Urban Power System Research Articles

Magneto-optical direct-current meter for urban traffic power systems

A simple magneto-optical dc current meter is described for use in traction substations of urban electric transport systems. The meter is based on a compensation circuit and measures dc currents from 0 to 5000 A with an accuracy of ∼0.2% in a wide range temperatures. Optimal sensor location for maximum noise immunity in face of different noise source topologies is considered.

High impedance fault detection in low voltage networks

High impedance faults are those with fault current magnitude similar to load currents. Experimental results were obtained that confirm operating experience that such faults can occur in the low voltage (600 V and below) underground distribution networks typically found in urban power systems. These faults produce current waveforms qualitatively similar to those found on overhead feeders, but quantitatively smaller. Loose connectors can produce similar, but cleaner current characteristics. Noisy loads remain a major impediment to reliable detection. Design and installation of an inexpensive prototype fault detector on the Seattle City Light street network is described. >

Engineering evaluation of high‐Tc superconducting cables by bean model and its assessment of application to urban power system

Engineering evaluation of high‐T_c superconducting cables by bean model and its assessment of application to urban power system

ビーンモデルによる高温超電導ケープルの試算評価と大都市系統への適用検討

ビーンモデルによる高温超電導ケープルの試算評価と大都市系統への適用検討

Short Term Load Forecasting Using Periodic Model for the Weekly Load Data

The paper presents two new recursive algorithms for forecasting load demand of an urban power system. The algorithms are based on new dynamic models for the weekly load data. It is shown that both the algorithms become simpler once a few weeks data are processed in order to obtain steady estimates of the unknown model parameters. The results are illustrated through a case study involving data for the Bombay Metropolitan area.

Effect of Unbalanced Voltage on the Operation of Polyphase Induction Motors

Three-phase electric power systems generally provide voltage supply at the generating station that is well balanced in both magnitude and displacement. For varying reasons, however, some degree of voltage unbalance occurs at the point of utilization, and, depending upon the amount of unbalance, this can have an adverse effect upon the operation of polyphase induction motors. A major cause of unbalanced voltage at the point of utilization is that single-phase loads on a system are not uniformly applied to all three phases. This is particularly true for some rural electric power systems, and it can also occur in large urban power systems where heavy single-phase demands are imposed by facilities such as extensive shopping plazas. A large manufacturing plant may have well balanced incoming supply voltage, but unbalance can develop within the plant from its own single-phase power requirements if these are not uniformly spread among the three phases. Regardless of the cause, unbalanced voltage is harmful to three-phase induction motors. The paper to follow concentrates upon that aspect of unbalanced voltage.

5005 Aluminum alloy cables for overhead lines

THE WIDESPREAD ADOPTION of aluminum conductors for urban overhead power systems during the last 10 years has created a demand for a homogeneous aluminum-alloy cable having better sag characteristics than one made of EC (electrical grade) aluminum. With 5005 aluminum alloy, cables have been developed which meet this demand. In addition, since 5005 is a nonheat-treatable alloy, wires can be produced on conventional equipment and manufacturing costs are low.

A New Frequency Relay for Power-System Applications

THE interconnection of large power systems with industrial and defense plants having a comparatively small generating capacity is not unusual in these days. These plants require a considerable block of power for 24-hour full-capacity operation, and this power is available by means of the interconnection with the power system. More than one interconnection would assure higher continuity of service, but the general practice of locating defense plants in rural or suburban areas, remote from urban power-system networks, often results in one transmission-line interconnection operating in parallel with plant generators. Like all lines, the interconnection is subject occasionally to faults with resulting temporary loss of power for the plant. During these emergencies, the local generator or generators at the plant which normally contribute to the total load are suddenly called upon to carry all of the plant load. The local generators are not able to supply this load and consequently are heavily overloaded. As a result, the frequency decreases rapidly. However, complete shutdown of the plant can be avoided by dropping some of the load and retaining within the capacity of the local generators the load of the most essential machines and processes.

A new frequency relay for power-system applications

THE interconnection of large power systems with industrial and defense plants having a comparatively small generating capacity is not unusual in these days. These plants require a considerable block of power for 24-hour full-capacity operation, and this power is available by means of the interconnection with the power system. More than one interconnection would assure higher continuity of service, but the general practice of locating defense plants in rural or suburban areas, remote from urban power-system networks, often results in one transmission-line interconnection operating in parallel with plant generators. Like all lines, the interconnection is subject occasionally to faults with resulting temporary loss of power for the plant. During these emergencies, the local generator or generators at the plant which normally contribute to the total load are suddenly called upon to carry all of the plant load. The local generators are not able to supply this load and consequently are heavily overloaded. As a result, the frequency decreases rapidly. However, complete shutdown of the plant can be avoided by dropping some of the load and retaining within the capacity of the local generators the load of the most essential machines and processes.