Presentation on theme: "An Introduction to On-line Partial Discharge Surveys"— Presentation transcript:
1 An Introduction to On-line Partial Discharge Surveys
2 PARTIAL DISCHARGEWhen high voltage insulating material breaks down Partial Discharges are created, measured in units of charge known as pico-Coulombs or millivolts.
3 WHAT IS PARTIAL DISCHARGE? Electrical discharges occurring inside medium and high voltage insulation (flaws, cracks, voids, irregularities).These imperfections create voltage stresses and cause eventual failure of the insulation.Insulation failures begin with and are characterized by small but detectable releases of energy or Partial Discharge.
4 PARTIAL DISCHARGE TESTING USED FOR QUALITY ASSURANCE For many years partial discharge testing has been an IEEE/ANSI standard to identify insulation problems in electrical apparatus before it leaves the factory floor.Many U.S. and International standards have been developed for partial discharge testing.Until recently Partial Discharge testing was limited to testing at manufacturer’s laboratories.Now computers and sophisticated equipment can isolate and detect Partial Discharge occurrences in the field.
6 NO OUTAGE EVALUATIONThese proven technologies exist today to evaluate medium or high voltage systems while the system is energized.Oil testing/DGA – limited to oil transformersInfrared testing – visible loose connections onlyVisual inspections – problems may not be visiblePower Quality – cannot detect insulation failuresVibration – limited to motors and transformersPartial Discharge Testing – single best all-around test
7 PARTIAL DISCHARGE VS. INFRARED How are Partial Discharge Inspections different from Infrared Inspections?Infrared identifies electrical current problems (looseconnections) that result in heat. The specimen must bevisible to the naked eye for the infrared camera to detect aproblem.Partial Discharge identifies voltage problems that result ininsulation breakdown and generation of Partial Discharges.The specimen does not need to be visible for PartialDischarges to be detected.
12 INSULATION BREAKDOWNWhy should we be concerned with insulation breakdown and Partial Discharges?
13 INSULATION BREAKDOWNNFPA 70B states that insulation breakdown is the number one cause of electrical failures.In medium and high voltage equipment, partial discharges are the first indication of insulation breakdown.
15 WHAT TYPE OF FACILITES ARE AFFECTED? INDUSTRIAL - Large Manufacturing,CogenerationCOMMERCIAL - Research Parks, High RisesINSTITUTIONAL - Campuses, HospitalsGOVERNMENTAL - Military Bases, LargeOffice ComplexesUTILITY - Investor Owned, Municipalities
16 WHERE DO PARTIAL DISCHARGES OCCUR? Electrical Systems > 600V (2.4KV, 4.16 KV, 12KV, etc.)Types of Equipment Subject to Partial Discharge-Cables -Transformers-Circuit Breakers - Instrument Transformers-Switchgear (CT’s, PT’s)-Insulators - Bushings-Generators - Motors-Surge Arrestors - Capacitors
17 ADVANTAGES OF PARTIAL DISCHARGE SURVEYS PREDICTIVE - failures can be prevented.NO OUTAGE NECESSARY - does not interruptoperations.NON-DESTRUCTIVE - no damage to electricalsystem.TRENDING - comparison to previous testspossiblePRIORITIZE MAINTENANCE ACTIVITIES -determine which equipment to service first.PLANNING - allows time to schedule repairs.FINANCIAL CONTROL – repairs can be budgeted.
18 TYPICAL MEDIUM VOLTAGE POWER CABLE CONSTRUCTION
19 TYPICAL HIGH VOLTAGE UNDERGROUND CABLE SYSTEM Load Unit SubstationSource SwitchgearVisible CableTerminationsVisible CableTerminationsGround LevelUnderground Cable in Conduit (not visible)
24 HOW CAN PARTIAL DISCHARGES BE DETECTED? Discharges are detected by special signal processing equipment designed to eliminate outside interference.Capacitive Methods - For Unshielded Components- Dry Type Transformers- Instrument Transformers- SwitchgearInductive Methods - metal enclosed components- Shielded Cables and ComponentsOil Filled TransformersRotating ApparatusAcoustic Emission MethodsDry & Oil TransformersSwitchgear- Unshielded Cables
47 PERFORMING A PARTIAL DISCHARGE SURVEY Analyze the single line drawing to develop planOnsite MeasurementRemoval of equipment covers.Record field data.Obtain signatures of atypical components.Offsite Data AnalysisCorrelate measurements to single line drawing.Compare atypical results to like insulation from database.Analyze signatures.Trend Results.Report GenerationRecognize immediate failure possibilities.Recommend possible repairs.Recommend possible resurvey frequency.
48 SUMMARY Electric Insulation will fail. Predicting failures is now possible throughPartial Discharge Analysis.No outage is required to survey theequipment.Results can be prioritized and trended.Partial Discharge Surveys should beperformed annually.
49 We apologize to every electrical professional for taking 252 years We apologize to every electrical professional for taking 252 yearsto prevent your failures.Benjamin Franklin discovered electricityin This year we launched an easyto use, cost effective “no-outage” electricalinspection technology that detectsmedium and high voltage equipmentproblems before they fail!