Condition Monitoring of Circuit Breakers

Condition Monitoring  Timing Measurement  Tan delta measurement of grading capacitors  Dew point measurement of SF6  Static Contact resistance measurement  DCRM with travel mea

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

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

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 OPERATION C-O DELAY TIME ABOUT 300MS

 100 AMP CURRENT IS INJECTED THROUGH CB

NEED FOR DCRM

 DURING NORMAL CONTACT RESISTANCE

MEASUREMSENT, HEALTHINESS OF MAIN

 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

once every 0.1ms This corresponds to 10kHz sampling frequency

 During Contact travel, to record travel

measurements with 1mm resolution

(10mm/msec), this require sampling every 0.1

ms and hence 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 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 Insertion

Arcing Contact Insertion

Contact speed

Trip velocity Close velocity

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 only on

Interrupter flanges and not on PIR or

grading Capacitor flanges

DCRM case Studies

Case Study-1

 400kV SF6 CB commissioned in 1997 was

controlling Bus Reactor

 CB had given about 8 years service with 1400 operations

Healthy Pole

Suspected Pole

De-shaped Arcing Contact

Loose Screw and marks on main

contact

Case Study-2

 This CB was commissioned in 1993 at Hissar and was controlling a

Transmission Line

 DCRM signatures after closing

operation were not stable and wide variations were observed

DCRM Signature of defective CB

operating lever had loosened

 This caused misalignment and

subsequent damage to moving contact Finger Contact Assembly

 Defective Components were replaced

Bearing Bush was missing

Case Study-3 400kV ABB make CB at Hyderabad

Disengaged coupling bolt

Moving Contact Long Rod

Assembly

Helicoil problem

Helicoil

DCRM Signatures after

rectification

Case-4 Interesting Case Study

 CB 952 inspected in March,2006 at

Hyderabad s/s

 After rectification, DCRM of B pole CT side not alright

 The Test kit was changed but same

problem was indicated in DCRM

 New spare pole was erected but same

problem was again indicated

 M/s Scope was called with new kit but

problem continued

 ABB then brought Contact Assembly from factory and then rectified the problem

952- B Isolator side

952-B CT side

Contact Assembly changed

After rectification on 30.03.2006

Case Study-5

Jamshedpur Substation on

26.04.2007

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 = 15-17mm

Main Contacts = 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

 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, 2 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 1 mbar (CIGRE- WG23)

 EXUDATION OF MOISTURE CONTAINED IN

ORGANIC INSULATING MATERIALS

 PERMEATION THROUGH SEALED SECTIONS

DEW POINT MEASUREMENT

DEW POINT MEASUREMENT

EASILY HYDRATED TO PRODUCE HIGHLY

FLUORIDES)

CHAMBER, MONITORING OF MOISTURE

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?