Document Z56drxnwaXrnQXw2z2mLb9k8

lCOCno Reverse Direction. Starting the stair- 'Vr#"*-**" "** way in down-direction Is the same as up, except that either of the down start *<* **"" switches is'closed. This completes a circuit through down-direction twitch coil D that doses contocta D, and Dt in the motor circuit, D$ in the brake- coil circuit, and Dt in the potential- trtttptfl r*t*rt UiftKtlK troll** i/tt* ,,*.:**/**' Hr***" /M,/ switch coil P circuit. From here, start ing operations are the same as for updirection, except current direction is re versed in motor leads Tx and TV Resistance Start. Fig. 3 is about the simplest form of o moving-stairway con trol. For the larger sizes of electric stairways, type S, Westinghouse uses a primary-resiatance-atart controller. TTili control is used with a power unit sim ilar to that on a horizontal-shaft worm- and-gear-driven elevator, except it is de l/p-VOer<-r/W toltotlrl-mmtth rv//J u fc signed for electric-stairway service. Fig. 4 is an elementary wiring dia gram for a type 5 stairway's motor con trol. Even though arranged somewhat ------------- - - -- . .. Across-tho-llne-irorr control tor on electric stairway that's driven by squlrrel-cogo motor 5.7*7 W/'r^ Oom\'4lrrtlh*-t*iU* (*ii Utf.l t , a Slratahl-llns diagram of electric-stairs ocrou-the-llne-stcrt control. I of on electric itolrwoy it driven by o vertical y,;'. J Dlreetion*irUch contacts obove motor, reverte-phoie roloy RP below differently It has many features similar to Pig. 3. At top of diagram is the up end down-direction switch contacts Uu Ut. and Dt, Dt. Below these are the thermal overload relays OLx and 01%, and the potential switch contacts Px and Pt. Then, come tho S-phaae motor Get Moving Stairways Of) a Good Start windings Aft, Aft and Aft that connect lo starting resistors, Rx, Rg and Rg. These resistors are cut out of circuit by closing contacts SPt and SP|. Connected to the 3-phase line Is a reverse-phase relay RP, as In Fig. 8, and two conirol-cireuit transformers To understand how stairs op erate, you must know their mo tor controls. So let's look at two starting methods: (1) across- fhe-/ine (2) primary-resistance By F A ANNITT Contributing Editor A movimc stairway it a slow, me dium-friction, medium-inertia, constantspeed load, and therefore, can be driven by a normal starting-torque motor. Where sc is available, and it generally is, the motor is often a single-speed ocroas-ihe-line-itart squirrel-cage type. Three-phase squirrel-eage motors, with all sU winding leads brought for stardelta starting, are used extensively, as is primary-resistance starting on the larger stairways. Two-Spsod Motors. On some applica tions where the stairway operates at a higher speed during certain periods, 2speed squirrel-cage motors ore used. On high-epeod operation the stairway runs 120 ft per min, and on low speed 90 ft per min. Compsred to elevator-inotor controls, those (or moving stairways are simple. They are usually key-awiteh-atart typo, arranged to readily reverse the power unit when necessary and actuate an elec tric brake. A feature of these controllers is the large number of safety devices that protect passengers- and equipment against about every operating haiard. Pewor-Orivs Unit. Fig, 3 is a wiring diagram of a Westinghouse Type L-l controller, Fig. 1, for an electric stair way driven by a vertical power unit (Powcn, April, p 122). It is designed for mounting in the top-end section of the truss close to the stairway at Af, Fig. 2. This unit is powered by an acrossthe-Une-atait, 850-rptn, 10- or lS-hp, squirrel-cage motor mounted direetly on a worm-ond-gear. A sprocket on the worm-gear shaft connects by roller chain to the stepchain-sprocket drive shaft of the stair way. A scrvico brake B is mounted af)ove the motor with an underspeed and overspeed governor at G above the brake. In addition to the service brake, an emergency one is mounted on the top step-chain sprocket assembly. Tti brake la applied mechanically by a ps'd that drops into o ratchet wheel V ii d* drive chain should break--whieb 1 never does. Wiring Diagram. At top of wirfai diagram, Fig. 3, are the motor, its fi rection- and potential-switch conutd The motor Is protected by thermil swr load relays OLi and OLg aod a restri* phase.relay RP. A contact RP forti latter is in tho