1939: Electrical Engineering

Electrical Power and Machinery.

It has been previously reported that hydrogen was used for the cooling of turbine-driven alternators, the method first being applied to small units. Hydrogen cooling has now been applied to units with ratings as high as 150,000 kw. operating at speeds of 1,800 r.p.m. There are now 500,000 kw. in hydrogen-cooled alternators operating in the United States. As has been previously stated, the advantages of hydrogen cooling are that hydrogen is a much more effective cooling agent than air because of its much greater specific heat and penetrative qualities, and the windage loss with hydrogen is materially less than with air. Of particular interest is the 75,000-kw., 1,800-r.p.m., hydrogen-cooled generating unit constructed by the Westinghouse Co. for the Duquesne Light Co. and located in the James Reed Station on Brunot's Island in the Ohio River near Pittsburgh. In view of the recent severe floods the generator has been made flood-proof at standstill, so that in case of flood the generator will be stopped, a few adjustments made, and it will not be affected by submersion.

A synchronous condenser is a synchronous motor operating without load (mechanical). By varying the direct-current field excitation, the condenser may be made to take a leading, in-phase or lagging current as may be desired. Hence, its power factor can always be controlled. By connecting such condensers to power systems, the system power factor may also be controlled. This control has several advantages. The system may be made to operate more efficiently because of the leading current of the synchronous condenser counteracting the lagging current of induction motors and other induction apparatus. The voltage at the receiver end of transmission systems may be controlled and the stability of such systems be greatly increased by proper adjustment of the power-factor made possible with the synchronous condenser. Hence more power can be transmitted over a line without fear of the system 'dropping the load.' Without synchronous condensers, present long-distance transmission systems, such as that from Boulder Dam to Los Angeles, would be impracticable.

This past year a 25,000 kilovolt-ampere, 60-cycle, hydrogen-cooled, synchronous condenser, departing radically from past designs, has been constructed. The speed is 3,600 r.p.m., and the condenser is constructed like a turbo-alternator with a smooth, cylindrical rotor. Instead of the direct current for the field being supplied by a direct-current generator exciter connected to the shaft, as is usual, a mercury-arc rectifier with an electronic regulator controlled by electronic devices is used. This eliminates the rather unsatisfactory 3,600 r.p.m. exciter, and since the rectifier and regulators are electronic their inertia is small and their response virtually instantaneous.

In power transformers, oil is used for two purposes, to carry the heat away from the windings to the case from which it is dissipated to the outside air; to add to the insulation of the transformer, particularly where the voltages are high. Until recently mineral oil was used exclusively for this purpose. Since such oil, when ignited above the flash temperature, is highly inflammable, it is required that in industrial locations oil-cooled transformers be installed in fire-proof vaults, so constructed that should the transformer case burst, the oil could not escape from the vault. To obviate the fire hazard of oil, General Electric developed a synthetic liquid Pyranol, which has all the desirable properties of transformer or mineral oil; but in addition is non-inflammable, non-explosive, non-oxydizing and chemically stable. The Underwriters Laboratories have approved the installation in factories and other industrial locations of transformers using Pyranol, without the restriction of fireproof vaults. This is a great advantage in many cases; for although Pyranol is more expensive than oil, there results a saving in the construction of the vault, and the transformer can be located near its load, resulting in a material saving in copper and conductor losses. This is particularly true of welding, where the voltage is low and the current high. In the year 1939 the use of Pyranol-cooled transformers has been widely expanded both in voltage and power ratings, as well as in applications. For example, a 12,000-kw., 44,000-volt to 200-volt unit for furnace application has been put in service and a 625-kw., 11,000-volt transformer is used in railway locomotives to eliminate fire hazard, particularly in tunnels. These are examples of the wide uses to which Pyranol-insulated transformers are being put.

Lightning Generators and Lightning Protection.

Radical improvements have been made in high-voltage testing transformers and in surge or artificial-lightning generators, such as were used for the General Electric demonstration in Steinmetz Hall at the World's Fair. To produce the colored (red, green and blue) 1,000,000 volt, 3-phase, 60-cycle arcs, three cascaded transformers were required for each of the three phases. Each transformer was rated at 1,000 kw., 350,000 volts. One transformer was set on the ground; and the other two, connected in series with this one, were set on insulating cylinders so as to give the 1,000,000 volts above ground without subjecting any one transformer to more than 350,000 volts between its winding and case. The insulating cylinders are of paper impregnated with a resinous varnish, Herkolite, the paper being rolled into a hollow cylinder with hard solid walls. The colored arcs are produced by placing different salts in each of the three electrodes.

The design of the 10,000,000-volt lightning generator is radically different from previous designs. The condensers or capacitors using Pyranol (an artificial insulating liquid) with paper for insulation, are stacked on Herkolite (an insulating varnish) cylinders, each pole of the generator consisting of three stacks each several feet high with cross-connections for the resistors and for connecting the capacitors in the three stacks in series. This construction simplifies the connections and makes a neat and compact generating unit. The mode of operation is to charge the capacitors in parallel through high resistances (the resistors). When the capacitors are charged, a 'trigger-gap' flashes over; and discharges across a series of ball gaps follow almost instantly, connecting the capacitors all in series and producing the very high instantaneous flash or lightning discharge.

