Powerful Mining Research Articles

Evaluating the performance of mine power shovels with composite indicators

Evaluating the performance of mine power shovels with composite indicators

Coordination-Free Ground-Fault Detection for Mine Distribution Systems

A ground-fault relaying scheme is presented that is intended to eliminate the need for time-delay relays for ground-fault detection on mine electrical distribution systems. The concept is based on pilot-relaying logic, and existing ground-check and grounding conductors are used to convey ground-fault information between adjacent relay units. The new scheme should not add any additional work during the installation of mine power systems and should minimize the expertise needed for power-system operation. To illustrate this concept, the design and development of the new relaying system is presented. The performance of a prototype relay during laboratory simulations is also given. Although the work is projected at underground coal mining, the relay appears feasible for any extensive radial distribution system.

Use of Cable Surface Temperature to Detect High-Resistance Splices

Mine power trailing cables are subject to considerable abuse and are quite often damaged severely enough to require a repair splice. Although recently developed splice materials provide a splice that is initially sound both mechanically and electrically, continual flexing of the cable can rapidly cause the splice connectors to loosen, resulting in a significant increase in electrical resistance. Although the added splice resistance does not affect the delivery of power through the cable, it can cause extreme local heating. If heavy current is drawn for several minutes, the splice can catch fire or rupture. Such a failure disrupts production and can be dangerous. Since the added resistance of the splice does not significantly alter the overall cable resistance, it cannot be detected by any measurement of the bulk properties of the cable. A method is suggested for determining splice resistance from a small number of temperature measurements made on the cable jacket while the cable is in use. The advantage of the method is that it requires no knowledge of cable current flow or other electrical parameters but only the cable size and its temperature profile. A theoretical analysis of cable splice heating is presented, relating the results to laboratory experimental data. Data are also presented from several cables in the field, including one which experienced a splice fire shortly after the data were taken. Results are encouraging, suggesting that the method can be developed into a practical periodic check of cable splice characteristics.

Analysis Techniques in AC/DC Power Systems

Many present-day industrial power systems have combined ac/dc power distribution systems. A typical example is a coal mine power system, where ac is used for running the mining equipment and dc is used for track haulage, etc. Also, the topology of the dc network is constantly changing due to the movement of locomotives along the track. Methods are described that can be used to carry out load-flow and short-circuit analyses of such a system.

A Technique for Optimal Sequential Maintenance Scheduling

This paper presents the mathematical development of, and a simple solution technique for, an optimal sequential maintenance scheduling problem. The model is shown to satisfy the Kuhn-Tucker conditions, the necessary and sufficient conditions for the existence of an optimal solution. Real-world systems consisting of mixtures of constant and increasing failure rate devices are considered in the model. Sequential preventive maintenance schedules are developed for groups of identical items with increasing failure rates. Provision is made for the corrective maintenance of these groups if failures occur in between the preventive maintenance schedules. Also, constant failure rate devices are accorded corrective maintenance when failures occur. Optimality is achieved by minimizing the total annual maintenance cost, subject to constraints on the system availability, number of maintenance personnel and intervals of preventive maintenance. The model is applied to a coal mine power system example.

Instantaneous Circuit Breaker Settings for the Short-Circuit Protection of Three-Phase 480-, 600-, and 1040-V Trailing Cables

Present Federal regulations which specify maximum instantaneous circuit breaker settings for the short-circuit protection of coal mine trailing cables are discussed. The characteristics of mine power systems that limit short-circuit current in three-phase trailing cables are analyzed and minimum expected short-circuit currents for three-phase 480-, 600-, and 1040-V trailing cables are tabulated. New maximum instantaneous circuit breaker settings, based on minimum expected short-circuit currents and typical breaker tolerances, are proposed with emphasis on safety. Finally, atypical mine power systems are discussed and field tests cited.

Instantaneous Circuit Breaker Settings for the Short-Circuit Protection of Direct Current 300-and 600-V Trailing Cables

Present Federal regulations which specify maximum instantaneous circuit breaker settings for the short-circuit protection of coal mine trailing cables are discussed. Characteristics of mine power systems, which limit short-circuit current in dc trailing cables, and minimum expected short-circuit currents for dc 300- and 600-V trailing cables are analyzed. New maximum instantaneous circuit breaker settings, based on minimum expected short-circuit currents and typical circuit breaker tolerances, are proposed with emphasis on safety, and tests are cited.

