Slide1 l.jpg
This presentation is the property of its rightful owner.
Sponsored Links
1 / 30

Construction and Condition Monitoring PowerPoint PPT Presentation


  • 77 Views
  • Uploaded on
  • Presentation posted in: General

Lightning Arresters. Construction and Condition Monitoring . LA Characteristics. Arrester Fundamentals. Need for High Resistance to limit Discharge Current Need Low Resistance during flow of lightning current to limit Surge Voltage . A non-linear resistance material required.

Download Presentation

Construction and Condition Monitoring

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Slide1 l.jpg

Lightning Arresters

Construction and Condition Monitoring


La characteristics l.jpg

LA Characteristics


Arrester fundamentals l.jpg

Arrester Fundamentals

  • Need for High Resistance to limit Discharge Current

  • Need Low Resistance during flow of lightning current to limit Surge Voltage

A non-linear resistance material required


Equivalent circuit of surge arrester l.jpg

EQUIVALENT CIRCUIT OF SURGE ARRESTER


Slide5 l.jpg

Concept of Leakage Current

  • Resistive Current

  • In phase with voltage

  • Increase with

    temperature

  • Increase with aging

  • Capacitive Current

  • In 90 Deg phase with voltage

  • Insignificant change with

    temperature and voltage

  • does not affect due to aging


Selection of surge arrester l.jpg

Selection of Surge Arrester

Voltage400/√3= 230kV

During single phase to ground fault, voltage on healthy phase may go upto 1.4 to 1.5 times

230 x 1.4/1.5= 323 – 346

Temporary O/V= 1.5 pu = 336kV

LAs are available at 336kV, 360kV, 372kV and 390kV

Higher ratings are selected taking into consideration of ageing of LA elements


Construction of disc l.jpg

Construction of disc

  • These are made by mixing ZnO with small amount of additives such as Bi2O3, CoO, Cr2O3, MnO and Sb2O3

  • ZnO grains (about 10μm dia) have low resistivity and surrounded by a granular layer which is a high resistive Oxide layer(0.1 μm thick). The two are strongly bonded.


Surge arrester failures l.jpg

Surge Arrester Failures


Failure of las l.jpg

FAILURE OF LAs


Failures of las in powergrid l.jpg

Failures of LAs in POWERGRID

  • Failures of LA stacks

  • Failures of Surge Monitors

  • Failures of LA stacks and LA monitors more in rainy seasons.

  • Many LAs removed based on Third Harmonic Resistive Current Measurements.


Failed la l.jpg

Failed LA


Another failure of la l.jpg

Another failure of LA


Gasket condition l.jpg

Gasket Condition


Conduction of zno discs l.jpg

Conduction of ZnO discs


Contamination on the internal surface of the la porcelain l.jpg

Contamination on the internal surface of the LA porcelain


Failures of las in powergrid17 l.jpg

Failures of LAs in POWERGRID


Improvements in manufacturing quality l.jpg

Improvements in Manufacturing Quality

Meter Terminal Fixing:

  • Change of the Terminal at the bottom of the Surge Monitor.

  • Separate grounding terminal is required on surge monitor for connection to 75X12mm GI flat used for LA earthing.

    Meter Enclosure :

  • IP – 66 test on the enclosure.

  • Water dip test on surge counter at 1.5 meter depth for 30 Minutes, Acceptance criteria as per IEC 60068-2-17-1994


Improvement in sealing arrangement of surge arrester stacks l.jpg

Improvement in Sealing Arrangement of Surge Arrester Stacks

  • Sealing arrangements for Surge Arrester Stacks for all manufacturers were reviewed.

  • Presently M/s Oblum and CGL are using O Rings (Neoprene Rubber) in the groove whereas M/s Elpro and Alstom are using Rubber gaskets.

  • Since most of LA failures have taken place due to moisture entry, it was decided to stop use of flat gaskets for sealing.


