Search

Selecting a system control voltage should be made based on careful consideration of several factors. The two common voltages being utilized in North American process-control applications include 120 Vac and 24 Vdc. The use of 120 Vac control is currently more common in industrial applications in North America. Extreme care should be taken to assure safety from potential electrical shock. Although this potential is presumed a low risk by most electricians that routinely work on equipment at much higher voltages, the fact remains that exposure to a live and poorly grounded 120 Vac circuit is a relatively frequent occurrence that can be fatal. The use of 24 Vdc control is growing, particularly in process-control applications. It is inherently safe and is aligned with the new codes and standards established for enhanced safety. It allows for a reduction in the times where lock-out/tag-out must be performed, and, often, control panels can be serviced while still energized. The devices are becoming extremely reliable, are often less expensive, and have better response times. 24 Vdc power supplies provide signal isolation and protection against shorted outputs and power quality issues. 24 Vdc allows direct interfacing with process-control equipment, reducing the need for interposing relays. Renewed emphasis on personal safety and improved performance gives a strong edge to 24 Vdc control for new applications. As new product designs become available, and costs continue to decrease, 24 Vdc will inevitably become the control system voltage of choice for industrial applications.

The Electric Power Research Institute (EPRI) has been involved in developing a software package designed to meet the needs of distribution engineers. The result of these efforts is a workstation software package (DEWorkstation) that provides an open architecture environment with integrated data and applications. Analysis, design, and operation modules access database data and exchange data through common functions. The open architecture allows external application modules to be added to the workstation. External measurements such as voltage, current, and temperature may be imported and displayed on the circuit schematic. These imported variables are made available to any application program running within the workstation. This distribution engineering tool is designed to meet the analysis, planning, design, and operation needs of distribution engineering through its available application modules. Modules perform the following types of analyses: power flow, load estimation, line impedance calculation, fault analysis, capacitor placement, phase balancing, and more. External data such as customer information system data and distribution transformer data may be imported. The workstation is designed to provide utilities with a platform suitable for distribution automation evaluations. >

The Electric Power Research Institute Distribution Engineering Workstation is a software package which provides an integrated data environment designed to meet the analysis, planning, design, and operation needs of distribution engineering. DEWorkstation features an open architecture design that provides access for anyone wishing to add applications. DEWorkstation concepts are introduced and the application programmer interface is described. >

For pt.I see ibid., vol.9, no.2, p.1108-14 (1994). An example protection system design is presented using an integrated expert system developed for an engineering workstation. The example problem consists of three interconnected distribution circuits. Dynamic knowledge, created by the expert system from the rules and system data, is used in the design. System data is presented pertaining to the circuits along with the created dynamic knowledge. The implemented rules dealing with the coordination, placement and selection of protective devices are presented, along with all associated parameter values. The final design and results are shown. >

Hourly load research data for residential customers is used to calculate diversity factors and kWHR-to-peak-kW factors. The customers are grouped into two classes based on their type of heating. The class-based diversity factors are a function of the number of customers, month and type of day. The class-based kWHR-to-peak-kW factors are a function of the month and type of day. With the use of control samples, comparisons are made between estimated and measured peak kW. Estimated daily load profiles are also calculated and compared to measured daily load profiles. >

A protection system design algorithm that encompasses all possible circuit configurations of a radial distribution system is presented. A predetermined set of coordination rules is incorporated to develop a relational database type managed coordination table. The algorithm performs both computerized placement and selection of devices which coordinate. Automated placement rules determine the location of any new devices required for circuit protection. Automated selection rules work with the coordination table in selecting groups of protection devices which mutually coordinate for the chosen circuit design. A design example is presented depicting a radial distribution system composed of three individual circuits. >

The authors describe water heater load control experiments on the Athens Utilities Board distribution system in Athens, Tennessee. Data from experimental days are compared to data from days of normal operation to assess the effects of the control experiments. Plots are presented to describe water heater operation. Water heater models are used to estimate water usage. Results indicate that water heater control reduces energy demands but may have adverse effects on daily load patterns. Analysis also shows that the operation of load control receivers deteriorates as the duration of the control period is increased. Methods used to improve data integrity are presented. The results are based on a filtered data set. The problems of identifying the associated time skew in the data and the timing-out of load control receivers are addressed. >