Condition Monitoring of Circuit Breakers

Condition Monitoring of Circuit Breakers INTERRUPTER DESIGN Breaker Operation Internal Details of Interrupter Typical Operating Links CB Operating Mechanism Operating Mechanism     Compressed Air Open/ Close Compressed Air Open/ Spring Close Hydraulic Open/ Close Spring Open/ Close Current interruption Ideal Interruption of Current Resistance Circuit 220kV CB at Rourkela s/s overhauled by CGL Engineer – B phase of 552 as on 24.11.2006 220kV CB at Rourkela s/s – Y phase of 552 as on 24.11.2006 Travel After lot of persuasion with CGL, Service Engineer was deputed on 23.05.2007 Following observations were found: Actual Wipe of Contacts = 27-28mm Arcing Contacts Main Contacts = 15-17mm = 10-12mm Wipe found as 21mm which was adjusted to 29mm on 24.05.2007 220kV CB at Rourkela s/s – B phase of 552 as on 24.05.2007 Internal Inspection of CBs    About 48 nos CBs have been opened so far based on DCRM evaluations Erosion of Contacts, Misalignment, loose connection etc problems were observed Timely inspection of CBs could help in rectification of CBs and hence avoiding major failures Conclusion    DCRM Test (non-invasive diagnosis) for CBs proved useful in indicating condition of main/ arcing contacts for erosion, misalignment and looseness etc Prevention of Major failures by timely diagnosis Major overhauling of Interrupters/ Arcing chamber can be decided based on DCRM POWERGRID PHILOSOPHY FOR MAJOR OVERHAULING OF CBs MANUFACTURER’S RECOMMENDATIONS   AFTER 10 YEARS OF COMMISSIOINING OR AFTER 5000 OPERATIONS WHICHEVER IS EARLIER POWERGRID’S PHILOSOPHY   BASED ON EVALUATION OF CONDITION MONITORING TEST RESULTS LIKE DCRM, OPERATING TIMINGS, CONTACT TRAVEL ETC INITIALLY, NOS CBs ARE INSPECTED/ OVERHAULED AND BASED ON THE EXPERIENCE GAINED, DECISION FOR OVERHAUL OF BALANCE CBs CAN BE TAKEN POWERGRID EXPERINCE ON OVERHAULING OF CBs POWERGRID has so far overhauled total of 198 Nos CBs Dew point measurement of SF6     Dew point measurement gives dryness of SF6 gas SF6 is green house gas with 23,900 times more active than CO2 Care to be taken not to let the gas left to the atmosphere Can be measured at atmospheric pressure or at rated pressure and interpretation to be made accordingly SOURCES OF MOISTURE IN CB  GAS HANDLING – FILLING AND EMPTYING THE CB AIR MAY BE LEFT DURING EVACUATION WHICH SHALL ADD TO IMPURITIES IN SF6 GAS EVACUATION TO BE DONE UPTO mbar (CIGREWG23)  EXUDATION OF MOISTURE CONTAINED IN ORGANIC INSULATING MATERIALS  PERMEATION THROUGH SEALED SECTIONS DEW POINT MEASUREMENT DEW POINT MEASUREMENT  IF SF6 GAS CONTAINS MOISTURE, IT IS EASILY HYDRATED TO PRODUCE HIGHLY REACTIVE H2SO3 AND HF(HYDROGEN FLUORIDES)  AS THESE CHEMICALS CAUSE DEGRADATION OF INSULATION AND CORROSION IN THE INTERRUPTING CHAMBER, MONITORING OF MOISTURE CONTENT IN SF6 GAS IS VERY IMPORTANT CONTAMINATION OF SF6 GAS BY MOISTURE Experience with CBs having PIR        Indian 400kV Transmission network has been conventionally using CBs with PIRs even for short lines During 1994/95, failures involving PIR assemblies were encountered in POWERGRID networks on 22 nos CBs CB failures were critically analyzed with CB manufacturer Defective components of PIR assembly like Pull Rod, moving contact assembly etc were modified for enhancing reliability of CBs PTI, USA System Studies suggested that PIR can be dispensed with for switching Transmission Lines up to 200km Length CBs with maximum failures were attended and PIR assemblies removed from 70 nos CBs New CB procurement are without PIR assemblies for lines upto 200km length Questions? [...]