Electric Utility Service Research Articles

Effect of Materials and Geometrical Variables on Creep Behaviour of Welds

Premature failure of welded steam piping in electric utility service led to the need for a life prediction tool. A software was developed that performs a global stress analysis and remaining service life prediction of these high temperature piping systems. Using the global stress results the local stresses at the seam weld location are computed for each pipe. These local stresses at the seam weld are used with a creep damage model to determine the remaining service life of each pipe. The scale factor for each stress component in the pipe is obtained from a library of data tables and curve fit equations that model the effect of several piping and weld parameters on the local seam weld stresses. The parameters used are the cylinder peak angle, the weld bevel angle, the axial to hoop stress ratio, the weld material to base material creep rate ratio, and the heat affected zone (HAZ) to base material creep rate ratio. Each of these parameters was varied over a range of typical values in an axial seam welded pipe analysis case study. The results of the case study were used to create a subroutine that computes the local seam weld stresses. The high temperature creep analysis was done using a finite element analysis (FEA) mesh of the pipe cross section. The FEA mesh models the shape of the pipe and the weld, the applied loads and temperatures, and the weld and base material values. The analysis captures the time varying creep behavior of the pipe. For the weld material 64 parameter cases were analyzed, and for the HAZ 60 parameter cases were analyzed. The FEA case study results of the creep analysis were tabulated or curve-fit for use in the stress scale factor calculation. The analyses were done using the Abaqus FEA software. The scale factors are calculated from the tables and curve fit equations by a Fortran subroutine. The scale factor subroutine is used in the life assessment calculations to determine the remaining service life of the pipe. Previous case study results for pipe girth welds were available and were also included in the Fortran subroutine. Using that existing information, the subroutine can also compute local scaled stresses in a pipe near the girth weld.

Power signature analysis

Nonintrusive load monitoring (NILM) can determine operating schedule of electrical loads in a target system from measurements made at a centralized location, such as the electric utility service entry. NILM is an ideal platform for extracting useful information about any system that uses electromechanical devices. It has a low installation cost and high reliability because it uses a bare minimum of sensors. It is possible to use modem state and parameter estimation algorithms to verify remotely the "health" of electromechanical loads by using NILM to analyze measured waveforms associated with the operation of individual loads. NILM can also monitor the operation of the electrical distribution system itself, identifying situations where two or more otherwise healthy loads interfere with each other's operation through voltage waveform distortion or power quality problems. Strategies for nonintrusive monitoring have developed over the last 20 years. Advances in computing technology make a new wealth of computational tools useful in practical, field-based NILM systems. This article reviews techniques for high-performance nonintrusive load and diagnostic monitoring and illustrates key points with results from field tests.

00/02757 Energy-efficiency and renewable energy options for risk management and insurance loss reduction

To provide electric utility service of desired quality at the lowest possible cost, voltage drop and power loss reduction is crucial for distribution network. Distribution systems with Distributed Energy Resources (DER) have shown an enormous potential for power loss and voltage drop reduction. This paper investigates existing islanding detection techniques for feeder performance and proposes a new islanding detection algorithm (NIDA) for node voltage profile improvement and power loss reduction in the distribution network.The NIDA has been validated with three case studies. It has been investigated for its capabilities to improve the feeder performance in electric distribution system. The proposed algorithm outperforms the conventional approaches, which have many limitations to detect the islanding operation. The non-uniform distribution of electric loads, unity power factor, complexities in the design of control interface and functioning of the system in multi-DER environment are the most common obstacles in implementation of existing islanding detection techniques. NIDA is capable of handling the above mentioned complexities. The simulation results show that NIDA can detect islanding formation during the fault condition. The DER(s) provide uninterruptible power supply to sensitive load in the island, maintaining the nodes voltage and the power loss within the permissible limits.

A multiprocessor for transient event detection

The multiscale transient event detector (TED) introduced by Leeb (1993) uses measurements of current and voltage made at the electric utility service entry of a building to help determine the operating schedule of all of the significant loads in the building. This paper describes a TED algorithm implemented on a custom multiprocessing machine with several inexpensive processors performing tasks in parallel. A parallel version of the serial TED algorithm is developed, and the hardware design for a multiprocessing TED is presented. The performance of the algorithm is illustrated with results from a prototype.

Transient event detection in spectral envelope estimates for nonintrusive load monitoring

This paper describes the theoretical foundation and prototype implementation of a power system transient event detector for use in a nonintrusive load monitor (NILM). The NILM determines the operating schedule of the major electrical loads in a building from measurements made at the electric utility service entry. The transient event detector extends the applicability of the NILM to challenging commercial and industrial sites. A spectral preprocessor for use in the transient event detector is introduced first. Then, the transient event detection algorithm is developed. The performance of the algorithm is illustrated with results from a prototype event detector. >

Overcurrent protection alternatives for underground distribution systems

Pad-mounted switchgear that is applied on underground distribution systems effects many aspects of electric utility service. Some of these include overcurrent protection characteristics, the ability of the line service crews to quickly restore service after a fault, the overall reliability of service to the customer, and, to some degree, the cost of the electric service to the customer. The user must develop a system design philosophy and then determine the equipment features needed to help meet the goals of the chosen system design. Since these goals may vary with the type of load being served, equipment features that may be selected are discussed for single phase and three phase services. The application benefits of pad-mounted sectionalizing switchgear, pad-mounted fused switchgear, and pad-mounted vacuum fault interrupter switchgear are compared in these applications. >

Emission Costs, Consumer Bypass and Efficient Pricing of Electricity

Electricity generation causes external costs because of the emission of air pollutants. Pricing an electric utility's service at the sum of the utility's marginal generation cost and marginal emission cost, however, is inefficient due to “bypass” by large industrial customers and the need to maintain the utility's financial viability. This paper derives the optimal tax on emission and efficient prices for retail service to two customer classes, one of which has the option to self-generate. These rules are used to evaluate the pricing proposals made in a recent rate case in California. These proposals are shown to be inefficient, in that they encourage over-consumption by residential customers who do not have access to alternative sources of electricity supply.

Industrial electricity demand in New York State

We will discuss electricity demand in manufacturing industries in upstate New York. Empirical results are presented based on data obtained at the electric utility service area level for the years 1969–1981. The equations are based on a partial adjustment model including relevant input prices and industrial output by SIC group. The estimated coefficients have the expected signs and are for the most part, statistically significant. There is considerable variation in price and output elasticities among SIC groups and between service areas, which suggests that energy policy and industrial policy at the state level should be tailored to specific industries and perhaps to specific subregions within the state. Forecasts of industrial electricity demand are based on assumptions of prices and industrial output growth made by the utility companies themselves. A comparison of these forecasts with those made by the utility companies indicates that electricity demand forecasts are sensitive to the inclusion of alternative fuel prices and to the level of sectoral disaggregation.