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The formula to calculate the number of turns in the field windings of an electric motor or generator, which is not standardized in a simple form across all applications due to the complexity of electric machine design, involves various factors such as the magnetic flux required, the area of the core, the current in the windings, and material properties. However, a commonly referenced equation in designing magnetic circuits (which can be applied for estimating the number of field winding turns in some contexts) relates the magnetomotive force (MMF) to the product of the current and the number of turns. This can be expressed as:
[ text{MMF} = N cdot I ]
where:
– ( text{MMF} ) is the magnetomotive force in Ampere-Turns (At),
– ( N ) is the number of turns,
– ( I ) is the current in Amperes (A).
For calculating the number of turns specifically, if you know the required MMF and the current, you can rearrange this formula to:
[ N = frac{text{MMF}}{I} ]
However, the actual determination of the number of turns for field windings requires a detailed design process, considering the electromagnetic design, which includes:
– The desired magnetic flux in the core,
– The permeability of the core material,
– The dimensions of the core,
– The type of winding material, its size, and thermal properties,
–
Answer: b
Explanation: The field mmf per pole at full load is calculated from the voltage across each field coil. Next, the field current is calculated and from these values the number of field turns is calculated.