,
Volume 1, Issue 1 (1-2005)
Abstract
In an environment such as underwater channel where placing test equipments are
difficult to handle, it is much practical to have hardware simulators to examine suitably
designed transceivers (transmitter/receiver). The simulators of this kind will then allow
researchers to observe their intentions and carry out repetitive tests to find suitable digital
coding/decoding algorithms.
In this paper, a simplified shallow water digital data transmission system is first introduced.
The transmission channel considered here is a stochastic DSP hardware model in which
signal degradations leads to a severe distortion in phase and amplitude (fades) across the
bandwidth of the received signal. A computer base-band channel model with frequency
non-selective feature is derived by the authors [10-11]. This system was based on fullraised
cosine channel modelling and proved to be the most suitable for vertical and shortrange
underwater communication csdfher), with a reflected path (specula component, when
the acoustic hydrophone receives reflected signals from surface and bottom of the sea) and
a random path (diffused component, when the acoustic hydrophone receives scattered
signals from the volume of the sea). The model assumed perfect transmitter-receiver
synchronization but utilized realistic channel time delays, and demonstrated the timevarying
characteristics of an underwater acoustic channel observed in practice. In this
paper, they are used to provide a full system simulation in order to design an adaptive
receiver employing the most advanced digital signal processing techniques in hardware to
predict realizable error performances.
M. Samami, H. Yaghobi, M. Niaz Azari,
Volume 13, Issue 2 (6-2017)
Abstract
This investigation deals with a mathematical model for a distribution transformer including saturation effect. To this end, the equations related to a three phase transformer are specified and the effect of an inter-turn fault is included. Naturally by applying an inter-turn fault the inductance and resistance matrix will change. Thus, unknown quantities of inductances and resistances for completing the matrix are calculated and the inputs, outputs and state variables are specified. All the equations will be rewritten in terms of state variables, subsequently saturation effect is added to the model. Finally the block diagram of the specified model based on the obtained equations are designed and the ultimate model is simulated. The saturation effect, added to the mathematical model and also the variable fault parameters are known as two significant contributions which distinguish this study from other investigations. Various results obtained from the simulation of the final model confirm the changes in the behavior of faulty transformer such as: a large circulating current flowing in the shorted turns, lower impact on terminal voltages and currents, a sudden increase in current flowing in the primary winding, asymmetrical flux distribution and inverse proportion of the fault severity and the limiting resistor.
