Shipboard Powerline Transformers: H Emission Characteristics, EMI Models, and a Test Procedure That Utilizes Simulated Input Signals

摘要

Harmonics of the powerline fundamental frequency (60/400 Hz) can be generated whenever nonlinear loads are connected to the power distribution system. In some cases, these currents can be the source of radiated magnetic field emissions that adversely affect shipboard equipment. In this memorandum, the magnetic fields from shipboard power transformers were determined using an offline broadband generator as a source of controlled powerline harmonics at frequencies up to 50 kHz. Normalizing the flux density, B, by the harmonic current spectral density in the primary winding, I, was found to be an effective method to compensate for impedance changes and harmonic distortion caused by the transformer magnetic core. It was shown that between 5 and 50 KHz the magnetic fields from transformers rated at 200 W to 5 kVA depend on the distance from the center of the transformer to the field point, the shielding effectiveness of the case, and the current spectrum of the input harmonics. In this frequency band, a transformer surface not containing seams or openings behaves similar to an ideal shielding boundary with respect to frequency (f to the minus 1/2 power dependence). At a distance close to the transformer, the magnetic fields are proportional to 1/R cubed (dipole source); at greater distances they are proportional to 1/R squared.