Question:
Which one of the following controls the speed of an energy meter ?
Which one of the following controls the speed of an energy meter ?
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In induction type energy meters:
• driving torque rotates the disc,
• braking magnet controls the speed of rotation. The braking torque is produced using eddy currents.
• driving torque rotates the disc,
• braking magnet controls the speed of rotation. The braking torque is produced using eddy currents.
Updated On: May 22, 2026
- Shunt Magnet
- Series Magnet
- Shading Band
- Braking Magnet
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The Correct Option is D
Solution and Explanation
Concept:
An induction type energy meter works on the principle of electromagnetic induction.
The rotating aluminum disc inside the energy meter rotates due to driving torque produced by magnetic fields.
To ensure correct meter operation, the speed of the rotating disc must be controlled properly.
This control is achieved using a braking system called the braking magnet.
The braking magnet produces a braking torque which opposes the motion of the disc and regulates its speed.
Step 1: Understanding the working of an energy meter. An induction energy meter mainly contains:
• Driving system,
• Moving system,
• Braking system,
• Registering system. The rotating disc moves because of interaction between magnetic fluxes.
Step 2: Understanding the need for speed control. If no braking arrangement exists:
• the disc may rotate too fast,
• readings become inaccurate,
• the meter loses calibration. Hence a controlled braking torque is essential.
Step 3: Role of braking magnet. A permanent magnet is placed near the rotating disc. As the aluminum disc rotates through the magnetic field:
• eddy currents are induced,
• these eddy currents interact with the magnetic field,
• braking torque is produced. This braking torque controls the speed of the disc.
Step 4: Checking each option carefully.
• Option \(1\): Shunt Magnet \(\rightarrow\) Produces operating flux, not speed control
• Option \(2\): Series Magnet \(\rightarrow\) Produces driving torque
• Option \(3\): Shading Band \(\rightarrow\) Used for phase adjustment
• Option \(4\): Braking Magnet \(\rightarrow\) Correct Therefore the correct answer is: \[ \boxed{(4)\; \text{Braking Magnet}} \]
Step 1: Understanding the working of an energy meter. An induction energy meter mainly contains:
• Driving system,
• Moving system,
• Braking system,
• Registering system. The rotating disc moves because of interaction between magnetic fluxes.
Step 2: Understanding the need for speed control. If no braking arrangement exists:
• the disc may rotate too fast,
• readings become inaccurate,
• the meter loses calibration. Hence a controlled braking torque is essential.
Step 3: Role of braking magnet. A permanent magnet is placed near the rotating disc. As the aluminum disc rotates through the magnetic field:
• eddy currents are induced,
• these eddy currents interact with the magnetic field,
• braking torque is produced. This braking torque controls the speed of the disc.
Step 4: Checking each option carefully.
• Option \(1\): Shunt Magnet \(\rightarrow\) Produces operating flux, not speed control
• Option \(2\): Series Magnet \(\rightarrow\) Produces driving torque
• Option \(3\): Shading Band \(\rightarrow\) Used for phase adjustment
• Option \(4\): Braking Magnet \(\rightarrow\) Correct Therefore the correct answer is: \[ \boxed{(4)\; \text{Braking Magnet}} \]
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