Friday 1 March 2024

Procedure Of High-voltage Circuit Breaker Maintenance & Testing

In This Topic Of Post, We Will Understand The Basic Procedure Of  High Voltage Circuit Breaker Maintenance & Testing.

Let's Follow The Below Step By Step Guide For High Voltage Circuit Breaker Maintenance & Testing:-

Average Of Inspections: The Majority Of Manufacturers Advise Comprehensive Interior And External Inspections Every Six To Twelve Months. Previous Experiences Have Indicated That Following The Manufacturer's Instructions For Internal Examinations At 6- To 12-month Intervals Entails A Significant Financial Outlay, Some Of Which May Be Redundant. One Way To Reduce Costs, Delays, And Labor Associated With Internal Inspections Without Sacrificing Reliability Is Through Appropriate External Checks.

A Schedule For Inspecting Newly Installed Breakers. After New Equipment Is Installed, Existing Equipment Is Modified Or Updated, Or Existing Equipment Is Replicated In A Different Setting, A Provisional Schedule Of Routine Inspections Is Required. The Temporary Plan Is Necessary To Correct Internal Faults That Often Manifest Within The First Year Of Service And To Establish A Correlation Between External Check Procedures And Interior Conditions, Which Will Serve As The Foundation For A More Conservative Maintenance Program In The Future. The Inspection Schedule Listed Below Is Advised, Assuming A Circuit Breaker Passes All Early Thorough Examinations Without Any Significant Flaws And That No Excessive Interrupting Duty Is Imposed:
  • Six Months Following Erection: Thorough Examination And Modification.
  • One Year Following The Preceding Examination: Final Inspection And Modification.
  • One Year Following The Preceding Examination: Final Inspection And Modification.
  • Twelve Months Following The Last Inspection: External And Internal Checks; No Internal Examination If The External Checks Are Found To Be Satisfactory.
  • One Year Following The Preceding Inspection: Final Examination And Modification.
Schedule Of Inspections For Current Breakers: The Interrupting Duty Placed On The Breaker Should Serve As The Foundation For The Inspection Program. After The First Significant Fault Interruption, It Is Advisable To Conduct A Thorough Internal Inspection. 

Before An Internal Examination Is Conducted, Gradually More Fault Interruptions May Be Permitted If Internal Conditions Remain Adequate. Based On Average Experience, Circuit Breakers Rated At 230 KV And Above May Have Up To Five Fault Interruptions Permitted Between Inspections, Whereas Circuit Breakers Rated At Less Than 230 KV May Have Up To Ten Fault Interruptions Permitted. Generally, There Should Be No More Than Two Years Or Four Years Between Internal Or External Inspections.

Guidelines For External Inspection:- 

A High-voltage Breaker's External Inspection Should Cover The Following Things.

Visually Examine The Operational Mechanism And PCB Externals. The Tripping Latches Need To Be Inspected Carefully Because Minor Adjustments, Clearances, And Surface Roughness Can Make The Breaker Fail To Latch Correctly Or Increase The Force Required To Trip It To The Point Where Electrical Tripping Is Not Always Successful, Particularly When The Tripping Voltage Is Low. Avoid Applying Too Much "Opening" Spring Pressure As This Can Result In Excessive Friction At The Tripping Latch. Additionally, The Electromagnetic Forces Created By The Large Short-circuit Currents Passing Through The Breaker May Be The Source Of Some Additional Pressure Against The Tripping Latch.

The Manufacturer's Instruction Manual Should Be Followed When Lubricating The Bearing Surfaces Of The Operating Mechanism. However, Excessive Lubrication Should Be Avoided As Oily Surfaces Tend To Gather Dust And Grit And Become Stiff In Cold Weather, Which Increases Friction.

