Microprocessor-based Devices Research Articles

Usage of CLPU curve to deal with the cold load pickup problem

Restoration of load after an extended power outage, whether planned or unplanned, raises various practical concerns. Previous studies have shown the cold load condition lasts between 2 to 60 minutes, or longer, depending on the duration of the outage, type of load and the local weather. The theory presented in this paper is applicable to all microprocessor-based overcurrent protective devices used at the distribution level. The example used in the paper is to provide a possible method to handle cold load pickup problems at line reclosers installed on the distribution system. The new approach is to control the pickup of the phase element of the recloser as a function of time. The pickup of the recloser starts at a preset value after an extended outage and slowly decreases and returns to the normal pickup in a predetermined manner. The relationship of the pickup level and time could be determined by considering the maximum cold load current and its gradual decay with time.

Intelligent microprocessor-based devices provide advanced motor protection, flexible control, and communication in paper mills

Intelligent microprocessor-based devices provide advanced motor protection, flexible control, and communication in paper mills

Development of highly reliable control systems for the gas-insulated switchgear

Microprocessor-based control, protection and monitoring devices, such as digital relays and diagnostic systems, have been applied to electric power fields. The highly reliable control systems (HRCS) based on microprocessor techniques for gas-insulated switchgear (GIS) have been developed. From the results of the CIGRE circuit breaker reliability survey, the need for improving the reliability of switchgear control circuits is presented. The HRCS for the GIS uses the programmable logic controller (PLC), solid-state electronics and optical sensors as a replacement for conventional hard-wired electromechanical control circuits which improves reliability and availability of the GIS control circuits. The HRCS has been verified and applied to the substation. This paper introduces the results of verification tests together with the principle of the HRCS. Also reported is application to the high voltage substation.

Real-time software testing for microprocessor-based protective relays

This paper describes a new practical method, the domain-partition boundary method with software probes, and a test platform for testing real-time software embedded in protective relays. The test scheme automatically and efficiently exercises all functions of a relay in all of its operating domains, especially in the error-prone domains. While the test-case generation methodology belongs to the function-test class, it uses knowledge of the software modularity, and takes into consideration system specification and behavior, critical parameter boundary values and software flow in generating the test specification. TSL/sup 1/ is used for managing the test-case generation process, and avoids redundancy. A microcomputer test platform was designed and assembled. It is a simulator which produces voltage or current levels that correspond to events in the system. A control program manages the overall process, including test case generation, wave-form production, process timing, event identification, data collection and result comparison. An implementation of the test scheme is described. Actual testing was conducted on a motor control and overload protection device for verifying its functions, but the test scheme is applicable to other microprocessor-based devices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Some Answers to the Problem of Safety in Microprocessor-Based Devices

What confidence can we have in a microprocessor based control or monitoring device when the safety of people or the reliability of an industrial process is a stake ?In order to provide some objective elements in answer to this delicate question, INRS carried out a series of tests on a dozen electronic microprocessor based devices which are widely used in industry.The tests were carried out using the DEF.Injector device which allows the operating safety of the equipment to be measured.The results show that certain devices designed for specific applications have a high level of safety while others including the programmable controllers do not guarantee a sufficient safety level in applications where risks are involved.

A proposed fault-tolerant microcomputer system

Past experience with fault-tolerant and other reliability techniques has focused on such specialized systems as spacecraft control computers and telephone switches. However, current technology trends strongly suggest that specific reliability techniques should be developed and implemented for a large number of low-cost systems such as microprocessor-based controllers, instruments, and other industrial devices. In this paper a fault-tolerant microcomputer architecture which is particularly designed for industrial control and manufacturing is proposed. For this system, voting has been considered as a very appropriate fault-tolerant technique. However, voting at the component level and at the bus-level have been ruled out due to the unreliability of the voters required and their high cost. System voting without an explicit voter is finally selected. Analysis shows that the system has a higher reliability than either a nonredundant system or a bus-level voting system. Its mission time has been increased by a factor of 2.5 over non-redundant systems.

New Concepts in Electrical Metering for Energy Management

With today's emphasis on managing energy in industry, many test measurements and recordings are required first to determine usage patterns before deciding what can be done to reduce consumption. A variety of portable test equipment is currently available that can be used to provide such one-time and/or periodic data. Developments in digital metering over the past several years have significantly improved both meter accuracy and repeatability. The advent of microprocessor-based test devices and meters has greatly improved the ease of operation, making the equipment ``user-friendly'' even to the novice. Details presented include an introduction to metering objectives; practical metering applications; metering techniques to employ and pitfalls to avoid; and a sampling of new portable and permanent metering equipment. All dollar values presented are approximate and based on 1985 energy and equipment costs in the Southeast. Brand names are included to present a cross section of equipment available; the listing is not intended to be all inclusive.

The Development of the Software for a Microprocessor-based Multivariable Controller

The software for a microprocessor-based multivariable controller, which controls the grinding circuit on a gold-recovery plant, has been developed. The process and the microprocessor hardware are surveyed briefly, and the functional requirements of the software are discussed. The necessity for a real-time executive software package is explained, the selection of such a package and its resulting performance are described and an account is given of the various languages and software utilities that were used in the preparation of the software. Special mention is made of the real-time nature of the software and the problems that were encountered regarding aspects such as reentrant procedures and shared data structures. The results of the four stages of testing that were carried out show clearly that the development laboratory should have a simulation of the process to be controlled. Finally the possibility is explored that one-off microprocessor-based devices can be developed that will be economically justifiable.

Modular hardware of reduced performance for dedicated microprocessor applications: examples and justification

There is a domain in which general-purpose modular hardware is the most economic approach for implementing microprocessor-based devices. Existing modular hardware, however, tends to be directed towards high performance rather than economy. The needs of the domain are inferred by analysing 32 past applications. A family of reduced-performance modular hardware, Greenbus, is discussed. The reduced-performance design approach is found to be justifiable, economic and well suited for a wide range of dedicated microprocessor applications.