Partial Discharge Analysis

Presented by:Presented by:Remya Rebecca Manuel,Remya Rebecca Manuel,S7 EEE, Roll No: 46S7 EEE, Roll No: 46MBCETMBCET

04/08/23 PDA; Remya Rebecca Manuel, S7 EEE. Roll No: 46 2

Contents

Introduction What is Partial Discharge? Types of Partial Discharge What causes Partial Discharge? Partial Discharge Process Effects of Partial Discharge Partial Discharge Testing Need for Partial Discharge Analysis Conclusion References


Introduction

Partial Discharges (PD) are the localized electrical discharges within an insulation system, restricted to only a certain part of the dielectric.

Partial Discharges are not the complete breakdown, but have an impact on the life of insulation, particularly solid and liquid dielectrics


What is Partial Discharge?

“Partial Discharge (PD) is the localized dielectric breakdown of a small portion of a solid or liquid electrical insulation system under high voltage stress.”

PD can occur in a gaseous, liquid or solid insulating medium.


Partial Discharge is often initiated - within gas voids enclosed in solid insulation, such

as voids in an epoxy insulator.

in bubbles within a liquid insulating material, such as gas bubbles dissolved within transformer oil.


Types of Partial Discharge

Partial discharges occur wherever the electrical field is higher than the breakdown field of an insulating medium

Some of the typical partial discharges: Cavity discharge Surface discharge Corona discharge Treeing Channels


1. Cavity Discharge

Occur due to the presence of cavities in solid or liquid insulation.

Discharges are formed when the gas within the cavity is overstressed.


2. Surface Discharge / Tracking

It is the formation of conducting path on the surface of dielectric due to surface erosion under voltage applications.


3. Corona Discharge

Discharges are due to the presence of inhomogeneous fields.

Phenomenon is accompanied by Violet glow Hissing sound Production of ozone Radio interference


4. Treeing Channel

Branching channels are created within/on the surface of solid dielectric material as a result of cumulative partial discharges

Continuous impact of discharges in solid dielectrics forming discharge channels


Causes of Partial Discharge?

Due to overloads, manufacturing defects, ageing.

Due to the presence of void and contamination

TEAM stresses of insulation Thermal, temperature Electrical, electric field Ambient (environmental) Mechanical Vibrations

Formation of Water Trees


Partial Discharge Process


Effects of Partial Discharge


Partial Discharge Equivalent Circuit


PD voltages & pulse currents at a cavity in the dielectric


Significance of Tan-delta/Dissipation factor/Loss Factor

Predicts the life expectancy of insulation


Partial Discharge Testing

Off-Line Testing Techniques Power Factor/Loss Factor Testing Very Low Frequency Testing (VLF)

In-Service Testing Techniques Ultrasonic PD Detection Partial Discharge Testing


Power Factor /Loss Factor Testing In a perfect insulation, angle ∂ = 0 As angle ∂ increases, resistive current increase, meaning

contamination Greater the angle, worse is the insulation.


Very Low Frequency / VLF Testing

It is a withstand test (pass/fail test)

VLF high voltage is supplied across the dielectric for 15+ minutes.

Supply Frequency is normally 0.1Hz


Ultrasonic PD Detection

A piezoelectric transducer is used to convert acoustic energy into electrical energy

Two types of sensors are used in acoustic detection Accelerometers Acoustic emission sensors.

Accelerometers have a useful frequency range of up to 50 kHz

Acoustic emission sensors have a frequency range between 30 kHz and 1 MHz


Sensors used for Acoustic Detection


Partial Discharge Testing Represents the insulation condition at the actual

operating voltage

High Frequency Current Transformer (HFCT) sensor can be easily connected to the earth cable connected to the cable screen.


HFCT Sensor used for PD detection

The High Frequency

Current Transformer (HFCT) sensor has a split core construction

Disconnection of the earth cable is not requires in order to insert the HFCT sensor.


Partial Discharge Analysis

Partial Discharge Analysis is a diagnostic approach which uses PD measurements in order to evaluate the integrity of the equipment

It is essential to measure the PD levels and sensitively monitor the deterioration of insulation as a function of time.


Need for Partial Discharge Analysis

To determine the condition of equipment frequently

To enhance electrical reliability To identify voids, cracks or any flaws where

electrical stresses exceed the insulation capacity

To reliably predict which electrical equipment is in need of maintenance.


Conclusion

PD – best indicator of electrical deterioration of high voltage insulation

PD provides early warning against future catastrophic insulation failure

Periodic PD testing and analysis of insulation will ensure safe operation of the electrical system.


References E.Kuffel, W.S. Zaengl: High Voltage Engineering Fundamentals,

Pergamon Press Publications, First edition, 1992

M S Naidu, V Kamaraju: High Voltage Engineering, Vol.1 Tata McGraw-Hill Publishing Company Ltd. Third Edition,2004.

Subir Ray: An Introduction to High Voltage Engineering, Vol.1 Prentice-Hall of India Private Ltd. First Edition, 2004

Ravindra Arora, Wolfgang Mosch, High Voltage Insulation Engineering:Vol.1, New Age International Publishers, First Edition:2005

Gabe Paoletti, Alex Golubev: Partial Discharge Theory and Applications to Electrical Systems, IEEE Journal - Pulp and Paper Industry Technical Conference,1999. Issue Date: 21-25 Jun 1999 On page(s): 124 - 138


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Partial Discharge Analysis