The correct answer is: D. high voltage side of high kVA rating transformers.
Helical coils are used on the high voltage side of high kVA rating transformers because they have a lower inductance than round coils. This is because the magnetic field lines are more concentrated in a helical coil than in a round coil. This means that less copper is required to produce the same amount of inductance, which makes helical coils more efficient.
Helical coils are also used on the high voltage side of high kVA rating transformers because they are less likely to overheat. This is because the heat generated by the current flowing through the coil is more evenly distributed in a helical coil than in a round coil. This means that helical coils are less likely to fail due to overheating.
Here is a brief explanation of each option:
- A. low voltage side of high kVA transformers
Helical coils are not typically used on the low voltage side of high kVA transformers because they have a higher inductance than round coils. This is because the magnetic field lines are more concentrated in a helical coil than in a round coil. This means that more copper is required to produce the same amount of inductance, which makes helical coils less efficient.
- B. high frequency transformers
Helical coils are not typically used in high frequency transformers because they have a higher inductance than round coils. This is because the magnetic field lines are more concentrated in a helical coil than in a round coil. This means that more copper is required to produce the same amount of inductance, which makes helical coils less efficient.
- C. high voltage side of small capacity transformers
Helical coils are not typically used on the high voltage side of small capacity transformers because they have a higher inductance than round coils. This is because the magnetic field lines are more concentrated in a helical coil than in a round coil. This means that more copper is required to produce the same amount of inductance, which makes helical coils less efficient.
- D. high voltage side of high kVA rating transformers
Helical coils are used on the high voltage side of high kVA rating transformers because they have a lower inductance than round coils. This is because the magnetic field lines are more concentrated in a helical coil than in a round coil. This means that less copper is required to produce the same amount of inductance, which makes helical coils more efficient.