To protect transmission lines effectively from surge due to lightning and other surges, lightning arresters are used. Lightning arresters correspond to safety valves in a steam boiler. If the voltage rises, as may be caused by a lightning stroke or switching surge, the arrester prevents excess voltage by providing an easy path for the lightning to take to ground; but the arrester cuts off the arc which the power of the system tends to maintain as a follow-up of the lightning discharge. Theoretically, lightning arresters should be connected at every vulnerable point, as at every insulator and transformer. However, owing to expense, this is not practicable. To meet such a need, protector or expulsion tubes have been developed which are so inexpensive that they can be applied at a large number of the transmission towers, particularly those in lightning districts. Practically these tubes are only a sealed hollow fiber tube with a metal electrode at each end. The heat of the discharge liberates gas from the walls of the fiber, which intermingles with the ionized gas of the discharge, and cools and deionizes it, thus suppressing the arc. The tubes are connected, one end to ground and the other in series with a gap to the live conductor. Usually two tubes are used, one with an end connected to ground and the other with an end connected to the live line, with an intervening gap between the two free ends. Obviously such tubes are inexpensive, and it is practicable to apply them in considerable numbers to a system. During the year these tubes have been applied in increasing numbers and their characteristics and degree of protection studied by transmission engineers.

To be most effective, a lightning arrester should be connected close to the apparatus which it is to protect. The Thyrite (General Electric) and New Autovalve (Westinghouse) arresters are relatively compact and inexpensive. This has made it possible to incorporate the arrester as an integral part of the transformer that it is to protect. The transformer and arrester are now sold as a unit.

Fulchronograph Lightning Recorder.

The study of natural lightning continues. Until now, our knowledge of lightning was obtained with a cathode-ray oscillograph which, by means of an electric beam, records the voltage of a lightning stroke, and surge-crest ammeters, which consist of small pieces or links of iron which, when placed near a conductor carrying lightning, became magnetized by the current in proportion to the crest value of the current in the stroke. The surge-crest ammeter gives no information as to the variation of the lightning current with time. Hence there was great need for an inexpensive apparatus which would give this further information. The Westinghouse engineers have produced such a device, which traps bolts of lightning, studies their characteristics and then discharges them harmlessly to ground. It is called a fulchronograph and consists of vanes of permanent-magnetic material mounted radially on a wheel, which rotates the vanes through two coils which carry the lightning current. From the magnetism induced in each vane by the current of the lightning stroke, the magnitude and wave shape of the current can be determined. In a normal lightning season of 200 days the wheel makes approximately a billion revolutions. The instrument is now installed atop the 42nd story of the University of Pittsburgh's Cathedral of Learning. The first direct stroke recorded showed a 21,000 amp. crest followed by a low-amplitude component of 18,000 microseconds' duration. The current had decayed to 100 amp. in 0.02 second, which is a much longer time than previous records had given as the duration of a lightning stroke.

Three fulchronograph lightning recording stations have been established on the lines of the Appalachian Electric Power Co., a subsidiary of the American Gas and Electric Co.

Dr. J. M. Meek of the University of California discovered that lightning strokes travel through air at a velocity of 1,000,000,000 cm. per sec. (22,000,000 miles per hour). The initial act of the lightning discharge is to create a 'pilot' streamer of comparatively low velocity, which nevertheless speeds along at 20,000,000 cm. per second, which is followed by the later discharge.

Transmission and Distribution.

Work on the first phase of the Ross Dam on the Skagit River by the City Lighting Department of Seattle, Washington, is now being completed. There are ultimately to be three dams, developing a total of 1,120,000 horsepower. The Ross Dam is farthest upstream of the three and will be 655 ft. over all. The cost of this particular development is $5,600,000, 45 per cent of which is PWA funds; the ultimate output will be 360,000 kw. The two lower plants will have a capacity of 240,000 kw. each. This dam will create a 3,000,000 acre-foot reservoir, equivalent to 600 days' flow of the river, giving complete storage for power and flood control.

The construction of the third 287,000-volt, three-phase line from Boulder Dam to Los Angeles is now under way, assuring an added source of power to the Pacific Coast. The line conductors are the General Cable's 1.4-inch, type-HH, hollow conductor built up of ten segments to form a smooth copper tube.

High-voltage underground cables have hitherto been insulated with paper tapes, wound spirally about the conductor and impregnated with either heavy mineral oils (called the solid type) or a light viscous oil that flows in and out through the hollow core to a sylphon or accordion-like drum, with contraction and expansion (called the oil-filled type). Such cables are, of course, enclosed in a lead sheath. A new development is the gas-filled cable. The bulk of the oil is drained from the paper, and the cable is filled with an inert gas at 10 pound pressure. Although this cable does not have the life of the oil-filled type, nevertheless it has a longer life than the solid type, and the cost is much less than that of the oil-filled type.

