Document O3RVv4M5G9BR2de6DdRGv69vp

found a 1% reduction in voltage in general is followed by o 1% cut in load. Generally speaking, voltage may be reduced at much as 7Vfe% with satis* factory results. Authors outline a pro* cedure for reducing voltage and fre quency under emergency conditions. Tests conducted by the Kansas City Light and Power Co, serving the metro politan area of Kansas City, Mo., show it is possible to lower system primary voltage up to 5%. decreasing frequency IV% at the same lime. AIEE technical paper 48-267, pre sented at the AIEE Midwest general meeting, Milwaukee, Wis* Oct IB-22, 1948. To Obtain Complete Text Material in these briefs eomei from one of two sources unless specifically identified after review of paper. American Institute ef Eleeiricol Engineers, Midwest general meet ing, Oct 14-22, 1948, Milwaukee, Wia. Available el AIEE, 29 W )9lh St, New York. American Society ef Meehanlcal Engineers, spring meeting, March 1-4, 1948, New Orleans, La.; fail meeting. Sept. 7-9, 1948, Portland, Ore. Available at ASME, 29 W 39th Si, New York. Stkam Station Costs, by A E Knowtton. Electrical World. Energy generated in o representative USA central-station power plant shows production .costs . ranging from as low as IS to as high as 14 mills with.on average value of 4.5 mills per netjtwhr. Nine years ago this average was about S mills. Average coat of net kwhr at the bus bar for plants from 5000 up to 300,000 kw roling fa 1947 ran 7.5 mills. With* this figure plus the average 4.S mills, production-cost fixed chargea can be set around 3.0 mills on a broad average basis. One point of considerable interest advanced by the oulhor was the fact that the 1947 load proved so great only one in six plants had a peak below rated capacity. In fact, peaks commonly reached 120. to 130% rated capacity. Plant factor (ratio of aetual net output to that obtainable over 8760 hours of full-rated capacity) showed up even more favorably, except for the largest plants, the national, sampled average ran about 70% in 1947. Survey, with 102 generating stations reporting, indicates a kilowatt of in stalled capacity has cost as much as $200 and, at one time, as little as $46. This phenomenally low figure `comes about from (1) an outdoor installation (2) a highly simplified design built specifically for 0 very low-cost fuel. General average runs about $90 to $130 for plants operating in 1947, regardless of age of the oldest operating unit. Progressively larger plants carried si lower costs per unit of rating than smaller ones. Largest plants, even If quite ancient, represent lower casta than middle-sized ones. The latter show up odvantageously in over-all costs per net generated kwhr. Plants of under 60 megawatts, built in 1920-1929 and not since expanded, cost on the average ebout $150 per kw. Those built in 1930-1934 average about $107, while those is 1935-1939 cost as low as $76. By 1940-1944, unit cost soared to $110, and by 1945-1947 to $135. According to the author this fig ure of $155 still does not touch the unit cost experienced in the inflation and boom after World War I. Investment costs for plants of 60-149 megawatt rating, built within the 19201929.decade, average about $100 per kw of rated copacity. By 194CM944 this average fell to $83, but by 1945-1950 came back to about $115. Investment cost regardless of plant vintage Indi cates that spread In dollar per kw runs much higher for small plants than for large. The largest represent $85 per kw, and iho smallest about $120. Boiler plants constitute the largest component of over-all costs. Structure and improvements for a $100 plant amount to $28, boilers and associated thermal equipment to $36, and turbinegenerator to an added $26. All office space, shop, electrical galleries, etc. aceount (or another $10. Higher boiler pressures and eteam temperatures afford better thermal per formance. The 1200- to 1600-psi hit below 11,500 Btu per net kwhr; 800to 1000-psi plants hover near 12,000. The 600- to 700-psi plants reflect about 13,000. Finolly, .the 200- to 400-psi plants range from about 14,000 to 26,500. July 3. 1948, Electrical World, 330 W 42nd St, New York City- STEAM EQUIPMENT SurF.nHEATcn Tuob Failures, by If B Snider and F H Ward, Humble Oil and Refining Co. Continued failures ol end superheater tubes In a 275,000-lbper-hr 650-psi boiler kepi causing un scheduled ahuldowna and interruptions to steaming capacity. Upon examination of the raptured tubes excessive deposits', showed up. A checkup of normal castes for car ryover, excess boller-water alkalinity, ' high total solids, high water love) ^ ` vealed no abnormal conditions. For this reason decision ws mode to carry oat a fairly comprehensive test of steam ;. leaving the boiler dram and entering' the superheoter. Standard sampling ap- ' paratus and sampling connections were set up to draw from the dram, twelve of the connector lubes between drum 1 and saturated header, saturated toperheater header, saturated header drab, j and eight end superheater tubes. Saturated header conatrucUoa is ! such that the apace through which steam enters the header from the drum' connector tubes is less than that ia, which steam leaves the saturated. header through.the superheater tubes. This construction forces a lateral Sow. of steam at the ends of the saturated header. The resulting 90-deg turn pre cipitates solids to the end of the saturated header where they concentrate. The end superheater tube obtains itssteam from this section and overheating', of the tube results. Steam samples indicated a-stum' quality of 0.60-ppm total solids average produeed in the drum. This quality held for the steam enteriag the satu- rated header. Since auperheaMMobe. failures from carryover ore rare with steam of a quality less than i ppm for solids, steam from the drum and the saturated superheater header were fell, not to cause these tube failures- Saturated header steam showed 1.4 ppm, and ot this header drain it was 13.35'ppm total solids. Alt evidence in-. dieoted the solid concentration ,u. developing ot this end of the saturated header. Steam samples from the superheater tube ends confirmed this evidence. The . end superheoter lube contained 3.15- ppm total solids, while samples the adjacent superheater lubes lad!' coted much less. To correct this feeding of heavuj concentrated solids to the end super heater tube It was decided 10 add an additional connector lube between sit1* rated header and drum, just PP9?*,'j the superheater tube next to the ra superheater tube. In addition, drum internala of the same desip *- the old ones were put in. When the boiler returned to data from sampling points *ho decided Improvement In steam qtn^T* From the drum it was 0.30 PP*** . from tho solurated superhester he* . (Continued on page J?4) 134. (803) POWER