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Megohmmeter
The document outlines the technical specifications and operational details of a 1 mega ohm meter used for insulation testing, including its construction, components, and testing voltage options. It also discusses factors affecting insulation resistance and precautions to take during use, highlighting the potential for shock when handling high voltages. Additionally, it describes the connections and configurations for accurate measurements.
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Megohmmeter
- 1. 1 Mega ohm Meter(Megger) Used for insulation testing
- 2. 2 Constructional Details DC Generator •Hand moved • Speed constant • Permanent magnet • Test voltage 500 V, 1000 V, 2500 V (selectable) • Handle, gears and centrifugally controlled switch • Brush less ac generator with rectifier also used
- 3. 3 Coils and Magnet •A permanent magnet with special design • Current coil (CC) on moving former • Two pressure coil (PC1 & PC2) on the moving element • A fixed C-shaped core • Spatial angle between CC and PC is 900 Constructional Details
- 4. 4 Constructional Details Coil connections •A pressure coil connected in series with a fixed standard resistance • Pressure coil along with fixed resistance is connected in parallel to the DC generator • Current coil in series with unknown resistance (insulation) and a fixed standard resistance •Guard rings prevents the error due to leakage currents
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- 6. 6 Constructional Details Non-linear scale •Torque produced by current coil will be in opposition to that by voltage coil • Pointer stabilizes when both torque are equal • Non-linear scale (similar to inverse Tan)
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- 8. 8 Factors Affecting InsulationResistance • Dirt, Moisture and temperature • A thumb rule – insulation resistance becomes twice for 10 0 C decrease in temperature • Naturally deteriorates with time
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- 12. 12 Precautions • Instrument developshigh voltages, hence the possibility of getting shock if terminals are touched during use • A capacitive circuit should be discharge
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