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Cable, Transformer, Generator, Motor, Bushing, Circuit Breaker Insulation Resistance Testing. A Must Course for All Engg
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Mastering Insulation Resistance Testing Theory + Practical
Content of CourseDefinition of Insulation ResistanceWhat Causes Insulation Resistance to DegradeHow Insulation Resistance Test Set workUnderstanding Insulation resistance distributionUnderstanding Leakage CurrentDirection of Leakage CurrentPrinciple of measurement for Insulation ResistanceEquivalent Circuit of Insulation ResistanceFormula to calculate insulation ResistanceUnderstanding types of leakage currentConductive Leakage CurrentCapacitive Leakage CurrentPolarization / Absorption Leakage CurrentSurface Leakage CurrentUnderstanding Charging CurrentCapacitance DistributionCapacitance Equivalent circuit of three phase circuitHow Cable Charging worksCharging Time ConstantCalculating 5TEffect of Charging Current on reading of IRPolarization / Absorption CurrentDie Electric absorption in detailUnderstanding Current Curves ( Conduction, Capacitive, Polarization)Selection of Applied Voltage as per IEEE standard 43Application of IR TestHow to make connections & different combinations to testUnderstanding Test ConnectionProof Testing / Installation TestingMaintenance TestingSpot / Short time resistance testTimed Resistance TestStep Voltage testAnalyzing Step CurveDi-Electric Absorption TestAnalyzing Curve for Di-Electric Absorption TestVarious Insulation Resistance TestTemperature correction for testing rotating machinesAnalyzing curve for Temperature Co-efficient FactorTesting WiringMegger Testing Calculation ExampleConnection Diagram of Cable testingConnection Diagram of Motor testingConnection Diagram of Generator testingConnection Diagram of Circuit Breaker TestingConnection Diagram of Bushing testingUnderstanding Voltage Characteristics for IR TesterAnalyzing Curve for IR TesterGuard TerminalGuard Terminal ConnectionGuard Terminal Equivalent CircuitExample of using Guard connection for accuracyThe Guard Terminal as Diagnostic ToolIntroduction to ANSI/IEEE Std 95-1977Demonstration of Megger VideoVideo How to Test CableVideo How to Test TransformerVideo How to Test Motorinsulation resistanceAn insulation resistance (IR) test measures the total resistance between any two points separated by electrical insulation. The test, therefore, determines how effective the dielectric (insulation) is in resisting the flow of electrical currentInsulation Resistance / Megger TestMost commonly referred to as simply a “megger,” the insulation resistance test set (or Megohmeter) is used to determine the condition of insulation on various types of electrical equipment like cables, transformers and switchgear. Tests are typically conducted by applying a direct current (dc) voltage to the conductor under test and measuring the current that flows through insulation (called the “leakage current”) and into the non-current carrying metal parts of equipment. Contaminated insulation can be determined by observing the absorption current or current absorbed by the insulation over a specified period of time. What Causes insulation to Degrade?Electrical StressMechanical StressChemical AttackThermal StressEnvironmental ContaminationHow an Insulation Resistance Tester OperatesThe Megger insulation tester is essentially a high-range resistance meter (ohmmeter) with a built-in dc generator. The instruments generator, which can be hand-cranked, battery or line-operated, develops a high dc voltage that causes several small currents through and over surfaces of the insulation being tested. The total current is measured by the ohmmeter, which has an analog indicating scale, digital readout or bothInsulation Resistance / Megger Test Record keepingInsulation-resistance test data may be used to establish a trending pattern with deviations from the baseline information permit evaluation of insulation. The results of these tests (typically expressed in Megohms) are dependent on the temperature of the insulating material and the humidity of the surrounding environment at the time of testing; therefore all readings must be corrected to a base temperature, such as 20C.How much voltage can a be produced?Insulation testers come in a variety of sizes and output voltages depending on its specific application. A handheld 1000V Megohmeter is usually sufficient for 600V class equipment while larger sets for use on high voltage apparatus can output up to 15,000V or more. Megger Test ConnectionsThere are three test terminals on an insulation resistance tester marked positive (+), negative (-) and Guard (G). Most basic measurements utilize only the positive and negative terminals, such as in cases when there is little possibility of adverse current paths that could affect the result. When testing at higher voltages, such as with cable or transformers, the guard terminal can be used to divert surface leakage from the measuring circuit. Not all insulation testers are equipped with a guard terminal. Note: Handheld megohmeters with outputs of 1000V or less may not be equipped with a Guard terminal. What is Insulation ResistanceNo insulation is ideal and hence there will be always some leakage current from insulation to ground, when voltag
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