System Transmission

Open-Arc Furnaces. Most of the open-arc furnaces are used in melting and refining operations for steel and iron (Fig. 1). Although most furnaces have three electrodes and operate utilizing three-phase a-c power to be compatible with power transmission systems, d-c furnaces are becoming more common. Open-arc furnaces are also used in melting operations for nonferrous metals (particularly copper), slag, refractories, and other less volatile materials. 

Absorber oil units offer the advantage that Hquids can be removed at the expense of only a small (34—69 kPa (4.9—10.0 psi)) pressure loss in the absorption column. If the feed gas is available at pipeline pressure, then Httle if any recompression is required to introduce the processed natural gas into the transmission system. However, the absorption and subsequent absorber-oil regeneration process tends to be complex, favoring the simpler, more efficient expander plants. Separations using soHd desiccants are energy-intensive because of the bed regeneration requirements. This process option is generally considered only in special situations such as hydrocarbon dew point control in remote locations. 

As early as 1966, natural gas was available to all of the lower 48 states in the United States. During the period 1967—1990, the U.S. transmission system grew from 362,700 km to 450,800 km. Over this same time period, the distribution mains increased from 867,800 km to 1,347,000 km. As plastic pipe and reUable joining technology became available, the use of plastic pipe expanded to include the distribution of gas in low pressure systems. By 1990, approximately 24% of the U.S. distribution system was based on plastic pipe (1). 

Natural gas production and transmission systems are complemented by underground storage systems. These systems provide the capabdity to respond to short-term gas demands which exceed the immediate production levels or transmission capabdities. They also provide an opportunity to sustain some production by refilling the storage areas when seasonal temperature variations lead to periods of reduced gas demand. In the United States in 1990, there were 397 storage pools having a combined capacity of 2.2 x 10 (1). 

It is common to employ microwave power monitoring by means of a dual-directional coupler in the waveguide transmission system between the power tube and the useful load. Part of the coupled signals may be used for examination with spectmm analy2ers, frequency meters, and other microwave instmmentation for special purposes. Generally, this is not necessary in a practical appHcation. Many microwave measurement techniques have been described (59,60). AvailabiHty of components, plumbing, and instmmentation is weU described in trade journals. 

Some U.S. natural gas pipeline companies are subsidiaries of gas hoi ding companies. The largest U.S. natural gas pipeline companies, in terms of overall length of transmission systems are Northern Natural Gas Company, 26,539 km Tennessee Gas Pipeline Corporation, 23,567 km Columbia Gas Transmission Company, 18,481 km Natural Gas Pipeline Company of America, 17,200 km and Transcontinental Gas Pipe Line Corporation, 17,071 km. For gas moved in 1994, the four largest pipelines were ANR Pipeline Company, 95,278 x 10 m (3,363,275 MMcf), of which 40.8% was gas moved for others Transcontinental Gas Pipe Line Corporation, 87, 050 x 10 m (3,073,801 MMcf), of which 99.7% was moved for others Natural Gas Pipeline Company of America, 83,089 x 10 m (2,933,940 MMcf), of which 87.1% was moved for others and Northern Natural Gas Company, 56, 523 x 10 m ... 

Entities involved in long-term contracts with electric utihties, such as fuel supphers and NUGs selling power to utihties, also have concerns that some utihties or industrial customers will not be able to honor their contracts under the new, more competitive system. Einahy, some utihties are concerned that they wih not be adequately reimbursed for opening up their transmission systems to competitors. The potential competitors in turn are concerned that utihties whl not provide unbiased access to their transmission systems if the utihties themselves are also in business of marketing power. There has also been some debate regarding which transmission facihties are eligible for open access. This is because some facihties are considered local distribution systems by utihties, which feel they should not be opened to competitors. 

In addition to the circuit breaker, there have been a number of other SMA appHcations for various functions in electric power generation (qv), distribution, and transmission systems. One such device is a thermal indicator that provides a signal visible from the ground of a hot junction or connector in a distribution yard. Such hot spots occur as a result of the loosening of bus bar connectors owing to cycHc temperature as the electric load varies. In addition to the use of SMA flags as a hot-spot indicators, actuators that automatically maintain the contact force in a bus bar connection have been demonstrated. Based on a BeUeviHe washer fabricated from a Cu—Al—Ni SMA trained to exhibit two-way memory, these washers, when heated by a hot joint, increase their force output and correct the condition. A 30 mm diameter washer 3 mm thick can produce a force of over 4000 N. Similar in purpose... 

The usual precautions must be observed around the high tension electrical equipment supplying power. The carbon monoxide formed, if collected in closed furnaces, is usually handled through blowers, scmbbers, and thence to a pipe transmission system. As calcium carbide exposed to water readily generates acetylene, the numerous cooling sections required must be constandy monitored for leaks. When acetylene is generated, proper precautions must be taken because of explosibiUty of air—acetylene mixtures over a wide range of concentrations (from 2.5 to 82% acetylene by volume) and the dammabiUty of 82—100% mixtures under certain conditions. 

