What is an induction measurement and why do you use it?

Inductance is the ability of those windings to oppose changes in current; with alternating current (AC) the coil creates a counter electromotive force (EMF) that resists the alternating current. Inductance is measured in henries (H) and millihenries (mH) and is only present when the current changes (AC).

How do you measure inductance?

To determine the inductance of a coil or motor winding, a test device sends an alternating voltage through the coil and measures the resulting alternating current. From the ratio between current and voltage and the phase shift, the instrument calculates the inductance using the formula XL=2πfLX_{\mathrm{L}} = 2 \pi f LXL​=2πfL. Unlike a DC resistance test, an inductance test measures how the coil behaves under changing currents.

Difference between the measurements

• Resistance test (DC) – measures the pure copper wire resistance of the winding; useful for identifying loose connections or poor solder joints.

• Inductance test (AC) – measures how strongly the coil resists changes in current; this helps to detect winding faults, short circuits between turns and core problems.

• Impedance test (AC) – measures the combined effect of resistance and inductive reactance; this provides an overall picture of how the winding behaves at a given frequency and makes it possible to compare phases.

Why is impedance measurement useful for motors?

In electric motors and transformers all phases should have the same impedance. A higher or lower impedance in one phase can indicate:

• Short circuits or open circuits in the winding;

• Imbalance in the magnetic circuit, for example due to deformed laminations or loose cores;

• Contamination or moisture, which changes the inductive and resistive properties.

By measuring resistance, inductance and impedance and comparing the results, you get a complete picture of the condition of the motor windings. This helps to identify early faults in time and carry out targeted maintenance or repairs.

The MotorAnalyzer 3 measures inductance, resistance and impedance in a single instrument. Contact IONIO for advice on induction measurements in your motor testing process.