DC Buyer's Guide

Application Information CD180AT-CD6900 Frames

Air Supply Quality Guidelines Cooling air quality can have an effect on machine

Information Outline Dimensions conducting dust , etc., when present , impose a severe hardship on the insulation system. Special consideration is required to determine the acceptability of a dripproof fully guarded enclosure, since the contamination itself may conduct shorting or grounding current over the insulation. This current gradually develops a permanent creepage path which can cause failure. The exposed uninsulated circuits on DC machines, such as the commutator brush rigging and bolted connections, allow early electrical failure when the enclosure is inadequate, regardless of the insulation system. Extra varnish dips will not correct this problem. An adequate enclosure should be used. Where contamination is expected, a study of the history of the application should be made to determine what degree of protection has been successful in the past . A standard dripproof fully guarded machine can often be applied successfully, but a totally enclosed machine will provide extra reliability. Modifications Motor Pricing General Information The exciting fields on all continuously rated, dripproof fully guarded blower ventilated and separately ventilated, and totally enclosed nonventilated motors are designed for R^]cX]d^db TgRXcPcX^] Pc UXT[S e^[cPVTb d_ c^ $ ^U cWT rated value while the motor is operating at any speed and load within the capability of the armature. Temperatures under these conditions will not exceed maximum allowable. However, insulation life will be shortened, particularly during prolonged operation at low speed. CAUTION : <^c^a 5XT[S 7TPcX]V € D][Tbb b_TRXUXRP[[h ^aSTaTS motors are NOT capable of continuous standstill excitation at rated field current . When the motor is shut down for more than 15 minutes, one of the following options must be used: 1. De-energize the field completely 2. Use field economy relays to limit the field current to a \PgX\d\ ^U $ ^U cWT ]P\T_[PcT aPcX]V 3. When applicable, fields may remain fully energized if the motor ventilation system (blower or customer duct) remains in operation. Environmental Effects On Insulation The insulation system used on GE DC motors is adequate for dbT X] Wd\XS Pc\^b_WTaTb 0RXSb P[ZP[XTb PQaPbXeT Sdbc

performance. Nonconducting contaminants such as cement dust , dirt , sand, and sawdust can promote overtemperature by restricting cooling passages and air circulation. Abrasive materials may erode insulations within the machine. Conductive contaminants such as carbon dust , metal particles, and salt can also provide shorting paths to ground. Periodic “blowing out” or vacuuming of dust accumulation will tend to avoid major problems if oil, grease, or other liquids are allowed to enter the machine, contaminants fX[[ |bcXRZ} c^ X]bd[PcX]V bdaUPRTb P]S \PZT TUUTRcXeT cleaning difficult . Corrosive gases in applications such as papermills can have an extreme effect on machine performance and service life. Chlorine, hydrogen sulfide, and sulphur dioxide can damage commutator copper, hardware, and varnish systems. On the commutator, severe contamination will cause unprotected copper (where the brushes don’t contact) to oxidize and turn bluish-gray developing scale that can bridge across insulating mica and cause commutation distress and possibly a flashover. Contamination produces high friction P]S d]TeT] UX[\ fWXRW aTSdRTb QadbW [XUT B_PaZX]V \Ph result from poor, uneven, or non-conductive commutator film which can lead to bar etching and further commutator surface erosion. If high corrosion is suspect , air sampling coupons can be placed in the cooling air to determine corrosion rates. Field experience has shown that corrosion rates of motor cooling air should be below .5 microns/year to limit corrosion damage effects. Air sampling coupons and analysis are commercially available. Periodic seater stone application can prevent buildup and uneven commutator filming. With high corrosion evident , further analysis can pinpoint the type of gases present . Elimination of high levels of gas can be made by relocating air inlets to other rooms or areas or simply raising an inlet off of a wet floor or away from open gutter-type drains. Additional filtering means such as charcoal filters can further improve air quality. Effects of Radiation Radiation can cause insulation degradation, if present in sufficient amounts. Where motors are exposed to the more common types of atomic radiation, nearly all standard insulations may be used if the radiation is below 10 7 Roentgens. Where radiation exceeds this value, specific information should be included in the requisition, proposition, or specifications.

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