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Braking system in single phase energy meter consists of
Bar magnet
Temporary magnet
Permanent magnet
Super magnet
Permanent magnet
The braking system in an induction-type single-phase energy meter consists of a permanent magnet, commonly known as a braking magnet ┬╖ It is positioned near the rotating aluminum disc to exert a retarding torque that opposes the driving torque, ensuring the disc speed is proportional to the power being measured.
The braking system in an induction-type single-phase energy meter consists of a permanent magnet, commonly known as a braking magnet ┬╖ It is positioned near the rotating aluminum disc to exert a retarding torque that opposes the driving torque, ensuring the disc speed is proportional to the power being measured.
TbтАЛ=KтЛЕ╧Х2тЛЕN тАФ where K is a constant, ╧Х is the magnetic flux, and N is the rotational speed of the disc.
TdтАЛ=TbтАЛ тАФ condition for steady-state speed where driving torque equals braking torque.
When the aluminum disc rotates through the field of the permanent magnet, eddy currents are induced in the disc ┬╖ According to Lenz's law, these currents produce a magnetic field that interacts with the permanent magnet's field to create a braking torque ┬╖ The retarding torque TbтАЛ is directly proportional to the speed of the disc, such that TbтАЛтИЭ╧Х2N, where ╧Х is the flux of the permanent magnet and N is the rotational speed.
The permanent magnet is typically a C-shaped Alnico magnet.
Braking torque is adjusted by changing the radial position of the magnet relative to the disc center.
Eddy currents are the primary mechanism for generating the retarding force.
The braking system prevents the disc from spinning indefinitely when the load is disconnected (prevents 'creeping' to an extent).
Provides linear braking characteristic relative to speed.
Stable over long periods of operation due to high coercivity of permanent magnets.
Susceptible to weakening if subjected to extreme heat or vibration.
Sensitivity to stray magnetic fields if not shielded properly.
Electromechanical induction-type watt-hour meters.
Rotating disc-type speed control systems.
If the permanent magnet is shifted towards the center of the disc, braking torque decreases; shifting it outward increases braking torque.
Option B (Temporary magnet) is incorrect because a temporary magnet's flux would vary with current, leading to non-linear braking.
C is correct тАФ The braking system in a single-phase energy meter utilizes a permanent magnet to induce eddy currents in the disc, creating a retarding torque.
Always remember that in moving-coil and induction-type instruments, braking is almost exclusively achieved via eddy current effects generated by permanent magnets.