The Political Side of Urban Development and Redevelopment

The fate of planned urban development and redevelopment largely depends on the political system. In the United States, political and governmental fragmentation has crucial consequences for development in physical, social, and political ways. The federal system, whatever its virtues, raises barriers which impede accommodation. The multiplicity of local units of government, not rationally determined, under mines co-ordination, power, and responsibility. The outcome of diffusion of power and dilution of responsibility is rigidity. Urban renewal is limited by the dichotomy of public and private control, tension between federal and municipal agencies, divi sion of power between different federal agencies, and fragmen tation of power at the local community level. Any change will require some adjustments in perspective. The possibilities for change, however, do not rest upon basic changes in political norms but, rather, on experimentation in their application. In conceptions of community, for example, the units have probably been too small, applying to limited, exclusive groups organized around shared activities. These come together, partially and fortuitously, in the urban scene. In that scene, the only en compassing organization is the political community. The political side of urban development and redevelopment is inescapable.—Ed.

坑内用新型高圧ケーブルについて

These are tests to examine quality of three types of mining power cable. i. e.(1) the GR-1 insulated cable(2) the polyethylen insulated cable(3) the P.T.A. type paper insulated cable.Test resultThe first two (synthetic material insulated) are superior to the last from the stand-point of safety, mechanical and electrical strength, and economical use.

Utilization of Electric Power in Open-Pit Copper Mining

At the outset it should be said that the utilization of electric power in the mining of copper ore as in many other branches of engineering requires only the application of sound electrical engineering knowledge, with particular attention applied to some of the special problems involved. It is well known to members of the Institute, and of the electrical engineering profession in general, that each industrial operation involves special features differing somewhat with the various processes, and so it is with the subject of copper mining. It becomes necessary, in order to illustrate specific principles, to restrict ourselves to the mining of one type of ore. It is our belief that many of these special problems arise in processing sulphide ore and the following outlines this interesting process together with descriptions of equipment and discussion of some of the problems involved.

A New Index of Industrial Production and Trade

trade around the rising line of trend determined from the annual indexes. Crop production, Curve II, likewise advanced during the interval, but at a slower pace than industrial production and trade. Industrial and agricultural production combined, Curve III, follows the year-toyear fluctuations as well as the trend of industrial production and trade more closely than those of agricultural production. This is a result of the greater weight given to industry and trade than to agriculture because of the relatively greater importance of the former in our economic life. The percentage increases of the ordinates of the trend lines for I932, as compared with I899, for each of the three groups shown in Chart i are: (I) industrial production and trade, I 76 per cent; (II) crop production, 48 per cent; and (III) these combined, I32 per cent. The three years, I930-32, record a decline in physical production far exceeding that of any other period in the interval covered. Using the annual figures, the decline from I929 to I932 in the combined index is fully 4o per cent, as compared with a drop of less than I7 per cent from I920 to I92I, and ii per cent from I906 to I908. In other words, the most recent depression may be described as a major economic decline followed directly by another equally severe collapse. The, index of industrial production and trade, here presented, is constructed from series representing six major industrial groups: manufacture, wholesale and retail trade, railroad freight traffic, building construction, mining, and electric power production. Each of these series is presented in Chart 2 (next page), on a ratio scale in order to bring out rates of growth. Among the major groups, electric power production expanded most rapidly, while the volume of manufacture, wholesale and retail trade, railroad freight traffic, and mining grew more gradually. Building construction, on the other hand, exhibits no clearly defined trend, either upward or d wnward. We may rema k, however, that the index of building construction is based on estimates of the value of construction deflated by an index of building costs and the figures are less dependable, previous to I919, than those for any other series included in the present study. In fact, it is impossible to say, on the basis of available data for building construction, what the long time trend of construction actually was. The series is included, nevertheless, because reliable figures are available for I919 and after. Just as the industrial groups represented by the six constituents display divergent rates of growth of physical output, so their relative economic importance, measured in dollars, varies widely during the period covered by the index. 1 The index for total crops (agriculture) is that of Warren and Pearson, Prices, pp. 44-45. Although live stock is not included, feed crops as well as food and other crops are included, and the index measures agricultural production relative to the base period.

Purchased power in coal mines

In this paper, the author points out the commercial aspects of purchased power, vs. the isolated plant in the bituminous coal fields of Western Pennsylvania and Eastern Ohio. The adverse conditions affecting the operation of isolated plants and the fundamental causes of high costs of power per ton of coal mines are given, and are contrasted with the advantages to the mine operation of the purchase of power when available. The characteristics of mine power business are briefly described with a view of showing the reasons why central stations can afford to make low rates for this class of business.

Purchased Power in Coal Mines

In this paper, the author points out the commercial aspects of purchased power, vs. the isolated plant in the bituminous coal fields of Western Pennsylvania and Eastern Ohio. The adverse conditions affecting the operation of isolated plants and the fundamental causes of high costs of power per ton of coal mines are given, and are contrasted with the advantages to the mine operation of the purchase of power when available. The characteristics of mine power business are briefly described with a view of showing the reasons why central stations can afford to make low rates for this class of business.