Partial Discharge Diagnostics on

Switchgears

Dipl.-Ing. Falk-Rüdiger Werner

Doble Lemke, Germany

info@doble-lemke.eu

Partial Discharge Diagnostics on Power Transformers

Contents

2

1. Introduction

2. PD Detection Principles on Switchgears

3. PD Measurements on Switchgears

4. Summary of PD Solutions for Switchgears

Partial Discharge Diagnostics on Power Transformers

1. Introduction

3

Why online PD diagnostics on

switchgears?

• Risk assessment

• Health assessment under online conditions

• No downtimes

• Detection of problems at an early stage

• Planning of maintenance work

• To ensure safe operation and to prolong the asset‘s

liftetime

1.1 Why online PD diagnostics on switchgears?

Partial Discharge Diagnostics on Power Transformers

1. Introduction

4

Why online PD diagnostics on switchgears?

1.1 Why online PD diagnostics on switchgears?

Partial Discharge Diagnostics on Power Transformers

1. Introduction

Partial Discharges in Gases:

Corona discharge

Sharp edges

Conductors with too small

diameter

Sharp edged particles

Surface discharges

Generally faced problem

Countermeasures

• Capacitive potential grading at bushings

• Geometric field grading at terminations

• Prolongation of leakage distance and hydrophobic surfaces on

insulators

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[Küchler, 1996]

Thin WireSharp Edge Particle

Glow discharges Streamer Discharges

Arrangements for Surface Discharges

1.2 PD Fault Scenarios

Partial Discharge Diagnostics on Power Transformers

1. Introduction

Defects in the dielectric causing PD:(solid insulation systems)

Voids, cavities

Cracks

Delaminations

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Voids without (1) or

with (2) electrode contact

and delamination (3)

Cable with Termination

(1) Voids through treeing

(2) Voids at boundary surface

Cracks, Gaps and

uncompleted Layers

Delamination at staple

boundary surfaces

1.2 PD Fault Scenarios

Partial Discharge Diagnostics on Power Transformers

1. Introduction

7

Cause of Fault

• 20% Free particles and alien objects

• 18% Shielding and electrostatitic contacts

• 11% Poor contacts

• 7% Moisture

• 5% Protrusions, particles on HV

Fault Distribution (CIGRE JWG 33/23.12)• 41% Switching Compartements: Circuit breakers

• 17% VTs, Surge Arrestors , Bushings

• 42% others…

1.2 PD Fault Scenarios

Partial Discharge Diagnostics on Power Transformers

1. Introduction

8

1.2 PD Fault Scenarios

Partial Discharge Diagnostics on Power Transformers

2. PD Detection Principles on Switchgears

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2.1 PD Detection Principles

PD Detection Principles

Acoustic

• Ultrasonic

transducers

UHF/VHF/RF

• UHF antenna

• UHF coupler

• TEV Sensor

IEC 60270

• Standard measurement

circuit

Partial Discharge Diagnostics on Power Transformers

2. PD Detection Principles on Switchgears

10

2.2 PD measurement according to IEC 60270

Impedance in Series to Ck

DUT

• Connection to conductor required (coupling capacitor, bushing)

• Mainly used for air insulated switchgears

Partial Discharge Diagnostics on Power Transformers

2. PD Detection Principles on Switchgears

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Apparent Charge Information

2.2 PD measurement according to IEC 60270

Partial Discharge Diagnostics on Power Transformers

2. PD Detection Principles on Switchgears

12

2.3 Acoustic PD Detection

Acoustic Partial Discharge Detection Acoustic signal as a result of the pressure

build-up caused by the generated spark

in the insulation

Frequency spectrum 10 Hz up to 300 kHz

Different wave types

(longitudinal and transversal waves)

with different propagation velocities

Measurement Technique Microphones and ultrasonic directional

microphones

Sound sensors, accelerometers and piezo-electric converters

Partial Discharge Diagnostics on Power Transformers

2. PD Detection Principles on Switchgears

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2.4 UHF PD Detection

Spacer

external sensor

ultra wide band

inductive coupler

external sensor

acoustic coupler

internal sensor

capacitive (sensor

external sensor

window sensor

standard coupling

capacitance

Partial Discharge Diagnostics on Power Transformers

2. PD Detection Principles on Switchgears

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2.4 UHF PD Detection

Transient electromagnetic waves (TEM, TE and TM modes)

generated by partial discharges

Frequency range 300 MHz to 3 GHz

Measuring technique

Narrow band-bandwidth appr. 5 MHz

Wide band-frequency range 300 MHz to 1,5 GHz

In 420 kV plants – upper critical frequency 1 GHz

In 123 kV plants – upper critical frequency 1,5 GHz

UHF – Partial Discharge Detection

Partial Discharge Diagnostics on Power Transformers

3. PD Measurement on Switchgears

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3.1 GIS Commissioning Test

(1) Resonance test set connected via bushings, (2) Sensors,

(3) PD Detector, (4) Sensitivity Check

Partial Discharge Diagnostics on Power Transformers

3. PD Measurement on Switchgears

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3.1 GIS Commissioning Test, Noise Properties

Comparison of IEC60270 and UHF decoupling in terms of noise supression

UHF decouplong at 770 MHz,

background noise: 9mV (baseline)

No noise

IEC 60270 compliant measurement,

noise by testset (1) and external

noises (2)

Partial Discharge Diagnostics on Power Transformers

3. PD Measurement on Switchgears

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No apparent charge information

- Detection and classification only

3.1 GIS Commissioning Test, Noise Properties

Partial Discharge Diagnostics on Power Transformers

3. PD Measurement on Switchgears

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3.2 Acoustic PD Measurement

DFA100 acoustic PD measurement

device with piezo electric sensor

Partial Discharge Diagnostics on Power Transformers

3. PD Measurement on Switchgears

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Acoustic PD measurements on GIS:1. Selection of one measurement point per chamber

2. At long chambers, one measurement point every

2-3 meters

3.2 Acoustic PD Measurement

Partial Discharge Diagnostics on Power Transformers

3. PD Measurement on Switchgears

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3.2 Acoustic PD Measurement

Partial Discharge Diagnostics on Power Transformers

4. Summary of PD Solutions for Switchgears

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PD Solutions

Acoustic UHF/VHF/RF

LDS-6/UHF, PD-Smart/UHF

• Sensitive PD detection

• PD Classification

PD-Guard/UHF

• Monitoring

IEC 60270

LDS-6, PD-Smart

• Factory tests

• Commissioning tests

DFA100

• PD location and

detection

• PD Classification

Partial Discharge Diagnostics on Power Transformers 22

Thank you for your attention