mohan-presentationpartial discharge monitoring system for gis-di8

7/28/2019 Mohan-PresentationPartial Discharge Monitoring System for GIS-DI8

http://slidepdf.com/reader/full/mohan-presentationpartial-discharge-monitoring-system-for-gis-di8 1/37

PD-TESTING AND MONITORING

Mohan Watwe

[email protected]

Matthias Boltze

[email protected]



Introduction Introduction--Failure rates of GIS Failure rates of GIS

Voltage level[kV]

International

experience, failures per100 bay years

125-145 0.26

245 0.67

300 -

420 1.8

550 3.9

All voltages 0.9

IEC 71 IEC 71--2 recommend target 2 recommend target failure rates for GIS to be 0.1failure rates for GIS to be 0.1failures per 100 bay failures per 100 bay--yearsyears

2



Distribution of failures according to location given byCIGRE JWG 33/23.12:

• 41% of the failures occur in the switchingcompartments, i.e. at the circuit breaker,switches,disconnectors (13% on spacers).

GIS- Failure Statistics

• 17% occurs at the voltage transformer, surge arrestersor bushing compartments (5% on spacers)

• 42% in other compartments (22% on spacers)i.e. 40% on spacers

3



Teething troubles

4



Most common defects

in Gas Insulated Switchgears

Protrutions at ground potential

Protrutions at high voltage potential

Particle on Spacer

Free particle Free potential

Void in Spacer

5



Defects Probable Causes:

•Presence of foreign bodies

•contaminants such as free metallic particles

•

•Incorrect assembly

•Damage during transport, storage or installation

This might give rise to an internal fault in service.

6



There have been flashovers on spacers where on-line PDdid not indicate prior discharges.

The failure track is often very faint with minimalcarbonisation of the epoxy.

This can be caused when the switchgear is operated and

GIS- trapped charge flashovers

the current is chopped at a voltage maximum. If there isno resistive path (ex-a voltage transformer) then thevoltage may remain until re-energisation. This has led toflashovers. But this is not a PD breakdown.

Ref- CX Wang, A Wilson and MW Watts. “Surface flashover sustained by electrostaticsurface charge on an epoxy resin insulator in SF6” IEE Proc A. 140 (5), September1993, pp346-350.

7



Failure rate statistic

Bath tub curve of the failure rate versus time

8



Partial discharge in gas •Partial Discharges (PD) occur due to excessive electrical stress of gas distances in any

dielectric media

• Partial Discharge activity leading to gradual

nsu a on e er ora on o en a es p ace e ore eventual breakdown or flashover of insulation.

•The characteristic of partial discharge for

different type of defects exhibit recognizable patterns.

9



Partial Discharge Detection Principles

Optical

Mechanical

Acoustic

Opto-acoustic

HV

Optical Effects (Light)

Pressure Wave (Sound)

Macroscopic-Physical

Effects Detection Methods

Chemical

Electrical IEC 60270

HF/VHF/UHF

Discharge Effects Dielectric Losses High Frequency Waves

Chemical Effects

Heat

Draft IEC 62 478

10



Advanced diagnosis technologies can be used toprevent catastrophes:

GIS catastrophes

11



Advanced Diagnosis Technologies

•The field conditions introduce noise in themeasurement and as such suitable techniques have

to be employed. The classical method ofmeasurement is not suitable for field measurementbecause of poor signal to noise (S/N) ratio. This ismainl because of the limitation of measurin

frequency which is in KHz range.• In fact a very small range of complete frequencyspectrum of the original PD pulse is used.•The signal to noise (S/N) ratio can be substantially

improved if the measurements are done in theUHF/VHF range which is typical for transients due toPD events.

12



PD – Measurements

(GIS – PD – Decoupling)

Spacer

external sensor ultra wide band inductive coupler

external sensor acoustic coupler

internal sensor capacitive (sensor

external sensor window sensor

standard coupling capacitance

13



UHF – PD-Sensors for GIS

Conductor

Detector

Conductor

Detector

Field grading electrodes

- UHF-Window Sensor - Internal UHF- Sensors

Cage Cage

14



The frequency response of the sensor is influenced by the shapeof the sensor.

