Equipment for Monitoring Synchronous Generators Condition through External Magnetic Field Waveforms

Abstract

This paper presents an equipment for monitoring synchronous generators condition through characteristics of the time derivative of the external magnetic field. The developed monitoring methodology allows the identification of established or incipient faults, by detecting changes in the magnetic signature of the synchronous generator. In this methodology, the measurement of signals outside the machine gives this equipment a non-invasive characteristic, allowing its monitoring without interfering or disturbing its operation. The developed system includes the specification of magnetic field sensors, signal measurement and processing equipment, as well as software for analysis and monitoring. The validation of the methodology used in this system was carried out through the analysis of experimental data, presenting efficient results in the detection of electrical and mechanical faults in synchronous generators of an experimental test bench and a hydroelectric power plant. As a result, the commercial specification of this equipment was obtained and two units were implemented in a hydroelectric power plant to monitor 305 MVA synchronous generators.

A Method for Statistical Processing of Magnetic Field Sensor Signals for Non-Invasive Condition Monitoring of Synchronous Generators

“…The induction sensors with nonmagnetic cores are associated with cascaded differential amplifier circuits with variable gains that internally adapt the output signal levels for the digitization step. The system is thus able to measure field amplitudes from mA/m to kA/m at the electrical fundamental frequency [8,22]. In this way, the installation of sensors around the machine becomes easier and adaptable to various configurations and machine types.…”

“…Different regions of the frequency spectrum can be sensitized depending on the type of fault [8]. An extensive experimental investigation performed on generators for different ratings indicates the need to analyze the spectrum in the range from 𝑓 to 3 kHz, or at least up to 1.5 times the slot frequency, defined as 𝑓 = 𝑓 𝑛 , where 𝑛 is the number of stator slots [22]. With the employed hardware [8,22], this strategy allows the detection of faults with greater influence in the high-frequency region, a typical behavior of stator Different regions of the frequency spectrum can be sensitized depending on the type of fault [8].…”

“…An extensive experimental investigation performed on generators for different ratings indicates the need to analyze the spectrum in the range from 𝑓 to 3 kHz, or at least up to 1.5 times the slot frequency, defined as 𝑓 = 𝑓 𝑛 , where 𝑛 is the number of stator slots [22]. With the employed hardware [8,22], this strategy allows the detection of faults with greater influence in the high-frequency region, a typical behavior of stator Different regions of the frequency spectrum can be sensitized depending on the type of fault [8]. An extensive experimental investigation performed on generators for different ratings indicates the need to analyze the spectrum in the range from f m to 3 kHz, or at least up to 1.5 times the slot frequency, defined as f s = f m n s , where n s is the number of stator slots [22].…”

“…Recent publications have reported the investigation of the magnetic signature characteristics obtained by measuring the external magnetic field for incipient fault detection purposes [4,6,[17][18][19][20][21][22]. Although several monitoring strategies have been proposed, most of these approaches are based on spot comparisons of measured frequency spectra, comparing only instantaneous magnetic signatures with and without a defect.…”

“…Although several monitoring strategies have been proposed, most of these approaches are based on spot comparisons of measured frequency spectra, comparing only instantaneous magnetic signatures with and without a defect. For the continuous condition monitoring of the SGs, necessary for the practical application of these methodologies in monitoring equipment, some works have already pointed out the need for periodic monitoring of these spectra, but have not approached any technique for automatic detection of changes that may be associated with incipient faults [8,20,22]. In addition, both the internal and external magnetic field monitoring techniques still lack standards to guide the interpretation of the measured quantities and the fault detection itself, such as those regarding mechanical vibration [23].…”