EE-471 HIGH VOLTAGE ENGINEERING

Voltage Testing & Partial Discharge

Measurement For Power Cable Accessories

PRESENTED BY : SYED ATIF CHISHTI

SUBMITED TO : PROF DOC :BULENT BILIR

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PRESENTATION SEQUENCE

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OBECTIVE

INTRODUCTION

AC TEST AFTER INSTALLATION

ACRF TEST SYSTEM

SCHEMATIC DIAGRAM OF TEST SYSTEM

PARALLEL OPERATION MODE OF TEST SYSTEM

PARTIAL DISCHARGE METHODS & PRINCIPLE.

DISCUSSION & CONCLUSION.

OBJECTIVE : To compare best practices for cable testing.

Predictive diagnostic programs to aging cable.

To determine the faulty joints cable defects

INTRODUCTION

Using Frequency tuned resonance

Test system (20-300 Hz) to calculate PD measurement.

PD measurement method are necessary to trace defect and insulation of cable.

Voltage testing provide information about defect in the insulation is dangerous or not for later operation.

Calibration is done through PD calibrator on the cable termination.

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Power Cables importance in Transmission & Distribution system

Consist of :

Cable

Joint

Termination

Identification & Localization of partial discharge.

AC TEST AFTER INSTALLATION

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Follow the international standards IEC 60840 and IEC

62067 for testing of Power cable insulation and their

accessories.

Apply : sinusoidal waveform, frequency: 20 and 300 Hz,

voltage applied for 1.7 U0 /1 hour

Methods of Voltage Generated

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By a reactor with variable inductance and fixed excitation

frequency 50 or 60 Hz (ACRL) test system.

By a reactor with fixed inductance and frequency tuned

voltage excitation (ACRF) test systems.

ACRF TEST SYSTEM

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HV Reactor

Exciter Transformer

Control Unit

Feeding Unit

Blocking Impedance

Voltage Divider & Software

Frequency Convertor + Protection Impedance.

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SCHEMATIC DIAGRAM OF TEST

SYSTEM

PARALLEL OPERATION MODE OF TEST

SYSTEM

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OPERATING RANGE OF THE RESONANT TEST

SYSTEM (ACRF)

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PARTIAL DISCHARGE

Partial discharges are a sensitive measure of local electrical

stress and the measurement is often used as a quality check of

the insulation.

Cable has small voids, cavities, insulating contaminant

conductive protrusions in different interfaces or mechanical cuts.

Erosion by ion bombardment and chemical effects gradually

change small defects to electrical trees with consequent final

breakdown.

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METHODS OF PD MEASUREMENTS

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HIGH FREQUENCY CURRENT TRANSFORMER

HFCT method at cross bonding box for 220 kV or earth wire of 66 kV for XLPE cable

systems Showed high sensitivity and calibration is possible using PD calibrator on the

cable terminations.

COUPLING CAPACITOR

PD detection of high frequency signal generated from PD activities. Measurement by use of

a coupling capacitor is physically limited to a maximum detectable cable length of

approximately 2 km, depending on cable parameters and PD background noise.

WORKING PRINCIPLE

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The sensitivity of the partial discharge detector has to be modified until the

detector shows the calibration charge.

For 220 kV, PD measurements carried out during HV tests, using a test

sequence providing several increase the voltage in steps of 127 Kv (U0) and take

a PD-measurement recording during 1 minute and afterwards increase the voltage in

further steps until 216 kV

At each step note the measured PD value.

Once reaching 216 kV leave this voltage applied for 1 hour and observes if

there is a change in the recorded PD pattern and value.

While ramp the test voltage down, take another PD measurement for 1 minute

at 127 kV.

Time characteristic of the 216 kV

Voltage test

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PARTIAL DISCHARGE

MEASUREMENT

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Internal sensors integrated in each accessory or external

sensors HFCT placed inside bonding link boxes.

The PD sensitivity using HFCT the central measuring

frequency is recommended is to lie between 2 MHz and 10

MHz in a flat zone of the frequency spectrum.

CROSS BONDING LINKS WITH MOUNTED THREE

HFCT SENSORS FOR PD

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Test carried out on two cables having specification

1x3x1600 mm2,CU /XLPE/LEAD/HDPE ,220 kV with approximately 13 km long,19

joints/phase, 3 straight joint box and 16 insulated joint box which are divided into two

sections by means of joints and it is terminated by composite three outdoor and three

GIS sealing ends per circuit.

The result was a resonant frequency of 35.53 Hz for test voltage 216 kV.

Inject a calibration pulse with known quantity of charge at the outdoor system

termination (i.e., between HV and ground terminals), the sensitivity of the PD detector

has to be modified until the detector shows the calibration charge.

PD pulses occur in very short time, the width and rise time of the pulses are in the

nanosecond region. Consequently, PD pulses with energy frequency up to hundred

MHZ are generated these PD pulses will travel through the cable earth conductor and

finally can be recorded by the sensors

TEST RESULT & DISCUSSION

PARTIAL DISCHARGE RESULTS FOR

CIRCUIT 1 & 2

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variation OF PC pattern during

PD measurement

PD measurement OF pattern

with some noise

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EXAMPLE OF JOINT FAILURE DURING

WITH STAND TEST BY USING RESONANT TEST

SYSTEM

CONCLUSION

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After installation of cable , test for HV/EHV XLPE cables system by using resonant test system of (20 Hz -300 Hz) combined with PD detection is performed by using HFCT sensors at each cross bonding (CB) link boxes reduces the risk from the service.

After detecting the location of fault and repair the cables and their accessories was done exactly in the same place given good results.

The experiences also show that the test voltage with U0 for 24 h is not feasible for incidence of failure after the test could be occurred.

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