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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Energy meter creeps
Due to change in supply
Due to reversal in polarity of voltage
Due to asymmetry in magnetic circuit
Due to turns ratio of transformer
Due to asymmetry in magnetic circuit
Quick Summary: Creeping in an energy meter is a phenomenon where the aluminum disc rotates continuously even when there is no load current, but only the voltage supply is present. This error is primarily caused by an imbalance in the magnetic circuit or excessive friction compensation.
Creeping in an energy meter is a phenomenon where the aluminum disc rotates continuously even when there is no load current, but only the voltage supply is present. This error is primarily caused by an imbalance in the magnetic circuit or excessive friction compensation.
Td∝ΦvΦisin(δ) — Torque equation where δ is the phase angle
Tcreep>Tfriction — Condition for the onset of creeping
The driving torque in an induction energy meter is proportional to the product of flux Φv (from voltage coil) and Φi (from current coil). When load current is zero, driving torque should be zero. However, due to asymmetry in the magnetic circuit or mechanical vibrations, a small unwanted torque is produced. If this torque exceeds the control of the braking magnet, the disc creeps. To prevent this, two small diametrically opposite holes are drilled in the disc to provide a 'parking' position.
Creeping is considered a major fault in electromechanical induction-type energy meters.
The anti-creeping holes ensure the disc comes to rest when the potential circuit is energized but the load current is zero.
Friction compensation is often done by placing a shading loop on the pressure coil core, which if over-adjusted, can lead to creeping.
Creeping results in false energy registration, leading to charges for energy not consumed.
Causes inaccurate energy billing for consumers.
Indicates improper calibration of the meter.
Calibration of induction type energy meters.
Testing of meter sensitivity and friction balance.
Modern static (digital) meters do not have moving parts like discs and are therefore immune to the creeping phenomenon.
Option A is incorrect as supply changes affect torque magnitude but do not specifically cause creeping. Option B is incorrect as reversal of voltage polarity would reverse the torque direction, not cause creeping. Option D is incorrect as turns ratio determines the voltage step-down/step-up, not the mechanical rotation of the disc.
C is correct — Creeping is an error caused by asymmetry in the magnetic circuit that creates a small unintended driving torque on the meter disc.
In competitive exams, always link 'Creeping' to the 'Anti-creeping holes' on the disc and 'Over-compensation of friction' as common theoretical questions.