Index to nasa tech briefs, issue number 2

Annotated bibliography on technological innovations in NASA space program

Temperature characterisation of an optically-interrogated Rogowski coil

An investigation into the performance of an optically-interrogated Rogowski coil over temperatures up to 80 °C is presented. Preliminary thermal tests reveal that the sensor response is temperature-dependent and the measurement errors are increased at higher temperatures. Compensation of temperature effects is, therefore, necessary in order for the sensors to meet the requirements of protection and metering classes specified by relevant IEC standards over the considered operating temperature range. This can, however, only be achieved when the utilised sensor interrogator is adapted to ensure sufficient resolution and accuracy from a generally low-output transducer. As such, the design of a new multiplexing, interferometric interrogation platform is also proposed in this paper

The danger of vibration in power transformers

A thin fiber optics sensor, VibroFibre, has been developed to fit into a 2 mm gap in transformer windings for directly measuring the winding vibration. The new innovation is aimed to help the transformer users to safely extend service lives of their assets and to mitigate risk of unscheduled shutdown due to premature equipment failure. The optic fiber based vibration sensor can be installed inside a transformer and the resulted vibration measurement is no longer affected by various noise sources from peripheral equipment. The vibration frequency spectrum measured inside an oil-filled transformer, shows a signature of wider band ranging between 20 Hz to 1000 Hz. The new sensor has shown superior performance, especially in its response to frequencies below 100 Hz. When combined with the new Long Gauge technology, the response goes as low as 5 Hz. The sensor’s small size makes it possible to install the sensors in the winding spacers with built-in cradle-like slots, which helps avoid possible disturbance to the cooling oil flow

Vibroacoustic transformer condition monitoring

Throughout the life of a transformer the effects of mechanical shocks, insulation aging, thermal processes and short circuit forces will cause deformations in the winding. This deformation can lead to vibration in the transformer and mechanical fatigue of the solid insulation. Defects which form in a transformers structure can cause faults such as partial discharge, hot spots and arcing. These faults generate combustible gases which can be analysed for condition assessment of the transformer. The development of a suitable and cost effective vibration measurement system forms a key part of this research project. A monitoring system is developed for real-time vibration analysis. An embedded capacitive accelerometer is used in conjunction with an Arduino microcontroller to record vibrations. The sensor platform is designed to communicate wirelessly via XBee radios to a terminal computer. A software program and user interface is designed as a tool for analysis. The outcomes and benefits of these works are primarily based on determining the condition of transformer insulation through measurements of vibration. Following a working measurement system, suitable transformer sites are monitored. Spectral analysis is performed in the frequency domain to determine a correlation with gas analysis results. The validity of vibroacoustic measurement as a predictive maintenance tool is subsequently evaluated. Six transformers are chosen for vibration monitoring with analysis of the vibration signatures correlated to the dissolved gas analysis reports at each site. The vibration signatures at each location are analysed using the Short Time Fourier Transform and frequency peaks compared for the different sites. It was noted that sensor location does not have a large impact on vibration magnitudes and identifying the frequency components present in the signal. However, from the signatures obtained there is not enough variation in magnitude or frequency components to suggest that this method can identify the type of fault present

Asset management strategies for power electronic converters in transmission networks: Application to HVdc and FACTS devices

The urgency for an increased capacity boost bounded by enhanced reliability and sustainability through operating cost reduction has become the major objective of electric utilities worldwide. Power electronics have contributed to this goal for decades by providing additional flexibility and controllability to the power systems. Among power electronic based assets, high-voltage dc (HVdc) transmission systems and flexible ac transmission systems (FACTS) controllers have played a substantial role on sustainable grid infrastructure. Recent advancements in power semiconductor devices, in particular in voltage source converter based technology, have facilitated the widespread application of HVdc systems and FACTS devices in transmission networks. Converters with larger power ratings and higher number of switches have been increasingly deployed for bulk power transfer and large scale renewable integration—increasing the need of managing power converter assets optimally and in an efficient way. To this end, this paper reviews the state-of-the-art of asset management strategies in the power industry and indicates the research challenges associated with the management of high power converter assets. Emphasis is made on the following aspects: condition monitoring, maintenance policies, and ageing and failure mechanisms. Within this context, the use of a physics-of-failure based assessment for the life-cycle management of power converter assets is introduced and discussed

Low-cost real-time internet of things-based monitoring system for power grid transformers

One of the most common causes of blackouts is unexpected failures at power system transformer levels. The purpose of this project is to create a low-cost Internet of things (IoT)-based monitoring system for power grid transformers in order to investigate their working status in real-time. Our monitoring system’s key functions are the gathering and display of many metrics measured at the transformer level (temperature, humidity, oil level, voltage, vibration, and pressure). The data will be collected using various sensors connected to a microcontroller with an embedded Wi-Fi module (DOIT Esp32 DevKit v1), and then supplied to a cloud environment interface with a full display of all the ongoing changes. This technology will provide the power grid maintenance center with a clear image of the transformers’ health, allowing them to intervene at the right time to prevent system breakdown. The method described above would considerably improve the efficiency of a power transformer in a smart grid system by detecting abnormalities before they become critical

Flight projects, for the period July 1 to August 31, 1968

Status of Mariner Mars 1969 program and advanced planetary missions technolog

Aeronautical engineering: A continuing bibliography, supplement 122

This bibliography lists 303 reports, articles, and other documents introduced into the NASA scientific and technical information system in April 1980