The Magne-Blast Air Circuit Breaker for 5,000-volt service has just been developed by the General Electric Co. Usually for such service, oil circuit breakers are used because they are compact; the oil extinguishes the arc readily; and there is no exposed flame (except in case of accident). However, air circuit breakers are coming to be used more and more as they are justified by performance. Their advantage is small deterioration of materials, economical operating life, and no fire hazard due to explosion and burning oil. In the Magne-Blast breaker, specially shaped contacts are used. When the arc is drawn out between the contacts, a blowout coil, energized by the current, forces the arc into an arc shute of insulating material which is formed of corrugated members. The corrugations of these members inter mesh so as to form a serpentine path for the arc. The arc is thus extended and cooled and is rapidly extinguished. These breakers have given very good results in service, and tests show that they can interrupt 100,000 kva, at 5,000 volts, 60 cycles, 3 phase in 4.3 cycles.

Illumination.

In the field of illumination progress is still being made in lamp improvements. Until recently the largest size lamp made for the ordinary screw base was 200 watts. By improvements in manufacture and by the use of a heat-reflecting mica disc, the size has been increased to 300 watts. This enables the larger lamps to be used without changing sockets and wiring in existing installations. Instead of using screw sockets, the larger lamps are now of the plug-in type (known as bi-post base). This type of lamp can now be obtained in the 250 and 500 watt sizes. The advantages of bi-post construction are more precise focussing, one plane filament, smaller size of bulb that can be exposed to weather because hard glass can be used, improved fixture construction, smaller fixtures, and high over-all efficiency because of the better grid to collect the tungsten deposit.

The high-intensity, mercury-vapor lamp is being made in more different forms. The 100-watt lamp consisting of a discharge an inch long and one-twelfth inch diameter in a quartz tube has become standard for different purposes, such as in combination with tungsten lamps to produce daylight; in red-purple glass that transmits long-wave ultra-violet light to produce 'black light'; and in a special clear glass that permits the transmission of 'sun rays.'

Further research has developed high-pressure mercury arcs that have a brightness of 30,000 candle-power per square centimeter, 1,500 times brighter than the ordinary 100-watt lamp or one-fifth the brightness of the sun. It is the most concentrated commercial lamp ever developed. The lamp has a core of light smaller than a toothpick in a quartz-surrounded atmosphere of mercury vapor at a pressure of 100 atmospheres. The lamp is water cooled and operates at 840 volts. Its high actinic rays and intensity make it useful for photo-engraving work, searchlights and landing-field lights.

The efficiency and reliability of Cooper-Hewitt mercury tubular lights have been materially increased. This has been done in part by the use of reactor ballast in place of resistance and by improving the resulting poor power factor by the use of a Pyranol 3-microfarad condenser operating with each lamp. A starter with tungsten contacts increases the reliability and speed of starting the light. The new bare 350-watt lamp (tube alone) gives 19.4 lumens per watt, and with the fixture 16.0 downward lumens per watt. A combination unit of a 275-watt Cooper-Hewitt lamp and four 150-watt incandescent lamps (to correct for color) gives a total of 8.5 lumens per watt and 8.2 downward lumens per watt.

In Oklahoma City's Civic Center an innovation in municipal illumination is now in operation. The lighting units consist of a mercury-arc and tungsten-lamp combination. In order to emphasize the white limestone of the buildings and the green shrubbery, as well as to provide a high intensity source of illumination, 400-watt mercury lamps were selected as the primary units; and two 100-watt incandescent tungsten lamps in combination are used for color correction. A capacitor for power-factor correction is also incorporated with each lighting unit.

Fluorescent lamps ordinarily operate with a lagging current and the resulting low power factor is disadvantageous, particularly to the power system. The General Electric Co. now makes a unit in which two tubes are combined, one of which takes a lagging current and the other a leading current; so that the two practically compensate, making combined power factor 95 to 100 per cent. Another advantage is the reduction of the 'stroboscopic' effect or flickering. The maxima of the flicker in one tube occur when that in the other tube is a minimum, so that the total light emitted by the two is essentially constant.

Sterilamp.

In a former article (1938) reference was made to the Sterilamp of the Westinghouse Company, the rays of which destroy bacteria. This lamp has also been found most useful in connection with refrigeration. Meat, fruit and vegetables, even when in cold storage, after a few days develop mold growth. By placing Sterilamps in the refrigerator, the mold growth does not develop. For example, grapes usually develop mold growth at the end of five days and are unsalable after twelve days. Stored with a continuously operating Sterilamp, they were in perfect condition after five weeks. Bananas were the only fruit on which the lamp had any undesirable effect. The skin became darkened although the fruit was not otherwise impaired. With the Sterilamp meat can be stored at a higher temperature, and hence 'ripen' etc. without deterioration due to the growth of mold. See also TELEPHONE; TELEPHONE, INTERNATIONAL.