Volume 12, Issue 4

Resistance to surface electrical discharge was investigated for epoxy alumina and epoxy silica nanocomposites. Epoxy alumina nanocomposites with 0.1, 1, 5, 10 and 15 wt% nanoalumina fillers as well as epoxy silica nanocomposites with 0.1, 1 and 5 wt% nanosilica fillers were prepared in the laboratory using direct dispersion method. Experiments were conducted at 10kV ac voltage for different durations using IEC (b) type electrodes. The degradation of the sample surfaces were analyzed using SEM techniques, surface roughness measurements and FTIR spectroscopy. The effect of interface on the material properties were investigated by DSC analysis. It was observed that the resistance to surface degradation improved for both epoxy alumina and epoxy silica nanocomposites as compared to the performance of unfilled epoxy. Also epoxy alumina nanocomposites showed better resistance to degradation as compared to epoxy silica nanocomposites for all the filler concentrations considered. The enhancement in degradation resistance for epoxy nanocomposites is attributed to the surface modifications of the nanocomposites when exposed to discharges and the nature of the interface in the region around the nanoparticles. The filler concentration and thereby the interparticle distance also has a significant effect on the discharge degradation resistance.

Dynamic transmission network expansion planning (DTNEP) decides when (which year) and where (which R.O.W.), the new lines are to be built so that the overall cost of the plan is minimum and the system is secure. Generally, this is done for a fixed time horizon window (3/5 years) at a time. DTNEP has been proved to be better than the incremental approach in which optimal investment plans are found out for each year separately. In DTNEP, 1st year and last/terminal years are given different treatment, and there is a complete disconnect between two DTNEP windows. Also DTNEP assumes that the conditions during optimization like the earlier year generation, transmission expansion plans get\ executed exactly as per plan &/or the load forecast for the entire period remains unchanged. However, it is well known that this is generally not true. In view of above, this paper presents a rolling window based approach which treats every year of investment in exactly the same fashion. It also has an inherent capability to take care of such changes. It involves successive, overlapping DTNEP for 3/5 years planning horizon. A harmony search algorithm is used for the solution of the problem. Results for two test systems have been obtained to demonstrate the potential of the algorithm.

Fair allocation of charges based on transmission facility availed by the entities present in the open access system is the need of the hour. In order to achieve transparency and fairness from the point of participants involved, it is necessary to get contributions from each generator (source) to loads, flows in the network and losses for the system. This paper attempts to evaluate real power flow in the lines of the network due to individual sources and its contribution to each load using the virtual flow methodology which is fairly simple and straightforward. The proposed method is compared against two well known tracing techniques adapted from proportional sharing principle. Virtual tracing method involves the network topology, parameters and the voltage gradients between buses as determined from a solved power flow/on-line state estimator. It is believed that this is more realistic in nature. Counter flow components are easily determined and loop flows are handled without any difficulty. Case studies on a sample 5 bus and a practical 11 bus Indian southern grid equivalent 400kV networks are presented.

Due to incorporation of Distributed Generation (DG), the traditional protection scheme for electric power distribution system lost its radial nature and behaves more like multifeed transmission system. Hence, there is a need to develop a new protection scheme for electric power distribution system which remains stable in all conditions. This paper presents a new directional protection scheme for distribution system containing DG. Authors have developed a laboratory prototype of the three-phase radial distribution system containing DG. The proposed scheme has also been simulated using the PSCAD/EMTDC software package with fault data generated by modeling the distribution systems. The proposed directional protection scheme has been tested for various types of faults in different sections of radial distribution network along with DG. At the end, a comparative evaluation of the results obtained using the developed laboratory prototype has been carried out with the simulation results obtained using PSCAD. It has been observed that the proposed scheme has the ability to isolate the faulted section without disturbing the healthy section in the presence of DG.

Most faults in medium voltage (MV) distribution lines are temporary line to ground (LG) faults. Three-phase auto reclosing (TPAR) is commonly used to remove this fault with temporary disconnection of all the phases. Multi-shot single-phase auto reclosing (SPAR) may also be used to remove the LG fault. But it produces highly unbalanced and low voltage across the load during the reclosure dead time. It is proposed to connect a zigzag winding grounding transformer at the load bus to maintain the 3-phase load voltage when one phase opens during the SPAR. With low value of grounding resistance the 3-phase voltage during the SPAR dead time becomes approximately balanced. Directional over current relays may be used for the protection. Analysis of a MV radial distribution system having a zigzag transformer connected to the remotest load bus is presented with the computation of voltages during the dead time of SPAR.

In this paper, we investigate the influence of voltage dependent load models on day ahead real power market clearing (DA-RPMC). The investigations clearly bring out the unsuitability of conventional single objectives such as production cost minimization (PCM) (or social welfare maximization (SWM)), due to reduction of load served. Hence, the multi-objective optimization is essential in this context. The paper proposes several objectives such as production cost minimization (PCM) (or social welfare maximization (SWM)), load served maximization (LSM), and Voltage Stability Enhancement Index (VSEI); which can be judiciously combined as per the needs of the operating condition. Multi-objective Strength Pareto Evolutionary Algorithm (SPEA) has been used to solve the DA-RPMC problem. The effectiveness of the proposed approach is tested on IEEE 30 bus system and the detailed simulation studies have been carried out by considering different operating conditions with voltage dependent load modeling.

The induction generators (IGs) are basic to wind energy conversion. They produce the active power and consume the reactive power, with the voltage characteristics fragile compared with that of the synchronous generators and doubly-fed IGs. In the stressed system states, they may intensify var imbalance, yielding undesirable operation of zone 3 impedance relays.In this paper, the operation characteristics of the zone 3 relays in the wind power systems is studied. With the theoretical and load flow analysis, it is proved that the equivalent impedance of the IGs lies in the 2nd quadrature, possibly seen as the backward faults by the mho relays, i.e. the apparent impedance enters into the protection region from the left side. The undesirable operation may be caused by more wind power, larger load, less var compensation, and larger torque angle.