The basic working principle of the sensor can be explained as acapacitive divider.The sensor plate forms a capacitance C1 to the inner conductorand has a stray capacitance C2 to the earth, as the sensor plate

UHF coupler for GIS.

.

Internal UHF coupler for GIS.

15



PD Monitoring

of Gas Insulated Switchgears

GIS Barrier (1-2) Window Sensor (3)

16



Sensors

17

GIS Barrier Sensor



The UHF adapter

for decoupling of the

PD Signals at inbuilt capacitances

PD Monitoring

of Gas Insulated Switchgears

The connections of the UHF adapter to

the inbuilt cap.and the PD

measuring system LDS-6

Inbuilt capacitance flanged at the GIS

18 18



The PD pulses derived from various sensors installed on theGIS are further processed either in time domain or frequencydomain.

Ultra wide band of the acquired signal is generally used in thetime domain mode. A fast peak detection of the wide bandsignal leads to phase related pulse sequence. This instrumento erates in time domain and records the eak value of PD

Instrumentation

pulse sequences in full spectrum of the ultra wide bandwidthfrom 100 MHz to 1 GHz.

PD Guard UHF.

19



Frequency Spectrum zero-span mode, center frequency 623 MHz, bandwidth 5 MHz

PD Measuring Results, PRPD Pattern, Needle

at high voltage potential in GIS

Phase Resolved PD Pattern Zero-span mode, center frequency 623 MHz, band width 5 MHz

20



PD Localization at GIS,

Schematic Diagram (I)

21



PD Localization at GIS,

Schematic Diagram (II)

22



Case Study A)GIS Inspection Test, China

Test Setup for Inspection Test at 110 KV Gas Insulated Switchgear

23



Performance Check

•Sensitivity verification at site is very difficult as thedecoupling capacitor used for measurements isrelatively much small which is insufficient to detectthe PD ulse.

24

•The performance check is functional check of thewhole measuring path including sensors and the PDmeasuring system



Case Study A)GIS Inspection Test, China

Measuring configurations

25



TEST SEQUENCE

• Setup of the PDM system incl. the UHF-PD-sensor

• Voltage synchronization• Performance Check (instrument functional check)• Recording of the measuring signals

26

• Evaluation of the measuring recordings by using theLDS-6/UHF Analysis software: PRPD PatternRecognition and Replay-Mode for signal evaluation



Case Study- GIS Inspection Test, China

Test Results

27



Case Study - GIS Inspection Test, China

Test Results MP7

28




#1 #2

29




The origin of the Pattern could be clearly assigned tothe GIS System #1 due to comparison of thedetected magnitudes at measured decoupling points(MP1 to MP7).

30

The PD source could be isolated between themeasuring points MP5, MP6 and MP7.



GIS Monitoring- System Configuration

1) UHF-PD-sensing,

2) PD instrumentation unit,

3) Transmission line and

General layout of the GIS-PD-Monitoring-System: sensing,

instrumentation unit PD Guard/UHF, data transmission line (FOL), data acquisition and evaluation server

31



System Configuration – GIS Monitoring

33

41

42

43

38

15

2732

31

20

21

22

23

24

16

8

1712

6

7

10

11

4

1 3

26

28

37

36

GIS Sensor Arrangement: GIS Barriers Sensors

44

403530

3934

19149

1813

5

2

29

32



System Configuration – GIS Monitoring

GIS PD Monitoring System: Acquisition unit PDGuard/UHF,data transmission line (FOL), data acquisition and evaluation server

33



Permanent PD Monitoring Layout

for GIS Systems

34 34



Concept – GIS Monitoring

Primary GIS PD Monitoring Software

The topographic overview allows quickly an assessment of the GIS status

Software concept for

GIS PD Monitoring System

35

.



Concept – GIS Monitoring

Primary GIS PD Monitoring Software in Data- / Realtime- View

36



Conclusion

sensitive UHF PD measurement with UHF probes applicable in

service provide advantageous robust and easy PD decoupling

significant diagnostic information are derived from advanced tools

for PD monitoring

. . -

monitoring, enabling time-based maintenance, etc. are at hand

37

mohan-presentationpartial discharge monitoring system for gis-di8

Documents