Please cite this article in press as: Ramírez-Niño, J., et al. Core saturation effects of geomagnetic induced currents in power transformers. AbstractSaturation of the magnetic core of transformers in a power system is an important effect that can be attributed to solar Geomagnetic Induced Currents (GICs). This saturation can conduce to voltage-control problems, generating harmonic currents, and heating of the transformer internal components, leading to gas relay alarm/operation and possible damage. This paper presents an analog physical reduced scale model of GICs in power transformers. The instrumentation employed to carry out this study consists of a single-phase reduced scale transformer, a controllable current source, a resistive load and a data acquisition system. The work establishes not only that it is possible to model the behavior of magnetic variables and to extrapolate the results to large full size power transformers, but also provides insight into GICs generation and their effects on power transformers. Obtained results are related to the non-linear behavior of GICs due to asymmetric saturation of the magnetic core in the power transformer, where computational model simulation is not able to give acceptable outcomes. Results are discussed for several GICs magnitudes, which include voltage, current, harmonics waveforms, magnetic core point of operation, the behavior of the stray flow, instantaneous power and core temperature. All Rights Reserved
A structural flood detection system for real-time health monitoring in the hollow sub-sea members of new offshore steel oilrigs is presented. Field-proven flood member detection techniques, integrated within the concept of health monitoring, offer an alternative to underwater nondestructive testing methods based on ultrasound and x-rays, which have been used to detect the presence of seawater in these applications, often with diverse or remote operating vehicles. The system employs a single piezoelectric transducer which can be permanently attached to the inner wall of every sub-sea structure and which is powered by a normally inert seawater battery. Upon activation, the sensor transmits ultrasonic chirp or tone encoded pulses, in the range of 21–42 kHz, to a monitoring receiver system at deck level for decoding and identifying flooded members. Experiments have been carried out using a jointed steel pipe structure, 7 m in length, 0.5 m in diameter and 16 mm in thickness. This structure was flooded and completely immersed in seawater. Two approaches to the system were considered during the investigation, depending on the communication channel exploited; the former utilized guided waves, on the basis of exploiting the steel structure as a wave-guide; the latter employed underwater ultrasound, based on using the seawater as a propagation medium. Although severe losses were encountered in both approaches, the system effectively identified the signals above the background noise. This work forms the foundation for the future development of a system that can be used with large, commercial offshore platforms.
An automatic guided wave pulse position modulation system, using steel tubes as the communication channel, for detecting flooding in the hollow sub-sea structures of newly built offshore oilrigs is presented. Underwater close visual inspections (CVI) are normally conducted during swim-round surveys in pre-selected areas or areas suspected of damage. An acceptable alternative to CVI is a non-destructive testing (NDT) technique called flood member detection (FMD). Usually, this NDT technique employs ultrasound or x-rays to detect the presence of seawater in the tubular structures, requiring divers or remote operating vehicles (ROVs). The field-proven FMD technique, integrated within the concept of structural health monitoring, offers an alternative to these traditional inspection methods. The system employs two smart sensors and modulators, which transmit 40 kHz guided wave pulses, and a digital signal processing demodulator, which performs automatic detection of guided wave energy packets. Experiments were performed in dry conditions, inside and outside the laboratory; in the former using a steel tube 1.5 m × 0.27 m × 2 mm, and in the latter using a tubular steel heliport structure approximately 15 m × 15 m in area and the base deck of an oilrig under construction. Results confirm that, although there was significant dispersion of the transmitted pulses, the system successfully distinguished automatically guided wave encoded information that could potentially be used in sub-sea oilrigs.
A novel and completely autonomous guided wave system for flood detection in the hollow cross-beam members of offshore steel oil rigs is presented. Underwater non-destructive testing methods such as ultrasound have been used to inspect for the presence of seawater in these applications, often in conjunction with remote operating vehicles. Alternatively, a monolithic PZT guided wave transducer which can be permanently attached to a sub-sea installation and that can be powered by the action of the seawater is now being developed. Upon activation, the transducer transmits an ultrasound-encoded signal to a receiver, in the form of a real-time digital signal processing system at the surface level. Experiments have been carried out using a jointed steel pipe structure, 10 m in length, 0.5 m in diameter and 16 mm in thickness, completely immersed in seawater. The transmitter was attached to the inner wall of a spur pipe and configured to generate narrow bandwidth, low frequency ultrasonic chirp signals, coupled to the pipe as an axisymmetric mode. Results confirmed that although some attenuation occurs, the system signal processing system successfully identified the signals above the background noise.
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