online condition monitoring systems for high voltage circuit breakers
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8/8/2019 Online Condition Monitoring Systems for High Voltage Circuit Breakers
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On Line Condition Monitoring Systems
For
High Voltage Circuit Breakers…
16th Sept 2006
S.B.PotnisCrompton Greaves Ltd
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245kV SF6 Circuit Breaker
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400kV SF6 Circuit Breaker
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1. Break Down Maintenance.
2. Preventive Maintenance.(Fixed Time)
3. Predictive Maintenance.(Experience Based)
4. Condition Based Maintenance.
Types of Maintenances
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Condition based Maintenance-
*Mainly in Developed countries.
*A few utilities in India have started Condition
based maintenance, but mainly off line.
*Limited data available within India.
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Case Studies
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A Collaborative Project undertaken by Utilities
and Circuit Breaker Manufacturers in USA
& Canada to evaluate
The state of the Art in….
On Line Monitoring Technology….
Study on single phase A/R Type245kV SF6 Circuit Breaker.
Case Study I
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Period of Evaluation…3 Years
Made use of Different types of Monitoring
Systems on each Phase and incorporateda large variety of Transducers.
The Breaker was operated 700 times atRated voltage and 300 times during
Maintenance over 3 years of monitoringPeriod.
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Primarily Two Classes of monitoring SystemsUsed:
1.Stand Alone System.
This system has all of the On Lineintelligence located at the device,has a limited storage of previous data &
Remote communication through Modem.
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1.Stand Alone System.Input Transducers Monitoring System with Local Analysis Remote Communications
Out put Alarms
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2.Distributed Intelligent System.
Input Transducers
Data Acquisition System
N
e
t
Net work Connections
Central Computer Server
And Analysis
RemoteCommunications
Out put Alarms
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Various Phase Current CTs
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There are some monitors available which can now
take CT inputs directly from the Station CTs
be it 1 Amp or 5 Amps.
All the settings are possible on the monitoring
equipment itself.
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Important question …..
.....what is to be monitored???
…….How is it to be monitored???
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Transducers Used in A Phase
1. Displacement- Optical Comb2. Primary CT- A Phase Only
3. Pump Motor- DC Shunt4. Control coil monitoring-injection of 1 K Hz signal.5. 52-a & b-- Auxiliary contacts.6. Heaters-- 4 Locations using Auxiliary CTs.7. SF6 Density-Quartz Crystal & SF6 Pressure and Temp8. Temperature-Ambient & Cabinet (RTD).
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Transducers Used in B Phase
1. Displacement-Resistive Transducer.2. AC CT- small CT from Protection Relay.3. DC Pump current.4. Coil Current using 1 Ohm shunt.
5. 52 a and b contacts.6. AC Heater current-using Current Converter.7. SF6 Pressure and Temp + Separate SF6
Monitoring system.8. Wind Speed,Barometer Pressure,Humidity
Ambient Temperature.
9. Mechanism Vibration A & B Phase.10.Metering IED-measuring 3 phase I & V.11.Control AC Voltage Transducer
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Transducers Used in C Phase
1. Displacement –Optical2. 3 AC Phase Currents
3. DC Pump Motor Current.4. Trip and close Coil Currents using CT.5. 52 a and b Contacts.
6. 2 Heater CT in Cabinet.7. SF6 Pressure and Temperature.8. Temperature RTD.
9. Mechanism Vibration.
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Experience and Insight in On Line Monitoring System
Data Acquisition system:
Worked well ,however experienced failure of
2 Pressure Transducers and 1 Travel Transducer.These failures ,however,were relatively simpleand easy to rectify.
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Computer and Computer Peripherals:
Following Problems were faced on this system:
1.Windows NT server hanged up intermittently.2.CPUs that lose communication and will not
restart unless master reset is performed.3.Defective Modems,phone switches.4.Excessively long communication and down
load times5.CPU Fan failure.
It was very time consuming to solve these problemsand required expertise in solving them.
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No Alarm may indicate everything is OK or theMonitoring system is not working.
People have expertise on Breakers but not in theComputer systems.
Skill sets and Competencies are required to operate
& upgrade monitoring system.
Detailed Instructions required to interpret the data.
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SF6 Gas Monitoring Results
A Total of 5 SF6/CF4 Gas Systems were installed.
Each system generated erroneous results at Ambient Temp of less than – 20 Deg C.
For this GCB there was a heater for heatingGaskets below –20 Deg C which were close to
RTD for the Gas Temperature.
This corrupted the Density and compensatedPressure readings below – 20 Deg C resultingin to false alarms
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Slight decline in SF6 Density indicates minute leakage, not possible to be
detected by normal means.
No Trace indicates problemIn monitoring system
SF6 Daily Average
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Notice the Oscillations in SF6 Density when Ambient
falls below – 20 Deg C.(Due to Heaters Switching on at – 20 C )
Absence of Data is due to failure of Transducer.
Slight negative slope in Density is due to minute
leak in the system.(Detailed investigation revealed that the leak isfrom the connection made for the gauge installedfor the monitoring system.).
The On line system did reveal the problem but theData is required to be interpreted correctly.
Observations..
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Vibration Analysis
Purpose:
1.To check if results are consistent over a long period.
2.To Derive method whereby the readings will be
Machine readable.
Observations:
1.The results were remarkably reproducible.
2.The signals showed consistent seasonal variation
in Summer and Winter.
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Vibration Correlation Matrix
Peaks represent winter
Valleys represent Summer
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Conclusions
1.Long Term Monitoring systems
can provide valuable data.
2.Data Analysis is required to be
done by Experts/qualified persons
to determine action plan.
3.Monitoring System itself isrequired to be maintained.
