Question

The "Creeping" phenomenon occurs in which type of instrument?

• A. PMMC Ammeter
• B. Induction type Energy Meter
• C. Digital Multimeter
• D. Dynamometer Wattmeter

Hint:

Creeping is prevented by drilling two diametrically opposite holes in the aluminum disc.
The disc can rotate at most half a revolution before one of the holes stops its motion under no-load conditions.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks to identify the type of electrical measuring instrument in which the "Creeping" phenomenon occurs.
Creeping is a slow but continuous rotation of the electromagnetic disc even when there is no electrical load connected to the circuit.

Step 2: Key Formula or Approach:
In an induction type energy meter, the deflecting torque (\( T_d \)) is produced by the interaction of magnetic fluxes generated by both the shunt magnet (voltage coil) and the series magnet (current coil).
Ideally, when no load is connected, the current coil carries zero current, and the deflecting torque should be zero.
However, due to specific adjustment forces, the disc can rotate slowly under the effect of the voltage coil alone, which is known as creeping.

Step 3: Detailed Explanation:
The causes, mechanism, and remedies of creeping are detailed below:

• Causes of Creeping:
- Friction Compensation Over-adjustment: To overcome the starting friction of the bearings, a small auxiliary deflecting torque is provided by using shading loops near the shunt magnet. If this adjustment is overcompensated, it can drive the disc even when the load current is zero.
- Overvoltage: If the system voltage is higher than normal, the flux from the pressure coil increases, generating enough torque to cause creeping.
- Stray Magnetic Fields: External stray magnetic fields can interact with the disk and induce motion.

• Prevention of Creeping:
- To prevent creeping, two diametrically opposite holes are drilled in the aluminum disc.
- When one of the holes comes directly under the edge of the shunt magnet pole, the path of the induced eddy currents is distorted.
- This distortion creates a small opposing electromagnetic torque that overcomes the light-load frictional compensation torque, stopping the disc from rotating further.

Step 4: Final Answer:
Therefore, the creeping phenomenon occurs in the Induction type Energy Meter.