Online Condition Monitoring Systems for High Voltage Circuit Breakers

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



245kV SF6 Circuit Breaker



400kV SF6 Circuit Breaker



1. Break Down Maintenance.

2. Preventive Maintenance.(Fixed Time)

3. Predictive Maintenance.(Experience Based)

4. Condition Based Maintenance.

Types of Maintenances



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.



Case Studies



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



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.



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.



1.Stand Alone System.Input Transducers Monitoring System with Local Analysis Remote Communications

Out put Alarms





2.Distributed Intelligent System.

Input Transducers

Data Acquisition System

N

e

t

Net work Connections

Central Computer Server

And Analysis

RemoteCommunications

Out put Alarms



Various Phase Current CTs



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.



Important question …..

.....what is to be monitored???

…….How is it to be monitored???



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).



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



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.



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.



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.



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.





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



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



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..



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.



Vibration Correlation Matrix

Peaks represent winter

Valleys represent Summer



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.



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



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.



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.)



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.)



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.



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.



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)





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.



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.



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.



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.



Techniques followed by

Indian Utilities for

Condition Monitoring….Presently.



•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:



DCRM Signature of a New Breaker



Thank You

DCRM Signature of Problematic Breaker

Abnormal Signature,Fluctuations at “A”



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.



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.



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.



Thermal Imaging



Thermal Imaging



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.



Thank You

Documents

Online Condition Monitoring Systems for High Voltage Circuit Breakers