For Oil Breakers, Check The Color And Strength Of The Oil Dielectric. Since The Interrupter's Operation Depends On Converting The Internal Arc Path From A Fair Conductor To A Good Insulator In The Brief Moment While The Current Is Flowing Through Zero, The Dielectric Strength Must Be Maintained To Avoid Internal Breakdown Under Voltage Surges And To Allow The Interrupter To Operate As Intended. The Lowest Permissible Dielectric Strength For Each Type Of Circuit Breaker Is Specified In The Manufacturer's Instructions. Maintaining The Dielectric Strength Above 20 KV Is Advised.

Filtering May Be Able To Remove Suspended Particles From Carbonized Oil, But Cleaning Of The Interrupters, Bushings, Etc., Is Still Necessary. If Moisture Lowers The Dielectric Strength, It Is Advisable To Evaluate The Fiber And Wood Components And Address The Moisture Source. These Factors Make It Uncommonly Beneficial To Filter A Circuit Breaker's Oil While It Is Still In Use.

Watch The Breaker While It's Under Load.

Check For Malfunctions By Manually And Electrically Operating The Breaker. Testing The Minimum Voltage Needed To Trip The Breaker Should Reveal Whether There Is Excessive Friction In The Tripping Mechanism And The Margin Of Safety In The Tripping Function. To Achieve This, Connect A Voltmeter Across The Trip Coil And A Switch And Rheostat In Series In The Trip-coil Circuit At The Breaker (Across The Terminals To The Remote Control Switch). Begin By Increasing The Voltage To No More Than 50% Of The Rated Trip-coil Voltage. Continue Doing So Until The Trip-coil Plunger Detects And Successfully Trips The Breaker. At That Point, Record The Minimum Tripping Voltage. Most Those Who Break. Approximately 56% Of The Rated Trip-coil Voltage Should Cause The Trip. 

The Trip Coils In The Majority Of Contemporary Breakers Will Burn Out Or Overheat If They Are Left Electrified For An Extended Length Of Time. When The Breaker Closes, An Auxiliary Switch Is Utilized In Series With The Coil To Open The Circuit. In Order To Successfully Terminate The Arc And Prevent Damage To The Contacts, The Auxiliary Switch Needs To Be Adjusted Correctly.

Additionally, Tests Should Be Performed To Find The Closing Coil Resistance And The Lowest Voltage Needed To Close The Breaker.

Trip Switch Produced By Safety Relays.

Verify The Changes Made To The Functioning Mechanism. It Is Necessary To Measure The Mechanical Clearances Of The Operational Mechanism Connected To The Pole Or Tank. A Noticeable Difference Between The Value Discovered And The Setting At The Time Of Erection Or During The Most Recent Maintenance Overhaul Is Typically A Sign Of Mechanical Issue. The Clearances Are Somewhat Impacted By Temperature And The Variations In Temperature Between The Various Components Of The Mechanism. These Impacts Are Often Permitted By The Tolerances Recommended By The Manufacturers.

Double Check The Breaker And Bushings.
High-voltage Circuit Breaker Maintenance & Testing
AIR CIRCUIT BREAKERS

High-voltage Circuit Breaker Maintenance & Testing
OIL CIRCUIT BREAKERS

Calculate The Resistance To Contact. 
The Contact Resistance Of High Pressure, Butt-type Contacts Is Essentially Independent Of Surface Condition As Long As There Is No Foreign Material Present. Measuring The Electrical Resistance Between Each Pole's Exterior Bushing Terminals, However, May Be Considered The Last "Proof Of The Pudding." Any Unusual Rise In This Circuit's Resistance Could Be A Sign Of Loose Bushing Connections, Loose Jumpers, Foreign Objects In The Contacts, Or Loose Contacts In The Support. Any One Of Them Could Lead To Localized Degradation And Heating. The Increase In Resistance And The Current Can Be Used To Easily Calculate The Amount Of Heat Over Normal.

The Most Practical Tools For Measuring Resistance Of The Primary Contact Circuits Are A "Ducter" Or A Portable Double Bridge (Kelvin). In Order To Prevent Any Damage To The Test Equipment, The Breaker Connections Should Not Be Opened During This Test.

The Maximum Contact Resistances For Common Kinds Of Breakers Are Listed In Table 1.

