Question

Eddy current in dynamometer type wattmeter can be minimised by using ________ within the region of magnetic field. (Metallic parts Non-metallic parts)

Hint:

To ensure high accuracy, precision dynamometer wattmeters are designed with non-metallic frames and cases. This eliminates unwanted parasitic magnetic fields caused by circulating eddy currents.

Answer 1

Step 1: Understanding Eddy Current Formation:
Eddy currents are loops of electric current induced within solid, conducting materials when they are exposed to a changing magnetic field. These currents cause localized heating and generate their own magnetic fields, which can interfere with the accuracy of precision instruments like wattmeters.

Step 2: Evaluating Structural Materials:
To prevent eddy currents in a dynamometer-type wattmeter:

• Metallic parts: Highly conductive metals (such as aluminum, steel, or brass) provide low-resistance pathways that encourage the flow of large eddy currents.
• Non-metallic parts: Materials like plastics, bakelite, or fiberglass are electrical insulators. Using these materials for internal structures within the alternating magnetic field prevents eddy currents from forming.

Step 3: Conclusion:
Therefore, eddy currents are minimized by using Non-metallic parts for structural elements in the magnetic field region.