phase cable with aluminium conductors. All phases have own alu-

minium sheaths and outer jackets. Phases are combined inside one outer jacket. The cable wastaken to measurements from store-house. During the measurements, metallic sheaths were con-

nected to ground. Voltage supply and measurement was connected to phase conductor under the

test. Guard connector of the IDA-200 termination box was connected to the other phases. Cur-

rent measurement was connected to the ground conductor.

The main difference between response of phases of cable 2 is that the response of phases B

and C is shifted slightly towards higher frequencies (Fig.14). The minimum of the response on

phase A show up at 25 Hz. For phases B and C the minimum values show up practically at thesame frequency 35 Hz, and their magnitudes are also practically equal. A slightly higher tanδvalue minimum can be seen on phase A.

The phases B and C of cable 2 are in the same condition with respect to the moisture content.

However, phase A may have a slightly higher moisture content.

Cable 3 is a 20 kV three phase cable with aluminium conductors. All phases are inside of one

lead sheath. The phases have no separate metallic sheaths. The cable does not contain outer

jacket. During the measurement, all phases were connected together. The lead sheath was con-

nected to the ground. Voltage supply and measurement were connected to the phases. Current

measurement was connected to the ground conductor. Guard connector of the IDA-200 termina-

tion box was left open.

The minimum of the response on cable 3 occurs at about 4 Hz (Fig. 15). The magnitude of

this minimum tanδ is almost equal to that measured on phase B and C of cable 2.

TanDelta Cable3

0,1

1

TanDelta

Phase A+B+C


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Fig 16 presents a combined measurement result on three different cables. In view of the

preliminary result of tanδ measurements performed in the laboratory the following remarks canbe made.

Generally, the minimum values of tanδ in cable 2 and cable 3 are lower than that of cable 1.This can be interpreted in term of moisture contents. The moisture contents in cable 2 and cable

3 appear to be lower that of cable 1.

It was observed in this preliminary investigation that the minimum values of cable response

do not generally occur at 50 Hz. In the cases studied the minimum value at 50 Hz was observedonly in one phase of one cable. In all the other cases this minimum values occur at different

frequencies below 50 Hz.

TanDelta

0,001

0,01

0,1

1

0,01 0,1 1 10 100 1000

T a n D e l t a

C1, PA

C1, PB

C1, PC

C2, PA

C2, PB

C2, PC

C3, PABC


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6 Discussion

A degraded insulation system shows increase of losses and decrease of dielectric strength.

Dielectric response in its all appearance is a tool which can indicate the degradation and hence

condition of electrical insulation of any kind.

Water trees initiate and grow under electric field after water has penetrated into polymeric

insulation. Water trees have long time been recognised as the most hazardous factor in life of

XLPE distribution cables and the major cause of insulation failure.

Water trees increase the tanδ and capacitance and decrease the electric strength of polymer-insulated cable. In addition, water and water trees modify leakage currents, DC absorption

current, polarisation and depolarisation current as well as discharge voltage decay and return

voltage. Field measurements of some of these parameters have proven to be a suitable means to

detect degradation and presence of water trees. However, many measurement techniques have

disadvantages, which have prevented their widespread application. For instance, tanδmeasurement gives overall condition of the cable system and not that of the deteriorated part of

the cable. Also leakage current in joint and termination appear in the leakage current of the cablesystem. [24].

The existing methods for cable diagnosis such at the measurement of the DC leakage current

and or tanδ require an interruption in electrical service and needs extensive installation work. Forthese reasons, in Japan some on-site on-line diagnostic methods such as the DC component

current method and the DC superposition method, are used to detect water tree deterioration.

Accuracy of the DC component current method and the DC superposition method iscompared. As a conclusion the on-line diagnostic methods are considered as efficient as the DC

leakage current method. However, the method based on the DC superposition may not be

applicable to all cables on-site. This is because with a low voltage (< 100 V), water tree can be

detected in some cable, while in others superimposed voltage of 10 kV or more is necessary. At

these relatively high DC voltages one must expect breakdown.

Combination of the measurement of tanδ and the total harmonic distortion in the loss current,

is a new method for diagnosis of power cable systems. However, this method is still on thelaboratory level. Moreover, the significance of the relative values of tanδ and the total harmonicdistortion current in the insulation is not yet understood.

Results of accelerated ageing studies show that tanδ and water trees of polymeric cableincrease with acceleration time and voltage, which both are important. However, as an example,


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Many researh groups have carried out measurement of dielectric response of oil-paper

insulation systems either in time domain or frequency domain. The dielectric response in bothdomains provides novel diagnostic methods for quality control of medium and high voltage

cables. However, the information obtained in frequency and time domain is equivalent only if

the insulation system is linear. In addition, dielectric response measurements in both domains

indicated that measurement of non-linearity in the dielectric response could become the basis for

diagnosis of water tree degradation in cable. Non-linearity in the dielectric response has been

subject of study in many doctoral theses [9, 18-20].