Luckily, These Issues Are Expected To Surface Early In Breaker Use And Would Be Discovered By Early Internal Inspections. The Frequency Of Internal Inspections Can Be Safely Reduced Once Unacceptable Internal Conditions Are Corrected And After One Or Two Inspections Reveal That Internal Conditions Are Satisfactory.

Implication Of Imposed Duty

Impact Of Light Duty: An Internal Circuit Breaker Check That Hasn't Involved Any Switching Or Interruption Duty Since The Last Inspection Won't Be Very Helpful, But It Won't Be A Complete Loss Either. Electrostatic Charge Current May Cause Erosion In The Form Of Uneven Grooves, Often Known As Tracking, On The Inner Surface Of The Interrupter Or Shields If The Breaker Has Been Powered But Left Open. A Deposit Of Carbon Sludge That Was Previously Produced By An Interrupted Operation Typically Makes This Worse. If The Breaker Has Stayed Closed And The Current Is Flowing, There May Be Indications That The Contacts Heated Up Because The Contact Surfaces Were Dirty, Oxidized, Or The Contact Pressure Was Not Adjusted Correctly.

Regardless Of Whether The Breaker Is Turned On Or Not, Any Shrinkage And Loosening Of Wood Or Fiber Parts (Caused By A Loss Of Absorbed Moisture Into The Dry Oil) Will Occur After Erection. On The Other Hand, Mechanical Operation Will Highlight Any Loosening. If At All Possible, It Is Beneficial To Purposefully Apply Multiple Switching Operations To The Breaker Prior To Examination. If This Is Not Possible, You Can Get Some Further Information By Measuring The Contact Resistance Of Each Pole Both At First And After Each Operation, And Operating The Breaker Multiple Times After It Has Been Deenergized.

Impact Of Regular Work. Depending On The Type Of Circuit Breaker Involved, Load Switching, Line Dropping, And Fault Interruptions Impose Varying Degrees Of Duty. Because Of Low Oil Pressure, Circuit Breakers That Use An Oil Blast Produced By The Power Arc May Deteriorate More When Small Faults Or Line Charging Current Are Interrupted Than When Severe Faults Within The Breaker's Rating Are Interrupted. Certain Designs That Make Use Of This Fundamental Interruption Principle Reduce Distress At Light Interrupting Duties By The Use Of Repeated Breaks, Quick Contact Travel, And Oil Turbulence Brought On By The Movement Of The Contact And Mechanism. Performance Is More Consistent In Designs That Use A Mechanically Powered Piston In Addition To The Arc-driven Oil Blast. 

When Assessing The Necessity For Maintenance Based On Service Records And The Effectiveness Of A Breaker Based On Inspection Evidence, These Differences In Characteristic Performance Across Different Designs Must Be Taken Into Account. Owing To These Differences, Some Firms' Approach Of Calculating Each Fault Interruption As Being Equal To 100 No-load Activities Is Inherently Highly Approximate, Even Though It Could Be A Helpful Guide In The Absence Of Any Other Information.

Impact Of Strict Obligation. Large Fault Interruptions May Cause Contact Erosion And Damage From Extreme Mechanical Pressures. Automatic Oscillograph Records Provide The Most Accurate Indication Of The Stress A Circuit Breaker Experiences During Fault Interruptions. It Is Reasonable To Suppose That The Circuit Breaker's Deterioration Is Proportionate To The Energy It Lost During The Interruption. The Energy Lost Is Roughly Proportionate To The Current And The Arcing Period, Or The Interval Between The Contacts Splitting And The Current Stopping. Nevertheless, Oscillograms Do Not Always Show The Separation Of The Contacts; In Such Cases, One Must Infer This Information From The Relay Time Given And The Known Parting Time Of The Breaker Connections.

Relay Operation Goals And Related System Circumstances Can Provide A Very Rough, But Still Helpful, Indicator Of The Fault Duty Placed On The Circuit Breakers In The Absence Of Automatic Oscillographs. A Tabulation Of All Such Data Ought To Be Kept In The Circuit Breaker Maintenance File.

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