Pole Transformer Research Articles

低圧配電線に生じる誘導雷過電圧の実験的検討

Problems have often been caused in low-voltage distribution lines such as single-phase 100/200 V and three-phase 200-V systems. For instance, the burning of low-voltage devices and the unnecessary operation of ground fault interrupters have occurred, which are caused possibly by lightning overvoltages. Experimental analysis was performed on the generation modes of lightning overvoltages on low-voltage distribution lines. A scale model line, one-fourth the size of an actual power distribution line of Tokyo Electric Power Company (TEPCO), was installed for experimental analysis on the lightning protection of an overhead ground wire, an overhead common grounding wire (system neutral conductor), surge arresters and pole transformers against the overvoltages induced on low-voltage distribution lines due to a nearby lightning stroke. A balloon was flown at a location 30 km away from the scale model line in a normal direction to it. A 200-m long wire is suspended from the balloon to simulate a lightning path. Pulse current is applied to the simulated path using a pulse generator and the voltages induced on the line conductors are measured. This paper analyzes those overvoltages by means of the experimental and the theoretical methods.

Fire hazards and welding action in service-entrance conductors

Service-entrance conductors between the customer's service-entrance equipment and the power company pole transformer are not covered by the National Electric Code (NEC) and often have entirely inadequate overcurrent protection. Power companies fuse to protect their transformer and not the individual service materials which may supply a number of customers. Thus currents in excess of a 1000 A can flow for a considerable time as a result of short circuits in the service-entrance conductors. Often these conductors are enclosed in a steel conduit between where they enter the building and meter box, and/or service equipment, and the welding action of shorts in this conduit melts the steel of the conduit and starts fires long before the pole-transformer fuse blows. Several such fires are documented in this report. Possible solutions to this hazard are proposed.

The development of grain-oriented silicon steel with high permeability

We explain the theoretical background, uses and new development of grain-oriented silicon steel with high permeability using A1N as a grain growth inhibitor. New production techniques have made it possible to get superior core loss values; for example, 0.99 W/kg at 1.7 Tesla and 50 Hz (0.30 mm thickness). The presence of A1N precipitated being controlled in the size of about 300 Å or under and in adequate distribution and quantity in the steel is very important for developing secondary grains with high permeability. Core loss improvements on actual transformers using high permeability materials are approximately 10–25% in wound type pole transformers and 5–20% in laminated type large transformers.

Computation of Reflection and transfer Coefficient Matrices for Switching Transient Studies

A non-iterative method has been developed for computing reflection and transfer coefficient matrices for use in traveling wave studies on three-phase power systems. The method has been programmed, verified by reproducing field tests, and applied to a practical study. The program has the capability of including three- phase untransposed transmission lines, multi-velocity waves, single- pole switching, lightning arresters, and transformer hysteresis. All calculations of reflection and transfer coefficient matrices are done automatically to minimize data preparation.

AIR-RAID DAMAGED AND ELECTRICITY SUPPLY

A FURTHER series of articles in the February issues of the Electrical Review record instances of the air-raid damage sustained by overhead lines, cables, and substation equipment, and the steps taken to effect repairs and restore supply (see also NATUBE of February 7, p. 173). Although many engineers fully expected that overhead lines in the path of bomb blast would be levelled to the ground, actual damage has not reached a quarter of that anticipated. Admittedly, line conductors have suffered, and on pin type insulator lines, conductor binders have been severely strained, but it requires direct hits on towers or poles to interfere seriously with supplies. Bomb splinters, not blast, are generally responsible for the damage, stranded conductors showing definite evidence of having been severed. Wood poles appear to withstand blast better than steel ones, one large rural undertaking reporting that out of many near misses, only one wood pole was rendered unserviceable. Damage to pole transformers is rare and is usually only a slight puncturing of the casing.

A Deep Therapy Installation Embodying Some Novel Features

THE purpose of this paper is to describe our installation at Stanford University Hospital, which we believe excels in ease and steadiness of operation and safety for the patient. The Generator For the production of undirectional current at 200,000 volts we have made use of a “Rieber” booster set, but feed it 100,000 volt current rectified by valve tubes instead of by a rotating switch. This is done in order to avoid the surges which are set up by sparking in any rotary switch. We are actually using universal Coolidge tubes instead of Kenotrons because they require only about a quarter the wattage to light. Heated to pass 10 milliamperes at a few thousand volts' drop, they will not pass more than about 50 milliamperes at full voltage. This limits any gas surges in the therapy tube, which may be important in tube life. Controls The voltage is adjusted by means of an autotransformer feeding the four 50,000 volt transformers in parallel. Supply is at 240 volts from an individual 25 kilowatt pole transformer with 00 leads in from the street, specially installed by the power company. Thus we avoid gross voltage fluctuations due to changes in outside load. The voltage is read by spark gap between 125 mm. spheres installed within the machine closet, but moved and read from the operator's hall outside. The treatment tube filament is heated by a Rieber Stabilizer (not shown in diagram) and filament transformer, which gives a constant heating current irrespective of line voltage fluctuations. The tube current is read from two milliammeters connected in series in the grounded neutral. There is also a milliammeter in one high voltage lead for a check (not shown in diagram). Time is marked and the current cut off automatically by means of an A.C. motor and train of reduction gears, which run only when the transformer current is switched on. As a final and direct check on the indirect measurement of X-ray production, there is mounted inside the tube shield, just within the filter, a small metal ionization chamber charged to 500 volts from a dry battery and connected to a sensitive galvanometer. This gives continuous readings of actual X-ray production. The Patient Complete X-ray and electrical protection for the patient has been attained by mounting the tube in the axis of a drum lined with 1/4 inch of lead and by enclosing the high voltage leads completely. In order to obtain maximum flexibility in use, the high voltage current enters the drum at the ends, so that it can be rotated through 360° and treatments conducted through a port in the side of the drum with the patient below, above or at the side. The couch is on castors and has an up-and-down adjustment on notched posts of 16 inches. To provide for long focus skin distances when the patient is underneath, the tube is mounted high. This necessitates raising the patient rather far toward the ceiling when the back is to be treated.