Measurement of loss angle of oil-paper cables as a function of frequency is normally

performed using a low voltage power supply. Higher moisture content of insulation will increase

loss angle. Anyhow, this behaviour is not so clearly seen through whole frequency range. Loss

angle curves representing different moisture contents can cross each other. The loss angle has a

minimum value which tends to increase with higher moisture content. This means that the

assessment of insulation condition for different mass impregnated cables regarding its moisture

content can be based on the minimum of loss angle.

Polarisation (charging) and depolarisation (discharging) currents of oil-paper insulation will

increase with moisture content. In addition to dielectric response function, the time domain

measurement of polarisation and depolarisation currents allow for estimation of the conductivity

of the test object. Increase in moisture content will increase conductivity. It is important to

observe that the conductivity of oil paper system is strongly dependent upon the temperature.

Without knowledge of temperature no simple criterion based upon the conductivity can be used

to estimate the moisture content.

Dielectric response gives an overview of average condition of the insulation system under

study, but no localisation of the possible deteriorated areas. Predicting the remaining life of the

insulation system based on DR and/or other measurements requires still further research work.


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References[1] M. Kuschel et al. 1995 “Dissipation Factor Measurement at 1 Hz as a Diagnostic Tool for

Service aged XLPE- Insulated Medium Voltage cables.” 9th

ISH Graz Austria, paper 5616.

[2] M Sturm and R Porzel 1995. “Progresses By the Computing Dielectrical Diagnostic of

High Voltage Insulation.” 9th ISH Graz Austria paper 5624.

[3] G. Hoff and H. G. Kranz 1999. “Correlation between Return Voltage and Relaxation

Current Measurement on XLPE Medium Voltage cables.” High Voltage EngineeringSymposium, IEE Conference Publication No. 467 paper 5.102.514

[4] M. Beigert et al. 1993. “ Computer-Aided Destruction free Ageing Diagnosis for Medium

Voltage Cables.” 8th

ISH Yokohama, Japan paper 67.11.

[5] M. Kuschel et al. 1997. “Dielectric response-a Diagnostic Tool for High Voltage

Apparatus.” 10th ISH Montreal, Quebec Canada paper 393-396.

[6] K. Soma et al. 1986 “Diagnostic Method for Power Cable Insulation.” IEEE Transactionson Electrical Insulation Vol. EI-21, No. 6, pp. 1027-1032.

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pp. 1513-1520.

[8] M. Hotta et al. 1995. “A Consideration of the Efficiency of Hot-Line Diagnostic Methods

for XLPE Power Cables.” 9th

ISH Graz 1995 paper 5635.

[9] S. Hvidsten 1999. “Nonlinear dielectric Response of Water Treed XLPE cable Insulation.”

Dr Ing thesis, NTNU, Trondheim, Norway, ISBN 82-471-0433-4.

[10] S. Hvidsten et al. 2000. “Condition Assessment of water treed service Aged XLPE Cables

by Dielectric Response Measurements.” Cigre 2000 Paris, paper 21-201.

[11] M. Muhr et al. 1997. “Investigations of 30 kV Polyethylene-Cables with the Discharge

Current Method.” 10th ISH Montreal, Quebec, Canada, pp. 409-412.

[12] E. Nemeth 1999. “Measuring Voltage Response: A non-destructive Diagnostic Test

Method of HV Insulation.” IEE Proc.-Sci. Meas. Technol., Vol 146, No. 5, pp. 249-252.

[13] A. T. Bulinski et al. 2000. “Measurement of the Harmonic Distortion of the Insulation

Loss Current as a Diagnostic Tool for High voltage Cable insulation.” IEEE Power


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[18] A. Helgesson 2000. “Analysis of dielectric Response Measurement Methods and Dielectric

Properties of Resin-Rich Insulation During Processing.” Doctoral thesis, KungligaTekniska Högskolan, Department of Electric Power Engineering, Electrotechnical design

Stockholm, Sweden. TRITA EEA-0002, ISSN 1100-1593, 210 p.

[19] R. Neimanis 2001. “On Estimation of Moisture content in Mass Impregnated distribution

Cables.” Kungliga Tekniska Högskolan, Department of Electric Power Engineering,

Electrotechnical design Stockholm, Sweden. TRITA EEK-0101, ISSN 1100-1593, 195 p.

