The correct answer is C. Wave traps are used to trap waves of either power frequencies or higher frequencies entering generator or transformer units.
A wave trap is a device that is used to prevent unwanted signals from entering or leaving a circuit. It is typically made up of a capacitor and an inductor, which are arranged in parallel or series to form a resonant circuit. When the wave trap is tuned to the frequency of the unwanted signal, it will absorb the energy of the signal and prevent it from passing through the circuit.
Wave traps are often used in power systems to prevent high-frequency noise from entering or leaving generators or transformers. They can also be used to protect sensitive equipment from electromagnetic interference.
Option A is incorrect because wave traps are not used to trap power frequencies. Power frequencies are the frequencies at which electricity is transmitted and distributed. Wave traps are used to trap higher frequencies, such as those that are generated by electronic equipment.
Option B is incorrect because wave traps are not only used to trap higher frequencies. They can also be used to trap power frequencies.
Option D is incorrect because wave traps are used to trap both power frequencies and higher frequencies.