M. A. El-Kady

Computer-Aided Planning of Distribution Substation and Primary Feeders

This paper presents an improved technique for optimal planning of substations and primary feeders in power distribution systems. The technique employs an accurate, time-phased cost model and incorporates a flexible planning formulation which suits detailed analysis of limited sized distribution networks as well as approximate analysis of large scale distribution networks. The cost model includes explicit time-dependent fixed and variable charges for planned facilities as well as the cost of power losses. The planning formulation incorporates user-defined constraints on voltage drop in primary feeders. Constraints on radial power flow are automatically set by the algorithm. The planning problem is solved using an advanced, sparsity-based mixed-integer linear programming code.

Bibliography on composite system reliability

A comprehensive bibliography on the subject of composite system reliability and closely related topics is presented. It is believed to fill a gap which exists in the literature, since approximately 2/3 of the items registered here have not appeared in previously published bibliographies on power system reliability. An author index for the listed references is included. >

Calculation of the Sensitivity of Power Cable Ampacity to Variations of Design and Environmental Parameters

The problem of evaluating power cable loading performance subject to variations of the thermal circuit parameters is formulated and solved by a fast sensitivity technique based on the finite element method. The technique provides useful sensitivity information which can be accessed and manipulated by the cable designer or operator to simulate, in a simple and efficient manner, various soil, ambient, loading and boundary variations. The sensitivity technique has been applied to a variety of practical cable systems including direct-buried and pipe-type cables as well as cables in duct banks. The technique reduces significantly the analysis and computations via identifying the important parameters which most affect the ampacity and it simplifies the thermal model by eliminating the low-sensitivity (non-important) parameters. Because the sensitivity values depend on the particular cable system and soil and boundary conditions and can vary significantly from one situation to another, the generalization of the results is not possible. Therefore, the paper describes the sensitivity technique and its direct implementation by illustrating its use for a variety of cable systems.

Risk Assessment of Grounding Hazards due to Step and Touch Potentials Near Transmission Line Structures

Excessive step and touch potentials near high voltage transmission line structures due to severe ground faults present a hazard to anyone in proximity to a structure when a fault occurs. This paper extends the probabilistic analysis of step and touch potentials near transmission line structures reported at the 1982 IEEE Summer Power Meeting [1] and presents a complete computerized methodology for assessing the overall effectiveness of grounding for any given network and right-of-way conditions. The paper also illustrates some applications of the method in the Ontario Hydro system.

Optimization of Power Cable and Thermal Backfill Configurations

The design problem of selecting the optimal parameter values associated with cable trench and thermal backfill is formulated as a nonlinear programming problem and solved using a multi-dimensional gradient optimization method. The technique considers all design parameters simultaneously and provides the optimal solution which either minimizes the cost of backfill and trench production subject to an ampacity constraint or maximizes the cable ampacity subject to a cost constraint. In either formulation, upper and lower bounds on design parameters as well as other thermal and physical constraints are included. The important role of backfill parameters in reducing the effects of environmental fluctuations on cable ampacity is exploited in the optimization analysis via defining functional sensitivity profiles which may be used to ensure secure and reliable designs. The paper includes a description of the computer program which was developed for the optimization of general cable configurations in thermal backfill.

An Advanced Probabilistic Short-Circuit Program

This paper presents a fully documented, sparsity-oriented probabilistic fault analysis program using Monte Carlo simulations. The program provides the probability distributions of bus and line currents in particular regions of a power network with provision for random variation of system and fault data. The program exploits a dynamic memory scheme and sparsity-based manipulations together with an advanced method of treating mutual coupling between lines for repeat faults in regions containing up to 680 buses (including network equivalents). The program is capable of simulating different types of symmetrical and unsymmetrical bus and/or line faults assigned randomly with complete flexibility for biasing the fault data. The program offers a variety of options for processing fault data and for printing brief or detailed intermediate and final output results.

Probabilistic Short-Circuit Uprating of Station Strain Bus System-Overview and Application

Increasing levels of fault currents in the Ontario Hydro system have made the designs of some existing 230 kV strain bus station Installations Inadequate if conventional deterministic design techniques are employed. Uprating costs could be reduced by several million dollars per station, if a greater short-circuit capability for the existing strain bus and structures could be established using new probabilistic techniques. For this purpose, a multi-discipline task force from a variety of divisions within Ontario Hydro was created to evaluate 230 kV Insulator string failure probabilities at Middleport Transformer Station (TS) and assess the impact of possible failures in terms of personnel safety, repair costs, outage costs, and system reliability. This paper and the three companion papers present an overview of the probabilistic uprating process as applied at Middleport TS. The study indicated that only marginal work (If any) Is required to maintain adequate safety, reliability and cost criteria, assuming that currents are limited to within the existing 230 kV circuit breaker ratings.

Probabilistic Assessment of Step and Touch Potentials Near Transmission Line Structures

Step and touch potentials at transmission line structures are sometimes important parameters in the design of the grounding system. To have confidence in conventional (deterministic) methods of potential calculation, worst-case values of the design parameters must be assumed. This often leads to overly pessimistic results. A probabilistic approach enables more realistic values to be obtained with the same degree of confidence. A study has recently been performed to calculate the probability distributions of step and touch potentials in Ontario Hydro 230 kV and 500 kV networks. This paper describes analytical and computational aspects of the efficient program developed during the course of the study and presents a number of illustrative examples.

Probabilistic Short-circuit Uprating of Station Strain Bus System—Overview, Application and Risk Assessment

ABSTRACT Increasing levels of fault currents in the Ontario Hydro system have made the designs of some existing 230 kV strain bus station installations inadequate if conventional deterministic design techniques are employed. Uprating costs could be reduced by several million dollars per station, if a greater short-circuit capability for the existing strain bus and structures could be established using new probabilistic techniques. Previous theoretical work has been extended by applying Monte Carlo probability simulations with advanced sparsity-oriented computer programs, to a full-scale substation uprating problem. Fault current probability distributions for the study location are transformed into conductor tension probability distributions using conventional computer programs for calculating short-circuit forces in bundled conductors. These stress distributions are then convolved with insulator strength distributions (established by mechanical dynamic testing) to evaluate insulator string failure probability. A multi-discipline task force from a variety of divisions within Ontario Hydro was created to evaluate 230 kV insulator string failure probabilities at Middleport Transformer Station (TS) and assess the impact of possible failures in terms of personnel safety, repair costs, outage costs, and system reliability. This paper presents an overview of the probabilistic uprating process as applied at Middleport TS and provides a description of the risk assessment and decision-making process. The study indicated that only marginal work (if any) is required to maintain adequate safety, reliability and cost criteria, assuming that currents are limited to within the existing 230 kV circuit breaker ratings.

A Probabilistic Approach to Power Cable Thermal Analysis and Ampacity Calculation

A technique is presented for calculating the temperature rise and load capabilities of power cables with provision for statistical variations of various soil, boundary and loading conditions. The novel. technique exploits the ampacity sensitivity algorithm described in a previous paper [1] in conjunction with statistical data gathered for a variety of soil materials, ambient parameters and load cycle characteristics. The technique provides useful information concerning the expected. values and confidence levels of. ampacity and cable temperature rise as well as the probabilities associated with excessive temperatures and thermal instability. The paper describes the probabilistic approach and illustrates a variety of its applications.