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Conclusions
4.Training required to operate system
and Analyze the data.5.Faults related to Transducers etc are
relatively simple to be solved,howeversoftware related faults take considerabletime and requires expertise.
6.Two main pit falls: Absence of Alarm due to improper settings
Generation of high numbers of false alarm
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Conclusions
7.There is “not a one size fits all”
monitoring system.
8.Data very useful to decideMaintenance Schedules for theparticular type of Breaker.
9.Data on one Type of Breaker
difficult to extrapolate for othertype of Designs.
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Conclusions
10.Reliability of Monitoring systemis required to be of much higher
magnitude than that of the Breaker.
(..As there was no failure on the breakerduring this 3 years period, no commentscan be made in this respect.)
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Case Study II
A Joint Project initiated by 3 major utilities in USA in 1990.(NYPA, Con Edison NY, ESEERCO.)
The first monitoring Prototype was installed on SF6 GCB
in 1993 called MONITEQ.
11 systems were installed by 1997 at various places and
on various types of breakers - Voltages 245kV to 800kV.6 are on 345kV-800kV SF6 GCBs and 5 on Air Blast CBs.
Made use of a system with Data acquisition locallyand Analysis Centrally.(Distributed intelligence system.)
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Case Study II
Monitored Parameters on Air Blast Circuit Breakers:
1.Dynamic Air Pressure Drop at Base of each column
2.Air Pressure in each single pole tank.
3.Moisture content of compressed Air in each pole.
4.Closing and Tripping Coil Currents and continuity.
5.Interrupted Current I2t and evidence of Restrike.
6.Control cabinet Temperature.7.Auxiliary Supply voltage.
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Case Study II
Significant observations:
1.Identified Defective Mechanical link on 800kV Air blast Circuit Breaker.
2.Identified incomplete Breaker contact Travel.
3.Identified a mechanical defect on Air Blast CB.
4.Helped electricians to trace Thermal InsulationProblem.
5.Helped in identifying root Cause of Catastrophicfailure of 245kV Air Blast CB.
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Case Study II
Failure on a 245kV Capacitor Bank Circuit Breaker
In 1995 MONITEQ was installed on a 245kV CB.
Till August 1996 the monitoring was uneventful.
On 6th August 1996,the C phase blasted during
opening operation at normal Cap Current Sw.
Moniteq was used to Analyze the recorded Data.
(Black Box)
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Case Study II
The signals indicated that the opening electro-valve
Perhaps has mal functioned.
Closer inspection of the Seals of valve revealed
that there were scratches on piston and the pistonassembly was not moving freely.
The internal Temperature and Humidity dataShowed that the breaker operated at 45 Deg CWhich was much more than normal 20 Deg C.
Tests on O ring Seals revealed that, over time, O ringsbecame prone to heat induced dilation.
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Case Study II
The chronology of events was reconstructed :
1.An opening command was transmitted to theBreaker.
2.Electrical command was Transmitted to theopening electro valve through its Trip Coil.
3.Due to Heat dilation,the opening electro valvepiston jammed half way.
4.The Breaker opened normally ,but the jammed Valve piston forced a pumping motion of pilot Valve.
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Case Study II
5.Cyclical operation of the pilot valve caused theRepetitive operation of blasting valves which inturn decreased the air pressure in the tank gradually.
6.The Loss of Air Pressure caused decrease in theDielectric Strength causing the failure.
7.Maintenance on similar breakers detected thattwo more seals on 800kV CB were also damagedand the timely replacement of these seals saved
the respective breakers.
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Case Study II
Conclusions:
The monitoring systems do help in timelyidentification of the expected failures in future,However at times they do not necessarily avoid100% occurrence of the probable failuresbut definitely help in identifying the root causeof the failures and help in avoiding failures on
similar other breakers.
This data is very useful for Design Engineers
to make robust Designs.
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Techniques followed by
Indian Utilities for
Condition Monitoring….Presently.
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•Dynamic Contact Resistance(DCRM).
• Adopted by PGCIL for @ last 2 years.
•DCRM signature of every Breakercarried out at site at the time of commissioning.
Off Line Condition Monitoring Method:
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DCRM Signature of a New Breaker
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Thank You
DCRM Signature of Problematic Breaker
Abnormal Signature,Fluctuations at “A”
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DCRM
•RECENTLY DEVELOPED CONDITION
MONITORING TEST.•HELPS IN PREDITCTIN OF CONTACT
CONDITION WITHOUT OPENING
INTERRUPTOR ASSEMBLY.
•THIS IS A COMPARISON OF DCRM
SIGNATURES OBTAINED AT VARIOUS
STAGES OF LIFE OF CIRCUIT BREAKER.
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DCRM
LIMITATONS OF TEST
•THIS IS NOT A MEASUREMENT TEST.
•TYPES & MAKES OF TEST EQUIPMENT MAY
CHANGE THE APPEARANCE OF DCRMSIGNATURE.
•CHANGE IN SAMPLING RATE OF TEST
EQUIPMENT MAY SHOW THE CHANGE INPATTERN OF SIGNATURE.
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DCRM
LIMITATONS OF TEST
•VERY HIGH SKILL IS REQUIRED TO JUDGE &
CONCLUDE FROM CHANGES OBSERVED IN
SIGNATURES…
•However this test has been giving some indications on
the abnormal contact conditions and has helped inidentifying a few problematic cases not only from the
contact erosion side but also in the connecting system
for any looseness etc.
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Thermal Imaging
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Thermal Imaging
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Thermal Imaging
• A recent Technique for measuring Temperaturesof various current carrying parts/ equipmentsin a sub station.
•Gives relative Temperatures of various parts.
•Requires expertise in identifying hot spots.
•Results can be compared with earlier data andconclusions can be drawn after gaining expertise.
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Thank You