d.c. machine diagnostics and engineering solutions for d.c. machine problems, including: basic d.c. machine construction and operation encompassing: general principles of operation applications of d.c. machines construction of d.c. machines d.c. machine configurations; series, shunt, compound long shunt and compound short shunt armature and field currents insulation ratings cooling paths bearings general maintenance of d.c. machines construction and use of lap and wave windings encompassing: coils and elements generated voltage equation for generator generated voltage equation for motors application of lap and wave windings commutation process encompassing: use of interpoles loading of machines brush shifting brush selection classes of brush grades: natural graphite, hard carbon, electrographite, metal-graphite and metal-carbon, "treated" grades carbon brush contact characteristics: specific resistance, thermal conductivity, density and porosity, elastic properties and contact properties carbon brush factors: pressure, current, polarity and speed brush construction: dimensions, tolerances, preferred sizes, surfaces, edges, bevels, flexible shunts, connection of flexible shunt to brush and insulation of flexible connections brush holders: types, brush angles, trailing holders, reaction holders, top bevel angles, reversible rotation, cantilever holders, effective arc of contact, construction of brush holders and pressure mechanism mounting of brush holders and brushes: clearances, brush angle, brush arm spacing, alignment, staggering, brush bedding and brush pressure brush operation: temperature rise, number and size of brushes, current distribution between brushes, slotting brushes, polarity effects, arc of contact, materials for commutators and mica selection of brush grades: machine data, current density, commutator peripheral speed, brush arc, pitch of segments, number of segments covered by brush and cooling surface armature reaction in d.c. machines encompassing: effect of armature reaction on d.c. machine characteristics use of compensating winding d.c. generators encompassing: relative advantages and disadvantages of the various d.c. generator configurations and their performance under various load conditions voltage regulation as a percentage or per unit value operation in parallel d.c. motors encompassing: relative advantages and disadvantages of the various d.c. motor configurations and their performance under various load conditions shape of motor speed/torque curves reversal of rotation starting and protection of d.c. motors encompassing: types of d.c. motor starters in use d.c. motor protection speed regulation and speed control of d.c. motors encompassing: methods in use effect on motor design and operation caused by the use of SCR speed control equipment braking of d.c. motors encompassing: plugging dynamic regenerative mechanical losses, heating and efficiency encompassing: copper losses iron losses mechanical losses efficiency acceleration of d.c. motors and loads encompassing: characteristics of typical loads matching a suitable motor to a given load heating of windings derating of motors special d.c. motors construction, operation and applications encompassing: permanent-magnet motors brushless motors (e.c. motors) coreless and moving coil motors linear motors printed circuit motor stepping motors voice-coil motors maintenance of d.c. machines encompassing: routine maintenance breakdown repairs types of faults encompassing: brushes/brush gear problems: sparking, excessive heating, excessive wear of brushes, commutator or slip rings, bad surface conditions, excessive maintenance, flexible burning, flexible corrosion, separation or grooving, blackening, copper picking, copper dragging and brush noise adjustment of machines encompassing: correct brush position machining and finishing of commutators problem-solving techniques machine parameters, specifications and performance requirements relevant manufacturer specifications and operating instructions relevant job safety assessments or risk mitigation processes relevant WHS/OHS legislated requirements relevant workplace documentation relevant workplace quality, instructions, policies and procedures. |