For pneumatic transmission systems, the signal range used for the transmission is 3 to 15 psig. In each pneumatic transmission system, there can be only one transmitter, but there can be any number of receivers. When most measurement devices were pneumatic, pneumatic transmission was the logical choice. However, with the displacement of pneumatic measurement devices by electronic devices, pneumatic transmission is becoming less common but is unlikely to totally disappear. 

In order for electronic transmission systems to be less susceptible to interference from magnetic fields, current is used for the transmission signal instead of voltage. The signal range is 4 to 20 miUiamps. In each circuit or current loop, there can be only one transmitter. There can be more than one receiver, but not an unlimited number. For each receiver, a 250 ohm range resistor is inserted into the current loop, which provides a 1- to 5-volt input to the receiving device. The number of receivers is hmited by the power available from the transmitter. 

PAFC systems are commercially available from the ONSI Corporation as 200-kW stationary power sources operating on natural gas. The stack cross sec tion is 1 m- (10.8 ft"). It is about 2.5 m (8.2 ft) tall and rated for a 40,000-h life. It is cooled with water/steam in a closed loop with secondary heat exchangers. The photograph of a unit is shown in Fig. 27-66. These systems are intended for on-site power and heat generation for hospitals, hotels, and small businesses. Another apphcation, however, is as dispersed 5- to 10-MW power plants in metropolitan areas. Such units would be located at elec tric utihty distribution centers, bypassing the high-voltage transmission system. The market entiy price of the system is 3000/kW. As production volumes increase, the price is projec ted to dechne to 1000 to 1500/kW. 

But Ihe GT is connected to a power grid and the grid to a transmission system. If we consider the fault level of the transmission system as 40 kA, as in Table 13.10, then Ihe maximum fault that can occur on the LV side of Ihe GT will be governed by Ihe fault level of the transmission system (40 kA) and not the GT (84 kA). 

We illustrate a typical powerhouse generation and transmission system layout in Figure 13.21, and reproduce in Table 13.10 the typical fault levels of different transmission and distribution networks in practice for different voltage systems. 

Figure 13.21 A typical powerhouse generation and transmission system, also illustrating power distribution to unit and station auxiliary services...

In Europe and Asian nations this is generally 110 or 110/ 2 V. (62.5 V) for phase-lo-phase or phase-lo-grotmd auxiliary circuits respectively. In the U.SA and Canada these voltages are 120 oiy l20/v2 V for distribution systems and 115 or 115/ v 2 V for transmission systems,... 

When we refer to a transmission system, we classify the different maximum voltage systems as follows ... 

We will notice subsequently that series and shunt compensation are complementary. What a shunt capacitor cannot do, a series capacitor does and vice versa. On a secondary transmission system, say up to 66 kV, a shunt compensation may always be necessary to improve the power factor, as the load would mainly be indtictive. A series compensation may become essential, to improve the stability of the system, to cope with load fluctuations, switching of non-linear loads and voltage fluctuations occurring on the other power system or the grid to which this system may be connected. 

The series capacitors tire connected in series with the power lines to provide reactive control to an individual load or to a power distribution or transmission system. They are therefore switched with the pow er lines and are thus permanently connected devices. 

E. D. Sunde, Earth Conduction Efiects in Transmission Systems, D. van Nostrand Company, New York 1949. 

The solution is to provide valves and aetuators that will operate in time to prevent exeessive overspeeding of the train. The eontrol piekup and transmission system must be eleetronie to provide essentially instantaneous response. Aetuators must be foolproof and powerful, as well as quiek aeting. 

In 1985, the first active magnetic bearing in a pipeline compressor for continuous use was installed on the Alberta Gas Transmission System of NOVA Corporation. Tlie bearings have been running smoothly, with a noted improvement in compressor operation and efficiency. 

San Diego Gas Electric s system was originally installed as a research project. The intent of the research project was to test the hardware in this application, test the feasibility of operating such a system remotely with no local operators, and to prove the economics. Similar systems had been installed within process plants where operators were present to start and stop the system and monitor its operation. However, this was the first system installed on a natural gas transmission system with completely remote operation. 

Figure 8-12. San Diego Gas Electric Company s gas transmission system.

The eomponent shown in Figure 4 is a spaeer from a transmission system. The eomponent is manufaetured by turning/boring at the rate of 25 000 per annum and the eomponent eharaeteristie to be eontrolled, X, is an internal diameter. From the statistieal data in the form of a histogram for 40 eomponents manufaetured, shown in Figure 5, we ean ealeulate the proeess eapability indiees, Cp and Cp. It is assumed that a Normal distribution adequately models the sample data. 

Data transmission system (eables, telephone link-up, or mierowave)... 

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