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What is the relation between the current flowing through the pressure coil and the supply voltage in an Energy meter?

What is the relation between the current flowing through the pressure coil and the supply voltage in an Energy meter? Correct Answer Current lags behind 90 degrees than the supply voltage

Lag adjustment:

  • In the induction type energy meters, in order to maintain the speed of rotation proportional to power The phase angle between the supply voltage and pressure coil flux should be equal to 90o. However, in actual practice, the angle between the supply voltage and pressure coil flux is exactly not 90o but few degrees less. Therefore, some lag adjustments require.
  • Lag adjustment adjusts the angle between current in pressure coil and supply voltage equal to 90othat means Current lags behind 90 degrees than the supply voltage.
  • Lag adjustment can be done by adjusting shading bands on shunt magnet. 

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Torque equation in energy meter:

Td = Is Ip sin(Δ - ϕ )

Td = Deflecting torque

v = Supply voltage 

IP = Current in pressure coil

Δ = 90o = Angle between V and IP  

Is = current in series coil

Td = Is Ip sin(90 - ϕ)  { Δ = 90o }

Td = Is Ip cosϕ 

Td ∝ V I cosϕ ∝ P

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