Moisture ingress test of the arrester l.jpg

Moisture Ingress Test of the Arrester :

  • Dip test routinely for LA stacks at 1.50 meter depth for 30 minutes and thereafter following routine tests shall be conducted:

  • Partial Discharge Measurement

  • Reference Voltage

  • Residual Voltage.

  • Insulation Resistance measurement.

  • Tests 1 to 3 shall be conducted as per IEC-60099-4 (Edition 1.2, 2001-12). The Megger values shall be higher than 10GOhm for 66kV and higher rating LAs and more than 1GOhm for below than 66kV rated LAs.

  • Facilities for water dip test developed by all manufacturers


As per iec 60099 5 techniques for the health monitoring of surge arresters in service l.jpg

AS PER IEC-60099(5), TECHNIQUES FOR THE HEALTH MONITORING OF SURGE ARRESTERS IN SERVICE

1.TOTAL LEAKAGE CURRENT MEASUREMENT

2.WATT LOSS MEASUREMENT

3.INSULATION RESISTANCE MEASUREMENT

4.THIRD HARMONIC RESISTIVE CURRENT MONITORING.

5.THIRD HARMONIC RESISTIVE CURRENT (THRC) MONITORING WITH COMPENSATION FOR THIRD HARMONICS IN SYSTEM VOLTAGE.


Slide22 l.jpg

LA


The measurement principle l.jpg

THE MEASUREMENT PRINCIPLE

  • HARMONICS ARE CREATED IN LEAKAGE CURRENT ON APPLICATION OF FUNDAMENTAL FREQUENCY, DUE TO NON LINEAR VOLTAGE-CURRENT CHARACTERSTIC OF SURGE ARRESTERS.

  • THIRD HARMONIC IS THE LARGEST HARMONIC COMPONENT OF THE RESISTIVE CURRENT


Effect of 3 rd harmonics in system voltage l.jpg

EFFECT OF 3RD HARMONICS IN SYSTEM VOLTAGE

  • THIRD HARMONIC IN SYSTEM VOLTAGE CREATES CAPACITIVE HARMONIC CURRENTS WHICH AFFECT THE MEASURED VALUE

  • ERROR IN THE MEASURED VALUES MAY BE CONSIDERABLE

  • AS REPORTED, 1% THIRD HARMONIC IN SYSTEM VOLTAGE MAY INTRODUCE ERROR UPTO 100% IN THE MEASURED VALUE


Basic circuit for la testing l.jpg

Basic circuit for LA testing


Identification of defective surge arresters l.jpg

IDENTIFICATION OF DEFECTIVE SURGE ARRESTERS.

  • IN POWERGRID, THE UPPER/SAFE LIMIT OF THRC HAS BEEN KEPT AS 350 MICROAMP.

  • MEASURED VALUE ARE TO BE DIVIDED BY A FACTOR 4.0.

  • ABOUT 40 SURGE ARRESTERS WERE REMOVED FROM SERVICE TO AVOID MAJOR BLASTING.

  • CAPACITANCE/ TAN DELTA, IR MEASUEMENT TESTS WERE ALSO CONDUCTED ON REMOVED LAs AND FOUND VIOLATING.


Capacitance and tan delta measurement on la having 560 micro amp l.jpg

Capacitance and Tan Delta Measurement on LA having 560 micro-Amp


Reasons of failure of surge arresters l.jpg

REASONS OF FAILURE OF SURGE ARRESTERS

  • MOISTURE ENTRY THROUGH SEALING SYSTEM/GASKETS HAS LED TO DEGRADATION OF DISCS AND CONSEQUENT INCREASE IN THRC.

  • ACCELERATED DEGRADATION OF THE ZnO DISCS, POSSIBLY DUE TO MANUFACTURING DEFECTS/PROCESS PROBLEMS


Thermovision scanning l.jpg

Thermovision Scanning


Slide30 l.jpg

Thank You for

your attention

please


  • Login