Which of the following is the cause of meter phase error in induction type energy meter?

Option 2 : Incorrect adjustment of the position of shading bands.

Energy meter will register true energy only if the angle Δ is made equal to 90°. Thus the angle between shunt the shunt magnet flux ϕ_p and the supply voltage V should be equal to 90°.

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Shading bands:

• In this arrangement shading bands L₁ and L₂ are placed around the central limb of shunt magnet.
• The adjustment can be done by moving the shading bands along the axis of limb.
• As the shading band are moves up the limb, they embrace more flux.
• This results in greater values for induced emf, current and the mmf produced by the shading bands and therefore the value of lag angle increases.
• When the shading bands are moved down limb, mmf decreases and the angle is reduced.
• The adjustment is so done that ‘θ’ is such that it makes Δ = 90°.
• By providing this arrangement, the shunt magnet flux ϕ_p can be brought exactly in quadrature with applied voltage V.
• This adjustment is known as lag adjustment.
• Incorrect adjustment of position of these shading bands cause phase error.