[20] Vahe Der Houhanessian 1998. “Measurement and Analysis of Dielectric Response in Oil-

Paper Insulation systems.” Dissertation for the degree of Doctor of Technical Science,Swiss Federal Institute of Technology Zurich, Diss. ETH No. 12832, 108 p.

[21] G. Kaul et al. 1993. “Development of a Computerized loss Factor Measurement System for

Different Frequencies, Including 0.1 Hz and 50/60 Hz.” 8th

ISH Yokohama, paper 56.04.

[22] S. Pöhler 1989. “Dissipation Factor Measurements on Water Treed and Non-Water Treed

XLPE Insulating Material.” 6th ISH New Orleans, LA, USA, paper 13.28.

[23] A. Paximadakis et al 1991. “Drying and Refilling of Water Trees in Medium VoltageCables.” 7

th ISH, Dresden Germany, paper 23-05.

[24] G. Bahder et al. 1977. "In Service Evaluation of Polyethylene and Crosslinked

Polyethylene Insulated Power Cables Rated 15 to 35 kV." IEEE Transactions PAS-96,

No. 6, pp. 1754-1766.


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Annex 1. Measurement of Dielectric ResponseMethod Description Voltage Place Commercial equipment Test duration

Return Voltage Return voltage is measured after a period of charging and

discharging the cable.

DC up to 24 kV On-site

*Off-line

CD30/31 Manufacture

by HAGENUK

1 h/phase

DC Leakage

Current

DC test voltage is applied between the conductor and

insulation shield of a cable and the current that flows on

application of test voltage is measured.

DC 2-10 kV On-site

*Off-line

Ac test voltages are applied between the conductor andinsulation shield of a cable, and dielectric dissipation factor or

each application of test voltage.

AC voltage up tothe rated line-

ground voltage

Laboratory Schering bridge

0.1 Hz

(0.1 Hz) but variable voltage.

AC 24 kV (rms) On-site

*Off-line

PHG TD Manufacture by

BAUR

10 min/phase

Capacitance and

frequency

voltage but variable frequency (1mHz - 1kHz).

AC 20 kV (peak) On-site

*Off-line

IDA 200 Manufacture by

PROGRAMMA

30 min/phase

DC Leakagecurrent and

A DC voltage is applied to the cable in step for some time anddc leakage current is measured at each stage.

On-site*Off-line

Depolarisation

Current

The cable is charge or polarise with a dc voltage. Then

grounded or circuited for short period. During the grounding,

discharging or depolarisation current is measured.

DC On-site

*Off-line

KDA 1 Manufacture by

SEBA

1 hour/phase

Polarisation

Current

The cable is charge or polarise with a dc voltage. During the

charging the charging or polarisation current is measure.

DC On-site

*Off-line

Polarisation

Current,Depolarisation

Current, Return

Voltage.

The cable is charge or polarise with a dc voltage. During the

charging the charging or polarisation current is measure.Then grounded or circuited for short period. During the

grounding, discharging or depolarisation current is measured.

Then open circuited, during this time return voltage is

measured.

On-site

*Off-line

Not Available

D i e l e c t r i cr e s p o n s e a s d i a g n o s t i c t o o l f or p o w er c a b l e s y s t e m s

2 3


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Method Description Voltage Place Commercial equipment Test duration

Total Harmonic

Distortion in the

Loss Current at

50/60 Hz

In this method the total harmonic distortion in the insulation

loss current is measured at a power frequency.

AC 35 kV Laboratory

Harmonic

Distortion in the

Loss Current at

50/60 Hz.

distortion in loss current are carried out. Both parameters give

information about cable ageing.

AC 35 kV Laboratory

DC Component

in AC Charging

Current

High AC voltage is applied to cable insulation. For a short

period dc component of current can be detected if the cable

has water tree. The magnitude of this dc component and its

polarity is use to judge deterioration of the cable insulation.

AC operating voltage On-site

*On-line

Developed and used in

Japan. Availability not

known.

DC

Superposition

Current

A DC-superposed voltage is imposed over the normal ac

operating voltage. The dc superposition current is obtained by

calculating the difference between two current values

measured with a superposed voltage of different polarity.

DC voltage On-site

*On-line

Developed and used in

Japan. Availability not

known.

Component in

AC Charging

Current

DC leakage current and dielectric dissipation factor are

measure for the purpose of diagnosing XLPE cables for

insulation deterioration. Combined measurements of these

parameters give an accurate diagnosis of insulation

deterioration. The diagnostic system was designed to consist

of three separate units, measurement section, charging current

detection section, and circuit breaker section.

Operating voltage On-site

*On-line

2 4

D i e l e c t r i cr e s p o n s e a s d i a g n o s t i c t o

o l f or p o w er c a b l e s y s t e m s

dielectric response power cable system

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