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Method used to measure resistance of winding is__________.
Voltage ratio test
Ammeter voltmeter method
Insulation resistance test
Test on tap changer
Ammeter voltmeter method
The Ammeter-Voltmeter method is the standard industrial procedure for measuring the DC resistance of transformer windings. It involves passing a known DC current through the winding and measuring the voltage drop across it to calculate resistance using Ohm's Law.
The Ammeter-Voltmeter method is the standard industrial procedure for measuring the DC resistance of transformer windings. It involves passing a known DC current through the winding and measuring the voltage drop across it to calculate resistance using Ohm's Law.
R=IVтАЛ тАФ Calculation of resistance using Ohm's Law, where V is voltage in Volts and I is current in Amperes.
A DC source is applied to the winding terminals. An ammeter (A) is connected in series to measure the current I, and a high-impedance voltmeter (V) is connected in parallel to measure the voltage drop VRтАЛ. The resistance is calculated as R=IVRтАЛтАЛ. This method is preferred because it effectively eliminates the effects of inductive reactance, which is zero at steady DC.
Used specifically to verify the ohmic value of transformer windings after maintenance or installation.
A DC supply must be used, as AC would include the effect of inductive reactance (XLтАЛ).
Stabilization time is required for inductive circuits; readings should only be taken after current stabilizes.
Temperature correction is necessary to compare results with factory test values.
Simple to implement using standard laboratory equipment.
Highly accurate for low-resistance measurements when corrected for lead resistance.
Requires high DC current source for large power transformers.
Time-consuming due to the long time constant (tau=L/R) of high-inductance windings.
Routine maintenance of Power and Distribution Transformers.
Detecting loose connections or shorted turns in winding assemblies.
The resistance value obtained should be within 2% of the factory test record for a healthy transformer.
Option A (Voltage ratio test) determines the turns ratio. Option C (Insulation resistance test) uses a Megger to check winding-to-ground integrity. Option D (Test on tap changer) checks for continuity and operation of tap positions.
B is correct тАФ The Ammeter-Voltmeter method is the standard approach for determining the DC resistance of transformer windings.
Always ensure the DC current does not exceed 10-15% of the rated winding current to prevent excessive heating and potential insulation damage during testing.