Document xnq84pR2G11B6XL60NVmZkmy

How U Slipring-Motor Resistance Calculated? Vi havi t ISO-lip 440-y 3-pfcaie tlipring conveyor motor that hae cqumH uo to chon| hookup twice. It i> apparent that the wrong eeeondary grid reeietor* bare been (hipped with tbie installation. Vo hare about doubled the eiic of the bank, but otill don't get proper speed regulation. Ve operate It from o llmcp dram-lypo controller on the secondary. It it itnrted ond mopped with itart-elop pushbuttons through a mognetle contactor in the etalor circuit. The primary currunt li 176 amp and the tecondary cur rent 190. Hie ipeed it 1 ISO rpm. On the firm tern, under no load the rotor marted at about 1000 rpm. Tbe grid* were then rearranged and some added, to giro about double refinance. Chi the teeond teat under full load the alerting apeed was mill -high us it was over 800 rpm. I would appreciate it If eomo Powca readers would give me a formula or other definite information that I can use to determine the correct cross section and resistance of the grids for the 12Hep controller. I want resistance that gtvea maximum safe starting torque and equal acceleration up to full short cir cuit of the rolor^-JWi' heavy toad of about 250 hia on fhe generator the belt slips on the engine flywheel, as the polished condition of the metal flywheel face thorn. Slip page heats the belt noticeably and Is shortening its life considerably. I have heard that a rider belt, about half the width of the main belt and riding on top of it, greatly helps this condition. Do Poteen readers agree or have they a better solution?--IM Change Tension And Adjust Idler Assuming avccucs alteuwatoh and belt efficiencies I find that about 360 hp it transmitted (or 250 kw. A 24-in. triple-ply heavy-leather belt should transmit 400 hp continuously without undue wear. Excessive load does not cause excessive slip. I will pass over expensive solutions, such as facing the flywheel or mounting the alternator on a pivoted base so re action torque increases bell tension with load. We can still make improve ments by relocating the idler or in* creasing bell tension, or by doing both. At present the idler is in position 6, see sketch below. This gives good belt wrop on the small pulley.* Actually, the coefficient of friction / tlltifcs iho angle of wrap need bo only the eame for each pulley. Since / lor paper is 1% limes / lor iron, the angle ol wrap on the fly wheel should be 1% times that on the paper pulley. It is about this withotn any idler at all. The ratio is now 214 to 145 deg. Hence, if the Idler is used to increase angle o! wrap, it would be far better mounted at C where it gives 270 deg on the flywheel and 180 deg on the generator pulley. The given speeds indicate 4.8% slip. A trial check shows that belt tension must be low. This con be increased by increasing the load on the idler, whether in position B or C, or by shortening the belt and forcing idler to po sition A. The vector diagrams on the sketch below indicate how much this increases belt tension without increas ing Idler bearing loads. It Is unusual to operate a belt wider than 26 In. on a 28*in. pulley face. Working along the edges of a 26*in. Readers' Answers How Can I Stop Belt Slippage on Flywheel? (Thti swuim w /um Oct ujm w(iA till M/wrn /ram reader*./ Wt have trouble with slippage of a hell fAar drives an ac generator from a steam engine. The unit, an 18x42-in. 400-Ap corliss with a )5-/f. flywheel, has a 28-in. face. The engine runs about 102 rpm and drives a 275-kw 60-cps ac generator through a 34-in. pulley. Gen erator speed is 514 rpm. Belt is 28 in. wide, of 3-ply leather. Center-to-eenter distance from generator pulley to en gine flywheel is 20 ft, 8 in. A heavily weighted idler at the generator gives a good belt wrap on its paper pulley. Usually the generator runs synchronised with an outside power source. Trouble is that when we carry a 114 (40) POWER January 1448 This is the 20th year of Webster heating service at Hecht Brothers Department Store in Baltimore, where management hoa long recog nized that heating comfort is an important foctor in successful de partment store operation. In 1927, when the present home of Hecht Brothers Department Store was built, a Webster Vacuum Sys tem of Steam Heating was specified by Abbott, Mcrkt Co., Inc., New Light 6l Power Co. On the recom mendation of the Gas & Electric Company, they decided to convert the installation to o Webster Mod erator System, then as now recog nized for comfort at low cost. Installation of a 3-Volve -4 Web ster Moderator System, controlling 15,824 square feet of Installed direct radiation, was completed during the heating season without interruption in store operations. Webster Radia tor Valves were fitted with expertly sized Webster Metering Orifices so chat all radiators would heat evenly. The existing piping was retained. Hecht Brothers Store faces north. The heating installation is zoned to compensate for the sun effect by delivering proportionately more steam to the north side of the build ing. Radiators in sections of the store warmed by 6olar heat receive leas steam. Steam savings are appreciable. Since the introduction of district steam service, there has been a no ticeable improvement in cleonliness, an important factor In department store operation. The dust, dirt and 6moke which go with many private plants are avoided. Sam Hecht, President of Hecht Stores, and William P. Calhoun, Store Manager, look upon theit Webster Heating System as an in vestment in customer satisfaction. Webster Service Is provided by Bal timore Representative H. M. Harris, with Webster for 18 years. York, Architects and Engineers. The installation included Webster Radiator Traps and Supply Valves, Webster Float and Thermostatic Traps ond Dirt Strainers and a Nash Vacuum Pump. Riggs, Distler&Co., Inc., Baltimore, wetc the heating contractors. In 1941, Hecht Brothers decided to discontinue theircool-burnlnq boiler plant and purchase street steam from the Consolidated Gas Electric If you are Interested in heating com fort at low cost backed by the ex perience of tong-service Webster Representatives, give us a few facts about your heating requirements. WARREN WEBSTER &. CO.. Camden. N. f. Rrpreaenuitvca In principal U. S. Odd 11 Eh. 1108 In CimJ*. Dilln| Ditma Limbed. Mnirral Wefoter HEATING SYSTEMS Webster Hcoting Equipment for Today's New Buildings [SiiuTl Mcwrtnc Orilce*. eciptrtlr rited. vtnt feature n* Moderator Stttm, 'n* dlitrlbailon and POMlbb atiml con- Vttalri Outdoor Thermo- ant Control automatical!* provide* (He Item pttmure for comforcible tnalda mm- Wcbnct Root nd ThermoKt<lc Drip Trap* irt tuoa on herrtnp colli of *tr tonal- and drip point* of ibe pfpfnp n>*tcn. Prefabricated Unli--Wcbner Spitcm Radiation convector* artth copper tuMns. huntmini fin*, faicjrd wtbaac* Trap* and Valve*. Newt Vtbmr Trp* Wl R*. dlatino torlnrallatton when* door oe wall tpace I*Itahed. *OWtR J,,,v4Py |'4g Its