safety-switch circuit it the bottom of the diagram. Below the motor is a seleniam-dis rectifier tint supplies de for all eoslnl and service-brake-coil circuits. Tbisrts tifier connects without a transferee direct to tho 220-v motor-power sapptfConiequently, its do voltage is simp higher than the 115-v required forti* brake and control circuits. Excess volt age is absorbed in variable resistor At in the brake-coil circuit and R| in ch* direction- and potential-switch-coil &'.] cuits. These resistors permit adjastblj the dc voltage to a correct value, whelk** the motor operates oa 208 or 220 v, std also compensates for any decrease O dc voltoge due to aging of the reettf**- Sofoty Contoctt. Four step-coo* lights, two for each terminal, are aboi| at the center of the drawing, separate from the control circuits- The lamps Cght the approach to the steps at each the coil opens contact V* to break the circuit through coil D. When contact Ut doses it completes terminal, operate from a 115-v power a circuit through potential-switch coll . supply; and ore controlled by eonlact P, which closes contacts P\ and Pg In Pt oo the potential switeh P. the motor circuit, and Ps in tba broke- Mott of the safety conlocts are shown coil circuit. The latter is now complete cooneetad in series in lower left hand through contacts Pg and Ug so tho brake sf the drawing. Purpose of each of these releases. On one line polarity tho motor contacts is given In the legend in upper Wit. lo lower right ere tho top end bottom starting-switch stations. These twitches are key operated, end ore gen circuit la also complete from, say, line - Lit contact Ux, tho motor, contacts P\ and Ut to lino L%. The other circuit Is from Lt through Pg, the motor, and to erally located in the newels or on a lino lt as before. Motor starts and when nearby column. To start the stairway stalrwoy is running at about 80% rated > kfcy Is pat ia(o the switch, turned to speed, governor closes its underspeed ibe start position, and held there .until contact Ci to bypass start switches. tb* stairway reaches a speed where the A circuit (or coils P and U now goes favtnior underspeed contact C, closes, directly from the rectifier through con 1 about 00% rated speed. tact C, without going through the top Starling the Stairway. Assume the up-stort twitch so the storting key can . jjsbway Is to start In the up-dlreetion be returned to neutral and removed. from the top termlnoL At this stetfon, The stairway witl now continue to run doling the up-switch completes a cir- until one of the stop buttons St, St or . how *f- on the rectifier through St or s safely switch upena. Ones the "i-ihe up-switch, up-direction switch stairway slows down and tho governor all the safety-switch contacts underspeed contact C, opens, it cannot 10 " on the rectifier. This coll closes start again except by using the key to Bkeis U, and Ug in the motor clr- close one of tho start switches. This contact U% in tho brako-eoll clr- prevents the stairway from being started ^ between colls V aod P. And except under absolutely safe conditions. grouped open-delta. These transformers have six sets of terminals (not shown) brought out on them that permit operat ing on 199-208 to 550-575 v circuits. Hiey provide tho correct voltage (or the 3- phase copper-oxide rectifier, , to Eg, that supplies de to the brake-coil nd control-circuits. Assume transformer polarity as shown,, then current flows down from 4- on the transformer* through recti fiers Eg and Eg to tho right-hand fuse. Current flow continues through the con trol circuits and up through rectifier Eg and to * between the two transformers. Whtn the center transformer top is + current flows from it through rectifier Eg and the control circuits as before, through rectifiers E, and Eg to the trans formers. Even though current flows re versed in the transformers the rectifiers kept it in the seme direction in tbe control circuits. Timing Relay. Below the reetifler Is the timing relay with colls T and Tj that control the time when resistors Ri to Rj are cut out of the motor cir cuits. Coils T and f, of this relay ore connected directly across the rectifier. As long as both soils are energized, con. (Continued on page 122) no PUNT OPERATION AND MAINTENANCf SECTION POWOj MlOUfT 1953 PIANT OPERATION AND MAINTENANCE SECTION 121