Ćemal B. Dolićanin

Time enlargement law for gas pulse breakdown

This paper investigates the possibility of applying the time enlargement law for predicting how gas-insulated systems would behave when exposed to pulse voltage loads of different shapes. For this purpose, the validity of the time enlargement law in this case has first been tested and the most suitable theoretical distribution function of the breakdown time random variable established. Pulse characteristics of the investigated insulating system have subsequently been determined, by applying the time enlargement law to experimental values of the breakdown time random variable, obtained in measurements with predefined shapes of the voltage load. Pulse characteristics thus obtained were compared with the corresponding pulse characteristics derived from the area law. The results demonstrate the advantages of the time enlargement law method, especially in the case of a non-homogeneous electric field. The experiments were conducted with SF6 gas, at different values of the pd product (pressure × inter-electrode gap), in a wide frequency range of applied pulse voltages, for a homogeneous, radial and point–plane electrode configuration.

Determination of Pulse Tolerable Voltage in Gas-Insulated Systems

In this paper we expound on the procedure of determining the pulse tolerable voltage characteristic in the voltage-versus-time frame, by applying the time enlargement law to the breakdown time random variable, and using a single statistical sample for this variable, obtained through experiments with a predefined shape of the voltage load. The suggested algorithm has been experimentally tested for Ar, N2, and SF6 gases, in the pd product (pressure × interelectrode gap) range from 10-4 to 300 bar mm. The testing was performed by comparing the pulse tolerable voltage characteristic of a two-electrode configuration obtained by applying a particular shape of the pulse voltage load with the values corresponding to other pulse voltage shapes, covering a wide range of frequencies. Satisfactory results have been obtained concerning the applicability of the procedure, with certain minor limitations, which are pointed out.

SSC diversity receiver over correlated α-µ fading channels in the presence of cochannel interference

This paper studies the performances of a dual-branch switched-and-stay combining (SSC) diversity receiver, operating over correlated fading in the presence of cochannel interference (CCI). Very useful, novel, infinite series expressions are obtained for the output signal to interference ratios (SIRs) probability density function (PDF) and cumulative distribution function (CDF). The performance analysis is based on an outage probability (OP) and an average bit error probability (ASEP) criteria. ASEP is efficiently evaluated for modulation schemes such as noncoherent frequency-shift keying (NCFSK) and binary differentially phase-shift keying (BDPSK). The effects of various parameters, such as input SIR unbalance, the level of correlation between received desired signals and interferences, nonlinearity of the environment, and fading severity on systems performances are graphically presented and analyzed.

Reliability of three-electrode spark gaps

Two types of three-electrode gas-insulated spark gaps have been investigated in this paper: one with the third electrode located inside the main electrode, and the other with a separate third electrode. Three types of insulating media have been used: vacuum, SF6 and N2. Additionally, three different electrode materials have been implemented: copper, steel and tungsten. The following characteristics have been tested experimentally: the influence of insulating gas parameters on spark gap operation, the influence of the polarity of working and trigger voltages on spark gap operation, and the influence of the rate of rise of the trigger voltage on spark gap operation and the degree of spark gap irreversibility. A theoretical model of the spark gap is presented in the paper, which provides a basis for explaining experimental results depending on specific characteristics of the spark gap.

SSC Diversity Receiver over Correlated

This paper studies the performances of a dual-branch switched-and-stay combining (SSC) diversity receiver, operating over correlated fading in the presence of cochannel interference (CCI). Very useful, novel, infinite series expressions are obtained for the output signal to interference ratios (SIRs) probability density function (PDF) and cumulative distribution function (CDF). The performance analysis is based on an outage probability (OP) and an average bit error probability (ASEP) criteria. ASEP is efficiently evaluated for modulation schemes such as noncoherent frequency-shift keying (NCFSK) and binary differentially phase-shift keying (BDPSK). The effects of various parameters, such as input SIR unbalance, the level of correlation between received desired signals and interferences, nonlinearity of the environment, and fading severity on systems performances are graphically presented and analyzed.

Channel Capacity Analysis Under Various Adaptation Policies and Diversity Techniques over Fading Channels

The lack of available spectrum for expansion of wireless services requires more spectrally efficient communication in order to meet the consumer demand. Since the demand for wireless communication services have been growing in recent years at a rapid pace, conserving, sharing and using bandwidth efficiently is of primary concern in future wireless communications systems. Therefore, channel capacity is one of the most important concerns in the design of wireless systems, as it determines the maximum attainable throughput of the system [1]. It can be defined as the average transmitted data rate per unit bandwidth, for a specified average transmit power, and specified level of received outage or bit-error rate [2]. Skilful combination of bandwidth efficient coding and modulation schemes can be used to achieve higher channel capacities per unit bandwidth. However, mobile radio links are, due to the combination of randomly delayed reflected, scattered, and diffracted signal components, subjected to severe multipath fading, which leads to serious degradation in the link signal-to-noise ratio (SNR). An effective scheme that can be used to overcome fading influence is adaptive transmission. The performance of adaptation schemes is further improved by combining them with space diversity, since diversity combining is a powerful technique that can be used to combat fading in wireless systems resulting in improving link performance [3].

Prospects of constructing 20 kV asynchronous motors

20 kV distribution networks with all its components, such as transformers, switches, cables etc., have existed and been operating safely for many decades. From an economic point of view, it would be convenient to replace the transformer-motor combination by just a single 20 kV asynchronous motor, even if the motor itself were more expensive. The cost of a transformer, facilities and maintenance gained in this way would easily cover the extra costs of a motor. Efficiency considerations also make elimination of the step-down transformer desirable. Furthermore, modern technological advances make the production of 20 kV asynchronous motors possible, which is proved by the existence of 32 kV generators. The main problem lies in overcoming the differences between the construction of the aforementioned network equipment and the high-voltage asynchronous motor. This paper analyzes the weak points in the insulation system of an asynchronous motor, and proposes improvements allowing motor supply voltage to be increased to 20 kV.

On dynamical equations in s-parameters for rigid body attitude motion

In the paper, the attitude motion of a rigid body in a potential force field is under consideration. The complete set of three modified Rodrigues-Hamilton parameters, also known as s-parameters, and corresponding three generalized momenta is used for rigid body attitude representation. A new form of canonical differential equations for rigid body attitude dynamics is constructed. Built equations are suitable for analytical and numerical studying the problem of rigid body attitude dynamics.

The Geometric Approach

We consider the problem on the existence of the limit of a trajectory of a subspace \(V\) and the construction of this limit in an explicit form. In the algebraic approach to this problem, one performs formal calculations with the associated \(d\)-vector \(\widetilde{v}\), the behavior of the trajectory of this vector depends on the relation between its coordinates in the Jordan basis of the operator \(\bigwedge \limits ^{d}A\).

The Action of a Linear Map on the Grassmann Manifold

The set of subspaces of a given vector space forms the Grassmann manifold, a linear non-singular operator \(A\) induces a homeomorphism \(\varphi _A\) of the Grassmann manifold. Let us find the explicit form or this map.