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Conventional and

Un-Conventional Partial Discharge

Detection Methods in High Voltage

XLPE Cable Accessories

Presented By:

Harshit Bhandari8th Sem Electrical

Guided by:

Prof. Harish Khyani

CONTENTS

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What Is XLPE ? Problem with XLPE cables Detection of Faults Partial discharge What causes partial discharge ? Partial discharge detection methods Classification Conventional MethodConclusion

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What is XLPE ?

XLPE stands for Cross-linked Polyethylene cables .

These are most extensively used power cables for transmission of High voltages

They are frequently used for both overhead and underground high voltage transmission system

XLPE Cable

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Power cable system basically consists of cables themselves and their accessories.

Cable accessories consist of joint and termination.

As the extensive application of Cross-linked Polyethylene (XLPE) cable in power grid, power accidents caused by insulation faults in cable equipments are increasing constantly.

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Insulation faults occur more often in cable accessories and the existence of insulation faults, can lead internal partial discharge (PD) to occur.

The cable laying method is mainly concerned with underground, which brings. problems on state testing and fault localization in cable systems

Therefore, how to judge the cable insulationsituation effectively and locate the fault site accurately is ofgreat practical significance

Partial Discharge Partial discharges are in general a consequence of local electrical stress concentrations in the insulation or on the surface of the insulation.

Generally, such discharges appear as pulses having a duration ofmuch less than 1 ps.

More continuous forms can, however, occur, such as the so-called pulse-less discharges ingaseous dielectrics.

For eg:- Corona Discharge7

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What causes Partial Discharge?

After installation or long time use, the insulation of cable or accessories may include small voids and cavities, conductive or insulating contaminants, or conductive protrusions in different interfaces.

The installation may also cause other defects like mechanical cuts.

During the service the temperature variation and other environmental stresses as well as electric filed and heating due to load current may enlarge these defects, and partial discharges may be incepted.

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These effects may also introduce cavities in originally sound cable insulation or enlarge original micro voids.

Partial discharge measurement methods are most important and preferred and they have received much attention in recent years.

Cont…

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Partial discharge (PD) measurement methods are most important and preferred in testing of underground high voltage cables and they have received much attention in recent years.

Apparent charge, partial discharge inception voltage as well as number and distribution of PD pulses are most important quantities for the determination of the insulation quality.

Identification with certain PD patterns and localization of PD are most important aspects.

Classification

Partial discharge detection method can be classified into two techniques

Conventional and

Un-conventional

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Conventional Method Conventional PD detection is a standardized method for PD measurement as described in IEC 60270.

This method based on measurement of apparent charge displacement q in the leads of the sample. This charge is usually expressed in Pico-Coulombs (pC)

Unconventional Method

Un-conventional PD measurement is based on detection of high frequency PD activities.

Conventional MethodPartial discharges that occur in the test object will produce

current or voltage pulses.

Output PD pulse magnitude is more or less a measure of the PD current amplitude and not for the apparent charge

This method based on measurement of the charge

displacement q, expressed in (pC), from the pulses which generated from partial discharge

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The tests are carried out in the Extra High Voltage Research Centre (EHVRC) PD Lab. In these PD measurements, 50Hz continuous AC voltage is used as an energizing method.

Using this PD detector several important parameters of PD occurrence can be obtained such as:

• PD inception voltage (PDIV) • PD magnitude in pC at PDIV • PD magnitude as a function of voltage applied • PD pattern

The PD measurements have been carried out according to IEC

for the XLPE cable sample 220 kV -1600 mm2 with two different type of joint and termination as shown in figure

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PD measurement is carried out in 2 minutes for each test voltage. During this period three quantities are recorded:

The number of PD pulses,The maximum value of PD magnitudes and The average value of PD magnitudes . These three quantities are plotted as a function of phase

angle of sinusoidal AC voltage. 1 and the PD measurements results as shown in next Figure

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Phase-position quantities Hqmax (φ), Hqn(φ) and Hn(φ)processed for discharges at a test voltage 190 kV for 2 minutes

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3D distribution as obtained at 190 kV

PD pattern for a joint at 127 kV

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Unconventional MethodUn-conventional PD detection is used to provide result with

suppressed noise or high signal to noise ratio.

Basically there are two main methods, High Frequency/Very High Frequency/ Ultra High Frequency (HF/

VHF/ UHF) Acoustic method.

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Fault Detection in Cable

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Fault Detection in Undergroundcable

This methods use HFCT (High Frequency Current Transformer).

Using ultrasonic detector acoustic waves due to partial discharge are detected .

This method does not requires any testing lab or heavy equipments

On-site detection of faults can be done easily with a semi skilled person

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Unconventional Method

CB Link with mounted three HFCT (PD Sensor)

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Query??

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