Multi-axis transient vibration testing of space objects: Test philosophy, test facility, and control strategy

IABG has been using various servohydraulic test facilities for many years for the reproduction of service loads and environmental loads on all kinds of test objects. For more than 15 years, a multi-axis vibration test facility has been under service, originally designed for earthquake simulation but being upgraded to the demands of space testing. First tests with the DFS/STM showed good reproduction accuracy and demonstrated the feasibility of transient vibration testing of space objects on a multi-axis hydraulic shaker. An approach to structural qualification is possible by using this test philosophy. It will be outlined and its obvious advantages over the state-of-the-art single-axis test will be demonstrated by example results. The new test technique has some special requirements to the test facility exceeding those of earthquake testing. Most important is the high reproduction accuracy demanded for a sophisticated control system. The state-of-the-art approach of analog closed-loop control circuits for each actuator combined with a static decoupling network and an off-line iterative waveform control is not able to meet all the demands. Therefore, the future over-all control system is implemented as hierarchical full digital closed-loop system on a highly parallel transputer network. The innermost layer is the digital actuator controller, the second one is the MDOF-control of the table movement. The outermost layer would be the off-line iterative waveform control, which is dedicated only to deal with the interaction of test table and test object or non-linear effects. The outline of the system will be presented

Controlled Switching of Reactive Loads and Commisioning Regimes

Switching is a vital task in any power system for ensuring its safe and reliable operation. Switching may be necessary for fault clearance, to ensure wider system stability and to prevent damage to plant. It is essential for isolation, to allow technicians to carry out maintenance tasks safely. Also, switching of reactive loads such as shunt capacitor banks and shunt reactors, is crucial for controlling system voltage. Switching of some loads however, may produce voltage transients and heavy transient inrush currents which can impact on wider system power quality, impact customers and cause damage or deterioration of the insulation of HV equipment. Therefore, it is important to provide some form of measure to control or mitigate transients caused by switching. The main control measures include: metal oxide surge arrestors, pre-insertion resistors, current limiting reactors and synchronised or controlled switching. Controlled switching is the favoured solution for frequently switched loads such as reactive plant, for economic benefits and as it reduces transients in the first instance. Controlled switching is defined as the use of electronic equipment to control the making or breaking of high voltage circuit breakers at pre-determined points on the system voltage and current waveforms. It has been implemented in Ireland for over 30 years for the energisation of shunt capacitor banks. Over the last two years, the benefits of controlled switching for different applications has become ever more apparent, with increased use such as switching of transmission shunt reactors and the energisation of large power transformers, particularly in remote areas of the network such as wind farm interfaces. The aim of this thesis is to provide a complete overview of the stages concerned in implementing controlled switching schemes, from examining the impacts of switching certain loads, to performing systems studies, up to site commissioning stage. The research in this thesis looks at both the theory and practice. It draws together the published work, manufacturers guidelines, international standards and simulation results, to give the total awareness of the issues involved in reactive load switching and commissioning regimes. The various solutions and strategies associated with controlled switching schemes are examined, to ensure that the best and most economical solution has being implemented. Several recent projects where controlled switching has been implemented for switching of transmission reactors and power transformers are also investigated

Parallelizing the Simulation of Shipboard Power Systems

As a result of this research the Navy has a simulation approach for ship power systems that is computationally effective enough to permit efficient simulation. In addition to simulating the basic power system, significant progress has been made in the simulation of the control system.United States Office of Naval ResearchCenter for Electromechanic

A Semi-Analytical Approach for State-Space Electromagnetic Transient Simulation Using the Differential Transformation

Electromagnetic transient (EMT) simulation is a crucial tool for power system dynamic analysis because of its detailed component modeling and high simulation accuracy. However, it suffers from computational burdens for large power grids since a tiny time step is typically required for accuracy. This paper proposes an efficient and accurate semi-analytical approach for state-space EMT simulations of power grids. It employs high-order semi-analytical solutions derived using the differential transformation from the state-space EMT grid model. The approach incorporates a proposed variable time step strategy based on equation imbalance, leveraging structural information of the grid model, to enlarge the time step and accelerate simulations, while high resolution is maintained by reconstructing detailed fast EMT dynamics through an efficient dense output mechanism. It also addresses limit-induced switches during large time steps by using a binary search-enhanced quadratic interpolation algorithm. Case studies are conducted on EMT models of the IEEE 39-bus system and a synthetic 390-bus system to demonstrate the merits of the new simulation approach against traditional methods

FPGA-Based Degradation and Reliability Monitor for Underground Cables

The online Remaining Useful Life (RUL) estimation of underground cables and their reliability analysis requires obtaining the cable failure time probability distribution. Monte Carlo (MC) simulations of complex thermal heating and electro-thermal degradation models can be employed for this analysis, but uncertainties need to be considered in the simulations, to produce accurate RUL expectation values and confidence margins for the results. The process requires performing large simulation sets, based on past temperature or load measurements and future load predictions. Field Programmable Gate Arrays (FPGAs) permit accelerating simulations for live analysis, but the thermal models involved are complex to be directly implemented in hardware logic. A new standalone FPGA architecture has been proposed for the fast and on-site degradation and reliability analysis of underground cables, based on MC simulation, and the effect of load uncertainties on the predicted cable End Of Life (EOL) has been analyzed from the results

Development of a general purpose airborne simulator

Variable stability system development for General Purpose Airborne Simulator /GPAS