Measurement of Resistance

MEASUREMENT OF RESISTANCE

Prepared by,

Madhumitha Jayaraj

WHY resistance of material is measured ???

Cable manufacturers

Electric motor & generator manufacturers

Installation & maintenance of power cables, switchgear & voltage tap changers

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CLASSIFICATION

< 1 Ω

LOW RESISTANCE

1Ω < R < 100kΩ

MEDIUM RESISTANCE

> 100kΩ

HIGH RESISTANCE

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MEDIUM RESISTANCE MEASUREMENT

Wheat stone Bridge

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Substitution method

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Ammeter-Voltmeter method

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LOW RESISTANCE MEASUREMENT

• AMMETER VOLTMETER METHOD

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KELVIN DOUBLE BRIDGE

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COMMERCIAL KELVIN DOUBLE BRIDGE

MEASUREMENT OF HIGH RESISTANCEDIRECT DEFLECTION METHOD

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Measurement of high resistance having metallic sheath

LOSS OF CHARGE METHOD

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R’ = t/(C loge V1/V2 )

While measuring insulation resistance of a cable ora capacitor the test need not be repeated. In thiscase C will be the capacitance of the cable undertest, which must be known and R1 will be theinsulation resistance to be measured. NO externalresistance is to be inserted in the circuit. The valueof R1 then can be obtained directly from theexpression.

R = t/(C log V2/V1 )

MEGOHM BRIDGE METHOD

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Modified Wheatstone Bridge

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QUERIES..?