... requirement of 10kHz DCRM can detect…        Erosion of Arcing Contact Erosion of main contact Contact misalignments Contact wipe of main and arcing contact Main & arcing contact resistance Healthiness of damping system Contact travel & speed Typical DCRM Signature Parameters to be monitored       Variations of Resistance values at the time of Arcing and main contact close/ trip Insertion of Arcing...Inductance Circuit Reactor Switching Line/ Filter Switching TRV Recovery Voltage and build up of dielectric strength of the medium Dielectric Strength TRV Unsuccessful arc quenching Dielectric Strength of different mediums FAILURE OF CBs IN POWERGRID MECHANICAL 74% (OPERATING COMPONENETS FAILURES) ELECTRICAL (DIELECTRIC FAILURE) 16% OTHERS 10% - Condition Monitoring      Timing... TO COMPUTE CONTACT RESISTANCE  VARIATION IN FINGER PRINT OF DCRM INDICATE PROBLEM IN ARCING AND MAIN CONTACTS NEED FOR DCRM     DURING NORMAL CONTACT RESISTANCE MEASUREMSENT, HEALTHINESS OF MAIN CONTACTS IS INDICATED Req = R*r/(R+r)= r/(1+r/R), r = MAIN CONTACT R = ARCING CONTACTS DCRM SIGNATURES/FINGER PRINTS INDICATE TRUE CONDITION OF CB ARCING CONTACTS DCRM ALONGWITH CONTACT TRAVEL MEASUREMENT... CONTACTS DCRM ALONGWITH CONTACT TRAVEL MEASUREMENT IS HELPFUL IN COMPUTING THE ARCING CONTACT LENGTHS Requirement of 10kHZ sampling frequency    While current transfers from main to arcing contacts, there is sudden increase in the dynamic resistance value resulting in the resistance peak of about 0.20 to 0.30ms width To accurately plot this peak, we require resistance measurement/ sampling atleast... POWERGRID MECHANICAL 74% (OPERATING COMPONENETS FAILURES) ELECTRICAL (DIELECTRIC FAILURE) 16% OTHERS 10% - Condition Monitoring      Timing Measurement Tan delta measurement of grading capacitors Dew point measurement of SF6 Static Contact resistance measurement DCRM with travel measurement DYNAMIC CONTACT RESISTANCE MEASUREMENT (DCRM)  CONTACT RESISTANCE MEASUREMENT DURING CLOSING AND TRIPPING... DCRM Signature Parameters to be monitored       Variations of Resistance values at the time of Arcing and main contact close/ trip Insertion of Arcing contact Insertion of Main Contact Contact travel Resistance during closed conditions and its comparison with static contact resistance value Damping system healthiness Contact Travel and Insertion Details Travel Total Contact Insertion Main Contact... Contact speed Trip velocity Close velocity 5-8 m/sec 3-4 m/sec Precautions to be taken while carrying out DCRM test      Sampling frequency of kit is 10kHz (min) DCRM to be taken for CO operation CO delay time to be atleast 300 ms hence requiring plot length of about 450ms CB flanges where Current and Voltage cables are to be connected, should be thoroughly cleaned by CTC Connection should be done... about 8 years service with 1400 operations Healthy Pole Suspected Pole Observations     Moving Arcing contact was found de-shaped and had expanded One Counter Head Screw of Moving Main Contact assembly was found loose PTFE Nozzle of moving contact assembly found cracked Scratch marks were also seen on Main Moving Contact De-shaped Arcing Contact Loose Screw and marks on main contact Case Study-2  ... Close Spring Open/ Close Current interruption Ideal Interruption of Current Resistance Circuit Inductance Circuit Reactor Switching Line/ Filter Switching TRV Recovery Voltage and build up of