Jun 1, 1981 - following areas for further investigation: (1) Challenge to develop a new insulation system and a mica- less ¡nsuJation system suitable forgas ...
June
0 atg air
,
humidity 38%RH/
10 /'
hydrogen 1.72 atg
5 10
Applied voltage (kV)
Fig. 1. y-voltage curves of windings of turbine generator {12.6kV220MW, operated for 17 years) measured in 0 agt air and 1.72 atg hydrogen.
Suggestions for Further Work
The results of the work described in this paper suggest the
1981, p. 2969
Optimal Distribution System Planning M. Ponnavaikko and K. S. Prakasa Rao Department of Electrical Engineering and Centre for Energy Studies, Indian Institute of Technology India A rapid rise in load demand is a common feature of most of the developing countries. It is often followed by a disproportionate and haphazard expansion of the distribution network, which results in voltage problems and excessive power and energy losses in the system. Further, the arbitrary expansion may lead to heavy loss of equipment and production, affecting the overall system economy. This situation in the distribution system management calls for optimal system expansion planning and design. The inherently large number of variables, operating constraints and problems associated with the distribution system have been creating considerable difficulty to the system planner. There have been some useful attempts in the past for the optimal distribution system planning making assumptions of varying depths. Most of these attempts have urban orientation and are based on simulation or cerain programming techniques like transhipment, Branch and Bound algorithms etc. Basically the simulation procedures need a lot of computational efforts, while the other methods have got limited application to the urban areas and cannot be used for the rural
following areas for further investigation: distribution systems, where the locations of the future loads are not (1) Challenge to develop a new insulation system and a mica- known in advance. less ¡nsuJation system suitable for gas filled system. Thus, there is a need to develop a more general and compre¬ (2) Simplification of the corona suppression method. hensive model for the distribution network planning and a method (3) Making diagnostic tests in the compressed gas. of optimally designing the same. The present work is an attempt in (4) Reduction of the insulation thickness or increase of the operating electric field.
June 1981, p. 2963
Lateral Capacity of Augered Tower Foundations in Sand N. F. Ismael Kuwait University, Kuwait, Arabia T. W. Klym Ontario Hydro, Toronto, Canada With the construction of the extra high voltage EHV transmission lines Ontario Hydro and many other power companies are facing the problem of increased foundation size and cost. This is especially true in difficult or marginal soil conditions such as loose wet sand or soft clay. Augered foundations, often known as drilled piers, caissons, or bored piles, are extensively used as tower foundations partially due to their ability to support substantial axial and lateral loads, and partially because of improved construction techniques allowing their installation in poor or adverse ground conditions. To achieve an economical foundation design and to learn more about the behavior of augered foundations in sand under lateral loading, a program of field tests was carried out on two in¬ strumented footings installed in submerged sand by the slurry displacement method. With the near absence of similar tests, these tests revealed the actual behavior under lateral loads and enabled evaluation of existing design methods. Both the ultimate lateral resistance and deflections at working loads were examined. The tests were essentially static tests carried out to failure on two cylindrical footings measuring 0.9 m (3 ft) diameter by 6.4 m (21 ft) deep and instrumented with strain gages and pressure cells to provide data on the lateral pressures and deflections during the test. Comments are made on the mode of failure under lateral loading and on the selection of a limited deflection criteria in tower
foundation design.
60
this direction to evolve a simple and efficient optimal design procedure for the distribution system. The suggested procedure is general in nature, so that it can be used for both the rural and urban distribution systems in practice. The design procedure provides optimal distribution system parameters such as substation feed area (size), feeder area (loading limits) and conductor size for both primary and secondary distribution systems. To start with mathematical models are formulated in terms of the variable system parameters to represent feeder voltage regulation, feeder load distribution, substation feed area, substation and feeder costs and the cost of losses in feeders and transformers. Based on these models, objective functions are defined for substation feed area with constant voltage drop and for feeder area with constant substation feed area. These objective functions have been minimized to obtain the optimal substation feed area and optimal feeder area. A two level optimization procedure is suggested in obtaining the optimal substation feed area and the optimal feeder area for the same percentage voltage regulation. During this optimization, the conductor size has been treated as a constant. In order to arrive at the most economical conductor cross section, the above optimization is carried out for different standard conductor sizes. The optimal conductor size, the corresponding substation feed area and the feeder area are thus obtained. Optimal distribution system parameters can also be obtained for several values of load density which can be expected in the future. This would enable the system planner to formulate general guidelines for the system planning policies. It also provides the sensitivity information with respect to the substation and feeder costs, which would be useful in economic design of lines or substations. The proposed method has been tested on a typical distribution system in India. The optimal parameters are obtained using the suggested algorithm for both secondary and primary distribution systems for load densities varying from 5 kW/sq.km to 100 kW/ sq.km. The proposed method is very fast and requires about 18 sec. of cpu time on IBM 360/44 computer system for obtaining the optimal parameters for the system studied for 8 different load densities. The simulation procedure adopted for the same study to obtain the above results requires nearly one hour of cpu time. The method is simple, efficient, fast and accurate. From the experience gained with the proposed method, the authors feel that this method is highly promising.
PER JUNE
