The time-varying low-frequency magnetic-field emitted from the ship’s inverter-fed induction motor

The dataset contains the magnetic field measurement results that are part of a comprehensive study on the assessment of the magnetic field emissions onboard of the research-training vessel. The measurements were carried out, nearby the bow thruster motor fed from the inverter, during maneuvering and the sea voyage. The bow thruster is assembled in the forepart of the ships’ hull and has constant pitch propeller. Using the control levers at the wings of the bridge, it is possible to change the speed and direction of the revolutions of the propeller, and in this way to move the bow of the ship during maneuvering. The bow thruster is driven with a squirrel cage asynchronous motor fed by the PWM frequency converter. The IGBT (Isolated Gate Bipolar Transistor) inverter was operating at 2 kHz (possible 4 kHz) switching frequency. The inverter output frequency was adjusted in the frequency range from 0 to 50 Hz. Measurements were performed in the bow thruster compartment with the ESM-100 H/E field meter, which was fixed on the wooden bar, about 1 m from the bow thruster motor (Figure 1).  
Data recording of magnetic field emissions was carried out with a/d converters of the data acquisition board (DAQ), which were connected to the analog outputs of an isotropic field meter (Figure 2). ESM-100 H/E field meter, which was applied in this system, enables the measurements of a magnetic field induction in the measuring ranges from 1 nT to 20 mT. Four wide-band analog outputs of this meter afford possibilities for measuring the time waveforms of the magnetic fields, separately in the three orthogonal directions, in the output voltage range from 0 to 600 mV (see Table). The measured analog signal is conditioned with the use of National Instruments sub-assemblies. The initial conditioning follows and is realized through the low-pass filter module (for antialiasing application) with programmable cut-off frequency. The applied module has 8th-order elliptic filters, which provide a very sharp roll-off. Matching of the signal level to the a/d converter the DAQ input is realized by the input amplifier with the programmable gain. The formation of the output digital signal from the analog signal takes place in the a/d converter with a 16-bit resolution and sampling rate equal to 20 kS/s. Discrete signals are next analyzed (off-line) with the use of virtual instruments (LabVIEW software). Figure 1. The ESM-100 H/E field meter located close to the bow thruster motor Figure 2. A block diagram of the measuring system for assessment of magnetic field emissions